Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Entropy change and origin of life

  1. Mar 22, 2009 #1
    i m new here. i 'll get straight to the point.
    we know that a thermodynamic system always tend to proceed to a higher entropy level
    then how did 'living organisms' that are highly organized and thus have low entropy emerge from a chaotic system that has very high entropy
    (here the chaotic system refers to the earth during its early stages)
  2. jcsd
  3. Mar 22, 2009 #2
    Well, if you take the Earth to be an isolated system. Life requires the sun, which involves a huge increase in entropy, to sustain it.
  4. Mar 22, 2009 #3
    the most probable microstate has the highest entropy
    but living beings as a whole is highly ordered and hence has low entropy .hence by second law of thermodynamics life should not exist.
    but thats not the case .so what caused this violation?
  5. Mar 22, 2009 #4
    The Universe is a big place. The odds of life happening randomly might be bad, but not that bad.

    The second law is statistical, anyway. Entropy could always just turn around if you get lucky.

    I would say that life, as a whole, does increase entropy. Highly ordered food is broken down and its energy is partially taken in (animals are imperfect heat engines). As for plants... well, same principle, I suppose. All it would have taken was some small, random initial creation of life, and it could have been a self-catalyzing process. Originally, life was small, simple, and unicellular. We can imagine that the "order" in these systems wasn't so drastic. And it just sort of snowballed from there...
  6. Mar 23, 2009 #5
    Thermodynamics only says that entropy keeps increasing in total, not locally; evolution is no more of a problem than refrigerators are.
  7. Mar 23, 2009 #6
    No, we don't know that. In fact, we know that your statement is utterly false. If your statement above were true, refrigerators would not work. But refrigerators work, reducing the entropy of their contents. Computers work, storing information in vastly unlikely arrangements of bits. Life works. So your statement of the 2nd Law is severely flawed.

    The entropy of sunlight is exceedingly low. Lower than that of living beings on Earth. Living beings do an excellent job of converting sunlight into urine.

    The problem here is with your lack of understanding of the 2nd law, not that there was ever a violation of it.
  8. Mar 23, 2009 #7


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Take it easy, ZikZak. As the other posters have pointed out, novince's statement is missing the qualifier "in a closed system," and this resolves the apparent paradox.

    This vague statement is surprising coming from one who is so critical. Lower how? Per volume? Per mass? Per incident energy? What two numbers are you comparing?

    I think I understand what you're trying to say, but if you're going to blast someone else's reasoning, make sure your own statements about physics are meaningful.
  9. Mar 23, 2009 #8
    Photons are delicious, I believe, is the intent. Good, light food, and you can't overcook them.
  10. Mar 23, 2009 #9


    User Avatar
    Gold Member

  11. Mar 23, 2009 #10
    Consider the following:
    The metabolic rate of homosapeans is about 100 watts. This applied to neanderthals. As soon as we learned to use fire for heat and cooking the number went up.
    Now we have learned to use (mostly) fossil fuel energy and invented internal combustion engines, electricity, electric motors, computers etc., we are using about 100 times as much energy (10,000 watts) per capita, so we are dissipating energy as fast as we can. Will we ever slow down?

    from Ziczac (above) The entropy of sunlight is exceedingly low. Lower than that of living beings on Earth. Living beings do an excellent job of converting sunlight into urine."

    ALL of our metabolic energy comes either directly or indirectly from sunlight via photosynthesis. Photosynthesis of sugars (saccharides, C6H12H6) is only about 0.1% efficient for Calvin (RuBisCO) cycle plants, compared to nearly 20% efficiency for photocells. Plants make (collect and concentrate) the energy we (animals) dissipate. The Calvin cycle is much more complex than the Krebs cycle (glucose to ATP). It takes 6 CO2 molecules and at least 24 photons to make one monosaccharide molecule (heat of combustion 29 eV).
  12. Mar 23, 2009 #11


    User Avatar
    Gold Member

    Excellent post, Bob. :approve:
  13. Mar 23, 2009 #12
    This is essentially what I had in mind. I didn't mean to sound "overly critical," but nor did I want to burden the discussion with a needless complex calculation.
  14. Mar 23, 2009 #13
    We know that primitive life forms did not use photosynthesis. So, we should not use this argument. The real question is how life evolved from simple molecules like methane carbon dioxide etc. This must have happened under far from equilibrium circiumstances. But this is more difficult to explain than explaining how life forms can continue to function without violating thermodynamics.
  15. Mar 23, 2009 #14
    Is it? It's more difficult to explain insofar as we don't know what the mechanism was, but there is nothing thermodynamically to stop it from happening, again for much the same reason that a refrigerator works.
  16. Mar 23, 2009 #15


    User Avatar
    Gold Member

    While it's true that the precursors to actual life didn't utilize photosynthesis, it was a very early development. Terrestrial lightning alone, interacting with the chemicals of the early environment, was enough to synthesize organic compounds (reference Stanley Miller's experiments in the 1950's). It was just a matter of probabilities that some of them hooked up and began to 'live'. When you have a few hundred trillion molecules floating around, some of them are bound to like each other.
  17. Mar 23, 2009 #16
    I'm not too interested in arguing the beginnings of life, but entropy and chaos theory does interest me. I think it is imperative to remember, as some have reminded us here, that total entropy in a system will increase, true. Within a system, and the more dynamic the better, order emerges in pockets here and there and entropy does decrease locally as complex systems appear. As a simple analogy: a river is a system ever flowing toward higher entropy. While flowing along, it is contained in it's channel, organized, flowing together as one thing in the same direction. As the river dumps out into a sea or ocean it's entropy is increased dramatically, even it's downhill flow is an increase of entropy. But, within the flow are little whirlpools and eddies that represent an almost spontaneous emergence of order. These can be quite tenacious one they are begun and also can increase in intensity. I say spontaneous but usually there is required some kind of obstruction in the flow to catalyse this system into being. Somehow order finds a way to spawn itself out of entropy and can be surprisingly self-replicating, no matter if the system as a whole is slipping innexorably toward a state of static equilibrium.
  18. Mar 23, 2009 #17


    User Avatar
    Science Advisor

    Actually, it is entirely sensible to think that the original emergence of life and complex pre-biotic chemistry was actually driven by the needs of thermodynamics. This sounds counter intuitive at first, but the key is precisely what ZikZak has said. The energy from the sun is very low entropy energy.

    Since it is a blackbody spectrum, and the entropy is simply 1/5780 per unit energy -- the inverse of temperature of the blackbody emitter. (Entropy has units J/K). The Earth then radiates this out into the cold of space, as radiation which with a spectrum of around 255K. Radiation into space goes mostly from high up in the atmosphere at a temperature of around -18C.

    It is normal, in all kinds of physical systems, for local dynamic structures to emerge that help to dissipate energy. As a simple example, the Earth has a water cycle, with water endlessly cycled up from the oceans and raining back down again, and flowing down rivers to the sea. This cycle is driven by the energy flow from the Sun. It works to help dissipate energy more effectively! That is, the evaporation and precipitation of water transports large amounts of energy from the warm surface up to the cooler reaches of the upper atmosphere. It's called "latent heat". Evaporation at the surface has a cooling effect, as energy goes into the liquid gas transition. In the atmosphere, condensation releases this energy back again. All told, this process is responsible to transporting, on average, more than 70 W/m^2 over the whole Earth's surface. That's a lot of energy! And it helps transport heat more efficiently up from the surface and into space, which is helping to move energy from warm regions to cold ones, which is the whole basis of the second law.

    Now the water cycle is a kind of local organization of matter. It is a structure, arising spontaneously in the presence of a large continuous flow of energy. There are many many other such examples, whereever there is a big energy flow from hot to cold. Structure tends to emerge in such a way that the energy flows faster, and so that entropy increases more rapidly.

    The spontaneous emergence of a water cycle may look like a spontaneous emergence of order; but in fact it is contributing to the increase in entropy by speeding up the rate at which energy is dissipated.

    Life is very good at dissipating energy as well. Living things, by their metabolism, are consuming energy, and emitting an equal amount of waste energy... but with higher entropy. The day to day operation of living things is helping to increase entropy faster than would occur if life was not around. Sure, the emergence of structure invariably involves some local decrease in entropy. This is overwhelmed, by many orders of magnitude, by the metabolism of life in operation to consume high grade energy sources and expel it as high entropy waste. It is expected for local structures to emerge that help consume energy in this way.

    Precisely how life emerged is, of course, still a mystery in many of its details. But thermodynamically speaking it is probably something that should be expected.

    This was best expressed by http://en.wikipedia.org/wiki/Ilya_Prigogine" [Broken], who pioneered developments in the thermodynamics of systems that are far from equilibrium, and the theory of "dissipative structures". He won the 1977 Nobel prize in chemistry for this work.

    Only months before he died, he was good enough to address this very issue, at my own request, for the benefit of the talkorigins website and our feedback column. This website deals with all kinds of popular confusions in relation to life and evolution. You can read the feedback response I wrote about Prigogine's work at talkorigins feedback for Jan 2003. My own real name is "Chris Ho-Stuart", and I used it in that response.

    Here's a brief repeat of some of that feedback. First, an extract from "http://www.aeiveos.com/~bradbury/Authors/Evolution/Prigogine-I/ToE.html"", by Ilya Prigogine, Gregoire Nicolis and Agnes Babloyantz, in Physics Today, Nov 1972, pp 23-28:
    What is the thermodynamic meaning of prebiological evolution? Darwin's principle of "survival of the fittest" through natural selection can only apply once pre biological evolution has led to the formation of some primitive living beings. A new evolutionary principle, proposed recently by Manfred Eigen. would replace Darwin's idea in the context of prebiotic evolution. It amounts to optimizing a quantity measuring the faithfulness, or quality, of the macromolecules in reproducing themselves via template action. We here propose an alternative description of prebiological evolution. The main idea is the possibility that a prebiological system may evolve through a whole succession of transitions leading to a hierarchy of more and more complex and organized states. Such transitions can only arise in nonlinear systems that are maintained far from equilibrium; that is. beyond a certain critical threshold the steady-state regime becomes unstable and the system evolves to a new configuration. As a result, if the system is to be able to evolve through successive instabilities, a mechanism must be developed whereby each new transition favors further evolution by increasing the nonlinearity and the distance from equilibrium. One obvious mechanism is that each transition enables the system to increase the entropy production. [...]

    For a very brief and non-technical statement of what Prigogine is proposing....

    The second law is, roughly, that entropy increases in all processes, or that heat will flow from hot things to cold things. Roughly speaking, entropy measures the extent to which energy is dissipated in a system. Open systems in a state of great energy flux (like the Earth) will tend to remain far from equilibrium. More importantly, Prigogine shows that in these conditions, ordered structures tend to form which facilitate the net dissipation of energy. Such systems help to drive the universe as a whole to states of increasing entropy, while being maintained in ordered state themselves. The paper goes on to give examples.

    Far from proposing thermodynamics as a problem for the origins of life, this paper is proposing that thermodynamics and the second law is a major contributing factor to the spontaneous formation of complex dissipative structures in prebiotic evolution.

    Cheers -- Sylas
    Last edited by a moderator: May 4, 2017
  19. Mar 23, 2009 #18
    What I was trying to point out in my comments above is that homo sapeans just by breathing increases enrtopy by using metabolic energy. Homo sapeans is now using his and her intelligence to manipulate the environment (e.g., use fossil fuels) to make entropy increase about 100 times faster. If we become even smarter, does this mean we increase entropy even faster? If true, how does this cycle end? If not, how does this cycle end?
    Last edited: Mar 24, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Entropy change and origin of life
  1. Change of entropy (Replies: 4)

  2. Entropy vs Life (Replies: 3)