what is gaia hypothesis

Who was James Lovelock, what is Gaia theory, and why does it matter today?

Science Who was James Lovelock, what is Gaia theory, and why does it matter today?

Australian climate scientist Andy Pitman only met James Lovelock once at a conference and remembers a "classic elderly, charming Englishman", but it's an image that belies nothing short of a revolutionary influence.

For someone like Professor Pitman, who studies the interaction of climate and vegetation, it's obvious that living things play a key role in regulating Earth's climate.

"If it wasn't for life, we would have cooked long ago, because life sucks the carbon dioxide out of the atmosphere into the land," says Professor Pitman, of the University of New South Wales.

But when Professor Lovelock first went public with his idea that the   Earth was a giant organism that could regulate itself (including its climate) by using feedback between biological life and the rest of the planet, it was seen as rather radical.

"It was just so out there. It wasn't taken very seriously by many," Professor Pitman says.

But that was back in the 1970s — and today, even though many of Professor Lovelock's ideas remain controversial, his Gaia theory underpins a whole field of research called Earth systems science .

"I cannot overstate how profoundly transformative his contribution was," Professor Pitman says

"There are many people who think he has had more impact on our understanding of the Earth than any other singular scientist through the 20th century."

Life on Mars

Professor Lovelock, who died last week on his 103rd birthday , has been described as the "ultimate polymath" and a "connoisseur of nature" for whom "intuition and feeling" were just as important as science and data.

"My role has been to bring separated things and ideas together and make the whole more than the sum of the parts," he once told The Guardian .

It all started back in the 1960s when Professor Lovelock, while working for NASA, designed an instrument to measure the chemical composition of Mars's atmosphere.

After comparing his measurements with those taken from Earth's atmosphere, he concluded there could be no life on the Red Planet.

Professor Lovelock argued the Martian atmosphere did not contain the signature balance of gases including oxygen, which is a sign of life on our planet.

"He basically was able to demonstrate without sending robots to Mars that there was no life there," Professor Pitman says.

The findings changed the way we understand Earth's atmosphere and its relationship to the rest of the planet.

In 1987, Professor Lovelock and colleagues proposed that phytoplankton in the ocean helps regulate the climate by giving off a gas, especially when it is sunny, which helps form clouds that shade the Earth, and bring rain that helps forests grow.

While scientists still debate how these cycles work , it was complex planet-scale interactions like this — involving biology as well as physics and chemistry, and the recycling of nutrients — that were key to Professor Lovelock's thinking.

Professor Pitman likens the feedback processes central to Gaia theory to what happens in our bodies to regulate temperature — we sweat when we're hot and shiver when we're cold.

He says Professor Lovelock's writings were "essential reading" for his own PhD back in the 1980s, and a vast amount of what we understand today is the result and direct consequence of such work.

Like minds with a planetary perspective

The idea of using the name Gaia — the Greek goddess who personifies the Earth — originally came from a chat with novelist William Golding of Lord of the Flies fame. And a Pentagon consultant by the name of Dian Hitchcock also appears on an early scientific paper of Professor Lovelock's.

But his key long-term intellectual collaborator was the evolutionary theorist, microbiologist and fellow maverick Lynn Margulis, who overturned our understanding of how life on Earth evolved.

Professor Margulis also had a planetary perspective on things, says Bruce Clarke, of the Texas Tech University, who is a co-author of Writing Gaia, a new book that analyses 300 letters exchanged between professors Margulis and Lovelock between 1970 and 2007.

"She understood life as a global or planetary phenomenon," Professor Clarke says.

That's not surprising given that Professor Margulis was once married to cosmologist Carl Sagan, who knew Professor Lovelock, and suggested his wife connect with him.

"Lynn believed Gaia is run by the microbes," Professor Clarke says.

As well as collaborating on ideas, professors Lovelock and Margulis (who died in 2011) supported each other, in justifying their opposition to mainstream ideas, he adds.

And during the '70s and '80s it was them against scientists like Richard Dawkins, who was reducing life to a "molecular gene-centred vision" that made living organisms all "lumbering gene robots" at the mercy of their environment.

"For the longest time, Richard Dawkins was their mutual nemesis."

Gaia myths and climate prophecies

The fact that Gaia had mystical or spiritual connotations that resonated with many in the New-Age movement undermined Professor Lovelock's ideas in the eyes of some scientists.

So he spent a lot of time explaining that Gaia was not some kind of benevolent Earth mother, but it would take care of itself first, even if that wasn't great for humans.

As his collaborator Professor Margulis said: "Gaia is a tough bitch."

Professor Lovelock is also well known for warning of the dire consequences of human activity pushing Gaia to the limit.

At the age of 86 he published a book called The Revenge of Gaia, which predicted destructive extreme weather from climate change would be the norm by 2020.

He even thought the COVID pandemic might be "a Gaian negative feedback mechanism to reduce human pressure on the Earth system".

At the same time, he argued humans were part of Gaia, and needed to use their consciousness to "give her a hand" to stave off the worst of climate change.

Professor Lovelock shocked many environmentalist fans, for example, by advocating the use of nuclear energy and then geoengineering as solutions to global warming.

His recipe for human salvation also included human retreat to megacities and artificial intelligence controlling the climate.

A free thinker

Whatever you think of James Lovelock, he will be remembered for being a truly independent scientist, which, Professor Pitman says, is "a very rare" thing in this day and age.

"He was a free thinker who thought outside the box … and had hard core scientific credentials."

Professor Lovelock was elected a Fellow of the Royal Society not long after his first paper on Gaia was published, and has received many other honours.

And it seems he was able to be so independent because he funded his own work, with the help of the income from no less than 40 patents from inventions he had created over the decades.

These included the electron capture detector, which ended up detecting ozone-depleting chemicals.

Professor Lovelock's protégé, Tim Lenton, a professor of climate change and Earth systems science at the University of Exeter, believes his mentor's ideas on the interconnectedness of Earth's systems will help humans build a more sustainable future.

"He will go down in history as the person who changed our view of our place on Earth," Professor Lenton says.

"We need Jim's way of thinking now more than ever, if we are to get out of a climate and ecological crisis of our own making."

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• 25 June 2019

James Lovelock at 100: the Gaia saga continues

• Tim Radford 0

Tim Radford was science editor of The Guardian until 2005. As a science journalist, he met and got to know James Lovelock. His latest book is The Consolations of Physics .

You can also search for this author in PubMed   Google Scholar

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James Lovelock proposes that Earth will be saved by artificial intelligence. Credit: Tim Cuff/Alamy

Novacene: The Coming Age of Hyperintelligence James Lovelock Allen Lane (2019)

James Lovelock will always be associated with one big idea: Gaia. The Oxford English Dictionary defines this as “the global ecosystem, understood to function in the manner of a vast self-regulating organism, in the context of which all living things collectively define and maintain the conditions conducive for life on earth”. It cites the independent scientist as the first to use the term (ancient Greek for Earth) in this way, in 1972.

On 26 July, Lovelock will be 100; his long career has sparkled with ideas. His first solo letter to Nature — on a new formula for the wax pencils used to mark Petri dishes — was published in 1945. But, unusually for a scientist, books are his medium of choice. He has written or co-authored around a dozen; the latest, Novacene , is published this month.

As that book’s preface notes, Lovelock’s nomination to the Royal Society in 1974 listed his work on “respiratory infections, air sterilisation, blood-clotting, the freezing of living cells, artificial insemination, gas chromatography and so on”. The “and so on” briefly referred to climate science, and to the possibility of extraterrestrial life. The story of Gaia began with a question posed by NASA scientists while Lovelock was a consultant at the Jet Propulsion Laboratory in Pasadena, California. That is, how could you tell if a planet such as Mars harboured life?

Final warning from a sceptical prophet

With microbiologist Lynn Margulis, Lovelock published a series of papers on the subject. In 1974, they developed a view of Earth’s atmosphere as “a component part of the biosphere rather than as a mere environment for life” ( J. E. Lovelock and L. Margulis Tellus 26 , 2–10; 1974 ). Earth’s atmosphere contains oxygen and methane — reactive gases, constantly renewed. That disequilibrium radiates an infrared signal, which Lovelock later described as an “unceasing song of life” that is “audible to anyone with a receiver, even from outside the Solar System”. Thus, the answer to NASA’s question was already written in the static Martian atmosphere, composed almost entirely of non-reactive carbon dioxide.

That was the beginning of a sustained and developing argument, in the face of sometimes dismissive criticism, that recast Earth as, in effect, a superorganism. Lovelock’s Gaia theory states that, for much of the past 3.8 billion years, a holistic feedback system has played out in the biosphere, with life forms regulating temperature and proportions of gases in the atmosphere to life’s advantage. Earth system science is now firmly established as a valuable intellectual framework for understanding the only planet known to harbour life, and increasingly vulnerable to the unthinking actions of one species. Colleagues and co-authors acknowledge that the argument continues, but endorse the importance of Lovelock and Margulis.

Entwined evolution

“The insight that the oceans and the atmosphere are thoroughly entwined with the living biosphere, and must be understood as a coupled system, has been completely vindicated,” says marine and atmospheric scientist Andrew Watson of the University of Exeter, UK. Lee Kump goes further. “Lovelock also showed us that Darwin had it only half right,” says Kump, a geoscientist at Pennsylvania State University in University Park. “Life evolves in response to environmental change, but the environment also evolves in response to biological change.” Despite severing formal links with universities decades ago, Lovelock has been showered with honorary degrees and awards from bodies as varied as NASA and the Geological Society of London.

The procession of engaging books began in 1979 with Gaia: A New Look at Life on Earth . Each volume made its case more forcefully than the last, exploring what was known first as the Gaia hypothesis, then simply as Gaia, and the hazards facing either the biosphere or humanity. The books include his endearing autobiography Homage to Gaia (2000), increasingly urgent warnings of climate devastation in The Revenge of Gaia (2006) and The Vanishing Face of Gaia (2009), and the less apocalyptic A Rough Ride to the Future (2014).

James Lovelock pictured in 1989. Credit: Terry Smith/The LIFE Images Collection/Getty

Novacene picks up from that note of hope, and showcases another big idea. Gaia might, after all, be saved — by the singularity. This artificial-intelligence takeover, which so alarms many doomsayers, will be our redemption. Lovelock argues that increasingly self-engineering cyborgs with massive intellectual prowess and a telepathically shared consciousness will recognize that they, like organisms, are prey to climate change. They will understand that the planetary thermostat, the control system, is Gaia herself; and, in tandem with her, they will save the sum of remaining living tissue and themselves. The planet will enter the Novacene epoch: Lovelock’s coinage for the successor to the informally named Anthropocene.

Lovelock welcomes this. “Whatever harm we have done to the Earth, we have, just in time, redeemed ourselves by acting simultaneously as parents and midwives to the cyborgs,” he writes. He takes the long view on this rescue, however. Climate change is a real threat to humanity, but Earth will inevitably be overtaken by a ‘big heat’ in a few billion years, as the Sun slowly waxes more fierce.

Although co-authored with journalist Bryan Appleyard, Novacene reads like undiluted Lovelock. From the start of his writing life — no matter how tortuous the narrative or complex the argument — Lovelock has written persuasively. In his debut, Gaia , he sidestepped evolution’s first and biggest obstacle (how to get from organic chemistry to a living, devouring, excreting, replicating organism) in two sentences that seem to me models of clarity and brevity: “Life was thus an almost utterly improbable event with almost infinite opportunities of happening. So it did.”

No place like home

In The Ages of Gaia (1988), a richer and more closely argued restatement, he answered the vexed question of how life contradicts the second law of thermodynamics. Life, he wrote, “has evolved with the Earth as a highly coupled system so as to favour survival. It is like a skilled accountant, never evading the payment of the required tax but also never missing a loophole.” This metaphoric brilliance is no rarity. A few pages on, he reminds us that Gaia is “a quarter as old as time itself. She is so old that her birth was in the region of time where ignorance is an ocean and the territory of knowledge is limited to small islands, whose possession gives a spurious sense of certainty.”

Lovelock’s Gaia theory is only one aspect of his nonconformism. His vigorous support for nuclear power annoys many environmentalists. Brought up as a Quaker, he registered as a conscientious objector in 1940, then changed his mind and prepared for military action in 1944 (the National Institute for Medical Research in London considered him more useful in the lab). Later, he became a consultant for the security services of Britain’s defence ministry. Among his inventions is an electron capture detector sensitive enough to identify vanishingly small traces of pollutants — such as the pesticides that spurred Rachel Carson to write the 1962 book Silent Spring — and chlorofluorocarbons, later implicated in damage to the ozone layer. In Novacene , he writes teasingly that he now sees himself as an engineer who values intuition above reason.

Lovelock to the last, he even has a kind word for the Anthropocene, marked by degradation of natural resources and the devastation of the wild things with which humanity evolved. He gives a “shout of joy, joy at the colossal expansion of our knowledge of the world and the cosmos”, and exults that the digital revolution ultimately “empowers evolution”. Is he right? Some of us might live to find out. In the meantime, if you want a sense of hyperintelligence in bipedal form, Novacene is a good place to start.

Nature 570 , 441-442 (2019)

doi: https://doi.org/10.1038/d41586-019-01969-y

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2.1.4.3: Gaia - Bioregulation of the Environment

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• Stephen Lower
• Simon Fraser University

The Gaia Hypothesis

The physical conditions under which life as we know it can exist encompass a relatively narrow range of temperature, pH, osmotic pressure, and ultraviolet radiation intensity. It seems remarkable enough that life was able to get started at all; it is even more remarkable that it has continued to thrive in the face of all the perils that have, or could have occurred, during the past 3 billion years or so.

During the time that life has been evolving, the sun has also been going through the process of evolution characteristic of a typical star; one consequence of this is an increase in its energy output by about 30 percent during this time. If the sun’s output should suddenly drop to what it was 3 billion years ago, the oceans would freeze. How is it that the earth was not in a frozen state for the first 1.5 billion years of life’s existence? Alternatively, if conditions were somehow suitable 3 billion years ago, why have the oceans not long since boiled away?

A rather non-traditional answer to this kind of question is that the biosphere is far from playing a passive role in which it is continually at the mercy of environmental conditions. Instead, the earth’s atmosphere, and to a lesser extent the hydrosphere, may be actively maintained and regulated by the biosphere. This view has been championed by the British geochemist J.E. Lovelock, and is known as the Gaia hypothesis .

Gaia is another name for the Greek earth-goddess Ge , from which root the sciences of geography, geometry, and geology derive their names. Lovelock's book Gaia: a new look at life on Earth (Oxford, 1979) is a short and highly readable discussion of the hypothesis.

Evidence in support of this hypothesis is entirely circumstantial, but nevertheless points to important questions that must be answered: how have the climatic and chemical conditions on the earth remained optimal for life during all this time; how can the chemical composition of the atmosphere remain in a state that is tens of orders of magnitude from equilibrium?

Although the Gaia hypothesis has received considerable publicity in the popular press, it has never been very well received by the scientific community, many of whom feel that there is no justification for proposing a special hypothesis to describe a set of connections which can be quite adequately explained by conventional geochemical processes. More recently, even Lovelock has backed away from the teleological interpretation of these relations, so that the Gaia hypothesis should now be more properly described as a set of loosely connected effects, rather than as a hypothesis. Nevertheless, these effects and the mechanisms that might act to connect them are sufficiently interesting that it seems worthwhile to provide an overview of the major observations that led to the development of the hypothesis.

Teleology is the doctrine that natural processes operate with a purpose. See No longer willful, Gaia becomes respectable. 1988: Science 240 393-395.

Bioregulation of the Atmosphere

The increase in the oxygen content of the atmosphere as a result of the development of the eucaryotic cell was discussed above. Why has the oxygen content leveled off at 21 percent? It is interesting to note that if the oxygen concentration in the atmosphere were only four percent higher, even damp vegetation, once ignited by lightning, would continue to burn, enveloping vast areas of the earth in a firestorm. Evidence for such a worldwide firestorm that may be related to the extinction of the dinosaurs has recently been discovered. The charcoal layers found in widely distributed sediments laid down about 65 million years ago are coincident with the iridium anomaly believed to be due to the collision of a large meteor with the earth.

• Oxygen : Regulation of the oxygen partial pressure is probably achieved by a balance between its production through photosynthesis and its consumption during oxidation of organic matter; the present steady state requires the burial of about 0.1% the carbon that is fixed annually, leaving one O 2 molecule in the air for each atom of carbon removed from the photosynthetic cycle. The large quantities of microbially-produced methane and N 2 O also constitute important oxygen sinks; if methanogenic bacteria should suddenly cease to exist, the O 2 concentration would rise by 1% in about 12,000 years. This type of regulation implies a negative feedback mechanism, in which an increase in atmospheric oxygen would increase the activity of organisms capable of generating metabolic products that react with it.
• Nitrous oxide : Nitrous oxide, in addition to serving as an oxygen sink, might also be a factor in the regulation of the intensity of the ultraviolet component of sunlight. N 2 O acts as a catalytic intermediate in the decomposition of stratospheric ozone, which shields the earth from excessive ultraviolet radiation.
• Ammonia : Ammonia, another atmospheric gas, is produced by the biosphere in approximately the same quantities as methane, 10 9 tons per year, and at the expense of a considerable amount of metabolic energy. The function of NH 3 could well be to regulate the pH of the environment; in the absence of ammonia, the large amounts of SO 2 and HCl produced by volcanic action would reduce the pH of rain to about 3. The fact that the atmospheric concentration of ammonia is only 10 –8 times that of N 2 should not imply that this “trace” component plays a less significant role in the overall nitrogen cycle than does than N 2 . In fact, the annual rates of production of the two gases are roughly the same; the much lower steady-state concentration of NH 3 is due to its faster turnover time.
• Nitrogen : As stable as the triply-bonded N 2 molecule is, there is a still more stable form of nitrogen: the hydrated nitrate ion. How is this stability consistent with the predominance of nitrogen in the atmosphere? The answer is that it is not: if it were not for nitrogen-fixing bacteria (powered directly or indirectly by the free energy of ATP captured from sunlight), the nitrogen content of the atmosphere would disappear to almost zero. This would raise the oxygen fraction to disastrously high levels, and the additional NO 3 – concentration would increase the ionic strength and osmotic pressure of seawater to levels inconsistent with most forms of life.

Bioregulation of the Oceans

The input of salts into the sea from streams and rivers is about 5.4 x 10 8 tons per year, into a total volume of about 1.2 x 10 9 km 3 yr –1 . Upwelling of juvenile water and hydrothermal action at oceanic ridges provide additional inputs of salts. With a few bizarre exceptions such as the brine shrimp and halophilic bacteria, 6 percent is about the maximum salinity level that organisms can tolerate. The internal salinities of cells must be maintained at much lower levels (around 1%) to prevent denaturation of proteins and other macromolecules whose conformations are dependent on electrostatic forces. At higher levels than this, the electrostatic interaction between the salt ions and the cell membrane destroys the integrity of the latter so that it can no longer pump out salt ions that leak in along the osmotic gradient. At the present rate of salt input, the oceans would have reached their present levels of salinity millions of years ago, and would by now have an ionic strength far to high to support life, as is presently the case in the landlocked Dead Sea.

The present average salinity of seawater is 3.4 percent. The salinity of blood, and of many other intra- and intercellular fluids in animals, is about 0.8 percent. If we assume that the first organisms were approximately in osmotic equilibrium with seawater, then our body fluids might represent “fossilized” seawater as it existed at the time our predecessors moved out of the sea and onto the land.

By what processes is salt removed from the oceans in order to maintain a steady-state salinity? This remains one of the major open questions of chemical oceanography. There are a number of answers, mostly based on strictly inorganic processes, but none is adequately supported by available evidence. For example, Na + and Mg 2 + ions could adsorb to particulate debris as it drops to the seafloor, and become incorporated into sediments. The requirement for charge conservation might be met by the involvement of negatively charged silicate and hydroxyaluminum ions. Another possible mechanism might be the burial of salt beds formed by evaporation in shallow, isolated arms of the sea, such as the Persian Gulf. Extensive underground salt deposits are certainly found on most continents, but it is difficult to see how this very slow mechanism could have led to an unfluctuating salinity over shorter periods of highly variable climatic conditions.

The possibility of biological control of oceanic salinity starts with the observation that about half of the earth’s biomass resides in the sea, and that a significant fraction of this consists of diatoms and other organisms that build skeletons of silica. When these organism die, they sink to the bottom of the sea and add about 300 million tons of silica to sedimentary rocks annually. It is for this reason that the upper levels of the sea are undersaturated in silica, and that the ratio of silica to salt in dead salt lakes is much higher than in the ocean.

These facts could constitute a basis for a biological control of the silica content of seawater; any link between silica and salt could lead to the control of the latter substance as well. For example, the salt ions might adsorb onto the silica skeletons, and be carried down with them; if the growth of these silica-containing organisms is itself dependent on salinity, we would have our negative feedback mechanism.

The continual buildup of biogenic sedimentary deposits on the ocean floor might possibly deform the thin oceanic crust by its weight, and cause local heating by its insulating properties. This could conceivably lead to volcanic action and the formation of new land mass, thus linking the lithosphere into Gaia.

Contributors and Attributions

Stephen Lower, Professor Emeritus ( Simon Fraser U. ) Chem1 Virtual Textbook

April 9, 2014

"Gaia Hypothesis" Originator James Lovelock Reflects on His Career

The scientist and futurist talks about self-regulating Gaia, climate change and peer review, as an exhibition featuring him opens April 9 in London

By Philip Ball & Nature magazine

A new exhibition at the Science Museum in London features the personal archives of one of the most influential modern scientists; James Lovelock. ‘ Unlocking Lovelock: Scientist, Inventor, Maverick ’ tells the story of the British scientist's work in medicine, environmental science and planetary science, and displays documents ranging from childhood stories, doodle-strewn lab notebooks and patents to letters from dignitaries such as former UK prime minister (and chemist) Margaret Thatcher. Also included are several of Lovelock’s inventions, such as the electron-capture detector that enabled the measuring of ozone-destroying chlorofluorocarbons in the atmosphere in the 1970s.

Lovelock, born in 1919, is best known for the ‘Gaia hypothesis’, which proposes that the Earth functions as a self-regulating system, similar to a living organism. The idea sparked controversy when Lovelock and microbiologist Lynn Margulis proposed it in the 1970s, but environmental and Earth scientists now accept many of its basic principles. In 2006, his book  The Revenge of Gaia  predicted disastrous effects from climate change within just a few decades, writing that  “only a handful of the teeming billions now alive will survive”.

This week Lovelock spoke to  Nature  about his career, his earlier predictions and his new book,  A Rough Ride to the Future  ( reviewed last week in  Nature ).

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Is climate change going to be less extreme than you previously thought?

The Revenge of Gaia  was over the top, but we were all so taken in by the perfect correlation between temperature and CO 2  in the ice-core analyses [from the ice-sheets of Greenland and Antarctica, studied since the 1980s]. You could draw a straight line relating temperature and CO 2 , and it was such a temptation for everyone to say, “Well, with CO 2  rising we can say in such and such a year it will be this hot.” It was a mistake we all made.

We shouldn’t have forgotten that the system has a lot of inertia and we’re not going to shift it very quickly. The thing we’ve all forgotten is the heat storage of the ocean — it’s a thousand times greater than the atmosphere and the surface. You can’t change that very rapidly.

But being an independent scientist, it is much easier to say you made a mistake than if you are a government department or an employee or anything like that.

So what will the next 100 years look like?

That’s impossible to answer. All I can say is that it will be nowhere as near as bad as the worst-case scenario.

Are you still pessimistic about the prospect of finding a political solution to climate change?

Absolutely.

In your latest book you advocate not trying to halt climate change but exercising what you call a sustainable retreat. Why is that?

I think it is the better approach. To rush ahead and advance is very much the Napoleonic approach to battle. It is far better to think about how we can protect ourselves. If we’re going to do any good, we should be making more effort to keep our own home a suitable place to live in for the future than desperately trying to save somewhere remote. This is particularly true of Britain. We nearly died in the Second World War for lack of food. Our agricultural production hasn’t gone up enough to supply today’s population with what we would need. This is something we should be looking at carefully, not just applying guesswork and hoping for the best.

Will nuclear energy be part of the future, despite the Fukushima nuclear disaster in Japan?

The business with Fukushima is a joke. Well, it’s not a joke, it is very serious — how could we have been misled by anything like that? Twenty-six thousand people were killed by the magnitude-9 earthquake and tsunami [that caused the nuclear meltdown], and how many are known to have been killed by the nuclear accident? None.

[On the Chernobyl nuclear disaster, Lovelock writes in  A Rough Ride to the Future : “The most amazing lies were told, still are told and widely believed… Despite at least three investigations by reputable physicians, there has been no measurable increase in deaths across Eastern Europe.”]

A lot of investment in green technology has been a giant scam, if well intentioned.

Do you feel vindicated about the way many of the ideas in the Gaia hypothesis have now been accepted by Earth-systems scientists?

I think it is a matter of scientific politics. In practice, most of the senior biologists I encountered in later times had no problem with the notion at all. But they fought bitterly at first. It was very funny to talk with John Maynard Smith, Bill Hamilton and Robert May [eminent evolutionary and population biologists], and to discover that none of them had read any of my books or papers — they were judging the idea by what their students told them.

Was some of that criticism helpful?

In the early stages it wasn’t. And on the geology side it was something quite different — the tendency of some geologists to keep their heads in the sediments is very strong, and they won’t shift it. I’m very intrigued by the latest attempt to resuscitate the idea that all of climate regulation is done by rock weathering. The geologists keep on ignoring the bacteria.

A 1984 rejection letter from  Nature  of your paper outlining the Gaia hypothesis is displayed in the exhibition. What do you think of peer review — is it necessary?

Well, as far as I’m concerned, I don’t have any peer review. But I don’t think it is practical to get rid of it. For run-of-the-mill papers, say if somebody comes up with a really neat method for analyzing some component of urine or that kind of thing, it is important to keep it. But not on larger topics.

This article is reproduced with permission from the magazine Nature . The article was first published on April 9, 2014.

Scientists finally have an explanation for the ‘Gaia puzzle’

Associate Professor of Sustainability Science, University of Southampton

Director, Global Systems Institute, University of Exeter

Disclosure statement

Tim Lenton works for the University of Exeter and receives funding from the Royal Society (Wolfson Research Merit Award) and the Natural Environment Research Council (NE/P013651/1).

James Dyke does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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We will likely never know how life on Earth started. Perhaps in a shallow sunlit pool. Or in the crushing ocean depths miles beneath the surface near fissures in the Earth’s crust that spewed out hot mineral-rich soup. While there is good evidence for life at least 3.7 billion years ago , we don’t know precisely when it started.

But these passing aeons have produced something perhaps even more remarkable: life has persisted. Despite massive asteroid impacts, cataclysmic volcano activity and extreme climate change, life has managed to not just cling on to our rocky world but to thrive.

How did this happen? Research we recently published with colleagues in Trends in Ecology and Evolution offers an important part of the answer, providing a new explanation for the Gaia hypothesis.

Developed by scientist and inventor James Lovelock , and microbiologist Lynn Margulis , the Gaia hypothesis originally proposed that life, through its interactions with the Earth’s crust, oceans, and atmosphere, produced a stabilising effect on conditions on the surface of the planet – in particular the composition of the atmosphere and the climate. With such a self-regulating process in place, life has been able to survive under conditions which would have wiped it out on non-regulating planets.

Lovelock formulated the Gaia hypothesis while working for NASA in the 1960s. He recognised that life has not been a passive passenger on Earth. Rather it has profoundly remodelled the planet, creating new rocks such as limestone, affecting the atmosphere by producing oxygen, and driving the cycles of elements such as nitrogen, phosphorus and carbon. Human-produced climate change, which is largely a consequence of us burning fossil fuels and so releasing carbon dioxide, is just the latest way life affects the Earth system.

While it is now accepted that life is a powerful force on the planet, the Gaia hypothesis remains controversial. Despite evidence that surface temperatures have, bar a few notable exceptions, remained within the range required for widespread liquid water, many scientists attribute this simply to good luck. If the Earth had descended completely into an ice house or hot house (think Mars or Venus) then life would have become extinct and we would not be here to wonder about how it had persisted for so long. This is a form of anthropic selection argument that says there is nothing to explain.

Clearly, life on Earth has been lucky. In the first instance, the Earth is within the habitable zone – it orbits the sun at a distance that produces surface temperatures required for liquid water. There are alternative and perhaps more exotic forms of life in the universe, but life as we know it requires water. Life has also been lucky to avoid very large asteroid impacts. A lump of rock significantly larger than the one that lead to the demise of the dinosaurs some 66m years ago could have completely sterilised the Earth.

But what if life had been able to push down on one side of the scales of fortune? What if life in some sense made its own luck by reducing the impacts of planetary-scale disturbances? This leads to the central outstanding issue in the Gaia hypothesis: how is planetary self-regulation meant to work?

While natural selection is a powerful explanatory mechanism that can account for much of the change we observe in species over time, we have been lacking a theory that could explain how the living and non-living elements of a planet produce self-regulation. Consequently the Gaia hypothesis has typically been considered as interesting but speculative – and not grounded in any testable theory .

Selecting for stability

We think there is finally an explanation for the Gaia hypothesis. The mechanism is based on “ sequential selection ”, a concept first suggested by climate scientist Richard Betts in the early 2000s. In principle it’s very simple. As life emerges on a planet it begins to affect environmental conditions, and this can organise into stabilising states which act like a thermostat and tend to persist, or destabilising runaway states such as the snowball Earth events that nearly extinguished the beginnings of complex life more than 600m years ago.

If it stabilises then the scene is set for further biological evolution that will in time reconfigure the set of interactions between life and planet. A famous example is the origin of oxygen-producing photosynthesis around 3 billion years ago, in a world previously devoid of oxygen. If these newer interactions are stabilising, then the planetary-system continues to self-regulate. But new interactions can also produce disruptions and runaway feedbacks. In the case of photosynthesis it led to an abrupt rise in atmospheric oxygen levels in the “ Great Oxidation Event ” around 2.3 billion years ago. This was one of the rare periods in Earth’s history where the change was so pronounced it probably wiped out much of the incumbent biosphere, effectively rebooting the system.

The chances of life and environment spontaneously organising into self-regulating states may be much higher than you would expect. If fact, given sufficient biodiversity, it may be extremely likely . But there is a limit to this stability. Push the system too far and it may go beyond a tipping point and rapidly collapse to a new and potentially very different state.

This isn’t a purely theoretical exercise, as we think we may able to test the theory in a number of different ways. At the smallest scale that would involve experiments with diverse bacterial colonies. On a much larger scale it would involve searching for other biospheres around other stars which we could use to estimate the total number of biospheres in the universe – and so not only how likely it is for life to emerge, but also to persist.

The relevance of our findings to current concerns over climate change has not escaped us. Whatever humans do life will carry on in one way or another. But if we continue to emit greenhouse gasses and so change the atmosphere, then we risk producing dangerous and potentially runaway climate change. This could eventually stop human civilisation affecting the atmosphere, if only because there will not be any human civilisation left.

Gaian self-regulation may be very effective. But there is no evidence that it prefers one form of life over another. Countless species have emerged and then disappeared from the Earth over the past 3.7 billion years. We have no reason to think that Homo sapiens are any different in that respect.

This article was updated on July 10 to add the reference to Richard Betts.

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"The Gaia hypothesis says that the temperature, oxidation state, acidity, and certain aspects of the rocks and waters are kept constant, and that this homeostasis is maintained by active feedback processes operated automatically and unconsciously by the biota." - James Lovelock, The Ages of Gaia

Suggested Readings:

• Margulis, L and J. Lovelock. 1976. Is Mars a Spaceship, Too? Natural History , June/July pp. 86-90

In this lesson, we learn:

• What are the weaknesses of the hypothesis? What are its strengths?
• What are some examples of Gaia-like feedbacks?

Jump to: [ Introduction ] [ Origin of the Hypothesis ] [ Examples of Regulation ] [ Alternatives to Gaia ] [ Many Gain Hypotheses ] [ Summary ]

1. introduction - gaia and global change, 2. the hypothesis and its originators.

3. Examples of Regulation of the Environment, According to Gaia

Perhaps life regulates the physical and chemical environment of the planet so as to maintain suitable planetary conditions for the good of life itself. If so, then the planet can be thought of as a single, integrated, living entity with self-regulating abilities. This is the radical view that Lovelock and Margulis have espoused. It can be thought of as the "strong Gaian model."

4. Alternatives to the Gaia Hypothesis

• The idea that climate and life influence one another is profoundly important. In some form or another, it has been recognized for a long time. Life and climate "grew up together" and influenced one another over most of earth history. But this is not to say that life somehow manages and self-optimizes its own environment. It is this idea -- the "strong form of Gaia" -- that is most controversial.

5. The Many Gaian Hypotheses

"...it is unlikely that chance alone accounts for the fact that temperature, pH and the presence of compounds of nutrient elements have been, for immense periods, just those optimal for surface life. Rather, ... energy is expended by the biota to actively maintain these optima" (Lovelock and Margulis, 1974).

6. Modeling Gaia

You can model feedbacks using the classic Gaia example of Daisyworld with Stella or using this interactive Java applet .  The latter is especially useful to get a first-order understanding of changing parameters.  The Stella model permit more sophisticated analysis.

• The hypothesis has been defined and argued in numerous ways, and has as many critics as adherents. It is in need of more explicit formulation before it can be examined and tested as a true scientific theory.  
• Two models emerge: The model that life influences planetary processes (i.e., it has a substantial effect on abiotic processes) has become known as the weak Gaia hypothesis .  This model is widely supported. The original Gaia hypothesis, that life controls planetary processes (i.e., life created Earth's system), has become known as the strong Gaia hypothesis .  It is not widely accepted.

All materials © the Regents of the University of Michigan unless noted otherwise.

• What is a Cosmopolis?
• Conferences and Publications
• Gaia Theory in a Nutshell

One of the most unpredicted outcomes of the space program was the Gaia hypothesis, the theory the biosphere itself works to regulate the temperature and chemical content of the Earth’s atmosphere. According to Gaia theory, life is a planetary-wide phenomenon that alters the environment on a planetary scale.

Table of Planetary Atmospheres, after Lovelock, The Ages of Gaia .

When the Earth was formed billions of years ago, the atmosphere was almost entirely made out of carbon dioxide, just like Mars and Venus. But with the emergence of blue-green bacteria and photosynthesis, carbon dioxide became a life-giving food. In the alchemy of Earth’s primordial oceans, the living metabolism of bacteria transmuted carbon dioxide and other elements into an expanding tapestry of life. The metabolic activity of the first bacteria started to give birth to a planetary-wide physiology. These first blue-green bacteria removed carbon from the atmosphere, which cooled down the planet, and gave off oxygen as a waste product. But around two billion years ago, the process gave rise to a planetary crisis—an “oxygen holocaust”—when too much oxygen had accumulated. Oxygen itself was highly toxic to the first bacteria. [1] This planetary-wide crisis provided a window of opportunity, however, when a new type of blue-green bacteria finally learned to synthesize oxygen into life-energy. Over immense periods of time, the biosphere transformed the atmosphere into its present composition. The atmosphere so composed was an atmosphere friendly to life, both in terms of its content and its stable, hospitable temperature.

While other planetary scientists had supported a “Goldilocks theory”—assuming that the temperature and atmospheric composition of the Earth had been “just right” for the emergence of life by chance—Lovelock showed that life itself had altered the planetary environment. Lovelock proposed that “the evolution of the species and the evolution of their environment are tightly coupled together as a single and inseparable process,” [2] a claim that was supported by his colleague, the microbiologist Lynn Margulis. Moreover, Lovelock and Margulis claimed that Gaia was a testable, scientific hypothesis.

During the past 4.5 billion years, solar luminosity has increased by at least 10–30%. [3] But the Gaian superorganism has successfully maintained a steady temperature through its metabolic processes. When critics complained that Lovelock’s theory smacked of teleology or design, he created a simple computer model called Daisyworld. Daisyworld contains two types of daisies, white and black, that naturally live in a certain temperature range and absorb different levels of heat. If the temperature is low on Daisyworld, the black daisies flourish because they absorb more heat. This causes the planet to warm up. If the temperature is high on Daisyworld, the white daisies flourish and reflect heat back off into space. Even if the luminosity of Daisyworld’s sun increases substantially, Daisyworld itself maintains a constant temperature—until the environmental conditions caused by the solar warming become just too extreme for the biota to regulate. Lovelock had proven that life can act like a planetary thermostat, and more complex models with twenty shades of daisies produced the same result. [4]

In addition to holding the temperature constant by reducing carbon dioxide, life has regulated the amount of oxygen in the atmosphere. Right now oxygen makes up 21% of the atmosphere, a level that must have remained constant for over 300 million years. If the concentration of oxygen was just a few points higher, devastating forest fires would engulf the planet. But if the oxygen level was a few points lower, animal life would perish.

As biologist Lynn Margulis points out, “life does not exist on Earth’s surface so much as it is Earth’s surface. . . . Earth is no more a planet-sized chunk of rock inhabited with life than your body is a skeleton infested with cells.” [5] Gaia’s radical challenge to traditional Darwinian biology is that life influences the environment. For Darwin, life was essentially passive, a process that was forced to adapt to a specific environment. Gaia theory shows that life and environment evolve as a single, coevolutionary process. On Earth, all life is an embodiment of the planetary environment, but the planetary environment is also product of life. Gaia theory and the new biology embodies the circular, metabolic logic of life. The universe brings forth life and mind—but life and mind work to shape the universe. Life and environment are folded back on themselves in a self-referential, evolutionary spiral. Gaia is not a single organism, but a superorganism. Like the single organisms of which it is comprised, it is self-regulating and autopoietic. Like my own body composed of many individual cells, Gaia has its own metabolism. As we breathe and exhale, we participate in the life-breath of the entire biosphere. Gaia theory is strongly supported by complexity science, which shows how complex systems with feedback loops spontaneously self-organize and develop metabolic patterns. From the Gaian perspective, our own lives are totally inseparable from the life of the larger planet.

[1] For a discussion of the oxygen holocaust, see chapter six in Margulis and Sagan, Microcosmos: Four Billion Years of Microbial Evolution (Berkeley: University of California Press, 1997) .

[2] James Lovelock, The Ages of Gaia (New York: W. W. Norton, 1988), 18. As he writes, “Through Gaia theory I now see the system of the material Earth and the living organisms on it, evolving so that self-regulation is an emergent property. In such a system active feedback processes operate automatically and solar energy sustains comfortable conditions for life. The conditions are only constant in the short term and evolve in synchrony with the changing needs of the biota as it evolves. Life and its environment are so closely couple that evolution concerns Gaia, not the organisms or the environment taken separately” (19–20).

[3] M. Newman, “Evolution of the Solar Constant,” in C. Ponnamperuma and Lynn Margulis, editors, Limits to Life (Dordrecht: D. Reidel, 1980) . See also Lawrence Joseph, Gaia: The Growth of an Idea (New York: St. Martin’s Press, 1990), 121–25.

[4] See Lovelock, The Ages of Gaia, chapter 3.

[5] Margulis and Sagan, What is Life? (New York: Simon and Schuster, 1999), 28.

Reprinted from chapter 11 of  Restoring the Soul of the World: Our Living Bond with Nature’s Intelligence by David Fideler. Copyright © 2014 by David Fideler. All rights reserved. May not be reproduced in any form without the written permission of the author.

“Viewed from the distance of the moon, the astonishing thing about the earth, catching the breath, is that it is alive. The photographs show the dry, pounded surface of the moon in the foreground, dead as an old bone. Aloft, floating free beneath the moist, gleaming membrane of the bright blue sky, is the rising earth, the only exuberant thing in this part of the cosmos. If you could look long enough, you would see the swirling of the great drifts of white cloud, covering and uncovering the half-hidden masses of land. If you had been looking a very long, geologic time, you could have seen the continents themselves in motion, drifting apart on their crustal plates, held aloft by the fire beneath. It has the organized, self-contained look of a live creature, full of information, marvelously skilled in handling the sun.” — Lewis Thomas, The Lives of a Cell

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Is the Earth itself a giant living creature?

An old, much-ridiculed hypothesis said yes. It’s time to take it seriously.

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In the 1970s, chemist James Lovelock and microbiologist Lynn Margulis put forth a bold theory: The Earth is a giant living organism .

When a mammal is hot, it sweats to cool itself off. If you nick your skin with a knife, the skin will scab and heal. Lovelock and Margulis argued that our planet has similar processes of self-regulation, which arguably, make it seem like the Earth itself is alive.

The idea wasn’t unprecedented in human history. “The fundamental concept of a living world is ancient,” says Ferris Jabr , a science journalist and author of the upcoming book Becoming Earth: How Our Planet Came to Life . The book explores all the ways life has shaped our physical world and, in doing so, inevitably revisits the question “Is the Earth alive?”

Lovelock and Margulis called the idea “the Gaia Hypothesis” — named after the ancient Greek goddess of the Earth. It was openly mocked by many in mainstream Western science. “For many decades, the Gaia hypothesis was considered kind of this fringe sort of woo-woo idea,” Jabr says. “Because for biologists,” Jabr says, life is a specific thing. “It is typically thought of as an organism that is a product of Darwinian evolution by natural selection. And Earth as a planet does not meet those criteria.”

It didn’t help that the original articulation of Gaia granted Earth a certain degree of sentience. The hypothesis argued “all of the living organisms on Earth are collaborating to deliberately create a climate that is suitable for life,” as Jabr says. But yet, this idea has persisted, for a few reasons. Scientists have never been able to precisely define what life is . So, it’s been hard to dismiss Gaia completely.

The Gaia hypothesis has also evolved over the years. Later iterations deemphasized that life was “collaborating” to transform the Earth, Jabr explains. Which still leaves a lot to be explored: Certainly living things don’t need to be thought of as conscious, or have agency, to be considered alive. Consider the clam, which lacks a central nervous system.

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Jabr found in the years since Gaia was first introduced, scientists have uncovered more connections between biology, ecology, and geology, which make the boundaries between these disciplines appear even more fuzzy. The Amazon rainforest essentially “ summons ” its own rain, as Jabr explains in his book. They learned how life is involved in the process that generated the continents. Life plays a role in regulating Earth’s temperature . They’ve learned that just about everywhere you look on Earth, you find life influencing the physical properties of our planet.

In reporting his book, Jabr comes to the conclusion that not only is the Earth indeed a living creature, but thinking about it in such a way might help inspire action in dealing with the climate crisis .

Brian Resnick spoke to Jabr for an episode of Unexplainable , Vox’s podcast that explores scientific mysteries, unanswered questions, and all the things we learn by diving into the unknown. You can listen to the full conversation here. This interview has been edited for length and clarity.

Brian Resnick

Do you think the Earth is alive?

Ferris Jabr

I do. I think Earth is alive. We can think of Earth as a genuine living entity, in a meaningful sense, and in a scientific sense. There are four parts to the argument that substantiate that statement.

What’s the first?

Life isn’t just on Earth. It literally came out of Earth. It is literally part of Earth. It is Earth. All of the matter that we refer to as life is Earth animated — that’s how I come to think about it. If you accept that, then at a bare minimum, you have to accept as a scientific fact that the surface of the planet is genuinely alive, because it is matter that has become animated.

Earth animated? What do you mean by that?

Every single living organism is literally made of Earth. All of its constituent elements and components are parts of the planet. We all come from the planet. We all return to the planet. It’s just a big cycle. And so life, the biological matter on the planet, is literally the matter of the planet, animated. It is living matter.

Imagine a vast beach and sandcastles and other sculptures spontaneously emerge from the sand. They are still made of sand, right? They’re not suddenly divorced from the beach just because they’ve arisen from the beach. Those castles and sculptures are still literally the beach. And I think it’s the same with life and Earth.

So, the physical components of Earth are the material of life. And so distinguishing these two — Earth and life — seems silly because they comprise each other?

The more you think about this, the more the boundaries dissolve.

Every layer of the planet that we’ve been able to access, we find life there. And in the deepest mines that we have dug, we continue to find microbes and sometimes even more complex organisms like nematodes, these tiny, worm-like creatures.

So all life contains Earth, and Earth contains life?

There are components of the Earth that are not alive in any way. The center of the planet, it’s all molten rock and there might be some solid metal in the core.

But think about a redwood tree: It is mostly dead wood in terms of its volume and mass. It is mostly nonliving tissue. And then a little bit of tissue that is laced with living cells. So, you know, most complex multicellular living entities are a jumble of the animate and inanimate. Earth is not unusual in that way.

What is part two of your argument?

All these organisms [on Earth], they give Earth a kind of anatomy and physiology. Life dramatically increases the planet’s capacity to absorb, store, and transform energy, to exchange gases, and to perform complex chemical reactions.

What’s a good example of this?

You can think of all of the photosynthetic life on the planet acting in concert. It’s not that they’re deliberately collaborating to do something, but they’re all doing their own thing at the same time.

NASA has made these amazing videos and animations and they’ve literally called them “ Earth breathing ,” because you can see how the levels of carbon dioxide and oxygen in the atmosphere fluctuate with the seasons. The amount of vegetation that rings the continents, especially in the Northern Hemisphere, in the mid-latitudes, it changes dramatically with the seasons. It has a sinuous rhythm. It looks like a pulse or like breathing.

So, are you saying something like all of the algae or plankton in the ocean are generating this together? … Is that kind of like how all of the cells in my lungs are working together to exchange gases? Or is that not quite the right way to think about it?

I think we have to be careful with making too direct a comparison. You as an organism are a product of evolution by natural selection. Your structure, your anatomy is something that was written into your genome. That’s not how the Earth system formed.

I’m realizing a key to this conversation is what you just corrected me on. When we’re discussing this notion about the “Earth being alive,” we’re not suggesting it’s not alive in the same way you and I are. But there’s these equivalent processes that look very similar to the way my body maintains homeostasis, for example. It’s not like the Earth is exchanging gases and doing metabolism-like things in the way I’ve been evolved to. It’s not achieving homeostasis the way you or I do. But yet it is doing something that seems analogous. Is that the kind of thing that you’re arguing here, overall?

Absolutely.

When we’re looking at the planet, we see life-like qualities, things that resemble the characteristics of the organism, which is the most familiar life form to us. But it is not exactly the same. It is still genuinely alive, in my opinion, but is not exactly an organism.

Life is a phenomenon that occurs at multiple scales. The way I think of it is that it’s not identical at all of those scales, but it rhymes and there are analogies between each of those scales.

I like to think of a leaf on a tree in a forest on a planet.

There’s no disagreement whatsoever within science that the cells that compose that leaf are alive. The tissues that those cells form are alive. The leaf as a whole is a living tissue. The tree we consider an organism that is also alive. We consider each of those layers to be alive. There’s no debate or controversy about that.

Once we go above the scale of the organism, this is where the debate begins. Can we think of the forest, the ecosystem, as alive as well? And then one more level higher. Can we think of the planet as alive?

My argument is, yes, that each of those levels, each of those scales is equally alive but not identical. And there are analogous processes that happen at each. But they’re not exactly the same.

What is the next plank of your argument?

Life is also an engine of planetary evolution. The planet evolves over time dramatically. It is not exactly the same as standard Darwinian evolution through natural selection, but it is very much a type of evolution.

Organisms and their environments continually co-evolve. Each is profoundly changing the other.

This reciprocal transformation is responsible for many of the planet’s defining features: for our breathable atmosphere, our blue sky, our bountiful oceans, our fertile soils. This is all because of life and because of the way that life has changed the planetary environments. These are not default features of the planet. Life has created them over time.

What is the most stunning example of how life has actually changed the planet?

In the beginning, Earth had essentially no free oxygen in its atmosphere, and the sky was probably a hazy orange. And when cyanobacteria began to oxygenate the atmosphere through the innovation of photosynthesis, the sky probably started shifting toward the blue part of the spectrum.

The entire chemistry of the planet changed. I mean, you suddenly had an oxygen-rich environment, whereas before it was an oxygen-poor environment. That changes absolutely everything.

Okay, so to get back to what you were saying before, it’s not that Earth evolves in the same way that organisms evolve. But it evolves with a different mechanism, is that right?

Evolutionary biologists will say a planet cannot evolve because it doesn’t have a cohesive genome. There’s no genetic inheritance going on; there’s no sexual reproduction going on.

But there are analogous processes by which changes are passed down from generation to generation that are not genetically encoded.

If we think about a bunch of large mammals, they’re transforming their landscape by walking through it with their immense hefts. They’re tearing down vegetation. They’re digging in, uprooting things. They’re changing the landscape.

Those changes persist. And so their descendants now are evolving in a new environment changed by their predecessors. These environmental changes are not themselves genetically encoded, but they are being passed from generation to generation, and they are inevitably influencing the evolution that follows.

If a fundamental part of life is that it changes the world in which it exists, how are we different for accelerating the climate crisis? Because you look at the history of the Earth and you say, well, life has powerfully changed it. Who’s to say what we’re doing is necessarily not a natural process?

It’s simultaneously humbling and empowering to recognize ourselves as simply the latest chapter in this long evolutionary saga of life changing the planet. It is a basic property of life to change its environment, and we’re not an exception to that.

But I do think there’s a major distinction between what our species has done and what has happened before in terms of the combined scale and speed and the variety of our changes to the planet. I don’t think there’s any species or creature before us that has changed the planet on such a large scale so quickly and in so many different ways simultaneously.

We have radically altered the atmosphere, the oceans, and the continents. We’ve done it in a couple of centuries. That’s a huge part of the reason for why the crisis we’re going through right now is a crisis. It has so much to do with the scale and the speed of it.

What’s part four of your argument?

This co-evolution, on the whole, has amplified the planet’s capacity for self-regulation and enhanced Earth’s resilience. Earth has remained alive for, you know, around 4 billion years, despite repeated catastrophes of unfathomable scale, unlike anything that we have ever experienced in human history. We have to account for that resilience, for that incredible persistence through time.

It is not a deliberate thing. You know, it is not a conscious or collaborative thing. It is simply an inevitable physical process, just as evolution by natural selection is an inevitable physical process.

Even in the mass extinctions in Earth’s history, life recedes to its most fundamental and most resilient forms: microbes . And then life sprouts from there.

Are you sure you’re right about all this? Is the scientific community coming around to accept this notion that Earth is indeed alive?

I mean, this book is my personal synthesis, an argument. You know, this is my viewpoint. This is how I have come to see the Earth. There are scientists who agree with me, but I would not say that this is the consensus of modern mainstream science. I think the statement that Earth is alive remains quite controversial and provocative. However, everything else we’ve been talking about, the co-evolution of life and environment, the fact that life has profoundly changed the planet. These are all well-accepted points.

Which part are you most likely wrong about? Or which part do you feel like has the most room for doubt?

We do not have a precise, universally accepted definition of life. We haven’t explained it on the most fundamental level. Like 100 years from now, will we have a fundamental explanation for life that we’re missing right now? And if we do, will that make thinking of planets as alive defunct? And so, I think open-mindedness is fundamental to any scientific thinking or scientific process. And we have to be open to the idea that a century from now, or even sooner, all of this will be wrong.

And that’s part of what I find thrilling: We don’t have all of the answers yet. Right? These are incredibly challenging ideas and concepts that we are still working out. If we had figured it out, then we wouldn’t be talking about the Gaia hypothesis anymore. The Gaia would have been officially dead a long time ago. But I think the reason that it remains relevant and continues to be debated means that we just haven’t figured it out yet.

Why is it useful to think of the Earth as alive?

There’s a massive difference between thinking of ourselves as living creatures that simply reside on a planet, that simply inhabit a planet, versus being a component of a much larger living entity. When we properly understand our role within the living Earth system, I think the moral urgency of the climate crisis really comes into focus.

All of a sudden it’s not just that, oh, the bad humans have harmed the environment and we need to do something about it. It’s that each of us is literally Earth animated, and we are one part of this much larger, living entity. It’s a realization that everything that we are all doing moment to moment, day to day, is affecting this larger living entity in some way.

So, the simple point that you’re making is that we are Earth, and don’t self-harm.

Right, exactly.

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Environment and Ecology

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Gaia Hypothesis

The Gaia hypothesis was first scientifically formulated in the 1960s by the independent research scientist James Lovelock, as a consequence of his work for NASA on methods of detecting life on Mars. [4] [5] He initially published the Gaia Hypothesis in journal articles in the early 1970s [6] [7] followed by a popularizing 1979 book Gaia: A new look at life on Earth .

The theory was initially, according to Lovelock, a way to explain the fact that combinations of chemicals including oxygen and methane persist in stable concentrations in the atmosphere of the Earth. Lovelock suggested using such combinations detected in other planets' atmospheres would be a relatively reliable and cheap way to detect life, which many biologists opposed at the time and since. Later other relationships such as the fact that sea creatures produce sulfur and iodine in approximately the quantities required by land creatures emerged and helped bolster the theory. Rather than invent many different theories to describe each such equilibrium, Lovelock dealt with them holistically, naming this self-regulating living system after the Greek goddess Gaia, using a suggestion from the novelist William Golding, who was living in the same village as Lovelock at the time (Bowerchalke, Wiltshire, UK). The Gaia Hypothesis has since been supported by a number of scientific experiments [8] and provided a number of useful predictions, [9] and hence is properly referred to as the Gaia Theory.

Since 1971, the noted microbiologist Dr. Lynn Margulis has been Lovelock's most important collaborator in developing Gaian concepts. [10]

Until 1975 the hypothesis was almost totally ignored. An article in the New Scientist of February 15, 1975, and a popular book length version of the theory, published in 1979 as The Quest for Gaia , began to attract scientific and critical attention to the hypothesis. The theory was then attacked by many mainstream biologists. Championed by certain environmentalists and climate scientists, it was vociferously rejected by many others, both within scientific circles and outside them.

Lovelock's initial hypothesis

James Lovelock defined Gaia as:

His initial hypothesis was that the biomass modifies the conditions on the planet to make conditions on the planet more hospitable – the Gaia Hypothesis properly defined this "hospitality" as a full homeostasis. Lovelock's initial hypothesis, accused of being teleological by his critics, was that the atmosphere is kept in homeostasis by and for the biosphere.

Lovelock suggested that life on Earth provides a cybernetic, homeostatic feedback system operated automatically and unconsciously by the biota, leading to broad stabilization of global temperature and chemical composition.

With his initial hypothesis, Lovelock claimed the existence of a global control system of surface temperature, atmosphere composition and ocean salinity. His arguments were:

• The global surface temperature of the Earth has remained constant, despite an increase in the energy provided by the Sun.
• Atmospheric composition remains constant, even though it should be unstable.
• Ocean salinity is constant.

Since life started on Earth, the energy provided by the Sun has increased by 25% to 30%; [11] however the surface temperature of the planet has remained remarkably constant when measured on a global scale. Furthermore, he argued, the atmospheric composition of the Earth is constant. [12] The Earth's atmosphere currently consists of 79% nitrogen, 20.7% oxygen and 0.03% carbon dioxide. Oxygen is the second most reactive element after fluorine, and should combine with gases and minerals of the Earth's atmosphere and crust. Traces of methane (at an amount of 100,000 tonnes produced per annum) [13] should not exist, as methane is combustible in an oxygen atmosphere. This composition should be unstable, and its stability can only have been maintained with removal or production by living organisms.

Ocean salinity has been constant at about 3.4% for a very long time. [14] Salinity stability is important as most cells require a rather constant salinity and do not generally tolerate values above 5%. Ocean salinity constancy was a long-standing mystery, because river salts should have raised the ocean salinity much higher than observed. Recently it was suggested [15] that salinity may also be strongly influenced by seawater circulation through hot basaltic rocks, and emerging as hot water vents on ocean spreading ridges. However, the composition of sea water is far from equilibrium, and it is difficult to explain this fact without the influence of organic processes.

The only significant natural source of atmospheric carbon dioxide (CO 2 ) is volcanic activity, while the only significant removal is through the precipitation of carbonate rocks. [16] In water, CO 2 is dissolved as a "carbonic acid," which may be combined with dissolved calcium to form solid calcium carbonate (limestone). Both precipitation and solution are influenced by the bacteria and plant roots in soils, where they improve gaseous circulation, or in coral reefs, where calcium carbonate is deposited as a solid on the sea floor. Calcium carbonate can also be washed from continents to the sea where it is used by living organisms to manufacture carbonaceous tests and shells. Once dead, the living organisms' shells fall to the bottom of the oceans where they generate deposits of chalk and limestone. Part of the organisms with carbonaceous shells are the coccolithophores (algae), which also have a role in the formation of clouds. When they die, they release dimethyl sulfide gas (DMS), (CH 3 ) 2 S, which is converted by atmospheric processes to sulfate particles on which water vapor condenses to make clouds. [17]

Lovelock sees this as one of the complex processes that maintain conditions suitable for life. The volcanoes produce CO 2 in the atmosphere, CO 2 participates in rock weathering as carbonic acid, itself accelerated by temperature and soil life, the dissolved CO 2 is then used by the algae and released on the ocean floor. CO 2 excess can be compensated by an increase of coccolithophoride life, increasing the amount of CO 2 locked in the ocean floor. Coccolithophorides increase the cloud cover, hence control the surface temperature, help cool the whole planet and favor precipitations which are necessary for terrestrial plants. For Lovelock and other Gaia scientists like Stephan Harding, coccolithophorides are one stage in a regulatory feedback loop. Lately the atmospheric CO 2 concentration has increased and there is some evidence that concentrations of ocean algal blooms are also increasing. [18]

Controversial concepts

Lovelock, especially in his older texts, used language that has later caused fiery debate. For instance, many of his biological critics such as Stephen Jay Gould and Richard Dawkins attacked his statement in the first paragraph of his first Gaia book (1979), that "the quest for Gaia is an attempt to find the largest living creature on Earth." [19]

Lynn Margulis, the coauthor of Gaia hypotheses, is more careful to avoid controversial figures of speech than is Lovelock. In 1979 she wrote, in particular, that only homeorhetic and not homeostatic balances are involved: that is, the composition of Earth's atmosphere, hydrosphere, and lithosphere are regulated around "set points" as in homeostasis, but those set points change with time. Also she wrote that there is no special tendency of biospheres to preserve their current inhabitants, and certainly not to make them comfortable. Accordingly, the Earth is a kind of community of trust which can exist at many discrete levels of integration. This is true for all multicellular organisms which do not live or die all at once: not all cells in the body die instantaneously, nor are homeostatic "set points" constant through the life of an organism.

Critical analysis

This theory is based on the idea that the biomass self-regulates the conditions on the planet to make its physical environment (in particular temperature and chemistry of the atmosphere) on the planet more hospitable to the species which constitute its "life". The Gaia Hypothesis properly defined this "hospitality" as a full homeostasis. A model that is often used to illustrate the original Gaia Hypothesis is the so-called Daisyworld simulation.

Whether this sort of system is present on Earth is still open to debate. Some relatively simple homeostatic mechanisms are generally accepted. For example, when atmospheric carbon dioxide levels rise, the biomass of photosynthetic organisms increases and thus removes more carbon dioxide from the atmosphere, but the extent to which these mechanisms stabilize and modify the Earth's overall climate are not yet known. Less clear is the reason why such traits should evolve in a system in order to produce such effects. Lovelock accepts a process of systemic Darwinian evolution for such mechanisms, creatures that evolve that improve their environment for their survival will do better than those which damage their environment. But many scientists do not believe such mechanisms exist. [20]

After initially being largely ignored by most scientists, (from 1969 until 1977), thereafter for a period, the initial Gaia hypothesis was ridiculed by a number of scientists, like Ford Doolittle, Dawkins and Gould. Lovelock has said that by naming his theory after a Greek goddess, championed by many non scientists [1] , the Gaia hypothesis was derided as some kind of neo-Pagan New Age religion. Many scientists in particular also criticised the approach taken in his popular book "Gaia, a New look at Life on Earth" for being teleological; a belief that all things have a predetermined purpose. Lovelock seems to have accepted this criticism of some of his statements, and has worked hard to remove the taint of teleological thinking from his theories, stating "Nowhere in our writings do we express the idea that planetary self-regulation is purposeful, or involves foresight or planning by the biota." – (Lovelock, J. E. 1990).

In 1981, W. Ford Doolittle, in the CoEvolution Quarterly article "Is Nature Motherly" argued that there was nothing in the genome of individual organisms which could provide the feedback mechanisms Gaia theory proposed, and that therefore the Gaia hypothesis was an unscientific theory of a maternal type without any explanatory mechanism. In Richard Dawkins' 1982 book, The Extended Phenotype , he argued that organisms could not act in concert as this would require foresight and planning from them. Like Doolittle he rejected the possibility that feedback loops could stabilize the system. Dawkins claimed "there was no way for evolution by natural selection to lead to altruism on a Global scale".

Stephen Jay Gould criticised Gaia as merely a metaphorical description of Earth processes [21] . He wanted to know the actual mechanisms by which self-regulating homeostasis was regulated. Lovelock argues that no one mechanism is responsible, that the connections between the various known mechanisms may never be known, that this is accepted in other fields of biology and ecology as a matter of course, and that specific hostility is reserved for his own theory for political reasons.

Aside from clarifying his language and understanding of what is meant by a life form, Lovelock himself ascribes most of the criticism to a lack of understanding of non-linear mathematics by his critics, and a linearizing form of greedy reductionism in which all events have to be immediately ascribed to specific causes before the fact. He notes also that his theory suggests experiments in many different fields, but few of them in biology which most of his critics are trained in. "I'm a general practitioner in a world where there's nothing but specialists... science in the last two centuries has tended to be ever-dividing" and often rivalrous, especially for funding which Lovelock describes as overly abundant and overly focused on institutions rather than original thought. He points out that Richard Feynman not only shared this opinion (coining the term cargo cult science) but also accepted a lack of general cause and effect explanation as an inevitable phase in a theory's development, and believed that some self-regulating phenomena may not be explainable at all mathematically.

One of the criteria of the empirical definition of life is its ability to replicate and pass on their genetic information to succeeding generations. Consequently, an argument against the idea that Gaia is a "living" organism is the fact that the planet is unable to reproduce.

Lovelock, however, defines life as a self-preserving, self-similar system of feedback loops like Humberto Maturana's autopoiesis; as a self-similar system, life could be a cell as well as an organ embedded into a larger organism as well as an individual in a larger inter-dependent social context. The biggest context of interacting inter-dependent living entities is the Earth. The problematic empirical definition is getting "fuzzy on the edges": Why are highly specialized bacteria like E. coli that are unable to thrive outside their habitat considered "life", while mitochondria, which have evolved independently from the rest of the cell, are not?

Maturana and Lovelock changed this with the autopoiesis deductive definition which to them explains the phenomenon of life better; some aspects of the empirical definition, however, no longer apply. Reproduction becomes optional: bee swarms reproduce, while the biosphere has no need to. Lovelock himself states in the original Gaia book that even that is not true; given the possibilities, the biosphere may multiply in the future by colonizing other planets, as humankind may be the primer by which Gaia will reproduce. Humanity's exploration of space, its interest in colonizing and even terraforming other planets, lends some plausibility to the idea that Gaia might in effect be able to reproduce.

The astronomer Carl Sagan also remarked that from a cosmic viewpoint, the space probes since 1959 have the character of a planet preparing to go to seed [22] . This might warrant interpretation as a rhetorical point, however, as it equivocates two differing meanings of "reproduction" otherwise.

Daisyworld simulations

Lovelock responded to criticisms by developing the mathematical model Daisyworld with Andrew Watson to demonstrate that feedback mechanisms could evolve from the actions or activities of self-interested organisms, rather than through classic group selection mechanisms. [23]

Daisyworld examines the energy budget of a planet populated by two different types of plants, black daisies and white daisies. The colour of the daisies influences the albedo of the planet such that black daisies absorb light and warm the planet, while white daisies reflect light and cool the planet. Competition between the daisies (based on temperature-effects on growth rates) leads to a balance of populations that tends to favour a planetary temperature close to that which is optimum for the daisy growth. Lovelock and Watson demonstrated the stability of Daisyworld by forcing the sun that it orbits to evolve along the main sequence, taking it from low to high solar constant. This perturbation of Daisyworld's receipt of solar radiation caused the balance of daisies to gradually shift from black to white but the planetary temperature was always regulated back to this optimum (except at the extreme ends of solar evolution). This situation is very different from the corresponding abiotic world, where temperature is unregulated and rises linearly with solar output. Later versions of Daisyworld introduced a range of grey daisies and populations of grazers and predators, and found that these further increased the stability of the homeostasis. More recently other research, modelling the real biochemical cycles of Earth, and using various "guilds" of life (eg. photosynthesisers, decomposers, herbivores and primary and secondary carnivores) has also been shown to produce Daisyworld-like regulation and stability, which helps to explain planetary biological diversity.

This enables nutrient recycling within a regulatory framework derived by natural selection amongst species, where one being's harmful waste becomes low energy food for members of another guild. This research on the Redfield ratio of Nitrogen to Phosphorus shows that local biotic processes can regulate global systems (See Keith Downing & Peter Zvirinsky, The Stimulated Evolution of Biochemical Guilds: Reconciling Gaia Theory with Natural Selection ).

First Gaia conference

In 1988, to draw attention to the Gaia hypothesis, the climatologist Stephen Schneider organised a conference of the American Geophysical Union's first Chapman Conference on Gaia, held at San Diego in 1989, solely to discuss Gaia.

At the conference James Kirchner criticised the Gaia hypothesis for its imprecision. He claimed that Lovelock and Margulis had not presented one Gaia hypothesis, but four -

• CoEvolutionary Gaia — that life and the environment had evolved in a coupled way. Kirchner claimed that this was already accepted scientifically and was not new.
• Homeostatic Gaia — that life maintained the stability of the natural environment, and that this stability enabled life to continue to exist.
• Geophysical Gaia — that the Gaia theory generated interest in geophysical cycles and therefore led to interesting new research in terrestrial geophysical dynamics.
• Optimising Gaia — that Gaia shaped the planet in a way that made it an optimal environment for life as a whole. Kirchner claimed that this was not testable and therefore was not scientific.

Of Homeostatic Gaia, Kirchner recognised two alternatives. "Weak Gaia" asserted that life tends to make the environment stable for the flourishing of all life. "Strong Gaia" according to Kirchner, asserted that life tends to make the environment stable, in order to enable the flourishing of all life. Strong Gaia, Kirchner claimed, was untestable and therefore not scientific.

Referring to the Daisyworld Simulations, Kirchner responded that these results were predictable because of the intention of the programmers — Lovelock and Watson, who selected examples which would produce the responses they desired.

Lawrence Joseph in his book "Gaia: the birth of an idea" argued that Kirchner's attack was principally against Lovelock's integrity as a scientist. Lovelock did not attack Kirchner's views for ten years, until his autobiography "Homage to Gaia", where he calls Kirchner's position sophistry . Lovelock and other Gaia-supporting scientists, however, did attempt to disprove the claim that the theory is not scientific because it is impossible to test it by controlled experiment. For example, against the charge that Gaia was teleological Lovelock and Andrew Watson offered the Daisyworld model (and its modifications, above) as evidence against most of these criticisms.

Lovelock was careful to present a version of the Gaia Hypothesis which had no claim that Gaia intentionally or consciously maintained the complex balance in her environment that life needed to survive. It would appear that the claim that Gaia acts "intentionally" was a metaphoric statement in his popular initial book and was not meant to be taken literally. This new statement of the Gaia hypothesis was more acceptable to the scientific community.

The accusations of teleologism were largely dropped after this conference.

Range of views

Some have found James Kirchner's suggested spectrum, proposed at the First Gaia Chapman Conference, useful in suggesting that the original Gaia hypothesis could be split into a spectrum of hypotheses, ranging from the undeniable (Weak Gaia) to the radical (Strong Gaia).

At one end of this spectrum is the undeniable statement that the organisms on the Earth have altered its composition. A stronger position is that the Earth's biosphere effectively acts as if it is a self-organizing system, which works in such a way as to keep its systems in some kind of "meta-equilibrium" that is broadly conducive to life. The history of evolution, ecology and climate show that the exact characteristics of this equilibrium intermittently have undergone rapid changes, which are believed to have caused extinctions and felled civilizations (see climate change).

Weak Gaian hypotheses suggest that Gaia is co-evolutive. Co-evolution in this context has been thus defined: "Biota influence their abiotic environment, and that environment in turn influences the biota by Darwinian process." Lovelock (1995) gave evidence of this in his second book, showing the evolution from the world of the early thermo-acido-philic and methanogenic bacteria towards the oxygen enriched atmosphere today that supports more complex life.

The weakest form of the theory has been called "influential Gaia". It states that biota minimally influence certain aspects of the abiotic world, e.g. temperature and atmosphere.

The weak versions are more acceptable from an orthodox science perspective, as they assume non-homeostasis. They state the evolution of life and its environment may affect each other. An example is how the activity of photosynthetic bacteria during Precambrian times have completely modified the Earth atmosphere to turn it aerobic, and as such supporting evolution of life (in particular eukaryotic life). However, these theories do not claim the atmosphere modification has been done in coordination and through homeostasis. Also such critical theories have yet to explain how conditions on Earth have not been changed by the kinds of run-away positive feedbacks that have affected Mars and Venus.

Biologists and earth scientists usually view the factors that stabilize the characteristics of a period as an undirected emergent property or entelechy of the system; as each individual species pursues its own self-interest, for example, their combined actions tend to have counterbalancing effects on environmental change. Opponents of this view sometimes reference examples of lives' actions that have resulted in dramatic change rather than stable equilibrium, such as the conversion of the Earth's atmosphere from a reducing environment to an oxygen-rich one. However, proponents argue these atmospheric changes improved the environment's suitability for life.

Some go a step further and hypothesize that all lifeforms are part of one single living planetary being called Gaia . In this view, the atmosphere, the seas and the terrestrial crust would be results of interventions carried out by Gaia through the coevolving diversity of living organisms. While it is arguable that the Earth as a unit does not match the generally accepted biological criteria for life itself ( Gaia has not yet reproduced, for instance; it still might spread to other planets through human space colonization and terraforming), many scientists would be comfortable characterizing the earth as a single "system".

Strong Gaia

A version called "Optimizing Gaia" asserts that biota manipulate their physical environment for the purpose of creating biologically favorable, or even optimal, conditions for themselves. "The Earth's atmosphere is more than merely anomalous; it appears to be a contrivance specifically constituted for a set of purposes" [7] . Further, "... it is unlikely that chance alone accounts for the fact that temperature, pH and the presence of compounds of nutrient elements have been, for immense periods, just those optimal for surface life. Rather, ... energy is expended by the biota to actively maintain these optima" [7] .

Another strong hypothesis is the one called "Omega Gaia" [24] . Teilhard de Chardin claimed that the Earth is evolving through stages of cosmogenesis, affecting the geosphere, biogenesis of the biosphere, and noogenesis of the noosphere, culminating in the Omega Point . Another form of the strong Gaia hypothesis is proposed by Guy Murchie who extends the quality of a holistic lifeform to galaxies. "After all, we are made of star dust. Life is inherent in nature." Murchie describes geologic phenomena such as sand dunes, glaciers, fires, etc. as living organisms, as well as the life of metals and crystals. "The question is not whether there is life outside our planet, but whether it is possible to have "nonlife".

There are speculative versions of the Gaia hypothesis, including versions in which it is held that the Earth is conscious or part of some universe-wide evolution such as expressed in the Selfish Biocosm hypothesis strain of a larger speculative Gaia philosophy. These extreme forms of the Gaia hypothesis, that the entire Earth is a single unified organism that is consciously manipulating the climate in order to make conditions more conducive to life, are metaphysical or mystical views for which no evidence exists, and which cannot be tested scientifically. Another strain which also goes further than science presently justifies, is the Gaia Movement, a collection of different organisations operating in different countries, but all sharing a concern for how humans might live more sustainably within the "living system".

Recent developments

Gaia Theory has developed considerably and in recent years both Lovelock's and Margulis's understanding of Gaia have gained some increased support as a potentially viable, testable scientific hypothesis or theory. [10] [25] . Margulis dedicated the last of eight chapters in her book, The Symbiotic Planet , to Gaia. She resented the widespread personification of Gaia and stressed that Gaia is "not an organism", but "an emergent property of interaction among organisms". She defined Gaia "the series of interacting ecosystems that compose a single huge ecosystem at the Earth's surface. Period." Yet still she argues, "the surface of the planet behaves as a physiological system in certain limited ways". Margulis seems to agree with Lovelock in that, in what comes to these physiological processes, the Earth's surface is "best regarded as alive". The book's most memorable "slogan" was actually quipped by a student of Margulis': "Gaia is just symbiosis as seen from space". This neatly connects Gaia theory to Margulis' own theory of endosymbiosis.

Second Gaia conference

By the time of the 2nd Chapman Conference on the Gaia Hypothesis, held at Valencia, Spain, on 23 June 2000, the situation had developed significantly in accordance with the developing science of Bio-geophysiology. Rather than a discussion of the Gaian teleological views, or "types" of Gaia Theory, the focus was upon the specific mechanisms by which basic short term homeostasis was maintained within a framework of significant evolutionary long term structural change.

The major questions were:

• "How has the global biogeochemical/climate system called Gaia changed in time? What is its history? Can Gaia maintain stability of the system at one time scale but still undergo vectorial change at longer time scales? How can the geologic record be used to examine these questions?"
• "What is the structure of Gaia? Are the feedbacks sufficiently strong to influence the evolution of climate? Are there parts of the system determined pragmatically by whatever disciplinary study is being undertaken at any given time or are there a set of parts that should be taken as most true for understanding Gaia as containing evolving organisms over time? What are the feedbacks among these different parts of the Gaian system, and what does the near closure of matter mean for the structure of Gaia as a global ecosystem and for the productivity of life?"
• "How do models of Gaian processes and phenomena relate to reality and how do they help address and understand Gaia? How do results from Daisyworld transfer to the real world? What are the main candidates for "daisies"? Does it matter for Gaia theory whether we find daisies or not? How should we be searching for daisies, and should we intensify the search? How can Gaian mechanisms be investigated using process models or global models of the climate system which include the biota and allow for chemical cycling?"

In 1997. Tyler Volk argued that a Gaian system is almost inevitably produced as a result of an evolution towards far-from-equilibrium homeostatic states that maximise entropy production, and Kleidon (2004) agreed stating: "...homeostatic behavior can emerge from a state of MEP associated with the planetary albedo"; "...the resulting behavior of a biotic Earth at a state of MEP may well lead to near-homeostatic behavior of the Earth system on long time scales, as stated by the Gaia hypothesis." Staley (2002) has similarly proposed "...an alternative form of Gaia theory based on more traditional Darwinian principles... In [this] new approach, environmental regulation is a consequence of population dynamics, not Darwinian selection. The role of selection is to favor organisms that are best adapted to prevailing environmental conditions. However, the environment is not a static backdrop for evolution, but is heavily influenced by the presence of living organisms. The resulting co-evolving dynamical process eventually leads to the convergence of equilibrium and optimal conditions."

Third Gaia conference

A third international conference on the Gaia Theory, sponsored by the Northern Virginia Regional Park Authority and others, was held in October 2006 at the Arlington, VA campus of George Mason University. Lynn Margulis, Distinguished University Professor in the Department of Geosciences, University of Massachusetts-Amherst, and long-time advocate of the Gaia Theory, was a keynote speaker. Among many other speakers: Tyler Volk, Co-director of the Program in Earth and Environmental Science at New York University; Dr. Donald Aitken, Principal of Donald Aitken Associates; Dr. Thomas Lovejoy, President of the Heinz Center for Science, Economics and the Environment; Robert Correll, Senior Fellow, Atmospheric Policy Program, American Meteorological Society and noted environmental ethicist, J. Baird Callicott. James Lovelock, the theory’s progenitor, prepared a video specifically for the event.

This conference approached Gaia Theory as both science and metaphor as a means of understanding how we might begin addressing 21st century issues such as climate change and ongoing environmental destruction.

Gaia hypothesis in ecology

After much criticism, a modified Gaia hypothesis is now considered within ecological science basically consistent with the planet Earth being the ultimate object of ecological study. Ecologists generally consider the biosphere as an ecosystem and the Gaia hypothesis, though a simplification of that original proposed, to be consistent with a modern vision of global ecology, relaying the concepts of biosphere and biodiversity. The Gaia hypothesis has been called geophysiology or Earth System Science, which takes into account the interactions between biota, the oceans, the geosphere, and the atmosphere. To promote research and discussion in these fields an organisation, "Gaia Society for Research and Education in Earth System Science" was started.

An example of the change in acceptability of Gaia theories is the Amsterdam declaration of the scientific communities of four international global change research programmes — the International Geosphere-Biosphere Programme (IGBP), the International Human Dimensions Programme on Global Environmental Change (IHDP), the World Climate Research Programme (WCRP) and the international biodiversity programme DIVERSITAS — recognise that, in addition to the threat of significant climate change, there is growing concern over the ever-increasing human modification of other aspects of the global environment and the consequent implications for human well-being.

"Research carried out over the past decade under the auspices of the four programmes to address these concerns has shown that:

• The Earth System behaves as a single, self-regulating system with physical, chemical, biological, and human components. The interactions and feedbacks between the component parts are complex and exhibit multi-scale temporal and spatial variability. The understanding of the natural dynamics of the Earth System has advanced greatly in recent years and provides a sound basis for evaluating the effects and consequences of human-driven change.
• Human activities are significantly influencing Earth's environment in many ways in addition to greenhouse gas emissions and climate change. Anthropogenic changes to Earth's land surface, oceans, coasts and atmosphere and to biological diversity, the water cycle and biogeochemical cycles are clearly identifiable beyond natural variability. They are equal to some of the great forces of nature in their extent and impact. Many are accelerating. Global change is real and is happening now.
• Global change cannot be understood in terms of a simple cause-effect paradigm. Human-driven changes cause multiple effects that cascade through the Earth System in complex ways. These effects interact with each other and with local- and regional-scale changes in multidimensional patterns that are difficult to understand and even more difficult to predict.
• Earth System dynamics are characterised by critical thresholds and abrupt changes. Human activities could inadvertently trigger such changes with severe consequences for Earth's environment and inhabitants. The Earth System has operated in different states over the last half million years, with abrupt transitions (a decade or less) sometimes occurring between them. Human activities have the potential to switch the Earth System to alternative modes of operation that may prove irreversible and less hospitable to humans and other life. The probability of a human-driven abrupt change in Earth's environment has yet to be quantified but is not negligible.
• In terms of some key environmental parameters, the Earth System has moved well outside the range of the natural variability exhibited over the last half million years at least. The nature of changes now occurring simultaneously in the Earth System, their magnitudes and rates of change are unprecedented. The Earth is currently operating in a no-analogue state."

Sir Crispin Tickell in the 46th Annual Bennett Lecture for the 50th Anniversary of Geology at the University of Leicester in his recent talk "Earth Systems Science: Are We Pushing Gaia Too Hard?" stated "as a theory, Gaia is now winning." [26]

He continued "The same goes for the earth systems science which is now the concern of the Geological Society of London (with which the Gaia Society recently merged). Whatever the label, earth systems science, or Gaia, has now become a major subject of inquiry and research, and no longer has to justify itself."

These findings would seem to be fully in accord with the Gaia theory. Despite this endorsement, the late W. D. Hamilton, one of the founders of modern Darwinism, whilst conceding the empirical basis of the planetary homeostatic processes on which Gaia is based, states that it is a theory still awaiting its Copernicus. The homeostatic nature of the global system has been recognized as a consequence of the 2 nd law of thermodynamics. [27] In their comprehensive book on the thermodynamics of life, Eric D. Schneider and Dorion Sagan argue that Gaia belongs to a class of complex thermodynamic systems, not just living ones, that are naturally purposeful; and that life optimizes rather than maximizes entropy production. [28]

The Revenge of Gaia

In James Lovelock's 2006 book, The Revenge of Gaia , he argues that the lack of respect humans have had for Gaia, through the damage done to rainforests and the reduction in planetary biodiversity, is testing Gaia's capacity to minimize the effects of the addition of greenhouse gases in the atmosphere. This eliminates the planet's negative feedbacks and increases the likelihood of homeostatic positive feedback potential associated with runaway global warming. Similarly the warming of the oceans is extending the oceanic thermocline layer of tropical oceans into the Arctic and Antarctic waters, preventing the rise of oceanic nutrients into the surface waters and eliminating the algal blooms of phytoplankton on which oceanic foodchains depend. As phytoplankton and forests are the main ways in which Gaia draws down greenhouse gases, particularly carbon dioxide, taking it out of the atmosphere, the elimination of this environmental buffering will see, according to Lovelock, most of the earth becoming uninhabitable for humans and other life-forms by the middle of this century, with a massive extension of tropical deserts.

Given these conditions, Lovelock expects human civilization will be hard pressed to survive. He expects the change to be similar to the Paleocene-Eocene Thermal Maximum when atmospheric concentration of CO 2 was 450 ppm. At that point the Arctic Ocean was 23 °C and had crocodiles in it, with the rest of the world mostly scrub and desert. He says of sustainable development and renewable energy that it came "200 years too late" and that more effort should go into adaptation, including more use of fission. He likens the Kyoto Protocol to the Munich conferences that failed to prevent World War II, including the likelihood that the disaster will cause people to come together in common cause. "We have been through no less than seven of these events as humans...comparable in extent to the change" likely to be wrought by global warming.

He claims that Gaia's self-regulation will likely prevent any extraordinary runaway effects that wipe out life itself, but that humans will survive and be "culled and, I hope, refined."

According to James Lovelock, by 2040, the world population of more than six billion will have been culled by floods, drought and famine. Indeed [t]he people of Southern Europe, as well as South-East Asia, will be fighting their way into countries such as Canada, Australia and Britain . [29]

" By 2040, parts of the Sahara desert will have moved into middle Europe. We are talking about Paris - as far north as Berlin. In Britain we will escape because of our oceanic position." [29]

" If you take the Intergovernmental Panel on Climate Change predictions, then by 2040 every summer in Europe will be as hot as it was in 2003 - between 110F and 120F. It is not the death of people that is the main problem, it is the fact that the plants can't grow — there will be almost no food grown in Europe. " [29]

" We are about to take an evolutionary step and my hope is that the species will emerge stronger. It would be hubris to think humans as they now are God's chosen race. " [29]

Lovelock believes it is too late to repair the damage. [29]

Influences of the Gaia hypothesis

Scientific literature.

Fritjof Capra, in his fourth book, The Web of Life, used Gaia theory to explain the complications and interconnections in the web of life.

Stephan Harding, a student of Lovelock, has written a book, Animate Earth: Science, Intuition, and Gaia .

John Gribben and Mary Gribben have written a book "James Lovelock - In Search of Gaia" and published by Princeton University Press. ISBN 978-0-691-13750-6. Reviewed briefly in EOS (Trans, AGU), Vol. 90, No. 20, 19 May 2009.

An oratorio by American composer Nathan Currier called Gaian Variations was premiered on Earth Day 2004 at Lincoln Center by the Brooklyn Philharmonic, using texts of James Lovelock, Loren Eiseley and Lewis Thomas.

A Heavy Metal/ Folk Rock band from Spain called Mago de Oz has also composed two songs "Gaia" and "La Venganza de Gaia" (Gaia's Revenge) which talk about man and his actions, altering the natural balance on earth. These songs claim that all bad things done to Gaia, will be brought upon man as well, given that we are all part of the same living entity. The Disco Biscuits, from Philadelphia, mention Gaia many times as the central theme in their song "Jigsaw Earth" on their 2002 album Senor Boombox

On his 1997 CD release Hourglass , Popular American songwriter James Taylor included a song called "Gaia".

The Melodic Death metal band At the Throne of Judgement, on their record "The Arcanum Order", includes a song "Martyrdom, Ruin of Gaia"

In 2009, Kevadbänd has reflected Gaia hypothesis in its hit song "Kasvaja" ("Tumor"), which states that the Gaia organism is suffering from lethal tumor: the human race

American heavy metal band God Forbid included a song entitled "Gaia (The Vultures)" on their 2009 release "Earthsblood".

Movies and television

The film Virus features a cyborg that believes humanity to be a virus that has infected its host organism, Earth.

The South Park episode Lice Capades addresses the Gaia hypothesis from an ironic standpoint – when one louse suggests that the planet (a child's head) is alive, another louse responds with "If the planet was alive, would it feel this?" and shoots the boy's head – the impact being so minute the boy barely notices.

Edge of Darkness a British television drama serial, produced by BBC Television in association with Lionheart Television International and originally broadcast in six fifty-five minute episodes in late 1985.

In Final Fantasy: The Spirits Within, a sci-fi movie, Dr. Sid and his assistant Aki are fierce promoters of the Gaia Theory. Though, in the film, "Gaia" is in reference to the underlying life force within the planet, very similar to the lifestream found in Final Fantasy VII.

The series Eureka Seven features a planet where coral structure engulfed the planet making it a super organism.

James Cameron's Avatar features a Gaia-like network on the planet of Pandora, in which all the organisms have a biological ability to "connect" and share mental communication. This is perhaps a metaphor for the interconnections and systems between organisms and the environment on Earth. The Gaia-like system in Avatar is referred to as Eywa, a goddess which the natives worship as a mother earth figure. This reference back to earth and the Gaia Hypothesis is further supported by a scene from the move where Jake Sully's Avatar, while "praying" to Eywa, says that they (referring to Earthlings) "Killed their mother".

A number of works of fiction use the Gaia hypothesis as a central part of the plot. In two of his science fiction novels, Foundation's Edge (1982) and Foundation and Earth (1984), Isaac Asimov describes the planet Gaia as one on which all things, living and inanimate, are taking part in a planetary consciousness to an appropriate measure. In Asimov's story Gaia strives for an even greater superorganism that it calls Galaxia, and that comprises the whole galaxy.

In Lovelock (1994), a novel by Orson Scott Card & Kathryn H. Kidd, Gaiaology is a fully fledged interdisciplinary science which will soon be put to use by the Earth's first interstellar colony ship. Assuming the target planet will need terraforming, the job of the ship's Gaiaologist will be to integrate the terrestrial species needed for the colonists' survival with the planet's existing ecology. The Gaiaologist's "Witness", a form of assistance animal whose job it is to record every waking moment in the life of such a prominent member of society, is the central character of the book, an enhanced Capuchin monkey named after Lovelock.

The Gaia hypothesis is used extensively by Brian Aldiss in his Helliconia Trilogy, where the planets of Helliconia and, to a lesser extent, Earth, are presented as the main characters in a story spanning the rise and fall of civilizations as influenced by Helliconia's 2,500-year-long cycle of seasons.

The Gaia hypothesis was also used as a central theme in the novel Portent , by James Herbert, in which Lovelock is mentioned by name.

David Brin's novel Earth discusses the Gaia hypothesis and features a fictional Gaia ecological movement.

The plot of the novel Gaia by David Orrell involves a Gaian cult that intends to purge the Earth of humanity by spreading a bioengineered disease.

American poet, writer and Deep Ecology activist Gary Snyder has a chapter of poems called "Little Songs for Gaia" in his collection of poetry "Axe Handles" (1983).

Maxis has specifically named the Gaia hypothesis and Lovelock as inspirations for their 1990 game, SimEarth.

The 1997 console role-playing game, Final Fantasy VII features a paradigm of so-called Lifestream, also appearing in the 2001 film, Final Fantasy: The Spirits Within as the 'Dr. Sid's Gaia Theory' (these theories look almost identical due to the same scenario writers, Hironobu Sakaguchi and Kazushige Nojima). According to it, all living beings are given some 'spiritual energy' by the spirit of the Planet (Gaia) prior to birth, live out their lives, and then die, with the energy then returning to the Planet. The entire planet (or Gaia) is really a single living organism with its own consciousness and will.

The 2008 Sega title Sonic Unleashed contains the character Eggman (Sonic's arch nemesis), fueled with the desire to control the Earth's 'Gaia force' and attempting to crack open the planet to unleash an Evil Entity confined within the Earth's core. Eggman also claims to have studied the 'Gaia Manuscripts'.

The 1999 turn-based strategy PC game, Sid Meier's Alpha Centauri , features a living (and eventually sentient) planet in the Alpha Centauri star system. One of the games factions is named "Gaia's Stepdaughters", a group of environmentalists who believe in living with the planet rather than trying to tame or destroy it.

Pop culture

The notion of Gaia has been applied to the networked society and the globalized Internet by cultural theorist Dr. Michael Strangelove , "Confronted with the inaccessibility of our physical frontiers, my generation has turned inward and discovered two new immanent and infinite frontiers. These new frontiers of the next millennium are the uncensored, distributed self, and cyberspace —the location of the virtual self/community— Electric Gaia." [30]

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• ^ a b Lovelock, James 2001
• ^ http://www.ecolo.org/lovelock/lovelock-online_chat-00.htm
• ^ Lovelock, James 2007
• ^ Lovelock, J.E. (1965). "A physical basis for life detection experiments". Nature 207 (7): 568–570. doi : 10.1038/207568a0 .
• ^ Geophysiology
• ^ J. E. Lovelock (1972). "Gaia as seen through the atmosphere". Atmospheric Environment 6 (8): 579–580. doi : 10.1016/0004-6981(72)90076-5 .
• ^ a b c Lovelock, J.E.; Margulis, L. (1974). "Atmospheric homeostasis by and for the biosphere- The Gaia hypothesis". Tellus 26 (1): 2–10.
• ^ J. E. Lovelock (1990). "Hands up for the Gaia hypothesis". Nature 344 (6262): 100–2. doi : 10.1038/344100a0 .
• ^ Volk, Tyler (2003). Gaia's Body: Toward a Physiology of Earth . Cambridge, Mass: MIT Press. ISBN 0-262-72042-6 .
• ^ a b Turney, Jon (2003). Lovelock and Gaia: Signs of Life . UK: Icon Books. ISBN 1-84046-458-5 .
• ^ Owen, T.; Cess, R.D.; Ramanathan, V. (1979). "Earth: An enhanced carbon dioxide greenhouse to compensate for reduced solar luminosity". Nature 277 : 640–2. doi : 10.1038/277640a0 .
• ^ Lovelock, James 2000
• ^ Cicerone, R.J.; Oremland, R.S. (1988). "Biogeochemical aspects of atmospheric methane" . Global Biogeochem. Cycles 2 (4): 299–327. doi : 10.1029/GB002i004p00299 . http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6704984 .
• ^ Volk, T. (2002). "Toward a Future for Gaia Theory". Climatic Change 52 (4): 423–430. doi : 10.1023/A:1014218227825 .
• ^ Gorham, E. (1991). "Biogeochemistry: its origins and development". Biogeochemistry 13 (3): 199–239. doi : 10.1007/BF00002942 .
• ^ Karhu, J.A.; Holland, H.D. (1 October 1996). "Carbon isotopes and the rise of atmospheric oxygen" . Geology 24 (10): 867–870. doi : 10.1130/0091-7613(1996)024<0867:CIATRO>2.3.CO;2 . http://geology.geoscienceworld.org/cgi/content/abstract/24/10/867 .
• ^ Harding, Stephan (2006). Animate Earth . Green Books. ISBN 1-903998-75-1 .
• ^ Interagency Report Says Harmful Algal Blooms Increasing , 12 September 2007, http://www.publicaffairs.noaa.gov/releases2007/sep07/noaa07-r435.html
• ^ Lovelock, J."Gaia:a new look at life on earth" (Oxford UP:1979,1)
• ^ Kirchner, James (March 2002). "The Gaia Hypothesis: Fact, Theory, and Wishful Thinking" . Climatic Change 52 (4): 391–408. doi : 10.1023/A:1014237331082 . http://seismo.berkeley.edu/~kirchner/reprints/2002_55_Kirchner_gaia.pdf .
• ^ Gould S.J. (June 1997). "Kropotkin was no crackpot" . Natural History 106 : 12–21. http://libcom.org/library/kropotkin-was-no-crackpot .
• ^ Sagan, Carl and Jerome Agel (1973). Cosmic Connection: An Extraterrestrial Perspective . Anchor Press. ISBN 0-521-78303-8 .
• ^ Watson, A.J., and Lovelock, J.E (1983). "Biological homeostasis of the global environment: the parable of Daisyworld.". Tellus 35B : 286–9.
• ^ Stages in the Evolution of Gaia , Kheper website . Retrieved 14 May 2008.
• ^ Schwartzman, David (2002). Life, Temperature, and the Earth: The Self-Organizing Biosphere . Columbia University Press. ISBN 0231102135 .
• ^ University of Leicester - Earth Systems Science: Are We Pushing Gaia Too Hard?
• ^ Karnani, M. and Annila, A. (2009). "Gaia Again". Biosystems 95 (1): 82–87. doi : 10.1016/j.biosystems.2008.07.003 . PMID 18706969 .
• ^ Schneider, Eric, D. and Sagan, Dorion (2004). Into the Cool: Energy Flow, Thermodynamics, and Life . Chicago: University of Chicago Press. ISBN 978-0226739366 .
• ^ a b c d e Daily Mail - 22 March 2008 - We're all doomed ! 40 years from global catastrophe - says climate change expert
• ^ Strangelove, Michael (1 September 1994). "The Internet, Electric Gaia and the Rise of the Uncensored Self" . Computer-Mediated Communication Magazine 1 (5): 11. http://www.ibiblio.org/cmc/mag/1994/sep/self.html .
• Bondì, Roberto (2006). Blu come un'arancia. Gaia tra mito e scienza . Torino, Utet: Prefazione di Enrico Bellone. ISBN 88-02-07259-0.
• Bondì, Roberto (2007). Solo l'atomo ci può salvare. L'ambientalismo nuclearista di James Lovelock . Torino, Utet: Prefazione di Enrico Bellone. ISBN 88-02-07704-8.
• Lovelock, James. The Independent . The Earth is about to catch a morbid fever, 16 January 2006.
• Kleidon, Axel (2004). "Beyond Gaia: Thermodynamics of Life and Earth system functioning". Climatic Change 66 (3): 271–319. doi:10.1023/B:CLIM.0000044616.34867.ec.
• Lovelock, James (1995). The Ages of Gaia: A Biography of Our Living Earth . New York: Norton. ISBN 0-393-31239-9.
• Lovelock, James (2000). Gaia: A New Look at Life on Earth . Oxford: Oxford University Press. ISBN 0-19-286218-9.
• Lovelock, James (2001). Homage to Gaia: The Life of an Independent Scientist . Oxford: Oxford University Press. ISBN 0-19-860429-7.
• Lovelock, James (2006), interviewed in How to think about science , CBC Ideas (radio program), broadcast January 3, 2008
• Lovelock, James (2007). The Revenge of Gaia: Why the Earth Is Fighting Back — and How We Can Still Save Humanity . Allen Lane. ISBN 0-7139-9914-4.
• Margulis, Lynn (1998). Symbiotic Planet: A New Look at Evolution . London: Weidenfeld & Nicolson. ISBN 0-297-81740-X.
• Marshall, Alan (2002). The Unity of Nature: Wholeness and Disintegration in Ecology and Science . River Edge, N.J: Imperial College Press. ISBN 1-86094-330-6.
• Staley M (September 2002). "Darwinian selection leads to Gaia". J. Theor. Biol. 218 (1): 35–46. doi:10.1006/jtbi.2002.3059. PMID 12297068. http://linkinghub.elsevier.com/retrieve/pii/S0022519302930596 .
• Schneider, Stephen Henry (2004). Scientists debate Gaia: the next century . Cambridge, Mass: MIT Press. ISBN 0-262-19498-8.
• Thomas, Lewis G. (1974). The Lives of a Cell; Notes of a Biology Watcher . New York: Viking Press. ISBN 0-670-43442-6.

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The Gaia hypothesis (/ˈɡaɪ.ə/), also known as the Gaia theory, Gaia paradigm, or the Gaia principle, proposes that living organisms interact with their inorganic surroundings on Earth to form a synergistic and self-regulating, complex system that helps to maintain and perpetuate the conditions for life on the planet. The hypothesis was formulated by the chemist James Lovelock and co-developed by the microbiologist Lynn Margulis in the 1970s. Lovelock named the idea after Gaia, the primordial goddess who personified the Earth in Greek mythology. The suggestion that the theory should be called "the Gaia hypothesis" came from Lovelock's neighbour, William Golding. In 2006, the Geological Society of London awarded Lovelock the Wollaston Medal in part for his work on the Gaia hypothesis. Topics related to the hypothesis include how the biosphere and the evolution of organisms affect the stability of global temperature, salinity of seawater, atmospheric oxygen levels, the maintenance of a hydrosphere of liquid water and other environmental variables that affect the habitability of Earth. The Gaia hypothesis was initially criticized for being teleological and against the principles of natural selection, but later refinements aligned the Gaia hypothesis with ideas from fields such as Earth system science, biogeochemistry and systems ecology. Even so, the Gaia hypothesis continues to attract criticism, and today many scientists consider it to be only weakly supported by, or at odds with, the available evidence.

1. Overview

Gaian hypotheses suggest that organisms co-evolve with their environment: that is, they "influence their abiotic environment, and that environment in turn influences the biota by Darwinian process". Lovelock (1995) gave evidence of this in his second book, Ages of Gaia , showing the evolution from the world of the early thermo-acido-philic and methanogenic bacteria towards the oxygen-enriched atmosphere today that supports more complex life.

A reduced version of the hypothesis has been called "influential Gaia" [ 1 ] in "Directed Evolution of the Biosphere: Biogeochemical Selection or Gaia?" by Andrei G. Lapenis, which states the biota influence certain aspects of the abiotic world, e.g. temperature and atmosphere. This is not the work of an individual but a collective of Russian scientific research that was combined into this peer reviewed publication. It states the coevolution of life and the environment through "micro-forces" [ 1 ] and biogeochemical processes. An example is how the activity of photosynthetic bacteria during Precambrian times completely modified the Earth atmosphere to turn it aerobic, and thus supports the evolution of life (in particular eukaryotic life).

Since barriers existed throughout the twentieth century between Russia and the rest of the world, it is only relatively recently that the early Russian scientists who introduced concepts overlapping the Gaia paradigm have become better known to the Western scientific community. [ 1 ] These scientists include Piotr Alekseevich Kropotkin (1842–1921) (although he spent much of his professional life outside Russia), Rafail Vasil’evich Rizpolozhensky (1862 – c. 1922), Vladimir Ivanovich Vernadsky (1863–1945), and Vladimir Alexandrovich Kostitzin (1886–1963).

Biologists and Earth scientists usually view the factors that stabilize the characteristics of a period as an undirected emergent property or entelechy of the system; as each individual species pursues its own self-interest, for example, their combined actions may have counterbalancing effects on environmental change. Opponents of this view sometimes reference examples of events that resulted in dramatic change rather than stable equilibrium, such as the conversion of the Earth's atmosphere from a reducing environment to an oxygen-rich one at the end of the Archaean and the beginning of the Proterozoic periods.

Less accepted versions of the hypothesis claim that changes in the biosphere are brought about through the coordination of living organisms and maintain those conditions through homeostasis. In some versions of Gaia philosophy, all lifeforms are considered part of one single living planetary being called Gaia . In this view, the atmosphere, the seas and the terrestrial crust would be results of interventions carried out by Gaia through the coevolving diversity of living organisms.

The Gaia paradigm was an influence on the deep ecology movement. [ 2 ]

The Gaia hypothesis posits that the Earth is a self-regulating complex system involving the biosphere, the atmosphere, the hydrospheres and the pedosphere, tightly coupled as an evolving system. The hypothesis contends that this system as a whole, called Gaia, seeks a physical and chemical environment optimal for contemporary life. [ 3 ]

Gaia evolves through a cybernetic feedback system operated unconsciously by the biota, leading to broad stabilization of the conditions of habitability in a full homeostasis. Many processes in the Earth's surface, essential for the conditions of life, depend on the interaction of living forms, especially microorganisms, with inorganic elements. These processes establish a global control system that regulates Earth's surface temperature, atmosphere composition and ocean salinity, powered by the global thermodynamic disequilibrium state of the Earth system. [ 4 ]

The existence of a planetary homeostasis influenced by living forms had been observed previously in the field of biogeochemistry, and it is being investigated also in other fields like Earth system science. The originality of the Gaia hypothesis relies on the assessment that such homeostatic balance is actively pursued with the goal of keeping the optimal conditions for life, even when terrestrial or external events menace them. [ 5 ]

2.1. Regulation of Global Surface Temperature

Since life started on Earth, the energy provided by the Sun has increased by 25% to 30%; [ 6 ] however, the surface temperature of the planet has remained within the levels of habitability, reaching quite regular low and high margins. Lovelock has also hypothesised that methanogens produced elevated levels of methane in the early atmosphere, giving a view similar to that found in petrochemical smog, similar in some respects to the atmosphere on Titan. [ 7 ] This, he suggests tended to screen out ultraviolet until the formation of the ozone screen, maintaining a degree of homeostasis. However, the Snowball Earth [ 8 ] research has suggested that "oxygen shocks" and reduced methane levels led, during the Huronian, Sturtian and Marinoan/Varanger Ice Ages, to a world that very nearly became a solid "snowball". These epochs are evidence against the ability of the pre Phanerozoic biosphere to fully self-regulate.

Processing of the greenhouse gas CO 2 , explained below, plays a critical role in the maintenance of the Earth temperature within the limits of habitability.

The CLAW hypothesis, inspired by the Gaia hypothesis, proposes a feedback loop that operates between ocean ecosystems and the Earth's climate. [ 9 ] The hypothesis specifically proposes that particular phytoplankton that produce dimethyl sulfide are responsive to variations in climate forcing, and that these responses lead to a negative feedback loop that acts to stabilise the temperature of the Earth's atmosphere.

Currently the increase in human population and the environmental impact of their activities, such as the multiplication of greenhouse gases may cause negative feedbacks in the environment to become positive feedback. Lovelock has stated that this could bring an extremely accelerated global warming, [ 10 ] but he has since stated the effects will likely occur more slowly. [ 11 ]

Daisyworld simulations

In response to the criticism that the Gaia hypothesis seemingly required unrealistic group selection and cooperation between organisms, James Lovelock and Andrew Watson developed a mathematical model, Daisyworld, in which ecological competition underpinned planetary temperature regulation. [ 12 ]

Daisyworld examines the energy budget of a planet populated by two different types of plants, black daisies and white daisies, which are assumed to occupy a significant portion of the surface. The colour of the daisies influences the albedo of the planet such that black daisies absorb more light and warm the planet, while white daisies reflect more light and cool the planet. The black daisies are assumed to grow and reproduce best at a lower temperature, while the white daisies are assumed to thrive best at a higher temperature. As the temperature rises closer to the value the white daisies like, the white daisies outreproduce the black daisies, leading to a larger percentage of white surface, and more sunlight is reflected, reducing the heat input and eventually cooling the planet. Conversely, as the temperature falls, the black daisies outreproduce the white daisies, absorbing more sunlight and warming the planet. The temperature will thus converge to the value at which the reproductive rates of the plants are equal.

Lovelock and Watson showed that, over a limited range of conditions, this negative feedback due to competition can stabilize the planet's temperature at a value which supports life, if the energy output of the Sun changes, while a planet without life would show wide temperature changes. The percentage of white and black daisies will continually change to keep the temperature at the value at which the plants' reproductive rates are equal, allowing both life forms to thrive.

It has been suggested that the results were predictable because Lovelock and Watson selected examples that produced the responses they desired. [ 13 ]

2.2. Regulation of Oceanic Salinity

Ocean salinity has been constant at about 3.5% for a very long time. [ 14 ] Salinity stability in oceanic environments is important as most cells require a rather constant salinity and do not generally tolerate values above 5%. The constant ocean salinity was a long-standing mystery, because no process counterbalancing the salt influx from rivers was known. Recently it was suggested [ 15 ] that salinity may also be strongly influenced by seawater circulation through hot basaltic rocks, and emerging as hot water vents on mid-ocean ridges. However, the composition of seawater is far from equilibrium, and it is difficult to explain this fact without the influence of organic processes. One suggested explanation lies in the formation of salt plains throughout Earth's history. It is hypothesized that these are created by bacterial colonies that fix ions and heavy metals during their life processes. [ 14 ]

In the biogeochemical processes of Earth, sources and sinks are the movement of elements. The composition of salt ions within our oceans and seas is: sodium (Na + ), chlorine (Cl − ), sulfate (SO 4 2− ), magnesium (Mg 2+ ), calcium (Ca 2+ ) and potassium (K + ). The elements that comprise salinity do not readily change and are a conservative property of seawater. [ 14 ] There are many mechanisms that change salinity from a particulate form to a dissolved form and back. Considering the metallic composition of iron sources across a multifaceted grid of thermomagnetic design, not only would the movement of elements hypothetically help restructure the movement of ions, electrons, and the like, but would also potentially and inexplicably assist in balancing the magnetic bodies of the Earth's geomagnetic field. The known sources of sodium i.e. salts are when weathering, erosion, and dissolution of rocks are transported into rivers and deposited into the oceans.

The Mediterranean Sea as being Gaia's kidney is found (here) by Kenneth J. Hsue, a correspondence author in 2001. Hsue suggests the "desiccation" of the Mediterranean is evidence of a functioning Gaia "kidney". In this and earlier suggested cases, it is plate movements and physics, not biology, which performs the regulation. Earlier "kidney functions" were performed during the "deposition of the Cretaceous (South Atlantic), Jurassic (Gulf of Mexico), Permo-Triassic (Europe), Devonian ( Canada ), and Cambrian/Precambrian (Gondwana) saline giants." [ 16 ]

2.3. Regulation of Oxygen in the Atmosphere

The Gaia theorem states that the Earth's atmospheric composition is kept at a dynamically steady state by the presence of life. [ 17 ] The atmospheric composition provides the conditions that contemporary life has adapted to. All the atmospheric gases other than noble gases present in the atmosphere are either made by organisms or processed by them.

The stability of the atmosphere in Earth is not a consequence of chemical equilibrium. Oxygen is a reactive compound, and should eventually combine with gases and minerals of the Earth's atmosphere and crust. Oxygen only began to persist in the atmosphere in small quantities about 50 million years before the start of the Great Oxygenation Event. [ 18 ] Since the start of the Cambrian period, atmospheric oxygen concentrations have fluctuated between 15% and 35% of atmospheric volume. Cite error: Closing </ref> missing for <ref> tag Carbon precipitation, solution and fixation are influenced by the bacteria and plant roots in soils, where they improve gaseous circulation, or in coral reefs, where calcium carbonate is deposited as a solid on the sea floor. Calcium carbonate is used by living organisms to manufacture carbonaceous tests and shells. Once dead, the living organisms' shells fall. Some arrive at the bottom of the oceans where plate tectonics and heat and/or pressure eventually convert them to deposits of chalk and limestone. Much of the falling dead shells, however, re-dissolve into the ocean below the carbon compensation depth.

One of these organisms is Emiliania huxleyi , an abundant coccolithophore algae which may have a role in the formation of clouds. [ 19 ] CO 2 excess is compensated by an increase of coccolithophorid life, increasing the amount of CO 2 locked in the ocean floor. Coccolithophorids, if the CLAW Hypothesis turns out to be supported (see "Regulation of Global Surface Temperature" above), could help increase the cloud cover, hence control the surface temperature, help cool the whole planet and favor precipitation necessary for terrestrial plants. Lately the atmospheric CO 2 concentration has increased and there is some evidence that concentrations of ocean algal blooms are also increasing. [ 20 ]

Lichen and other organisms accelerate the weathering of rocks in the surface, while the decomposition of rocks also happens faster in the soil, thanks to the activity of roots, fungi, bacteria and subterranean animals. The flow of carbon dioxide from the atmosphere to the soil is therefore regulated with the help of living beings. When CO 2 levels rise in the atmosphere the temperature increases and plants grow. This growth brings higher consumption of CO 2 by the plants, who process it into the soil, removing it from the atmosphere.

3.1. Precedents

The idea of the Earth as an integrated whole, a living being, has a long tradition. The mythical Gaia was the primal Greek goddess personifying the Earth, the Greek version of "Mother Nature" (from Ge = Earth, and Aia = PIE grandmother), or the Earth Mother. James Lovelock gave this name to his hypothesis after a suggestion from the novelist William Golding, who was living in the same village as Lovelock at the time (Bowerchalke, Wiltshire, UK). Golding's advice was based on Gea, an alternative spelling for the name of the Greek goddess, which is used as prefix in geology, geophysics and geochemistry. [ 21 ] Golding later made reference to Gaia in his Nobel prize acceptance speech.

In the eighteenth century, as geology consolidated as a modern science, James Hutton maintained that geological and biological processes are interlinked. [ 22 ] Later, the naturalist and explorer Alexander von Humboldt recognized the coevolution of living organisms, climate, and Earth's crust. [ 22 ] In the twentieth century, Vladimir Vernadsky formulated a theory of Earth's development that is now one of the foundations of ecology. Vernadsky was a Ukrainian geochemist and was one of the first scientists to recognize that the oxygen, nitrogen, and carbon dioxide in the Earth's atmosphere result from biological processes. During the 1920s he published works arguing that living organisms could reshape the planet as surely as any physical force. Vernadsky was a pioneer of the scientific bases for the environmental sciences. [ 23 ] His visionary pronouncements were not widely accepted in the West, and some decades later the Gaia hypothesis received the same type of initial resistance from the scientific community.

Also in the turn to the 20th century Aldo Leopold, pioneer in the development of modern environmental ethics and in the movement for wilderness conservation, suggested a living Earth in his biocentric or holistic ethics regarding land.

Another influence for the Gaia hypothesis and the environmental movement in general came as a side effect of the Space Race between the Soviet Union and the United States of America. During the 1960s, the first humans in space could see how the Earth looked as a whole. The photograph Earthrise taken by astronaut William Anders in 1968 during the Apollo 8 mission became, through the Overview Effect an early symbol for the global ecology movement. [ 24 ]

3.2. Formulation of the Hypothesis

Lovelock started defining the idea of a self-regulating Earth controlled by the community of living organisms in September 1965, while working at the Jet Propulsion Laboratory in California on methods of detecting life on Mars. [ 25 ] [ 26 ] The first paper to mention it was Planetary Atmospheres: Compositional and other Changes Associated with the Presence of Life , co-authored with C.E. Giffin. [ 27 ] A main concept was that life could be detected in a planetary scale by the chemical composition of the atmosphere. According to the data gathered by the Pic du Midi observatory, planets like Mars or Venus had atmospheres in chemical equilibrium. This difference with the Earth atmosphere was considered to be a proof that there was no life in these planets.

Lovelock formulated the Gaia Hypothesis in journal articles in 1972 [ 28 ] and 1974, [ 29 ] followed by a popularizing 1979 book Gaia: A new look at life on Earth . An article in the New Scientist of February 6, 1975, [ 30 ] and a popular book length version of the hypothesis, published in 1979 as The Quest for Gaia , began to attract scientific and critical attention.

Lovelock called it first the Earth feedback hypothesis, [ 31 ] and it was a way to explain the fact that combinations of chemicals including oxygen and methane persist in stable concentrations in the atmosphere of the Earth. Lovelock suggested detecting such combinations in other planets' atmospheres as a relatively reliable and cheap way to detect life.

Later, other relationships such as sea creatures producing sulfur and iodine in approximately the same quantities as required by land creatures emerged and helped bolster the hypothesis. [ 32 ]

In 1971 microbiologist Dr. Lynn Margulis joined Lovelock in the effort of fleshing out the initial hypothesis into scientifically proven concepts, contributing her knowledge about how microbes affect the atmosphere and the different layers in the surface of the planet. [ 33 ] The American biologist had also awakened criticism from the scientific community with her advocacy of the theory on the origin of eukaryotic organelles and her contributions to the endosymbiotic theory, nowadays accepted. Margulis dedicated the last of eight chapters in her book, The Symbiotic Planet , to Gaia. However, she objected to the widespread personification of Gaia and stressed that Gaia is "not an organism", but "an emergent property of interaction among organisms". She defined Gaia as "the series of interacting ecosystems that compose a single huge ecosystem at the Earth's surface. Period". The book's most memorable "slogan" was actually quipped by a student of Margulis'.

James Lovelock called his first proposal the Gaia hypothesis but has also used the term Gaia theory . Lovelock states that the initial formulation was based on observation, but still lacked a scientific explanation. The Gaia hypothesis has since been supported by a number of scientific experiments [ 34 ] and provided a number of useful predictions. [ 35 ]

3.3. First Gaia Conference

In 1985, the first public symposium on the Gaia hypothesis, Is The Earth A Living Organism? was held at University of Massachusetts Amherst, August 1–6. [ 36 ] The principal sponsor was the National Audubon Society. Speakers included James Lovelock, George Wald, Mary Catherine Bateson, Lewis Thomas, John Todd, Donald Michael, Christopher Bird, Thomas Berry, David Abram, Michael Cohen, and William Fields. Some 500 people attended. [ 37 ]

3.4. Second Gaia Conference

In 1988, climatologist Stephen Schneider organised a conference of the American Geophysical Union. The first Chapman Conference on Gaia, [ 38 ] was held in San Diego, California on March 7, 1988.

During the "philosophical foundations" session of the conference, David Abram spoke on the influence of metaphor in science, and of the Gaia hypothesis as offering a new and potentially game-changing metaphorics, while James Kirchner criticised the Gaia hypothesis for its imprecision. Kirchner claimed that Lovelock and Margulis had not presented one Gaia hypothesis, but four:

• CoEvolutionary Gaia: that life and the environment had evolved in a coupled way. Kirchner claimed that this was already accepted scientifically and was not new.
• Homeostatic Gaia: that life maintained the stability of the natural environment, and that this stability enabled life to continue to exist.
• Geophysical Gaia: that the Gaia hypothesis generated interest in geophysical cycles and therefore led to interesting new research in terrestrial geophysical dynamics.
• Optimising Gaia: that Gaia shaped the planet in a way that made it an optimal environment for life as a whole. Kirchner claimed that this was not testable and therefore was not scientific.

Of Homeostatic Gaia, Kirchner recognised two alternatives. "Weak Gaia" asserted that life tends to make the environment stable for the flourishing of all life. "Strong Gaia" according to Kirchner, asserted that life tends to make the environment stable, to enable the flourishing of all life. Strong Gaia, Kirchner claimed, was untestable and therefore not scientific. [ 39 ]

Lovelock and other Gaia-supporting scientists, however, did attempt to disprove the claim that the hypothesis is not scientific because it is impossible to test it by controlled experiment. For example, against the charge that Gaia was teleological, Lovelock and Andrew Watson offered the Daisyworld Model (and its modifications, above) as evidence against most of these criticisms. [ 12 ] Lovelock said that the Daisyworld model "demonstrates that self-regulation of the global environment can emerge from competition amongst types of life altering their local environment in different ways". [ 40 ]

Lovelock was careful to present a version of the Gaia hypothesis that had no claim that Gaia intentionally or consciously maintained the complex balance in her environment that life needed to survive. It would appear that the claim that Gaia acts "intentionally" was a statement in his popular initial book and was not meant to be taken literally. This new statement of the Gaia hypothesis was more acceptable to the scientific community. Most accusations of teleologism ceased, following this conference.

3.5. Third Gaia Conference

By the time of the 2nd Chapman Conference on the Gaia Hypothesis, held at Valencia, Spain, on 23 June 2000, [ 41 ] the situation had changed significantly. Rather than a discussion of the Gaian teleological views, or "types" of Gaia hypotheses, the focus was upon the specific mechanisms by which basic short term homeostasis was maintained within a framework of significant evolutionary long term structural change.

The major questions were: [ 42 ]

• "How has the global biogeochemical/climate system called Gaia changed in time? What is its history? Can Gaia maintain stability of the system at one time scale but still undergo vectorial change at longer time scales? How can the geologic record be used to examine these questions?"
• "What is the structure of Gaia? Are the feedbacks sufficiently strong to influence the evolution of climate? Are there parts of the system determined pragmatically by whatever disciplinary study is being undertaken at any given time or are there a set of parts that should be taken as most true for understanding Gaia as containing evolving organisms over time? What are the feedbacks among these different parts of the Gaian system, and what does the near closure of matter mean for the structure of Gaia as a global ecosystem and for the productivity of life?"
• "How do models of Gaian processes and phenomena relate to reality and how do they help address and understand Gaia? How do results from Daisyworld transfer to the real world? What are the main candidates for "daisies"? Does it matter for Gaia theory whether we find daisies or not? How should we be searching for daisies, and should we intensify the search? How can Gaian mechanisms be collaborated with using process models or global models of the climate system that include the biota and allow for chemical cycling?"

In 1997, Tyler Volk argued that a Gaian system is almost inevitably produced as a result of an evolution towards far-from-equilibrium homeostatic states that maximise entropy production, and Kleidon (2004) agreed stating: "...homeostatic behavior can emerge from a state of MEP associated with the planetary albedo"; "...the resulting behavior of a symbiotic Earth at a state of MEP may well lead to near-homeostatic behavior of the Earth system on long time scales, as stated by the Gaia hypothesis". Staley (2002) has similarly proposed "...an alternative form of Gaia theory based on more traditional Darwinian principles... In [this] new approach, environmental regulation is a consequence of population dynamics. The role of selection is to favor organisms that are best adapted to prevailing environmental conditions. However, the environment is not a static backdrop for evolution, but is heavily influenced by the presence of living and vibration-based beings and organisms. The resulting co-evolving dynamical process eventually leads to the convergence of equilibrium and optimal conditions", but would also require progress of truth and understanding in a lens that could be argued was put on hiatus while the species was proliferating the needs of Economic manipulation and environmental degradation while losing sight of the maturing nature of the needs of many. (12:22 10.29.2020)

3.6. Fourth Gaia Conference

A fourth international conference on the Gaia hypothesis, sponsored by the Northern Virginia Regional Park Authority and others, was held in October 2006 at the Arlington, VA campus of George Mason University. [ 43 ]

Martin Ogle, Chief Naturalist, for NVRPA, and long-time Gaia hypothesis proponent, organized the event. Lynn Margulis, Distinguished University Professor in the Department of Geosciences, University of Massachusetts-Amherst, and long-time advocate of the Gaia hypothesis, was a keynote speaker. Among many other speakers: Tyler Volk, co-director of the Program in Earth and Environmental Science at New York University; Dr. Donald Aitken, Principal of Donald Aitken Associates; Dr. Thomas Lovejoy, President of the Heinz Center for Science, Economics and the Environment; Robert Correll, Senior Fellow, Atmospheric Policy Program, American Meteorological Society and noted environmental ethicist, J. Baird Callicott.

4. Criticism

After initially receiving little attention from scientists (from 1969 until 1977), thereafter for a period the initial Gaia hypothesis was criticized by a number of scientists, including Ford Doolittle, [ 44 ] Richard Dawkins [ 45 ] and Stephen Jay Gould. [ 38 ] Lovelock has said that because his hypothesis is named after a Greek goddess, and championed by many non-scientists, [ 31 ] the Gaia hypothesis was interpreted as a neo-Pagan religion. Many scientists in particular also criticized the approach taken in his popular book Gaia, a New Look at Life on Earth for being teleological—a belief that things are purposeful and aimed towards a goal. Responding to this critique in 1990, Lovelock stated, "Nowhere in our writings do we express the idea that planetary self-regulation is purposeful, or involves foresight or planning by the biota".

Stephen Jay Gould criticized Gaia as being "a metaphor, not a mechanism." [ 46 ] He wanted to know the actual mechanisms by which self-regulating homeostasis was achieved. In his defense of Gaia, David Abram argues that Gould overlooked the fact that "mechanism", itself, is a metaphor — albeit an exceedingly common and often unrecognized metaphor — one which leads us to consider natural and living systems as though they were machines organized and built from outside (rather than as autopoietic or self-organizing phenomena). Mechanical metaphors, according to Abram, lead us to overlook the active or agent quality of living entities, while the organismic metaphors of the Gaia hypothesis accentuate the active agency of both the biota and the biosphere as a whole. [ 47 ] [ 48 ] With regard to causality in Gaia, Lovelock argues that no single mechanism is responsible, that the connections between the various known mechanisms may never be known, that this is accepted in other fields of biology and ecology as a matter of course, and that specific hostility is reserved for his own hypothesis for other reasons. [ 49 ]

Aside from clarifying his language and understanding of what is meant by a life form, Lovelock himself ascribes most of the criticism to a lack of understanding of non-linear mathematics by his critics, and a linearizing form of greedy reductionism in which all events have to be immediately ascribed to specific causes before the fact. He also states that most of his critics are biologists but that his hypothesis includes experiments in fields outside biology, and that some self-regulating phenomena may not be mathematically explainable. [ 49 ]

4.1. Natural Selection and Evolution

Lovelock has suggested that global biological feedback mechanisms could evolve by natural selection, stating that organisms that improve their environment for their survival do better than those that damage their environment. However, in the early 1980s, W. Ford Doolittle and Richard Dawkins separately argued against this aspect of Gaia. Doolittle argued that nothing in the genome of individual organisms could provide the feedback mechanisms proposed by Lovelock, and therefore the Gaia hypothesis proposed no plausible mechanism and was unscientific. [ 44 ] Dawkins meanwhile stated that for organisms to act in concert would require foresight and planning, which is contrary to the current scientific understanding of evolution. [ 45 ] Like Doolittle, he also rejected the possibility that feedback loops could stabilize the system.

Lynn Margulis, a microbiologist who collaborated with Lovelock in supporting the Gaia hypothesis, argued in 1999 that "Darwin's grand vision was not wrong, only incomplete. In accentuating the direct competition between individuals for resources as the primary selection mechanism, Darwin (and especially his followers) created the impression that the environment was simply a static arena". She wrote that the composition of the Earth's atmosphere, hydrosphere, and lithosphere are regulated around "set points" as in homeostasis, but those set points change with time. [ 50 ]

Evolutionary biologist W. D. Hamilton called the concept of Gaia Copernican, adding that it would take another Newton to explain how Gaian self-regulation takes place through Darwinian natural selection. [ 21 ] More recently Ford Doolittle building on his and Inkpen's ITSNTS (It's The Song Not The Singer) proposal [ 51 ] proposed that differential persistence can play a similar role to differential reproduction in evolution by natural selections, thereby providing a possible reconciliation between the theory of natural selection and the Gaia hypothesis. [ 52 ]

4.2. Criticism in the 21st Century

The Gaia hypothesis continues to be broadly skeptically received by the scientific community. For instance, arguments both for and against it were laid out in the journal Climatic Change in 2002 and 2003. A significant argument raised against it are the many examples where life has had a detrimental or destabilising effect on the environment rather than acting to regulate it. [ 53 ] [ 54 ] Several recent books have criticised the Gaia hypothesis, expressing views ranging from "... the Gaia hypothesis lacks unambiguous observational support and has significant theoretical difficulties" [ 55 ] to "Suspended uncomfortably between tainted metaphor, fact, and false science, I prefer to leave Gaia firmly in the background" [ 56 ] to "The Gaia hypothesis is supported neither by evolutionary theory nor by the empirical evidence of the geological record". [ 57 ] The CLAW hypothesis, [ 9 ] initially suggested as a potential example of direct Gaian feedback, has subsequently been found to be less credible as understanding of cloud condensation nuclei has improved. [ 58 ] In 2009 the Medea hypothesis was proposed: that life has highly detrimental (biocidal) impacts on planetary conditions, in direct opposition to the Gaia hypothesis. [ 59 ]

In a 2013 book-length evaluation of the Gaia hypothesis considering modern evidence from across the various relevant disciplines, Toby Tyrrell concluded that: "I believe Gaia is a dead end*. Its study has, however, generated many new and thought provoking questions. While rejecting Gaia, we can at the same time appreciate Lovelock's originality and breadth of vision, and recognize that his audacious concept has helped to stimulate many new ideas about the Earth, and to champion a holistic approach to studying it". [ 60 ] Elsewhere he presents his conclusion "The Gaia hypothesis is not an accurate picture of how our world works". [ 61 ] This statement needs to be understood as referring to the "strong" and "moderate" forms of Gaia—that the biota obeys a principle that works to make Earth optimal (strength 5) or favourable for life (strength 4) or that it works as a homeostatic mechanism (strength 3). The latter is the "weakest" form of Gaia that Lovelock has advocated. Tyrrell rejects it. However, he finds that the two weaker forms of Gaia—Coeveolutionary Gaia and Influential Gaia, which assert that there are close links between the evolution of life and the environment and that biology affects the physical and chemical environment—are both credible, but that it is not useful to use the term "Gaia" in this sense and that those two forms were already accepted and explained by the processes of natural selection and adaptation. [ 62 ]

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• Gaia Hypothesis

What is Gaia Hypothesis?

Gaia hypothesis can also be referred to as Gaia theory or Lovelock Gaia because it was conceived and introduced to the world by a chemist, James E. Lovelock in the early 1970s. The James Lovelock Gaia hypothesis provides a newer perspective to look at the global ecology and its evolution. The Gaia model was formed by James E. Lovelock and biologist Dr. Lynn Margulis. It is different from the traditional portrayal of ecology, which presents it as a consequence of a biological response to the classical menu of physical conditions. 

Meaning of Gaia Hypothesis 

Gaia hypothesis meaning can be understood by the Gaia hypothesis definition that can be stated as an interaction between living organisms on the Earth with their inorganic surroundings forming a complex, self-regulating and synergistic system that helps perpetuate and maintain optimum conditions for life on the planet. 

It was hypothesized that by using the Gaia principle one can detect life in the atmosphere of other planets. The Gaia theory of James Lovelock was a relatively cheaper and reliable way to use such interactive combinations to find the possibility of life on planets other than the Earth. 

Initial Gaia Hypothesis 

The initial Gaia hypothesis states that the Earth has maintained its habitable state through a self-regulating feedback loop that is automatically carried out by the living organisms that are tightly coupled to their respective environments. The observations made in the James Lovelock Gaia Hypothesis were: 

Despite an increase in energy provided by the sun, the earth’s global surface temperature has been constant. 

Owing to the activities of life of the living organisms, the atmosphere is in an extreme state of disequilibrium of thermodynamics and yet the aspects of its composition are astoundingly stable. Even with so many atmospheric components of varying degrees like 20.7 percent of oxygen, 79 percent of nitrogen, traces of methane, and 0.03 percent of carbon dioxide, the atmospheric composition remains constant rather than unstable.

Constant ocean salinity for a very long time can be contributed to the seawater circulation via the hot basaltic rocks that emerge on ocean spreading ridges as hot water vents. 

The earth system has consistently and continuously recovered from massive perturbations owing to its self-regulation complex process. 

James Lovelock views this entirety of complex processes on the Earth’s surface as one, to maintain suitable conditions for life. The earthly processes from its formation to its disturbances, eruptions, and recovery is all considered to be one self-regulating system. 

Criticisms and Refinements of the Gaia Hypothesis

The Gaia theory named after the Greek Goddess Gaia, which represents the Earth was however heavily criticized initially against the natural selection principles proposed by Charles Darwin. The other criticism of the Gaia theory was its teleological nature of stating finality and not the cause of such occurrences in Lovelock Gaia. The refined Gaia hypothesis that aligned the Gaia model with the production of sulfur and iodine by sea creatures in quantities approximately required by the land creatures that supported and made the Gaia theory stating interactions stronger that bolster the hypothesis. 

Arguments and Criticism

The theory and hypothesis were criticized due to the following reasons.

The significant increase in global surface temperatures contradicts the observatory comment according to the theory. 

Salinity in the ocean is far from being at constant equilibrium as river salts have raised the salinity. 

The self-regulation theory is also disregarded as evidence against it was surfaced by reduced methane levels and oxygen shocks during the various ice ages that are during the Huronian, Sturtian, and Marinoan or Varanger Ice Ages. 

Dimethyl sulfide produced by the phytoplankton plays an important role in climate regulation and the process does not happen on its own as stated by James Lovelock. 

Another claim that stated the Gaia theory is contradictory to the Natural Selection theory and is far from the survival of the fittest theory that was the greatest diversion according to Lovelock’s theory. 

The other criticisms stated that Gaia had four hypotheses and not just one.

(a) Coevolutionary Gaia stated the environment and the life in it evolved in a  coupled way that was criticized stating Gaia theory is only claiming that it has already been a scientifically accepted theory.

(b) Homeostatic Gaia stated that the stability of the natural environment is maintained by life and that stability enables life to exist disregarded stating it was not scientific because it was untestable.

(c) The Geophysical Gaia hypothesis stated new geophysical cycles that only aroused curiosity and piqued interest in researching the terrestrial geographical dynamics. 

(d) The optimizing Gaia hypothesis was also disregarded because of its untestability and therefore unscientific nature that stated the planet shaped by Gaia made life for the environment as a whole. 

Daisyworld Simulations

The refined New Gaia hypothesis was a counter-argument by James Lovelock. Lovelock along with Andrew Watson developed a new model that is the Daisyworld Simulations which is a mathematical model. Daisyworld is to be considered a planet where only daisies grow and there are black daisies and white daisies. The conditions in the Daisyworld are in many respects similar to that of the Earth.

Water and nutrients are abundant in Daisyworld for the daisies.

The ability to grow and for the daisies to spread across this imaginary planet’s surface depends entirely on the temperature.

The climate system in Daisyworld is simple with no greenhouse gases and clouds.

The planetary incident light and radiation that affects the surface temperature depends on the aerial coverage of the grey soil by the white and black daisies. 

In this model, the planetary temperature regulation is underpinned by ecological competition by examining the energy budget which is the energy provided by the sun and with high energy temperature increases, and with low energy the temperature decreases. 

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The graphical presentation of the Daisyworld simulations shows it is parabolic with minimum temperature, optimum temperature, and maximum growth temperature. 

The albedo that is the reflection and the absorption of light is influenced by the colour of daisies. 

Light- The black daisies warm the Daisyworld by absorbing more light and white daisies cool the planet by reflecting more light.

Growth-  Black daisies grow and reproduce best at temperatures relatively lower than the white daisies that thrive at a higher temperature.

When the temperature rises Daisyworld’s surface is filled with more white daisies that reduce heat input and consequently cooling the planet. For instance in figure 3 given below.

With the decline in temperatures, the scenario in figure 2 takes place wherein the white daisies are outnumbered by the black daisies making the planet warmer by increasing absorption of the energy provided by the sunlight. 

Plant reproduction becomes equal when temperatures converge to the value of both their reproductive rates, both will thrive as shown in figure 1.

Result of The Refined Gaia Hypothesis

The Gaia hypothesis through the Daisyworld simulations proved that the percentage of black daisies in comparison to white ones will continuously change so both could thrive. This further shows that competition and even with a limited range of conditions like on the planet Daisyworld can also support life with stabilized temperatures. In other words, if the sun’s energy output changes the temperature of the planet will greatly vary due to wide and different degrees of albedo. 

Gaia Hypothesis Summary 

The Gaia hypothesis has had its fair share of criticism because of its need for more explicit formulation and consequently it being untestable and hence not scientifically proven. Even with this through the years various modifications have been done and via these two models of Gaia emerges the weak Gaia hypothesis that suggests the planetary processes are substantially influenced by the life on the planet which is widely supported. The other model is known as the strong Gaia hypothesis that states that life creates the earth’s systems in other words planetary processes are controlled by life which is not supported and widely accepted. 

FAQs on Gaia Hypothesis

1. Is the Gaia Hypothesis No Longer Valid?

Ans. When initially presented by James E. Lovelock, the Gaia hypothesis was heavily criticized, and scientists and biologists were apprehensive of considering it to be valid.  With researches and findings over the years since its inception, the idea of Gaia being full of homeostasis is not valid due to the Gaia hypothesis one has been able to research and find out stronger evidence that aligns with the Gaia model. For instance, the fact that living alone is not responsible for the equilibrium, it is the entire ecosystem or the Earth system that works in stabilizing the life process which allows life to exist and thrive. 

2. Has the Gaia Hypothesis Been Accepted?

Ans. The Gaia hypothesis has since been supported by several scientific experiments through which one was able to make several useful predictions. The original hypothesis was wrong and discarded but the newer models that are known as the weak Gaia hypothesis have been accepted and widely supported. The acceptance of the Gaia hypothesis has not been widely acknowledged yet and one is constantly researching and finding shreds of evidence to either support or disregard it.

3. What are the Uses of the Gaia Principle?

Ans. The Gaia theory predicted the causal link between increased biodiversity and contrary to the popular belief of it contradicting the natural selection theory the Gaia principle supported it by drawing connections with increasing stability of populations. The Gaian influence furthermore solidifies the evolutionary theory development of the fact that be found in the idea that life on the earth can be considered to be in works with the abiotic environment as a self-regulatory system and both contribute to making the planet a place for stability and constant growth.

Sleeping giant surprises Gaia scientists

Wading through the wealth of data from ESA’s Gaia mission , scientists have uncovered a ‘sleeping giant’. A large black hole, with a mass of nearly 33 times the mass of the Sun, was hiding in the constellation Aquila, less than 2000 light-years from Earth. This is the first time a black hole of stellar origin this big has been spotted within the Milky Way. So far, black holes of this type have only been observed in very distant galaxies. The discovery challenges our understanding of how massive stars develop and evolve. 

Matter in a black hole is so densely packed that nothing can escape its immense gravitational pull, not even light. The great majority of stellar-mass black holes that we know of are gobbling up matter from a nearby star companion. The captured material falls onto the collapsed object at high speed, becoming extremely hot and releasing X-rays. These systems belong to a family of celestial objects named X-ray binaries.  

When a black hole does not have a companion close enough to steal matter from, it does not generate any light and is extremely difficult to spot. These black holes are called ‘dormant’.

To prepare for the release of the next Gaia catalogue, Data Release 4 (DR4), scientists are checking the motions of billions of stars and carrying out complex tests to ­see if anything is out of the ordinary. The motions of stars can be affected by companions: light ones, like exoplanets; heavier ones, like stars; or very heavy ones, like black holes. Dedicated teams are in place in the Gaia Collaboration to investigate any ‘odd’ cases.

One such team was deeply engaged in this work, when their attention fell on an old giant star in the constellation Aquila, at a distance of 1926 light-years from Earth. By analysing in detail the wobble in the star’s path, they found a big surprise. The star was locked in an orbital motion with a dormant black hole of exceptionally high mass, about 33 times that of the Sun.

This is the third dormant black hole found with Gaia and was aptly named ‘Gaia BH3’. Its discovery is very exciting because of the mass of the object. “This is the kind of discovery you make once in your research life,” exclaims Pasquale Panuzzo of CNRS, Observatoire de Paris, in France, who is the lead author of this finding. “So far, black holes this big have only ever been detected in distant galaxies by the LIGO–Virgo–KAGRA collaboration, thanks to observations of gravitational waves.”

The average mass of known black holes of stellar origin in our galaxy is around 10 times the mass of our Sun. Until now, the weight record was held by a black hole in an X-ray binary in the Cygnus constellation (Cyg X-1), whose mass is estimated to be around 20 times that of the Sun.

“It’s impressive to see the transformational impact Gaia is having on astronomy and astrophysics,” notes Prof. Carole Mundell, ESA Director of Science. “Its discoveries are reaching far beyond the original purpose of the mission, which is to create an extraordinarily precise multi-dimensional map of more than a billion stars throughout our Milky Way."

Unmatched accuracy

The exquisite quality of the Gaia data enabled scientists to pin down the mass of the black hole with unparalleled accuracy and provide the most direct evidence that black holes in this mass range exist.

Astronomers face the pressing question of explaining the origin of black holes as large as Gaia BH3. Our current understanding of how massive stars evolve and die does not immediately explain how these types of black holes came to be. 

Most theories predict that, as they age, massive stars shed a sizable part of their material through powerful winds; ultimately, they are partly blown into space when they explode as supernovas. What remains of their core further contracts to become either a neutron star or a black hole, depending on its mass. Cores large enough to end up as black holes of 30 times the mass of our Sun are very difficult to explain.

Yet, a clue to this puzzle may lie very close to Gaia BH3.

An intriguing companion

The star orbiting Gaia BH3 at about 16 times the Sun–Earth distance is rather uncommon: an ancient giant star, that formed in the first two billion years after the Big Bang, at the time our galaxy started to assemble. It belongs to the family of the Galactic stellar halo and is moving in the opposite direction to the stars of the Galactic disc. Its trajectory indicates that this star was probably part of a small galaxy, or a globular cluster, engulfed by our own galaxy more than eight billion years ago.

The companion star has very few elements heavier than hydrogen and helium, indicating that the massive star that became Gaia BH3 could also have been very poor in heavy elements. This is remarkable. It supports, for the first time, the theory that the high-mass black holes observed by gravitational wave experiments were produced by the collapse of primeval massive stars poor in heavy elements. These early stars might have evolved differently from the massive stars we currently see in our galaxy.

The composition of the companion star can also shed light on the formation mechanism of this astonishing binary system. "What strikes me is that the chemical composition of the companion is similar to what we find in old metal-poor stars in the galaxy,” explains Elisabetta Caffau of CNRS, Observatoire de Paris, also a member of the Gaia collaboration.

“There is no evidence that this star was contaminated by the material flung out by the supernova explosion of the massive star that became BH3.” This could suggest that the black hole acquired its companion only after its birth, capturing it from another system.

Tasty appetiser

The discovery of the Gaia BH3 is only the beginning and much remains to be investigated about its baffling nature. Now that the scientists’ curiosity has been piqued, this black hole and its companion will undoubtedly be the subject of many in-depth studies to come.

The Gaia collaboration stumbled upon this ‘sleeping giant’ while checking the preliminary data in preparation for the fourth release of the Gaia catalogue.  Because the finding is so exceptional they decided to announce it ahead of the official release. 

The next release of Gaia data promises to be a goldmine for the study of binary systems and the discovery of more dormant black holes in our galaxy.  “We have been working extremely hard to improve the way we process specific datasets compared to the previous data release (DR3), so we expect to uncover many more black holes in DR4,” concludes Berry Holl of the University of Geneva, in Switzerland, member of the Gaia collaboration.

Notes for editors

" Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry " by Gaia Collaboration, P. Panuzzo, et al. is published today the journal Astronomy & Astrophysics (A&A).

Gaia is a European mission, built and operated by ESA. It was approved in 2000 as a European Space Agency Cornerstone Mission within ESA’s Horizon 2000 Plus science programme, supported by all ESA Member States. Member States also have a key role in the science portion of the mission as part of the Data Processing and Analysis Consortium (DPAC) responsible to turn the raw data into scientific products for Gaia Data Releases, in collaboration with ESA. DPAC brings together more than 450 specialists from throughout the scientific community in Europe. Gaia was designed and built by Astrium (now Airbus Defence and Space), with a core team composed of Astrium France, Germany and UK. The industrial team included 50 companies from 15 European states, along with firms from the US. The spacecraft was launched by Arianespace on 19 December 2013.

A listing of the researchers involved and the role of ESA Member States is available for media here [PDF].

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Dr Stephan Harding - Gaia - A Kingdom Beyond Measurement THE SPACESHIP EARTH PODCAST

• Society & Culture

Originally released in June 2022, I’m rebroadcasting for Earth Day Episode 60 with Dr Stephan Harding - Holistic Scientist, Deep Ecologist, Author and Co-founder of Schumacher College who was mentored by the scientist James Lovelock - responsible for the Gaia Theory Hypothesis. Earth Day began in 1970 the year before I was born, and here we are 54 years later experiencing the accelerated unravelling of our Earth’s System, essentially from a perception problem, a relationship problem, a separation crisis. Capitalist Modernity has failed to understand or accept that the Earth is alive, an ongoing complex, mysterious entanglement of intelligent living relationships which have created the conditions for life to emerge, including human life. This is Gaia. A way of seeing the Earth that humans throughout the majority of our time as a species on this planet have always known. The Earth and all life on it is sentient, animate and sacred. Decades of destructive and extractive ways of being in relationship with the Earth means we’re facing into the consequences of that in profound ways now, how quickly can we wake up at scale and re-learn to see the Earth as alive ? What Stephan would call Gaian consciousness… “So lets call it a Gaian consciousness. It’s gradually taking root inside people, people are waking-up to it more and more. But it’s slow. Waking up is far slower than the rate of destruction. And what we need now is the rate of waking-up to overtake the rate of destruction. And the waking-up has got to happen on a massive scale. But I don’t know how that is going to happen. The positive side is that cultural revolutions can happen very quickly. Revolutions in consciousness can happen very quickly. This one has got to happen quicker than any other, and happen fast and on a global scale. And it has got to transcend national boundaries, political boundaries, all the sorts of boundaries that we humans have erected between ourselves, gender boundaries, all those boundaries they have got to fall down. And we all have to unify to protect our very own planet, for her own sake and our sake and the sake of all beings. Is that going to happen?” In this episode we explore - Who is Gaia and what’s her history?  - James Lovelock independent scientist, mentor and Gaia Theory Hypothesis - From the scientific study of the Muntjac Deer to the deep connection of the wholeness of nature - We are not just thinkers. We’re equally, feelers, sensors and intuitors - We’re inherently animistic with a spiritual connection to nature. And we can still value science - A cultural revolution needs to happen quicker than any other time, for the sake of all life - Gaia Alchemy. Why put alchemy with science?  - Healing a crisis of meaning and the Azoth of Philosophy - Valuing the psyche over the ego. Do we invent ideas or do we receive them? - Finding your Gaia place I hope you enjoy this conversation. Get full access to Becoming Crew at becomingcrew.substack.com/subscribe

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