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A question about life

  1. Aug 27, 2009 #1

    ShayanJ

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    Hi
    We all know that the hydrocarbons are the corner blocks of life.My question is that what makes them such different?In fact what is the difference between the hydrocarbons and other molcules that gives them such property and what is this property?(I don't know how to tell.I hope you understand.)
    thanks a lot
     
  2. jcsd
  3. Aug 27, 2009 #2
    hydrocarbons are not the basis of life but carbon is. and the singular ability of carbon is to form stable chains with itself, thereby providing a way of forming the endless variety of substrate and molecules needed for something as complex as life to sustain.
     
  4. Aug 27, 2009 #3

    ShayanJ

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    Is it possible for other elements to treat like carbon in some special situation such as a special pressure or temperature?
    And is such a property of carbon the reason of that scientists say that just in places that there are water or oxygen molcules,can life be made?
    thanks
     
  5. Aug 28, 2009 #4
    i am not sure whether any other element can replicate the properties of carbon under any temperature or pressure. elements are usually unique in their properties. and we seem to need a good solvent to provide a good medium where easy interchange of chemicals can take place. this solvent better have a high heat capacity too to stabilize the temperature. it must be abundant too and not very volatile. it must be chemically very stable. i dont think there is any liquid that suits all these requirements other than water. sure there are liquids with higher heat capacities, but they are chemically unstable whereas water does not dissociate except at a cost of very high energy. there are solvents which are better than water, but they are too volatile and reactive. there are liquids more abundant than water (eg liquid hydrogen in jupiter), but they are themsleves too reactive and cannot provide as a medium of interchange of complex molecules without disintegrating those very molecules.

    on the other hand oxygen is not very necessary for life. life evolved in earth in absence of oxygen. in fact for those forms of life which still do not depend upon oxygen (as the archea class of living beings deep under the bed of oceans), oxygen is toxic for them. oxygen is just a means of extracting energy from the fuel needed for life. if there is a reductive atmosphere (whether it is gaseous or liquid doesn't matter), life can still evolve to take advantage of that.

    but the most essential is that there must not be a thermal equilibrium else no net interchange of matter and energy can take place. thermal equilibrium is equivalent to death. that is why a net oxidative (like ours) or net reductive (like early earth) atmosphere, whether gaseous (like it is for us) or liquid (as it is for whales) or solid (as for the soil bacterium) is necessary for evolution and survival of life.
     
  6. Aug 29, 2009 #5

    Nirax, I really enjoyed your thread Thanks! Hope Shyma is okay now!!
    But only one thing I didnt really got you on the concept Thermal equilibrium Do you mean its the situation of no reaction or a situation of no net oxidation-reduction reactions!!
    Thank you!!
     
    Last edited: Aug 29, 2009
  7. Aug 29, 2009 #6
    i am not sure what you mean by Shyma. is it the name of a person supposedly known to me ? in that case perhaps you identified me wrongly.

    thermal equilibrium is a state of constant tempreature and thermodynamic equilibrium. in this state there is no interchange of matter or energy that happens inside the system (which is in thermal equilibrium). so no chemical reactions too. in other words, the entropy of the system is at the highest level obtainable within its boundaries as long as it is as isolated as it is at the time when it is in equilibrium.

    life by definition implies processing of information, energy and matter. so presence of life would serve to constantly increase the entropy of the system. moreover the system cannot be isolated else it will quickly reach equilibrium. life on earth is nurtured by the low entropy energy constantly beamed upon it by the sun. sun is no way part of the system where life is. i mean life itself doesn't exist on sun. earthly life as we know exists only in earth.

    in fact a very good way to look for life on outer space is to look for planets which radiate a lot of waste heat. if there is life on any planet it must radiate the waste energy outside that planet. and this waste radiation must be of high entropy, in other words of longer (and diffused) in wavelength. and this radiation must be irregular else it implies low entropy of outgoing radiation. it must constantly shed this high entropy radiation to keep its own entropy low making existence of life possible. the disadvantage is that such a radiation will most likely be blocked by the interstellar dust and we must have very sensitive equipments to detect it.

    someday we will have the technology to do it !! till then we speculate here on this forum :))

    Amen !
     
  8. Sep 14, 2009 #7

    Entropee

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    So now im wondering if thermal equilibrium is even possible.
    If it were, that would mean there could be no movement, for it would cause friction, and thus heat. Particles would not even move in thermal equilibrium, there would be no time at all, because no events would happen. Also how does the sun lower the entropy of Earth?
     
  9. Sep 15, 2009 #8

    Borek

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    Thermal equilibrium doesn't mean there is no energy transfer - it means energy transfer in both directions is identical.

    --
     
  10. Sep 15, 2009 #9

    Entropee

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    Oh yeah I hadnt thought of it that way, but even then is it possible?
     
  11. Sep 15, 2009 #10

    Borek

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    This is called dynamic equilibrium and it happens all the time in nature.

    --
    methods
     
  12. Sep 15, 2009 #11

    alxm

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    I don't see why any of these criteria would apply. Yes it should be stable, but bear in mind that living organisms create and destroy water all the time, and that we ourselves are living in an atmosphere of 20% oxygen, which is a quite reactive chemical by most measures.

    Solvent-wise there are plenty of things that could serve a role similar to water, athough the resulting pH chemistry would probably not enter into it. Say, acetone for instance.

    Wrong way around. Life evolved to utilize oxygen.

    Thermal equillibrium of what with what?

    Removing your parenthesis, all you're saying is that there has to be an atmosphere that's either oxidative or reductive, which are relative terms that make no sense. Everything is either oxidative or reductive against something else, unless they happen to be equipotent.

    You're also saying the atmosphere is 'gas, liquid or solid'. Who would've thought?
     
  13. Sep 15, 2009 #12

    Entropee

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    Thanks Borek! Man this website just makes me wanna be a physics professor even more.
     
  14. Sep 19, 2009 #13
    Mr I really liked your presentation but you always left me behind when you speak of entropy am not yet really familiar in this but i think i can understand you well if you give me some little explanations, and the radiations you are talking(that a planet with life produces) about are they in the form of heat or what type? And may you tell me more on this i think am interested.

    Surely. thermal equilibrium cannot be attained due to fact that(as i have just understood you) As long as life exists energy changes occurs, convention of energy suitable for every living thing. And since there is dependence of living organisms in nature nothing like thermal equilibrium!

    But caution! I think human beings are dominating the life existence and to what i think this will end to what you say thermal equilibrium but by then there would be no life, I can call it end of the world!!!
     
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