Free Energy and the Meaning of Life

By Sean Carroll | March 10, 2010 9:06 am

When we think about the “meaning of life,” we tend to conjure ideas such as love, or self-actualization, or justice, or human progress. It’s an anthropocentric view; try to convince blue-green algae that self-actualization is some sort of virtue. Let’s ask instead why “life,” as a biological concept, actually exists. That is to say: we know that entropy increases as the universe evolves. But why, on the road from the simple and low-entropy early universe to the simple and high-entropy late universe, do we pass through our present era of marvelous complexity and organization, culminating in the intricate chemical reactions we know as life?

Yesterday’s book club post referred to a somewhat-whimsical vision of Maxwell’s Demon as a paradigm for life. The Demon takes in free energy and uses it to maintain a separation between hot and cold sides of a box of gas — a sustained departure from thermal equilibrium. But what if we reversed the story? Instead of thinking that the Demon takes advantage free energy to help advance its nefarious anti-thermodynamic agenda, what if we imagine that the free energy is simply using the Demon — that is, the out-of-equilibrium configurations labeled “life” — for its own pro-thermodynamic purposes?

From a slide by Eric Smith

Energy is conserved, if we put aside some subtleties associated with general relativity. But there’s useful energy, and useless energy. When you burn gasoline in your car engine, the amount of energy doesn’t really change; some of it gets converted into the motion of your car, while some gets dissipated into useless forms such as noise, heat, and exhaust, increasing entropy along the way. That’s why it’s helpful to invent the concept of “free energy” to keep track of how much energy is actually available for doing useful work, like accelerating a car. Roughly speaking, the free energy is the total energy minus entropy times temperature, so free energy is used up as entropy increases.

Because the Second Law of Thermodynamics tells us that entropy increases, the history of the universe is the story of dissipation of free energy. Energy wants to be converted from useful forms to useless forms. But it might not happen automatically; sometimes a configuration with excess free energy can last a long time before something comes along to nudge it into a higher-entropy form. Gasoline and oxygen are a combustible mixture, but you still need a spark to set the fire.

This is where life comes in, at least according to one view. Apparently (I’m certainly not an expert in this stuff) there are two competing theories that attempt to explain the first steps taken toward life on Earth. One is a “replicator-first” picture, in which the key jump from chemistry to life was taken by a molecule such as RNA that was able to reproduce itself, passing information on to subsequent generations. The competitor is a “metabolism-first” picture, where the important step was a set of interactions that helped release free energy in the atmosphere of the young Earth. You can read some background about these two options in this profile of Mike Russell (pdf), one of the leading advocates of the metabolism-first view.

I was reading a bit about this stuff because I wanted to move beyond the fairly simplistic sketch I presented in my book about the relationship between entropy and life. So I did a little research and found some papers by Eric Smith at the Santa Fe Institute. Smith has taken quite an academic path; his Ph.D. was in string theory, working with Joe Polchinski, and now he applies ideas from complexity to questions as diverse as economics and the origin of life.

On Saturday I was on a long plane ride from LA to Bozeman, Montana, via Denver. So I had pulled out one of Smith’s papers and started to read it. A couple sat down next to me, and the husband said “Oh yes, Eric Smith. I know his work well.” This well-read person turned out to be none other than Mike Russell, featured in the profile above. Here I was trying to learn about entropy and the origin of life, and one of the world’s experts sits down right next to me. (Not completely a coincidence; Russell is at JPL, and we were both headed to give plenary talks at the annual IEEE Aerospace Conference.)

So I explained a little to Mike (now we are buddies) what I was trying to understand, and he immediately said “Ah, that’s easy. The purpose of life is to hydrogenate carbon dioxide.” (See figure above, taken from one of Eric Smith’s talks.)

That might be something of a colorful exaggeration, but there’s something fascinating and provocative behind the idea. An extremely simplified version of the story is that the Earth was quite a bit hotter in its early days than it is today, and the atmosphere was full of carbon dioxide. At high temperatures that’s a stable situation; but once the Earth cools, it would be energetically favorable for that CO2 to react with hydrogen to make methane (and other hydrocarbons) and water. That is to say, there is a lot of free energy in that CO2, just waiting to be released.

The problem is that there is a chemical barrier to actually releasing the energy. In physicist-speak: the Earth’s atmosphere was caught in a false vacuum. There’s no reaction that takes you directly from CO2 and hydrogen to methane (CH4) and water; you have to go through a series of reactions to get there. And the first steps along the way constitute a potential barrier: they consume energy rather than releasing it. Here’s a plot from one of Russell’s talks of the free energy per carbon atom of various steps along the way; it looks for all the world like a particle physicist’s plot of the potential energy of a field caught in a metastable vacuum. (Different curves represent different environments.)

From a slide by Michael Russell

Here is the bold hypothesis: life is Nature’s way of opening up a chemical channel to release all of that free energy bottled up in carbon dioxide in the atmosphere of the young Earth. My own understanding gets a little fuzzy at this point, but the basic idea seems intelligible. While there is no simple reaction that takes CO2 directly to hydrocarbons, there are complicated series of reactions that do so. Some sort of membrane (e.g. a cell wall) helps to segregate out the relevant chemicals; various inorganic compounds act as enzymes to speed the reactions along. The reason for the complexity of life, which is low entropy considered all by itself, is that it helps the bigger picture increase in entropy.

In ordinary statistical mechanics, we say that high-entropy configurations are more likely than low-entropy ones because there are simply more of them. But that logic doesn’t quite go through if you can’t get to the high-entropy configurations in any straightforward way. Nevertheless, a sufficiently complicated system can bounce around in configuration space, trying various different possibilities, until it hits on something that looks quite complex and unlikely, but is in fact very useful in helping the system as a whole evolve to a higher-entropy state. That’s life (as it were). It’s not so different from other cases like hurricanes or turbulence where apparent complexity arises in the natural course of events; it’s all about using up that free energy.

Obviously there is a lot missing to this story, and much of it is an absence of complete understanding on my part, although some of it is that we simply don’t know everything about life as yet. For one thing, even if you are a metabolism-first sympathizer, at some point you have to explain the origin of replication and information processing, which plays a crucial role how we think about life. For another, it’s a long road from explaining the origin of life to getting to the present day. It’s true that we know of very primitive organisms whose goal in life seems to be the conversion of CO2 into methane and acetate — methanogens and acetogens, respectively. But animals tend to produce CO2 rather than consume it, so it’s obviously not the whole story.

No surprise, really; whatever the story of life might be, there’s no question it’s a complicated one. But it all comes down to the elementary building blocks of Nature doing their best to fulfill the Second Law.

  • Joseph Smidt

    “Life is Nature鈥檚 way of opening up a chemical channel to release all of that free energy bottled up in carbon dioxide in the atmosphere of the young Earth.”

    Wow, guaranteed that quote will show up on some anti-science website to try to vilify how scientists view life. :)

    I do find your idea of needing a sufficiently complex system to go around releasing “hard to get to” free energy fascinating. Something interesting to think about for sure.

    I wish I could have been hovering around your conversation with Mike Russell.

  • Bj酶rn 脴stman

    When I’m flying, I always wish that someone that interesting would sit next to me. Never happened.

    I’ll be forwarding all people who claim that the second law prevents evolution to this page from now on.

  • Metre

    But, but, but … life is built around amino acids, which are are bit more complex than methane. Is an amino acid endo or exothermic? Does it represent a higher or lower entropy state than it’s dissociated atoms? And how do we get to the amino acids before we hydrogenate the CO2?

  • Aaron Sheldon

    There are a couple more subtleties, such as where do the acidic conditions come from that can allow for serpentization of CO2 to CH4?

    Presumably proton donation to form acids occurred during the formation of the proto-oceans during an early bombardment, when olivine + water was exothermically converted to serpentine + protons.

    More imaginatively, after that initial kick start of acidification life must have evolved enzymes to acidify the environment of the metabolic process, which should be very early precursors of the modern photosynthetic enzymes.

  • Josh Neal

    I was just talking about this concept to my wife a few days ago. I don’t have the educational background to think about it very concretely, but I thought the key idea was of a system bumping up against some maximum rate of entropy. This forces it to find a more efficient way to produce entropy.

    The plot shown here is interesting. It reminds me of a plot in Endless Universe by Steinhardt and Turok, showing the conversion of dark energy from an attractive force to a repulsive one. I’m just thinking out loud – I know trying to tie two speculative theories together with a plot graph isn’t terribly scientific 馃槈

  • Arun

    But it all comes down to the elementary building blocks of Nature doing their best to fulfill the Second Law.

    Sean here gives the elementary building blocks of nature purpose – “they do their best”, etc. But this is religion.

  • Aaron Sheldon

    I should add that the above process only works in shallow bodies of water laying on olivine formations (which there would have been a lot of in the early Earth). But once the accessible olivine had been converted, and the oceans became deep enough, then one has the same problem of being at a false minimum of entropy. Presumably one of the chief activities of life is then to access normally inaccessible olivine minerals and make them available for serpentization. Which begs the question: exactly how deeply into the Earth’s crust has bacterial life infiltrated, has it gotten beneath the sedimentary layers?

  • Charles

    Sean makes it sound a little dramatic by saying Nature “found a way” to use all the free energy that was just lying around. I think it would sound a little less wild if we acknowledge that it’s not “Nature” per se that’s doing anything but the energy itself. That is, energy enables molecules to sample many configurations, combinations, and reactions. This allows systems from emerge from a local minimum and try alternate, more efficient configurations (like a marble moving rapidly in a bowl, eventually it will fall off the edge). Heat from the sun and from the early earth allowed many combinations of molecules to emerge, providing the “push” that led to complexity and to life.

  • Timothy McWhirter

    The German philosopher Friedrich Nietzsche described life and the “world” in terms of what he called the “will to power.” I have developed a thermodynamic interpretation of this concept (“Nietzsche’s Physics,” in International Studies in Philosophy XXXI/3 (1999): 5-17). One of the most controversial quotes from his unpublished notes is “This world is the will to power–and nothing besides! And you yourselves are also this will to power–and nothing besides!”(The Will to Power, 1067) Nietzsche was aware of the early formulations of the second law and I believe he had prescient view of its implications.

  • Sean

    If you live your life in fear of being quote-mined by anti-science types, you will have less fun and still be quote-mined by anti-science types.

  • Jason A.

    Arun, it’s called poetic license. He was putting the idea in terms that are easier to understand. He’s not seriously proposing that there is a conscious intent there. If you have to be intentionally obtuse just to make your point, then your point is wrong.

  • Low Math, Meekly Interacting

    Though which chemical pathway was favored on prebiotic Earth is still quite open to debate, the notion that self-organizing systems decrease entropy locally, but are still dissipative on the scale of an open system is not news or controversial. Yes, catalysis of some sort certainly played a role in bringing prebiotic chemistry anywhere near the levels of complexity we associate with even the simplest organisms, but that’s a historical subject, not really a fundamental one. I think the most interesting question about life is not “How” (in the specific case of Earth, though that’s still an immensely interesting question), but more related to “If”. I.e., if we observe self-organization everywhere, does the efficient dissipative nature of such systems indicate a kind of “attractor” that makes life inevitable in any environment that can sustain some threshold level of complexity for a long enough span of time. For this argument, I think the the order of emergence of replicators or metabolomes is pretty much irrelevant, since you wind up with one or the other eventually. On Earth, people keep finding clever ways to support RNA chemistry in hypothetical prebiotic environments, and since RNA makes for a decent information storage medium as well as raw material for enzymes (ribozymes), in the RNA world, you’re almost getting both for the price of one. And lets not forget some of these building blocks may have come directly from space. Perhaps the fact that it’s so hard to get over that hump in the Gibbs free-energy plot on Earth is tells us it didn’t happen on Earth.

  • Marshall

    This is an interesting idea, but I’m not sure I buy it quantitatively.

    The total atmospheric content of CO2 today is about 3e15 kg, or 7e16 moles. Using the ~ 120 kJ/mol free energy release from CO2 to CH4 according to Russell’s plot, that implies the total stored free energy in the Earth’s atmosphere is about 8e21 J.

    Well, the Earth receives that much energy from incident solar radiation in about a day and a half (factoring in the current mean albedo of 0.4; the raw incident solar power is 1.7e17 W). So the amount of energy stored in CO2 is just utterly negligible in terms of the total energy balance of the biosphere. Even if you factor in a massively higher CO2 bath (say, a mass equal the entire atmosphere of Venus, 5e20 kg) then solar energy still equals the CO2 stored free energy after a mere 400 years.

    So it’s a cute story, but I don’t think it describes well the energy balance of the real biosphere we live in.

    (P.S. It was nice to meet you after your talk here at UCLA last week, Sean. Thanks for a very stimulating and thought-provoking afternoon!)

  • Samuel A. (Sam) Cox

    All of the comments above are interesting. I appreciated Charles’ thoughts especially…they have profound implications.

    In biology we reflect that “ontogeny recapitulates phylogeny”…we can observe the processes of organic evolution over cosmological time by observing the short-term development of life from pre-conception through maturity in a given individual of the species. I won’t get into an involved analysis of the implications of that process…believe anyone can evaluate those for themselves. However, let me say that….

    there is something analogous between organic evolution and classical Newtonian physics, and that the 4D “processes” we observe probably are not cosmologically significant. They are significant to US for the simple reason that the universe we live in is defined by space, time, motion and change…entropy- stuff life that.

    We all know that Newtonian physics is a very good approximation of the real universe, a nice model. Relativity is an even closer approximation of reality. In the biological realm, the processes of organic evolution are indisputable.

    I think one of the things which makes me edgy when these creationists assert their bizarre ideas is that I realize that organic evolution may, like newtonian physics or relativity be a close approximation of reality, a very good model, but far from the cosmological truth…biological evolution “happens” when we observe the universe from certain coordinates in a manifold of space and time.

    However, we live in a quantum universe. That is why I thought Charles reflections were so appropriate.

    A quantum universe has a certain singular, instataneous quality about it, and Quantum Mechanics is our best model of reality…better than Newton or Einstein.

    To understand where life “comes from” we need to understand what energy really is, what invariant frames of reference are and how all information and complexity from one side of the universe to the other is eternally and near instantly entangled.

    When we realize that the living material in our bodies has never known death as we define death…the border between the inorganic and organic universe….for 3.2 billion years…a time span of cosmological significance, we get a serious hint that life and consciousness are not some universal after-thought…these things are fundimental to existence itself.

    If I am a 4D object occupying a fixed set of coordinates in a manifold, in all probablity I really developed as a person as a complex molecule develops from less complex molecures in an organic soup. That REALLY makes investigating the nature of energy important to a knowledge of what I am, where I REALLY came from and my purpose in the universe.

    It makes some people kind of angry when a scientist starts to investigate “purpose”. My only comment on that is that my grandchildren and great grandchildren would not exist if I had not existed EXACTLY the way I have, nor would I exist, had not my forebears existed EXACTLY as they existed. My purpose, the purpose of all life, is support; we are a part of the living whole. Like the “keystones” in a cathedral, if one is removed, everything comes down…the structure disintegrates. This means that the time when I “come down”…when everything “comes down” is important to the universal structure. Biblical intuition says it this way: “Are not two sparrows sold for a farthing? Yet none of them falls to the ground without your father. Fear not…you are worth much more than sparrows!”

    I originated in the universe exactly where I “am”. Organic evolution only hints at the extent of my entanglement with the entire inorganic and organic whole of reality. Unquestionably the developent of organization and complexity in evolution is a reflection of the phylogenic development of our individual selves over eternity…Ontogeny recapitulates Phylogieny.

    Everybody has a problem avoiding personification of the inorganic. The reason is that the inorganic and organic universe of information and complexity are completely entangled. Where, REALLY can we draw the line between the inorganic and organic worlds?

    I’m reminded once again of Fred Hoyle. When he found that, in the center of stars, the exact conditions demanded for the existence of the necessary proportion of carbon to permit life in the universe, were duplicated…he exclaimed that “life monkeys around”. Life sure does “monkey around”! How it “monkeys around” will be determined when we understand what energy really is….

  • eric gisse

    Here I’ve always thought that the meaning of the universe was to produce iron and black holes, with any intermediate step of ‘life’ just acting as a distraction.

  • Aaron Sheldon

    Of course in the modern era the with the biosphere’s ability to convert a part of an incident 5500K black body spectrum to a 300k black body spectrum results in about a 17 fold increase in entropy per mole of converted photons, calculated through conservation of the Gibbs Free Energy (scattering by itself results in a negligible increase in entropy). The same logic has Venus increasing entropy per mole of converted photons by only 6 fold.

  • Charon

    “So it鈥檚 a cute story, but I don鈥檛 think…”

    Marshall, I’m curious what potential energy barrier you see involving the energy from the Sun. Because if there isn’t one… then you missed the entire point of this discussion.

  • Low Math, Meekly Interacting


    Interesting comments, but I had a couple questions, as my knowledge of primordial geochemistry vis prebiotic stews is fairly limited.

    On the subject of acidification, my understanding of the relevance of acidity to photosynthesis is limited to the fact that the low pH in the thylakoid space provides a proton gradient which, long story short, couples ATP synthesis to work done by light. The key is not acidification per se but the potential difference across a membrane, so what’s in it for an enzyme or primordial cell to simply follow the low pH? Some enzymes catalyze reactions better in an acidic environment, e.g. lysosomal, but it takes a lot of work to a) synthesize those enzymes, and b) decrease the pH of the lysosome, and c) protect the rest of the cell from this environment while getting things in and out of it in an orderly fashion. So it’s the differences in pH that matter, not any particular pH. What’s the significance of an overall acid environment to the evolution of early enzymes and life?

    Also, could you expound a little on the conversion of black body spectra and how that relates to life? Is the Earth vs. Venus increase in entropy an indirect measure of photosynthesis? Could the ratio of some range of values explicable by abiotic planetary surface and/or atmospheric conditions and some measured value be used to suss out the presence of life on exoplanets, in principle?

  • Matt

    So does that make us a short-term entropic experiment, doomed to die off quickly, as we increase net CO2 no matter what we do?

  • Aaron Sheldon

    Actually my comments on the pH wasn’t based on biological reasoning but rather physical chemistry. The graph for the serpentization process Sean reported required donor protons which, don’t quote me because I haven’t worked out the pK’s, wouldn’t be in enough of excess from the equilibrium of dissolved CO2 with carbonic acid. Which got me reading as to where the excess acidity could come from, a natural fit is the conversion of olivine. But this is all a vast stretch of my limited knowledge of undergraduate physical chemistry. This process would be rate limited by diffusion: CO2 from the top of the body of water, and protons from the bottom. The wildly imaginative part is hypothesizing that the earliest proto-enzymes were thermodynamic improvements on this process.

    I don’t know if the fractional increase in entropy is a measure of life; because by the same earlier logic Mars’ black body spectrum gives a 25 fold increase of entropy per mole of converted photon gas. The calculation just shows that thermodynamically life on Earth is not so much out of place, and might plausibly be the optimum for the particular configuration of orbit, incident radiation, chemical composition, etc…

  • Aaron Sheldon

    One more thing…the place to look for signals of exo-life is in heat capacity. Someone should sit down and plot a graph of the heat capacities of the solar planets versus orbit. I have a hunch that Earth lies off the curve, specifically Earth has a higher heat capacity then should be expected; because of the more entropically favorable conversion of incident radiation.

  • Arfnotz

    I went to that IEEE conference one year at the request of my boss. I don’t ski and immediatly got altitude sick, plus I had to give my paper at 10 pm. I did learn a few things (none as provactive as this) and wish they would relocate to lower ground.

  • Ted Erikson

    Interesting. From a strict physical viewpoint, it can be shown that there is a free energy availability maximizes as size decreases, i.e. from large to small to tiny. Consider the only two processes, motion and growth. Motion describes change in position, while growth must describe change in “size”, i.e., mass. A link to my chapter in a new book to be published shortly is on the web site,, that goes into such detail.

  • Patrick Dennis

    Help! Brain lock: “…there is a lot of free energy in that CO2, just waiting to be released.” I thought that carbon dioxide is the low energy compound. Doesn’t the reaction (hydrocarbon) + oxygen -> carbon dioxide plus water release energy that was originally supplied from the environment to facilitate the reverse reaction?

  • Aaron Sheldon

    Took a couple of moments to do a few napkin calculations.

    If the Earth could perfectly thermalize the 1350 W/m2 5500K incident radiation, then the from the Stefan-Boltzmann Law the Earth would have to be at a temperature of about 390K. This corresponds to about a 13 fold increase in entropy per mole of converted light. As it stands, again from the Stefan-Boltzmann Law, the Earth at 300K is converting about 450W/m2 of the 1400W/m2 incident radiation. To get a rough comparison of the actual total entropy change one can use the ratio of the converted fluxes times the ratio of the ratios of entropy per mole , so with life, Earth is at about 42% of the maximum possible change of entropy if every mole of incident flux was thermalized.

    Unfortunately for everything except thermophilic bacteria 390K is uncomfortably close to the boiling point of water, I suspect there is something optimum about keeping the Earth near the triple point of water in terms of thermal physical feed back (that is hotter configurations of the atmosphere are not stable and result in long term cooling below 300K), then again maybe runaway heating is the inevitable thermodynamic fate of Earth’s atmosphere.

    I haven’t had time to work out the comparisons for the other planetary bodies.

    I’m sure this must all be in the literature somewhere, I’ve just been to lazy to look it up. Some of it is vaguely reminiscent of the problems in my second year modern physics course.

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  • Aaron Sheldon


    Good point, the Gibbs Free Energy of Formation of products from reactants depends on the chemicals, the reaction path, and the conditions under which the reaction occurs. So if one calculated the Gibbs Free Energy of Formation of methane and oxygen from water and carbon dioxide via the path of breaking down the reactants to individual constituent atoms and then forming the products one would have to provide about 818 kilojoules per mole to make the reaction occur.

    The point of the graph is to show that their are other formation processes and paths that are not as unfavorable in terms of the Gibbs Free Energy (e.g. Fischer-Tropsch synthesis). But just because you can release energy along a reaction path still does not mean it is globally favorable in terms of the total entropy of the heat bath (solar radiation) plus system (Earth).

    Certainly given the extent of fossil fuel deposits, and limestone sedimentary formations, a good part of the biosphere has been busy sequestering carbon, but why is this entropically favorable?

    More wild speculation runs like this:

    Without sequestration: Carbon dioxide builds up->Earth warms to optimum 390K->atmospheric gases lost due to gravitational escape->Earth loses insulation->lowers change in entropy of incident photon gas->long run less change in entropy

    With biological sequestration carbon dioxide build up is kept in check, so while the Earth never reaches the maximum 390K, it maintains at 290k+-20k, allowing for a greater increase in entropy over longer time scales.

    But like I said that is wildly hypothetical.

    I guess the poetic way to put it is that life occurs when entropy equivocates.

    The other question is whether we capable of seriously disrupting this process in the long run? Probably not. But are we capable of disrupting this process enough in the short run to kill billions of our fellow humans? Probably yes.

  • noiv

    The whole picture is described as ‘photon mill’ with high value energy as input and lower value energy as output. There are even opinions saying live may evolve almost instantly under these circumstances. In such an environment live is capable of creating regions of low entropy (e.g. oilfield), leading to an economic opportunity. However, to me it looks like there are not enough resources available for an infinite economic growth and the limit can be computed now.

  • Andr茅 Cardoso

    Summary : the meanin of life is breathing and do crap …

  • Sandy Baron

    Sean’s question was – which came first the replicating molecule or the capture of free energy?
    I asked myself, where does RNA get energy for replication? It’s from breaking bonds when releasing phosphates. So, “metabolism” has to come first. Yet, chemical reactions can happen in the absence of life. It was the segregation of chemical reactions in space that had to happen first. Molecules other then ones that can replicate may take this first step. But, the ones that replicate can evolve. By evolve I mean both be subject to natural selection, and be a program running forward in time.

  • Aaron Sheldon

    There is a significant flaw in my hypothesis concerning the atmospheric evolution in the abscence of biological sequestration: the half life for thermal lose of atmosphere is on the order of hundreds of billions of years…so not really applicable.

    For a clue to an alternative explanation one can look at Venus. The entropy maximizing thermalization temperature given a solar flux of 2580W/m2 from the Stefan-Boltzmann Law is about 460K, quite a bit cooler than the surface temperature of about 750K, however the overlying cloud cover scatters about 60% of the incoming radiation, giving a Stefan-Boltzmann thermalization temperature of about 370K, which is plausibly close to the thermodynamic range of the sulfuric acid condensation cycle. This also corresponds to an altitude of about 50km in Venuses atmosphere, which is also a plausible altitude for where the atmosphere is nearly completely insulating, maximally convective, and chemically reactive. Succinctly Venus is maintaining the bulk of its thermal budget with incoming radiation at an altitude of 50km. Interestingly this also means that Venus is increasing entropy in the solar flux at about 41% of the maximum possible.

    The analogous situation with Earth would require investigating the altitude, thickness, and scattering of the water cloud cover with run away warming, an area of vigorous debate. However if this configuration is thermodynamically unfavorable when compared to the existence of life then the cloud cover would have to scatter more than 66% of the incoming radiation. This is also plausible because a temperature of 273K corresponds to about 76% of the radiation being scattered.

    This also leads to hypothesizing that the altitude of maximum convection, phase transition, and chemical activity is the altitude where the thermal budget with the incoming solar radiation is maintained. Which for Earth is near ground level, but for other planetary bodies not so.

  • Aaron Sheldon

    On final note of the IR power of Mars. The average is 390 W/m^2, which corresponds to a temperature of 290K, considerably warmer than any of the atmospheric temperatures, indicating that the bulk of Mars thermal budget with incoming solar radiation is maintained by the heat capacity of the ground.

    Again adding a little more provocation to the idea that a critical ingredient for life is that the solar thermal budget is maintained near the ground, but not by the ground.

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  • Tim Tyler

    It seems like a bit of a reiteration of the idea in “Contribution to the energetics of evolution” – Lotka, A. J., 1922. Search for “Survival of the Likeliest” and “Maximum entropy thermodynamics” for modern iterations of the idea.

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  • Brian Too

    I spent some time years ago philosophizing on Life, the Universe, and Everything. It ocurred to me that maybe the purpose of life is to resist the process of entropy. Then I extended the idea to include a scientific definition of good and evil. Good would, in this framework, decrease entropy and evil would increase it. You could also then have relative good and relative evil.

    Pretty abstract I know and quite possibly unmeasurable.

  • Samuel A. (Sam) Cox

    #39…but very thoughtful and I can assure you that you are not the first person to have had that idea occur to you!…Life as a servomechanism to tilt the observed universe (the only one which empirically- and scientifically- exists) away from the chaos of the Second Law of Theromodynamics- and keep a closed universe of finite mass and marginally closed space in a state of perpetual existence- and gradually increasing order and complexity…is a profound idea.

    Don’t assume that concept is un-measurable either! Not now, maybe- but…

    I have never read a satisfactory explanation why so many scientists strongly assert that space is open and flat when EVERY major experiment has indicated an Omega total of 1.01-1.02 something.

    I have the greatest respect for Ned Wright…he said that the cosmological constant (whatever that is…depends on your conceptual framework), if included would produce perfectly flat space. Recent developments have revived talk of a cosmological constant but, wait a minute!

    The cosmological constant was developed by Einstein to render the universe static! It is an experimentally determined fact that, cosmological constant or no cosmological constant, the universe is NOT static! Given that fact, we would do well to watch our step when we discuss “the cosmological constant”. Yes, there may be something happening there, true, but whatever it is, it is NOT a cosmological constant!…not what Einstein was thinking about, anyway.

    Most criticism’s of quasi-static cosmologies are based on their poor fit with experimental results- ASSUMING a FOUR dimensional universe. That is a big assumption and, also in the light of recent experimental results, an untenable assumption.

    A great thread….

  • Lab Lemming

    The problem with this idea is that the assumption that there are no abiogenic ways to complete this reaction is demonstrably false. There are many methane-producing reactions, that occur in all kinds of environments from cooling magma chambers to laboratory experiments.

    An additional problem is that there this energy “minimum” for for the H-C-O system in the absence of rock. Once you add an actual planet into the equation, there are more energentically favorable compositions which include things like carbonates and hydrous minerals.

    Also, hydrogen escapes the earth’s atmosphere,, so you can’t keep it around long enough to react with your CO2.

    And finally, the chemical potential energy (in the form of oxygen) in the atmosphere now is much greater than when life began, which is the opposite effect than what you would expect from a system designed to dissipate free energy.

  • Keith Beatty

    My own curiosity about the anti entropic contradiction of life versus thermodynamics was quenched by a law from non linear thermodynamics: A flow of energy creates order. Thus the flow of energy from the sun to earth and into space requires the creation of ordered forms such as life.

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  • Dov Henis

    Reconceive Cosmic and Life Evolution:

    Pre-History Of History?
    Life’s Genesis Was Not Cells, But
    First Gene’s Self Reproduction

    A. From “Pre-History of Life: Elegantly Simple Organizing Principles Seen in Ribosomes”

    – Hints from relics of…evolution left behind in MODERN cells.

    – Evolution of the MODERN genetic code likely followed a long period of chemical evolution.

    – Before the last universal common ancestor the ribosome emerged from an early evolutionary stage of life to help with the translation of the genetic code.

    – We believe:
    – that the genetic code was established in two different stages. Our data does not shed much light on the early code, consisting of prebiotically available amino acids.
    – once some primitive translational mechanism had been established, new amino acids were added to the mix and started infiltrating the genetic code based on specific amino acid/anticodon interactions.

    B. This comment is NOT re the genetic mechanism of specifying amino acids compositions of proteins. It is only re the origin and scenario of life’s genesis.

    I have been proposing:

    * Life’s genesis was not cell(s), but the self reproduction of yet uncelled ungenomed gene(s).

    * There was NOT any “Pre-History Of Life” evolving in an archaic pre-modern life cell.

    * Cells were definitely NOT life’s genesis. Cells were products of evolution of Earth’s primal organisms, of Earth’s first stratum organisms, the RNA genes that have always been and still are running the show of life, the energy-storing biosphere survival, since Earth life’s day one.

    * A gene’s self reproduction was distinctly an evolutionary, enhanced energy constraint event, above the earlier, random, radiated-energy-induced genes formations.

    * Every evolutionary step is inherently an event of an enhanced energy constraint.

    * Genomes, RNA and DNA, are functional organs evolved by the primary RNA genes. Cell membranes are also functional organs evolved by the primary RNA gene.

    * Life is but one of the many many mass formats in the universe, and its evolution is driven as the evolution of all cosmic mass formats, to gain temporary enhanced energy constraint, i.e. to survive as long as possible.

    Dov Henis
    (Comments From The 22nd Century)
    03.2010 Updated Life Manifest
    Cosmic Evolution Simplified
    “Gravity Is The Monotheism Of The Cosmos”

  • BarMonger

    It’s an incredible idea, and it really does make sense in explaining why, in a world where rising entropy seems to go against the notion of complex life, we have evermore complex life forms evolving.

    I read this post when it was first posted but returned again today to re-read it. It’s still an amazingly simple solution to what might seem an incredible complex problem :)


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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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