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B Does thermodynamics tell us that life will eventually end?

  1. Aug 6, 2017 #1
    Hi. I apologize if this question has already been made. Unfortunately it's also difficult for me to formulate, especially in english.

    If you consider the Sun and Earth as an isolated system, where the Sun is able to produce energy indefinitely (it's not going to become a red giant), will life on Earth eventually end anyway?

    I mean, because of the second law of thermodynamics I believe that everytime energy transforms (for instance when I eat some living being) a fraction of it will not be usable again. Eventually all useful energy to sustain life will end. Is this right?

    What about the Sun? If the previous reasoning is correct, can some life form exist thanks only to the energy produced by the sun? I honestly don't think so; unless new life is created like in the beginning (see last question).

    So, my belief is that there is only a certain amount of energy on Earth that is exchanged with loss among living beings and eventually all energy will be lost and life cannot be anymore.

    But, then, the ultimate question remains: how the hell did life even begin?
     
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  3. Aug 6, 2017 #2

    Vanadium 50

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    Your question has two contradictory premises, that the sun's energy supply is infinite and that eventually the energy will run out. If the energy is continually replenished, you cannot run out.
     
  4. Aug 6, 2017 #3

    CWatters

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    No that's wrong.

    The earth receives a huge amount of new useful energy from the sun and radiates a similar amount out into space, however it's not all just reflected directly back out. Something like 2% of the energy that arrives is turned into biomass (aka life) by photosynthesis. A fraction of that biomass is eaten by humans and animals which convert it into waste heat which may eventually be radiated into space.

    However to be clear.. Life is dependant on that 2%, not on using up some sort of energy store that is going to run out.

    It's true we dig up and use a lot of energy stored in the form of coal, oil and gas but life on earth survived for billions of years without doing that.
     
  5. Aug 6, 2017 #4

    jim mcnamara

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    Where did you find this? Citation please.
    And no, thermodynamics will not "play out" as you describe because too many other shorter term probabilities exist.
    Several other statements you made also appear to have similar problems. Try:
    https://en.wikipedia.org/wiki/Future_of_Earth

    Anything like the wikipedia article, by nature, is extrapolation, not demonstrated science - NASA has a lot more published stuff on stellar life cycles, for example.
     
  6. Aug 6, 2017 #5

    Drakkith

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    My impression was that the OP wasn't claiming that the Sun would never turn into a red giant, they were only using the idea of an inexhaustible energy source to clarify their question.

    Only because the amount of energy from the Sun is finite. If it were inexhaustible, then life could remain indefinitely (unless something else killed it all, such as environment changes, asteroid impacts, etc).

    We don't know, but we have several ideas: https://en.wikipedia.org/wiki/Abiogenesis
     
  7. Aug 6, 2017 #6
    I mean, the energy useful for sustaining life. Every living being in order to survive needs the energy of other living beings, it cannot survive only through the energy of the sun as I explained I believe in the 4th paragraph. But CWatter just explained that vegetation is able to produce life itself from light. Is it true? But anyway, even plants also need to feed. They can't survive only with the sun, they need also other forms of energy, some kind of nourishment.

    No, no. I'm supposing the Sun will survive indefinitely and no other factor will threaten life on earth, other than thermodynamics.


    Are you also confirming that the sun is able to produce life? I mean, suppose that some external event removes all traces of life from Earth, do you think the Sun is able to produce life again from nothing?


    I'm going to read the wikipidia article now, but I'm not interested right now with the beginning of life (the two questions seem linked though). I want to know if life can exist indefinitely with a single random type of energy source (light in particular, the sun) that lasts itself indefinitely. Drakkith gave me an affirmative answer.
     
  8. Aug 6, 2017 #7

    Nugatory

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    All the energy plants need comes from the sun. They need other things (water, carbon, nitrogen, phosphorus, oxygen, potassium, smaller amounts of other key elements) but as long as the sun provides energy these are continuously recycled through the ecosystem.
     
  9. Aug 6, 2017 #8

    Drakkith

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    Life on Earth has evolved considerably over the past 3.5 billion years or so and the end result is an immensely complex ecosystem that, ultimately, depends on the Sun for its primary source of sustainable energy. This energy is used by certain forms of life, namely green plants, algae, and such, to break apart molecules and use their atoms to form other molecules (namely sugars). These new molecules are then used within cells to start and maintain the enormous number of chemical reactions that ultimately create the proteins, fats, and other molecules that cells are built out of and use to sustain themselves.

    These atoms and molecules do not come from the Sun, but almost all of the energy needed to ultimately power all of these biological processes does.

    The origin of life is not the work of a single event or a single source. Here on Earth, life likely arose from a complex serious of chemical reactions that built up more complex molecules over time. Some of these molecules are theorized to have been able to catalyze their own production, which means that they are able to interact with other chemicals in such a way as to greatly enhance the reactions that create themselves. As all of these reactions are occurring over hundreds of millions of years, eventually the first proto-cells are thought to have arisen and then quickly become more and more complex until they can unambiguously be called true life.

    It is possible that life could arise again if wiped out for some reason, but it would likely take a similar path as before, and take many millions or billions of years. So I would not say that the Sun created life, but that it was a very important part of the system that did.
     
  10. Aug 6, 2017 #9

    DrGreg

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    You are asking (quote 2) what does the 2nd law of thermodynamics say about a situation (quote 1) in which the 2nd law of thermodynamics does not apply. There is no answer to that.
     
  11. Aug 6, 2017 #10

    russ_watters

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    @Vanadium 50 is right that your contradictory premises are leading you to the wrong answer. The answer is that almost all of the energy for life on Earth* is provided by the Sun, so the Earth is an open system and in the case of an infinitely long-lived sun could sustain life forever.

    *I can only think of three other sources of energy used on Earth: one species has learned to harness nuclear energy, the internal heat of the Earth (which I understand at this point is also mostly nuclear) and tidal energy.
     
  12. Aug 6, 2017 #11
    Thank you all for the replies.

    I understand that the final answer seems to be that life exists whenever it can use any form of energy available.

    This means that, given enough time, some kind of life form may come to exist even on the moon. Is that correct? But, if the moon is about 4 billion years old, why isn't there any life there?
     
  13. Aug 6, 2017 #12

    russ_watters

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    That question is totally unrelated to your original question. Energy is not the only essential ingredient for life. You also need the appropriate chemicals and environment.
     
  14. Aug 6, 2017 #13

    mfb

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    I don't see how you got that conclusion, and it is wrong.
     
  15. Aug 6, 2017 #14
    After all the nonsense I said, I think it's time to meditate on this on my own. Do you have any book to suggest about this topic?
     
  16. Aug 6, 2017 #15

    Drakkith

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    About thermodynamics or about life? Or something else?
     
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