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Entropic degradation of the earth

  1. Oct 31, 2008 #1
    I don't know if this is the appropriate forum for this topic, but I've at least found some controversy surrounding the subject on the internet.

    The Earth is as far as I know basically a closed system for matter, with the exception of a few meteorites falling to the earth and some rockets leaving it, the exchange of matter between space and the earth is minimal.

    What does this mean for the Entropy of the planet as a whole? Is it increasing with time because no new forms of low-entropic matter is reintroduced to replace that which has already been degraded? Plants (of all types) are the only form of life that through photosynthesis are able to somehow "export" entropy to the surrounding universe by concentrating matter and creating complex structure. But can they do so indefinitely. Isn't thermodynamic equilibrium (death) the final state of the Earth, as it is for Mars?

    Aren't we also rapidly degrading the low-entropic dowry of our planet by rapidly consuming our natural and mineral resources, thus taking our planet very quickly closer to its (inevitable?) death?

    I hope this stimulates interesting discussion and would appreciate it if the administrators moved this topic to the appropriate forum if I've posed my questions in the wrong place.

    Thank you,
    Wynand.
     
  2. jcsd
  3. Oct 31, 2008 #2

    D H

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    While the Earth basically is a closed system with respect to mass, it is not at all closed with respect to energy. Entropy is concerned with energy, not mass.
     
  4. Oct 31, 2008 #3
    I of course agree, the clausius inequality tells us that explicitly.

    But isn't it also true, for instance, that burning fossil fuels turns concentrated forms of energy, the chemical bonds in hydrocarbons, into dispersed forms of energy (i.e. dispersed matter of greater relative thermodynamic stability, in this case CO2 and H2O) semi-irreversibly in the sense that we're burning it so much faster than it can be recaptured and effectively concentrated in higher forms of plant life, like hardwood trees?

    I guess I don't understand how the earth could "export" entropy indefinitely if so many of the processes taking place on it are real, i.e. irreversible.

    Isn't it just like our bodies, which are open systems themselves, but which must succumb to entropy eventually when we die?
     
    Last edited: Oct 31, 2008
  5. Oct 31, 2008 #4

    CRGreathouse

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    We have a constant influx of new energy from the sun, so I don't see any problem. Indeed, the fossil fuels are solar (as opposed to terrestrial) in origin!
     
  6. Oct 31, 2008 #5

    russ_watters

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    I see no reason why the earth could not function similar to its current form for billions more years. It receives energy from the sun at high short wavelength and radiates it at long wavelengths. Whatever happens in between is basically one big thermodynamic cycle. Burning fossil fuels is just one part of that cycle and the CO2 will be absorbed back into plants and turned back into oil and coal again. There need not be any increase in entropy on earth itself.
     
  7. Oct 31, 2008 #6

    Mapes

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    This is obviously not true. You and I are relatively low-entropy matter, and we're not plants. For that matter, it's unremarkable for inanimate materials to obtain relatively low entropy; look at ice or any other polycrystal.
     
  8. Oct 31, 2008 #7
    Could burning fossil fuels alter the density? In a sense, slightly reducing gravity over time? If so, that would eventually have a huge impact on solar energy absorbtion, no?
     
  9. Oct 31, 2008 #8

    Vanadium 50

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    All this talk of living things and fossil fuels obscures the main effect: the earth imports a large number of 5000K photons and exports an even larger number of 300K photons. This is a HUGE increase in entropy, far more than anything else that's been discussed.
     
  10. Oct 31, 2008 #9
    Thanks to everyone for their replies, I'm very glad that I could generate discussion about this.

    I was clearly wrong when I said that only plant life is capable of producing complex low-entropy structures, because all life is obviously able to do so. What I meant is I think that ONLY plant life can take up dispersed matter like CO2 directly (via photosynthesis) and turn it into complex low-entropy structure (please correct me if I'm wrong here and have left out any other life forms that can also do so). I think we and other animal life forms have to do it by consuming plant life or life forms that themselves have to consume plant life.

    Now, if the earth receives lots of high energy photons (5000K) and turns them into an even larger number of lower energy (300K) photons, which it emits, signifying a huge increase in Entropy, what accounts for the low entropy of the planet? Qin > Qout because some of Qin is used by the biosphere (to grow plants amongst other things). It is what Russ commented above, the "everything else" thermodynamic cycle in between.

    So life forms capture some of that energy in the chemical bonds of their structures. Isn't this a dynamic situation in which many irreversible processes take place which could mean that we're not really dealing with a steady state situation here, though it may appear to be so over a short period of time?

    My studies of Organic Chemistry introduced me to the concept of Thermodynamic versus Kinetic control in chemical reactions, for example catalytic reaction pathways. I've also read about cross-catalytic reactions (one reaction is the catalyst for the next reaction, which then catalyzes the one after that etc.) being able to generate complex structure in the form of a spiral in a petri dish.

    In addition, I've read about something called "homeostasis" which is basically, as I understand it, a state in which a kinetic mechanism (or a myriad kinetic mechanisms) dominates over thermodynamic equilibrium, which could explain why life on the planet is able to continue to exist for billions of years. I don't doubt that life on the planet could continue to exist for billions years. However I do worry when we interfere with its ability to maintain "homeostasis" by destroying biodiversity and resources, natural and mineral alike (though mostly natural). I.e. When we "metabolise" low-entropy matter (of whatever form) turning it into NET high-entropy matter by consuming it faster than the planet can reconvert it into low-entropy matter via photosynthesis.

    Also, aren't we alive because we constantly consume low-entropy matter, which kinetically controlled reaction mechanisms (mostly catalytic in nature?) then incorporate into our structure to so maintain our homeostasis? But then don't we eventually die because ultimately thermodynamics must prevail?

    I know I've posed a barrage of questions, but I really look forward to your thoughts on these.
     
    Last edited: Nov 1, 2008
  11. Nov 5, 2008 #10
    The overall entropy of the universe increases during the energy transfer to/from the earth but it remains low on earth due to order induced by living things. We as humans have destructive effects on the order(this order is in the entropy sense) in the way we live now of course, but we receive so much excess energy that we can induce low entropy conditions on earth but the overall entropy will increase in the universe. For example, using metals and minerals and throwing them in dumps, we generate entropy(configurational). But we can use solar energy to collect and reuse these. Same thing for CO2. We'd be in trouble if our only energy source was fossil fuels but thats not the case. So no need to worry about entropy for now.It will only be trouble when the sun is dying, and when the universe has expanded too much, for there will be less and less quality energy like 5000K photons.
     
  12. Nov 6, 2008 #11

    Vanadium 50

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    No, no, no. The fact that there is living matter is a tiny perturbation.

    Think about this - the earth can "unmix" saltwater by evaporation and rainfall. This is clearly a decrease in entropy and has no dependence whatsoever on anything biological.
     
  13. Nov 6, 2008 #12
    Very good posts both Emreth and Vanadium 50, thanks.

    I hadn't quite thought about water evaporation in that way, it's a very interesting point.

    I would just like to ask you, Emreth, can we really recover all the metals and minerals, in a concentrated form, once we've used them? Take for example railroad tracks. When a train runs on them, some of the iron gets rubbed off due to friction between the train wheels and tracks. Can we really recover the "atomized" iron that gets dispersed into the environment?

    I've come across an interesting book. It's called "Into the cool" and it's by Eric D. Schneider (former EPA national marine water quality laboratory director) and Dorion Sagan. I have yet to purchase it, but I have read a bit about its principal arguments at www.intothecool.com.

    Its essential argument has to do with nature abhorring a gradient (of whatever kind), say, between an open system (or closed for matter but not energy) and its surroundings. We all know that. Now, obviously, the most effective way to oppose a thermodynamic gradient is to maximize heat dissipation from the system to its surroundings. This is apparently best achieved when the system decreases its local entropy at the cost of maximizing entropy production to the surroundings, which, for example, gives rise to the "hexagonal" shapes seen in a benard cell. The cell has clearly decreased its entropy because a once uniform liquid (silicon oil) becomes an ordered and structured convective heat dissipator. But this involves maximum heat dissipation because convection does exactly that.

    They go on to argue that an open system can maintain its state of high order by constantly importing low-entropy matter (low-entropy energy in the case of the benard cell). That is exactly what we do. We eat low-entropy matter and metabolize it to relatively high-entropy "waste". This waste is food for other organisms though, but it's entropy value is clearly higher than that of the original substance.

    However, eventually, we lose the capacity to maintain our ordered state, and we die. Doesn't the same apply to the earth?
     
  14. Nov 6, 2008 #13
    Well you cannot get an overall decrease in entropy in earth that way, it separates here but mixes there. I can't think of any natural process to result in net entropy drop on earth. With no living matter, be it algae,bacteria or plants, the world would probably turn into a highly mixed-entropy state like the moon or mars. Remember, the evolution of earth through its life is highly dependent on these organisms, at least in theory.
     
  15. Nov 6, 2008 #14
    Yes we can, yes we can :smile: .Of course it will be terribly expensive and energy hungry process but it can be done. And will be done at some point when iron is not viable for mining.

    The reason why we die is not thermodynamic. There is no reason why humans cannot live forever, but it has not been favored by evolution. The reason has two parts,1) older organisms are exposed more to the environment, which causes degradation of genes, 2)resources are limited so you have a limit on number of individuals. Basically its better to have 10 young people instead of 10 old people in terms of protecting genes.
    The earth is different. The planet doesn't care if there are organisms or not. It would be just as happy to be a desert planet. But if you think it cares, then you might consider it similar, if we say living organisms can cause disease, humans are a virus, etc.
     
  16. Nov 6, 2008 #15

    vanesch

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    What Vanadium was pointing out is that living material itself, though on average slightly lower-entropy than material in thermodynamic equilibrium, represents a tiny tiny amount of entropy as compared to the entropy variations you find throughout natural processes on the earth.

    That said, now that I think of it, the oxygen atmosphere itself is pretty low-entropy and is a product of life.
     
  17. Nov 6, 2008 #16

    Mapes

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    Think harder! The entropy decrease when Earth's molten crust cooled and solidified was tremendous, far more than any effect living creatures have had. Remember that an open system's entropy decreases with decreasing temperature and with condensation and solidification.
     
  18. Nov 6, 2008 #17
    I'm not going to comment anymore because this discussion is diverging from the original post as usual with irrelevant remarks. Crust cooled. Yeah?What is that to do with anything now?When the earth formed, it decreased entropy by combining all the particulate matter. But this is irrelevant as well. You have melting, solidification, all sorts of phase changes. But then you have mixing and rearrangement as well. Eventually, these natural processes yield dead planets. What i cant think of is any natural process "now" that decreases the overall entropy. There might be some,i dont know. Organisms always drive uphill reactions using excess energy, you dont see that with any natural process at our current state(phase state). And then we have the previous post which is contradicting itself. Why dont you people think before posting stuff here?
    Look at the first post. What is he asking?Are we quickening the impending doom of the earth by creating entropy?The answer is no.As long as we have energy from the sun, we can reverse those effects. (i'm not saying we will, we should).It depends on energy, not mass. The rules that govern human metabolisms are not similar planets, at time scales that we can directly observe, we cant get any conclusion by comparing humans to planets.
     
  19. Nov 8, 2008 #18
    You will never get any oil again. One reason is that it takes billions of years to accumulate the oil we are going to exhaust soon. The Earth have no so many time to have another try. Second, the oil is "prokaryotes" sediments, the "inefficient" type of organisms which died out two billion years ago and will never return!
     
  20. Nov 8, 2008 #19
    Then lets get back on track then.

    If you consider the earth as an closed system, the only significant energy transfer you have is radiation from the sun to the earth coming in and the radiation from the earth to space going out. My intuition, which could be wrong, leads me to believe that the energy in our system is always increasing. Because of this energy transfer, entropy is always increasing as well. I believe this to be the main cause of "global warming". Is there another way entropy is being removed from the earth that I am not seeing?
     
  21. Nov 8, 2008 #20
    The influx is not constant because of Global Dimming. This is quite serious problem.
    http://video.google.com/googleplayer.swf?docid=-2058273530743771382 [Broken]

    Not to say, I would like to have ores and other material wealth of the Nature.
     
    Last edited by a moderator: May 3, 2017
  22. Nov 8, 2008 #21
    Yes but these photons are from an external source. If low entropic photons come in and leave as high entropic photons then the huge increase in entropy is external in the long run. In fact this increase in the entropy being carried away from the Earth in this manner reduces the entropy of the Earth itself. This reduction of entropy on Earth is then expressed in terms of photosynthesis and mechanisms like the disassociation of water and salt that Vanadium spoke of. Of course we are using concentrations of high enthalpy deposits very rapidly compared to the rate at which life and physical processes produced them. However, life doesn't depend on these deposits else life couldn't have produced them in the first place. Life does depend on the enthalpy influx from the sun and other enthalpic reactions that occur as a result, with a few exceptions like under sea thermal vents.
     
  23. Nov 8, 2008 #22

    vanesch

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    But what "extra entropy increase" that is in any way significant are we causing ?
    If anything, the separation of oxygen in the atmosphere and the buried fossil fuels are a low-entropy state which has been caused by life. If anything, although it is pretty small, life is rather entropy-lowering as compared to thermodynamic equilibrium. But again, this small diminishing of entropy is small compared to the overall entropy increase that is the result of solar irradiation and the conversion of light photons into IR photons.

    BTW, from the moment that we don't receive anymore any "low entropy" heat from the sun, the first thing that will happen is the end of life on earth. (although probably we will first be boiled away when the sun will swallow the earth as a red giant...)
     
  24. Nov 9, 2008 #23
    We burn the fuels million or billion times faster than it took to accumulate them, does it mean that we as live beings reduce the entropy?

    BTW, the entropy is a measure of disorder. On a course of environment protection we were taught that the garbage is "useful resources in a wrong place." I would say "in unusable form" rather than in a wrong place, that is high entropy. I do not understand your concentration on renewable energy, therefore.
     
  25. Dec 12, 2008 #24
    Thanks for the ongoing discussion.

    I'm currently reading the book I mentioned earlier in this thread, Into the cool, and it is shedding more light on the subject.

    It basically comes down to this, for Non Equilibrium Thermodynamic systems, i.e. systems that are open or closed, not isolated, and at the same time subject to energy gradients, the best way to maximise entropy production, and hence mitigate the energy gradient, is to create structure.

    Examples: Eddy currents in turbulent flow: little whirlpools (eddy currents) form just after the widening of a stream (lower pressure) from a very narrow section (higher pressure), and a whirlpool IS highly structured compared to an ordinary body of flowing water. Tornadoes and hurricanes also fall into this category. Even though the coriolis force determines the direction of a hurricane, it doesn't cause it's formation. The highly structured hurricane, compared to winds blowing in random directions, is the best way for the atmosphere to decrease the energy gradient between the sea's warm surface temperature and the upper atmosphere's colder temperature (the primary driving force for hurricanes).

    So, entropy production as such, it would turn out, is not the problem we should worry about when considering the Earth's demise. As many of you have already pointed out, mechanisms exist to 'export' entropy to space via infrared radiation. The trouble comes when we interfere with those mechanisms. I.e. If we keep on cutting down forests, the biosphere's ability to export entropy will be reduced. At the same time, if we blanket the atmosphere with more infrared-loving CO2, less infrared can escape to space, and we're stuck with all that extra heat which is already having far-reaching effects on the biosphere. A good comparison might be the ecosystem of a lake next to a nuclear power station. What happens to the ecosystem as the nuclear plant returns water at higher than ambient temperatures back to the lake? As far as I've heard, not very good things.

    I would not be too worried about global dimming. The stricter regulations on the emission of aerosols are in fact reducing the effects of global dimming and strengthening the CO2 forcing.
     
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