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Is Earth Alive? Scientists Seek Sulfur For An Answer

Image of Earth taken by ESA's Rosetta spacecraft in 2009

Researchers at the University of Maryland have discovered a way to identify and track sulfuric compounds in Earth’s marine environment, opening a path to either refute or support a decades-old hypothesis that our planet can be compared to a singular, self-regulating, living organism — a.k.a. the Gaia theory.

Proposed by scientists James Lovelock and Lynn Margulis in the 70s, the Gaia theory likens Earth to a self-supporting singular life form, similar to a cell. The theory claims that, rather than being merely a stage upon which life exists, life — in all forms — works to actively construct an Earthly environment in which it can thrive.

Although named after the Greek goddess of Earth, the Gaia theory is not so much about mythology or New Age mysticism as it is about biology, chemistry and geology — and how they all interact to make our world suitable for living things.

Once called the Gaia hypothesis, enough scientific cross-disciplinary support has since been discovered that it’s now commonly referred to as a theory.

Marine phytoplankton -- like these diatoms -- may produce sulfur compounds that can be transmitted into the air, affecting climate. (NOAA image)

One facet of the Gaia theory is that sulfur compounds would be created by microscopic marine organisms — such as phytoplankton and algae — and these compounds could be transmitted into the air, and eventually (in some form) to the land, thus helping to support a sulfur cycle.

Sulfur is a key element in both organic and inorganic compounds. The tenth most abundant element in the Universe, sulfur is crucial to climate regulation — as well as life as we know it.

In particular, two sulfur compounds — dimethylsulfoniopropionate and its atmospherically-oxidized version, dimethylsulfide — are considered to be likely candidates for the products created by marine life. It’s these two compounds that UMD researcher Harry Oduro, along with geochemist and professor James Farquhar and marine biologist Kathryn Van Alstyne (of Western Washington University) have discovered a way to track across multiple environments, from sea to air to land, allowing scientists to trace which isotopes are coming from what sources.

“What Harry did in this research was to devise a way to isolate and measure the sulfur isotopic composition of these two sulfur compounds,” said Farquhar. “This was a very difficult measurement to do right, and his measurements revealed an unexpected variability in an isotopic signal that appears to be related to the way the sulfur is metabolized.”

The team’s research can be used to measure how the organisms are producing the compounds, under which circumstances and how they are ultimately affecting their — and our — environment in the process.

“The ability to do this could help us answer important climate questions, and ultimately better predict climate changes,” said Farquhar. “And it may even help us to better trace connections between dimethylsulfide emissions and sulfate aerosols, ultimately testing a coupling in the Gaia hypothesis.”

Whether or not Earth can be called a singular — or possibly even sentient — living organism of which all organisms are contributing members thereof may still be up for debate, but it is fairly well-accepted that life can shape and alter its own environment (and in the case of humans, often for the worse.) Research like this can help science determine just how far-reaching those alterations may be.

The study appears in this week’s Online Early Edition of the Proceedings of the National Academy of Sciences (PNAS).

Read more on the University of Maryland’s news page here.

Image credit: ESA ©2009 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA. Edited by J. Major.

About 

A graphic designer in Rhode Island, Jason writes about space exploration on his blog Lights In The Dark, Discovery News, and, of course, here on Universe Today. Ad astra!

Comments on this entry are closed.

  • 1mh4rdc0r3 May 16, 2012, 5:32 AM

    if it is, what does that make us, cancer?

    • milosmeeth May 16, 2012, 6:41 AM

      Our purpose could be to offset a coming ice age.

      • squidgeny May 16, 2012, 8:58 AM

        We have no “purpose”, but you might be right with climate change ultimately being a better path (for our survival, at least) than the natural glaciation cycle.

        However it’s worth noting that it will never be as simple as adding the heat of global warming to the cold of an ice age and coming out with an intermediate temperature that works for us. For one, we might be setting the Earth up for an even steeper decline into unavoidable ice-age temperatures, which would give life less time to adapt. Or we might prevent an ice-age, so the “coldening” never comes and never offsets our warming. Or our warming might somehow trigger a worse ice-age than those that have gone before. We don’t know for sure, but we definitely are playing with fire…

        • twas brillig May 18, 2012, 12:10 AM

          Who says we have no purpose??? You are thinking on purely material terms when actually, the human being is far more than purely material. It does not take blind faith to see the human being is ALSO a sentient, conscious, emotional and spiritual, yes spiritual being. There is a wealth of material evidence for the spiritual reality and while it is ignored by large segment of the scientific community doesn’t negate it. If we were merely robotic or instinctual denizens, we wouldn’t be able to make conscious decisions, question ourselves or reality. The fact that we can question and ponder the idea of a deeper meaning to life alone supports the idea that there is one. We could easily exist to provide for not just material evolution, but a spiritual and emotional evolution as well.

      • super_earth May 17, 2012, 5:04 AM

        The increase in greenhouse gases is something unprecedented in billions of Earth history. In just 200 years we erased 15 million years of CO2 decline.

        15 million years ago there weren’t big ice sheets in the Northern Hemisphere and sea level was 10 meters higher. And this is from just the *already* emitted greenhouse gases (a little more than 100 ppm of CO2 equivalent). We are on track to reach 1000 ppm at the end of century.

        That will cause at least 6ºC of warming, that is more than the difference between glacial and interglacial. And that not in just 100 years. The earth will be trown into a hothouse, ice-free state (i.e. no ice ages for millions of years) in the next centuries, like 50 million years ago. The warming will last thousands if not millions of years.

        The more appropiate analogy with a living organism is fulminant fever. This is cannot be our mission, unless the Earth wants to commit suicide.

    • ren00r May 16, 2012, 6:49 AM

      people tend to think that humanity is something unnatural, bad for Earth, against nature’s laws. But the fact is we are part of biosphere. We don’t stand above it. We are nature. Deal with it!

      • Eppur_si_muove May 16, 2012, 7:36 AM

        Natural, doesn’t necessarily equal good; and I feel we’ve longed gained independence of our natural ecosystem. Our biosphere no longer governs us, as we have direct influence over it, and can alter it to meet our demands.

        • ren00r May 16, 2012, 8:54 AM

          I understand your point. But good for who? If you imagine you are a dinosaur 65 million years ago, you’d consider extinction of your kind as bad thing, but from our point of view it gave rise to bigger forms of mammals and eventually us, humans.

        • kevjoewalsh May 16, 2012, 8:29 PM

          “long gained independence of our natural ecosystem”?

          Every single bite of the food we eat is either a chunk of a plant, or chunks of animals that ate plants. Every inward breath is a dose of oxygen spat out of the chloroplasts of some plant or other. Every drink is unequivocably a mouthful of molecules that have cycled through millions of years of changing natural ecosystems, and will continue to do so long after our brutal arrogance has been extinguished, the way of all organisms, be it personal extinction or species-wide.

          We’ve learned to build homes, and control the temperatures within them–and of that we feel profoundly proud, and to some degree, perhaps deservedly so (although was this not just nature spinning herself out through us as well?)–but when your pride gets too large take this beautifully engineeredhome of yours onto Mars, far away from this ‘natural ecosystem to which we no longer belon’ and–see how long before you are dead and frozen. We are one of nature’s own. There’s no fighting it. Deny it, separate yourself for 5 minutes and you will be dead of asphyxiation. And every single atom in your body will return back into the natural cycles of the earth, exactly from whence it came.

          When we fight this feeling of belonging, when we claim superiority, we wind up living inside a world that deteriorates for the lack of care we then feel it is owed. When we embrace our nothingness, our insignificance, we find ourselves instead inside a world where the very material which makes us is that of rivers, skies, thunder storms and rain, rocks and everything in between. We look around and see that this is all, in a very real sense… us.

    • Eppur_si_muove May 16, 2012, 7:08 AM

      Yes, we ‘re like a virus, except earth has a cure for us. :)

      • squidgeny May 16, 2012, 9:01 AM

        If we are a parasite on Earth, then it’s worth noting that a good parasite will keep its host alive and healthy, so that that parasite might persist in comfortable conditions.

        Parasites that kill their host usually have another host to move to, but we don’t have that luxury.

        • Damian May 16, 2012, 11:50 AM

          Perhaps the right question is, what purpose does the human organism serve the earth ?

          Perhaps if we abandon the idea of outright free will and apply a bit of determinism to the role of humanity within the constraints of the Gaia Theory some interesting conjecture can be drawn.

          For instance; if we spread our biology to other planets then you have a very good purpose for the human organism. :)

  • pmarston May 16, 2012, 6:47 AM

    Lovelock and Margulis gave rise to a new discipline, Earth Systems Science, which understands that life is an integral part of the process cycles of the planet and is incorporated in most of them, including the carbon and nitrogen cycles and even the rock cycle (think limestone). But it’s a bit of a leap from there to considering the Earth as a single organism. It’s perhaps better to understand the planet as the substrate on which life occurs and although it’s the only such substrate we know about it may not be the only one possible.

  • Eppur_si_muove May 16, 2012, 7:35 AM

  • maurizio52 May 16, 2012, 8:45 AM

    I think that life as we know is based on a very important principle. Replication.
    Replication is accomplished by complex, normally carbon based, molecules (e.g. DNA).
    Those molecules can make copies of themselves and their success is related to the capacity of replication, so, during the darwinian evolution, they developed mostly anything that improves this capacity. Viruses, bacteria, multicellular organisms, trees and animals, are the product of this basic principle. Replication.
    The Earth has no replication system, so I think it can not be alive.
    Now may be trivial that the Earth could well be a complex self regulating system having many, mostly negative, feedbacks, to compensate perturbations, but life… it’s different.

    • bookmanjohn May 16, 2012, 1:34 PM

      If we terraform a few dozen planets, has Gaia reproduced?

      • maurizio52 May 16, 2012, 2:08 PM

        I don’t think so. What is reproduced is our idea of gaia (the Gaia’s Meme), the terraformed planets were still there and what changes on them is the possibility of hosting our kind of life.

      • Terrill Kincaid May 16, 2012, 2:54 PM

        If we went out and gathered asteroids, pushed them together into a planet sized blob, filled it with the basic elements of earth, and then tereformed that…

        You might be able to say she had reproduced then… Maybe…

        • maurizio52 May 16, 2012, 8:44 PM

          In this case we act like doctor Frankestein, building up a (planetary) body using spare (dead) parts.
          Anyway, Why should we limit our fantasy to the Earth planet?
          Maybe that this is the common reproduction system between planets, it may also be that Jupiter is Saturn’s father (or viceversa) and all the nine planets (now eight, pluto is out) are relatives… and the sun… ;-) A couple of questions.
          Only Gaia is alive?
          Since It looks pretty vintage “geocentric” style, but why not…
          Can anybody “prove” gaia?

  • squidgeny May 16, 2012, 8:51 AM

    a decades-old hypothesis that our planet can be compared to a singular, self-regulating, living organism — a.k.a. the Gaia theory.

    The Gaia theory isn’t that the planet can be compared to a self-regulating organism (which is undoubtedly true), it’s that it is a self-regulating organism.

    The Gaia theory is initially very compelling, because it does indeed appear that the Earth is self-regulating. But that’s all it is – an appearance in much the same way that species sometimes appear to deliberately regulate their own populations (group selection) or appear to strive towards a particular evolutionary development (Lamarckian selection).

    But genes are what drive every organism, and this branch of biology has thoroughly debunked the Gaia theory (along with the idea of group selection, which is basically a microcosm of the Gaia theory, I suppose).

    Afterall, it’s genes which compelled the earliest organisms to pollute the atmosphere with deadly oxygen, ultimately killing off those very organisms which had held sway for hundreds of millions of years – where was the Gaia theory to prevent that self-destruction from happening?

    • gopher652003 May 16, 2012, 2:30 PM

      I agree. Earth gives the *appearance* of being fully self regulating, but it is just that, an appearance. Life on Earth isn’t self-regulating, it merely has a large number of negative feedback loops that developed through well understood evolutionary processes. These negative feedback loops are surprisingly fragile and often short-lived (on a geologic timescale, with a few exceptions), unlike the long-term robustness that would be expected if Earth were fully self-regulating.

      Example, thought experiment style:

      You have three species, Carrots, Rabbits, and Wolves. For the purposes of discussion they are they only three species in existence. Rabbits eat Carrots, Wolves eat Rabbits.

      When too many Rabbits are bred into existence they hurt their food source, Carrots. If they kept breeding they would extinct themselves. However, when their are a lot of Rabbits, Wolves have a plentiful food supply. Since there is plenty of food, more Wolves survive pup-hood until they have brought the Rabbits back down into parity with the Carrots (or below parity). But then their are too many Wolves, which starve to death. Cycle resets, and repeats.

      Is that an example of a stable self-regulating system? On the surface, yes. In reality, no. Each component of the system is merely doing what is right for it, and it alone. The Wolves don’t care that there are too many Rabbits that are exterminating their food supply, they are only responding to the fact that there is a lot of tasty meat hopping around. Because of this the system is highly unstable, subject to chance. At any time a decrease in Carrot or Rabbit populations (at a bad time) could result in the extinction of Wolves, thereby destroying the system.

      Since the Wolves are merely responding to the increase in Rabbit population, *not* to a decrease in Carrot population, it isn’t a fully self regulating system, it’s merely a naturally occurring Rube Goldberg Machine, set up by evolutionary processes.

      That is the difference between a true self-regulating system (Wolves respond to Carrots, and breed to save them) and a system that only appears to be self-regulating, but can easily break (Wolves indirectly responding to Rabbits, which by coincidence brings Rabbits back into parity with Carrots).

      It is that robustness or lack thereof that designates a system as truly self-regulating. If a system isn’t robust enough to survive minor disturbances, then it can’t quality as a long-term self regulating system of the type that the Gaia Hypothesis requires to justify its central conceit.

      (Side note: neither a self-regulating natural system nor a Rube Goldberg natural system require intelligence, but both should be able to incorporate it in their chains without any issues.)

      • gopher652003 May 16, 2012, 2:39 PM

        Oh, and Jason? I don’t know what alternative geology publication you are getting your information from, but the Gaia Hypothesis has *not* been proven to be true to within a shadow of a doubt with all other alternative hypotheses rejected (AKA, scientific theory). Various systems on the Earth are either self-regulating (long-term) or give that appearance to creatures as shortlived as humans, but that doesn’t put enough evidence in Gaia’s court to put it on the same level as Gravity, Relativity, or Evolution. Not even close.

        Even though I lean against the Gaia Hypothesis in general, I can’t say for certain that it is false. But it is *not* accepted by the mainstream, whatever your alternative publications might try and tell you.

        • Jason Major May 16, 2012, 2:57 PM

          I never stated anything was proven to be true beyond shadows of doubts. What I said was that it’s now commonly referred to as a theory — which it is — and has gathered supporting scientific evidence over the years. Whether this means that Earth IS a single living organism and the theory is “proven” true (or, it isn’t and it’s false) is not, like you said, for certain. But as I’ve heard it quoted, a theory with gaps can still be a theory.

          A statement from Ken Rubin, Professor of Geology at the U. of Hawaii:
          ” I would like to point out that while this theory seems “far out” to some (and certain aspects are difficult for me to believe), almost any Earth scientist, ecologist or other natural scientist will tell you that complex and delicate balances that keep the oceans and atmosphere and lakes and forests and other things ‘functioning properly’ are so intricate and orderly that if it isn’t a living being that controls it all, it certainly sometimes acts like one. Thus, whether Gaia is a sentient being or simply a device for explaining the very complex functioning of nature in a way humans can relate to (by placing them under the control of a supreme being), the theory of Gaia has a well-deserved place in modern scientific paradigms.”

          • Torbjörn Larsson May 17, 2012, 9:19 PM

            That quote is mined. What Rubin said was this:

            “The theory you asked about is known as the “Gaia Hypothesis”. The Gaia hypothesis has both scientific and philosophical components. Gaia is theorized to be a living entity that is greater than the sum of all the living and non-living aspects of the Earth.”

            He goes on to describe it as a possible explanation for “how things work”, as well as a useful social device (“perspective”) to make Earth livable.

            So while Rubin describes it as a theory he also describes how it is not commonly referred as one and how weakly predictive it is (having philosophical components). The best he presents is that it can predict that there will be “aspects” of Earth “balancing”. In that case, the hydrostatic surface of Earth is a prediction of Gaia theory. (It is not.)

            Gaia is a religious kind of idea that predicts everything by being unconstrained in its predictions, so predicts nothing. To call it predictive theory is misdirection IMHO.

  • Zoutsteen from Holland May 16, 2012, 10:32 AM

    Gaia, A word that works it magic
    from simplicity to each implicitely:
    where Selfs and Needs more than tick
    and tag the whole Earth its role’s Worth.

  • Paul Harris May 16, 2012, 12:04 PM

    we are here and someone eles is billoins of light years away.fact

    • wjwbudro May 17, 2012, 8:13 PM

      And a bunch in between and bunch more that have come and gone just as we will.

  • lcrowell May 16, 2012, 2:01 PM

    There are a number of cycles, the carbon cycle, the nitrogen cycle, oxygen, water, and so forth. They all function within a geological, atmospheric, oceanic and biological context. This is clearly a self-adaptive and self-regulating system that has analogues to a living system. The Lovelock-Margulis conjecture is then really the statement that the total active genetic content on this planet forms a sort of molecular regulatory system. Anything which evolves to adapt to its environment also influences that environment. The net sum of this activity is then an emergent system that forms a regulatory structure on these various cycles.

    This system emerged with the early abiogenesis of life, where prokaryotic life established a global network some 3.5 to 3 billion years ago. The network is fundamentally based on prokaryotes. Eukaryotes are really just assemblies of prokaryotes that have evolved more complex structure. We might then see this as a way prokaryotes collectively evolved in order to increase the energy flow through on this planet. Plants are the energy gatherers, animals the intermediary processors and fungi are the recyclers that provide the organic compounds and energy to soil ecosystems with prokaryotes.

    The system has faced crisis in the past. It has faced massive volcanic episodes (Deccan flats etc), asteroid impacts and probably has down regulated organisms which populate or bloom out of proportion for eco-homeostasis. I have read that during mass extinctions H_2S producing bacteria blooms, and that recently there has been an upsurge of H_2S producing bacteria in estuaries. Other population booms have doubtless occurred in the past, which doubtless have ranged from some species of prokaryote to large animals. There is even a conjecture that methane from brontosaurus (to use the old name) flatulence changed the climate, which may have had some down regulating effect on those animals

    We humans just represent the latest such crisis. I doubt in the course of natural history there has been an animal our size, with our dietary requirements, and certainly our auxiliary resource demands that numbered 7 billion at one time. The system will in some manner give a negative feedback against us. Already with energy we see a rapid rise in tar sand and fracking to acquire hydrocarbon sources previously regarded as “stranded.” We appear to be reaching the logistic cycling plateau commonly seen in population overshoots that later crash. So the crash, or the collapse of the human condition, may well be in our future — maybe this century or the next. In other ways this sort of thing has probably happened in the past, and regional episodes of locust swarms or red tides may just be smaller short term versions of what we are facing.

    Life on Earth will carry on, and in 25 million years the biological matrix will be functioning fine without us. It will have recovered from our engineered mass extinction and evolution will have recovered the biological diversity that we have and continue to demolish. It is not likely that we are going to kill the Earth.

    LC

    • squidgeny May 16, 2012, 2:57 PM

      Good post, but it’s been suggested that biodiversity peaked about 200 million years ago, and it’s all been downhill from then on ;) So the Earth might not truly ‘recover’ from our impact, and we may have hastened the decline quite significantly.

      I’m unsure of the veracity of the claim though. It cropped up in the book The Life and Death of Planet Earth

      • gopher652003 May 16, 2012, 3:21 PM

        I’ve read that there are single “fossils” (in this case groups of sea creatures fossilized in mud) from a few hundred million years ago that contain more biodiversity than all animal life on Earth today. Life has definitely… specialized.

        But I’m not sure that says anything for or against either Gaia or the likelihood of life surviving humans.

      • lcrowell May 16, 2012, 3:50 PM

        I am definately no expert on this. I have seen graphs that estimate the biodiversity of life, large scale multicellular life, since the Cambrian. It does seem to have reached its peak in the early or middle Mesazoic. Depending upon who you talk to it has fallen and risen on an average plateau of comparable biodiversity, or it has dropped on average.

        Biodiversity is likely to remain fairly high for another 500 million years. After then the Earth will start to heat up from the increase in solar irradiance, which will start to bring trouble for life. By around 1 billion to 1.5 billion years life will have retreated into the subsurface as prokaryotes. 2 to 3 billion years from now life will be kaput and Earth will become a Venus-like planet.

        LC

        • gopher652003 May 16, 2012, 4:16 PM

          I don’t know what the latest research on this says, but I’ve read that in ~250ma if the orbit of the Earth hasn’t swiveled outward a little bit one of two things will happen. Either the surface temperature will rise to levels too high for most life to exist, or the greenhouse effect will be decreased. In this case the primary mechanism for that would be removal of some CO2 from the atmosphere (methane breaks down into CO2 relatively quickly and for some reason water vapour doesn’t look likely to decrease… no idea why).

          As CO2 levels drop, they will eventually reach the point where they are below the minimum threshold for plants to assimilate properly. I didn’t read further, but I assume there is a theoretical minimum ppm required for efficient plant respiration, just like there is for animals and O2. Plants will mostly die, as will most animals.

          If this model is correct then Earth has only about 250 million years left before biodiversity will crash, with nothing left but a few non-photosynthetic bacteria.

          If life on Earth is 3.8 billion years old, and life is (essentially) going to end in 250ma, then Earth is ~75 years old in human years, assuming humans live to be 80. It’s on its last legs, retired, and heading gracefully toward death by old age.

          • lcrowell May 16, 2012, 5:31 PM

            Back in the 1990s I did research on the question of whether the orbit of the Earth increases it radius with time. Based on some numerical and perturbation calculations I performed I do think this happens, but it is not absolutely predictable. The gravitational influence of Jupiter is the main driving force for increasing the orbital radius. My analysis indicates the Earth 3.5 billion years ago was .85AU from the sun, compared to 1 AU today, and this would have increased the Earth’s solar irradiance by 35%. This would have substantially warmed the Earth given the solar output was 30% lower than today. The early Earth atmosphere was primarily nitrogen with about 10-20% CO_2. This would have increased the average temperature of the Earth from -30C to 0C. So if the Earth continues to evolve this way then in one billion years the Earth will be 1.05AU in radius. The solar output will be around 10% higher than today, and this motion will almost exactly cancel the increased brightness of the sun. So it is possible that life in a billion years might be doing just fine here

            The open question is now the orbital radius can increase in such as way that the periodicity of the Earth’s orbit crosses the 1/11 resonance condition with that of Jupiter. Right now Earth has 1:11.85 ratio between orbital periodicities of Earth with Jupiter. This increase in orbital radius means crossing the resonant condition of 1:11 — a sticky mathematical problem. The orbits of planets tend to stay close to certain resonant conditions, where we are now near an 8:95 resonance ratio.

            So if I were to run with this, in about a billion years Earth will reach the 1:11 resonance condition. So we may have a billion years until then. If Earth crosses that resonance threshold it would imply life could exist for a much longer time period. The resonance condition has the effect of amplifying small perturbations (chaos theory) so it acts a bit like a barrier, and some stochastic fluctuation has to kick Earth over the “hump.” Once across we are good for another billion years. So Earth may have a billion years and maybe up to 2 billion years before becoming overheated.

            There are of course other mitigating circumstances. The UV breakup of water in the atmosphere and the absorption of water by tectonic subduction will decrease oceans over time. In about a billion years the oceans may only be 50% of the Earth’s surface. That will be a game changer. Also in 300 million years North America will crash into Asia by tectonic drift, which will recreate Pangea. Most of the Earth’s surface will become desert, putting a huge stress on life. The diversity of life might start to take a huge hit around that time.

            The heating of the sun will start to outpace any orbit drift of the Earth around a billion years from now. So even with the orbital corrections it is likely that by a billion year in the future life will start to become pretty tough. As a result if my scenario is correct Earth might be compared to a 50-60 year old person approaching retirement, but is still in a reasonable degree of health and productivity. It also should be pointed out that even if the oceans boil off in a billion years that prokaryotic life may persist for a considerable time beyond then. There might be microbial life on Earth in rock layers two or even three billion years from now.

            LC

          • Torbjörn Larsson May 17, 2012, 9:51 PM

            As a background, the astrobiological baseline for the case study of Earth is:

            1. Orbital parameters roughly as today.

            2. Early atmosphere was probably a very dense carbon dioxide atmosphere. After Earth-Moon impactor the CO2 pressure was likely reminiscent of Venus, todays mantle carbon was all up in the Earth. The primordial atmosphere was likely ~ 170 bar H2O (right after the impact) and 40 – 210 bar CO2. (Faure 1991, Zhang and Zindler 1993.)

            The water rained out of course, leaving a dense CO2 atmosphere. That recycled rapidly down the mantle by subduction over a period of some tens to hundreds of millions of years.

            It is the model of Kasting 1993 that speaks of something like todays atmosphere ~ 3.8 Ga bp. There are few, if any, constraints. The N2 is assumed to be the same as today, or ~ 0.8 bar. The rest is mainly CO2 that prevented early Earth deep freeze due to a weak early Sun combined with point 1 above.

            The later Kasting IIRC changed that model. (I can’t remember why as I write this.) But I find it reasonable.

        • bfmorris May 16, 2012, 4:28 PM

          Perhaps humans, assuming they survive the short term, will have the technology to alter Earth’s orbit as needed. Which would seemingly also mean that imperative technology for space travel outside our system would be feasible.

          • lcrowell May 16, 2012, 5:40 PM

            The average duration of a large complex mammal is a few million years. If we consider our evolution from Homo erectus our species evolutionary lineage has existed for over 2 million years. It is likely that our species will cease to exist for a range of reasons long before this becomes a real problem.

            LC

          • bfmorris May 16, 2012, 11:04 PM

            We intelligent humans have the unprecedented ability to manipulate our environment and develop technologies. Thus, such a prediction may prove to be an inaccurately short period of time. Or, too long. haha

          • lcrowell May 17, 2012, 1:43 PM

            Our species is quite remarkable in its ability to exploit the environment. I think the change of the word manipulate to exploit frames this a bit better. These manipulations of the environment mean that we are able to devise our own controlled environment at considerable expense to the natural environment. We have done this for many thousands of years, but in the recent centuries it has exponentially grown and begun to reach certain limits. The ultimate problem we face is that we will run out of environment, or we will render our biological life support system here on Earth incapable of supporting our species, at least in the large numbers we have now. We may face a collapse in the not too distant future.

            The time frame for our species is biologically probably on time scales of 100,000 years, and our historical times scale is 1000 times less. We generally think of fairly long term historical trends on a time scale of centuries, and our historical time line is about 50 of these main increments. This is different than geological time scales on the order of 10s of millions of years, and much shorter than grand time periods of 100 million or a billion years. Further, in recent times our technologically progress involves a compression of time; we move faster and on much shorter time frames than in the past. So our focus with respect to time is much narrower. It does not at all appear likely that our species operates on time scales commensurate with vast time scales of the future, such as when the sun becomes too luminous or becomes a red giant.

            I think these speculations about Type I through V civilizations to be idle speculation. That we will control the sun (Type II or III) and eventually the whole galaxy and then build ourselves new cosmologies (Type V) before this cosmology reaches heat death some 10^{100} years, or even just star death in 10^{12} years, amount to pseudoscientific eschatology. To be honest it will be hard enough for us to survive in a civilized form through the next couple of centuries or 1000 years, or for our species to survive 10^5 years, let alone think about surviving through vast time periods into the future.

            LC

          • twas brillig May 18, 2012, 12:20 AM

            LC and others, you think only in terms of materialism or a purely material reality and thus, you are operating on a basis of false reality or at the very least, an incomprehensibly narrow perception.

          • lcrowell May 18, 2012, 12:33 AM

            Well if that is the case the rest of us can stick hot knives in our gonads and howl at the moon.

            LC

        • Torbjörn Larsson May 17, 2012, 9:29 PM

          I don’t have time to dig into this either, but as I remember it diversity, commonly measured by number of species, has increased, while number of Cambrian early body plans have decreased as many early major clades disappeared.

          • lcrowell May 17, 2012, 10:40 PM

            Stephen Gould made a statement similar to this with regards to the Burgess shale. In the Cambrian explosion there were a huge number of various forms of trilobite-like animals which defined a large number of clades. Most of these vanished.

            LC

    • gopher652003 May 16, 2012, 3:09 PM

      After reading your comment I had a bit of self doubt, so I went to Wikipedia and read the Gaia article. I think my confusion is a result of the fact that there are, essentially, two seperate Gaia Hypothesis. Weak Gaia, and Strong Gaia.

      Strong Gaia is what Jason is talking about in his article, and it’s a load of new-age crap (living Earth and all that nonsense).

      The idea behind Weak Gaia can be summed up in this sentence: “Biota influence their abiotic environment, and that environment in turn influences the biota by Darwinian process”. I don’t think there is much doubt about that sentence. Weak Gaia takes that sentence a little bit further (and some people take it in a ridiculous direction), but, crucially, Weak Gaia doesn’t require there to be a “set environment” that all life works together to maintain. It allows largescale environmental changes of the type that have been observed and hypothesized to exist (IE, the change to an oxygen atmosphere that annihilated much of then current life on Earth).

      Weak Gaia still makes some silly claims (depending on who is talking about it), but the idea isn’t outright laughable like Strong Gaia. The big issue with Weak Gaia is that it requires extra non-Darwinian evolutionary processes that haven’t been observed. It requires that evolution positively select for creatures that do help the environment, rather than what Darwinian evolution would suggest, which is that creatures that harm the environment have a selection pressure against them. That’s a deal breaker in my mind, at least until someone can come up with a mechanism for said positive selection pressure.

      • lcrowell May 16, 2012, 4:20 PM

        I am not really a believer in either of these, the weak or strong Gaia hypotheses, just as in general scientific hypotheses are not something to believe, but rather to think about and try to figure out ways to test them. Even those that pass these tests and become theories are not particularly believed in as such.

        The standard Darwinian selection does state that an organism which does not adapt to the environment is selected against and may go extinct. A corollary of this is that any species that over exploits its environment will overshoot and its numbers will plummet. There is a risk of going extinct this way. However, some species of animals have evolved a strategy for surviving these episodes, such as grasshoppers that become locusts in a swarm. If we call S the survivability of a species and E its positive impact on the environment the Darwinian thesis might then say

        ?E then ?S

        where ? means “not”. Therefore if we observe ?E, the species is damaging the environment, we conclude ?S in the syllogism

        ?E then ?S
        ?E
        ————
        ?S

        and the species is not survivable. The logical complement of this is S then E, called modus tolens. Hence if the species is survivable we conclude it has some positive or constructive role with the environment. This is an inference we could draw just from Darwinian evolution.

        We can’t conclude E then S, where clearly this is the sufficient condition on the above. This does not mean it is false. Since both of these, the Darwinian statement and this Gaia statement, are empirical this would have to be supported by actual data. This hypothesis would amount to saying the feedback loops on species of life close off evolutionary paths that are deleterious to the environment, but at the same time open up paths that are beneficial. This would then suggest the whole system does function to promote the evolution of species which integrate together most effectively.

        I am not sure how this could ever be supported by data. Those in the ecological field are in a much better position than I to design the appropriate research protocols to address this question.

        LC

        • Torbjörn Larsson May 17, 2012, 9:26 PM

          I don’t have time to dig into this now, but as I remember it all the claims from lemmings to locusts that they have developed group behaviors to mitigate overpopulation has been put to shame. (For example, locusts show a common stress response among insects.)

          Also, I don’t think you can call it “the Darwinian thesis” as evolution theory is silent on what functionality populations will evolve. It is your thesis based on a potential (but as I note above likely erroneous) response, but it has no theoretical support.

          Evolution has no foresight, and while it isn’t impossible for populations to evolve group behavior and potentially mechanisms to survive recurrent stresses, it is an unlikely outcome.

          • lcrowell May 17, 2012, 10:30 PM

            I don’t think I am arguing for group behavior. I am talking about an average impact on the environment. If that is negative the population of a species may decline or crash. Some individuals able to adapt to the new conditions may survive and be the continuing lineage of that species.

            LC

      • squidgeny May 16, 2012, 4:24 PM

        Strong Gaia is what Jason is talking about in his article, and it’s a load of new-age crap (living Earth and all that nonsense)

        That’s not what Jason is talking about at all. In fact he explicitly states the opposite:

        Although named after the Greek goddess of Earth, the Gaia theory is not so much about mythology or New Age mysticism as it is about biology, chemistry and geology — and how they all interact to make our world suitable for living things.

        • gopher652003 May 16, 2012, 4:59 PM

          “…the Gaia theory likens Earth to a self-supporting singular life form, similar to a cell.”

          That’s not Weak Gaia, that’s fantasy. He tries to make it more palatable with weasel words, but it is what it is. (Gaia doesn’t “liken” Earth to a singular life form, it states that it *is* a singular life form.)

  • gopher652003 May 16, 2012, 2:46 PM

    I have more to say elsewhere in the comments about the veracity of the Gaia Hypothesis, but all I wanted to say here was that that was an *awesome* choice of photo for this article, Jason:).

    I hadn’t seen that particular Rosetta photo before. Thanks for sharing. I’ve put it in the rotation of my desktop images.

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  • Scott Williams May 16, 2012, 3:41 PM

    I don’t think skin mites have the capacity to understand that they reside on a living organism.

    • Jeff Boerst May 16, 2012, 5:14 PM

      So you then suggest that upward extrapolation is impossible?

  • HeadAroundU May 16, 2012, 4:22 PM

    Are those people wackos like the panspermia ones?

  • Cam Kirmser May 16, 2012, 10:33 PM

    The earth is a rock.
    Rocks are not alive.

    There. Problem solved.

    Sheesh, the moronic things researchers will come up with to justify getting money from someone else.

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  • philippines May 17, 2012, 6:00 AM

    What? Sulfur???? I think this isnt the solution. We, people should start to change how we live and how we interact with nature. That’s the best answer to this problems

    http://ilavph.blogspot.com

  • Viva_Kevin May 17, 2012, 10:28 AM

    and we – human beings – are the programed cell death of that living organism.

  • Cat Thunder May 17, 2012, 6:50 PM

    This is exactly what the aliens want us to develop such companies to form this materials for their breathing habitat.This is the only air these alien can breath.Now they want this for their own purpose.B-careful who we are dealing with here.A
    Aliens have small noses and and their nasal are so sensitive to our atmosphere that causes asthma and now they want this sulfur to be developed.Aliens live in a sulfuric world underground.The smell of nature isn’t what these aliens want.Sulfuric acid is what they want.

  • Daniel Bennigan's May 17, 2012, 9:07 PM

    It’s kind of interesting to think about the Earth that way. If you think about the clusters of organisms and cells that make up our body and relate that to the Earth, the Earth in turn really could be considered a large life form. Also if you look at the human effect on the Earth and consider it a life form, then we could also be considered parasites in a way because of our destructive nature. Very interesting.

  • Torbjörn Larsson May 17, 2012, 9:08 PM

    Browsing the thread, I don’t contribute much that isn’t already said:

    – Homeostasis is not a crucial requirement for live as much as heredity is, as the latter is the foundation for evolution, the process of all life. Of course biospheres can potentially reproduce, but that is not that the Gaia idea is modeled after.

    – As opposed to the article, I have the impression that Gaia ideas are pretty much dead. Few if any of the material cycles on Earth are self regulating in the homeostatic sense.

  • andrewp3 May 19, 2012, 11:26 PM

    A self-regulating system does not equate necessarily to a sentient living system. Do you have long, meaningful conversations with your thermostat?

  • get this May 20, 2012, 6:15 AM

    for crying out loud, the earth is made of rocks that were pulled together by gravity. just give me the grant money and I’ll write you a paper.

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