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

Help with Article: Life as we don't know it.

  1. Dec 9, 2009 #1
    Ok I'm currently exploring other forms of life, mainly silicone and ammonia based life
    I found out they can replace carbon and water in our system but I'm a bit stuck on the fact if they can replace both.

    So we would have SI instead of C and NH3 instead H2O.
    I think that assimilation (12H2O(l) + 6CO2(g)+ light→ C6H12O6 (glucose)(s) + 6O2(g) + 6H2O(l))
    would become something like: Si3H4(s) → 3Si(NH)2(s) + H2(g)

    This would make it rather tricky to live since your breathing H2 and thats a bit too flammable

    So I need someone to help me work this and some more problems out, if your interested please reply. And Id also love someone to read the whole thing and give some constructive feedback.
  2. jcsd
  3. Dec 9, 2009 #2
    Your proposed reaction is incomplete. You're missing two nitrogens; is N2(g) supposed to be a product?

    A few other thoughts: I don't know much about the biology side of this, but I know for a fact that Si-Si bonds are weaker than C-C bonds. I suppose this idea is plausible, from a chemical standpoint, but it's unlikely that silicon based life would form over carbon based. It may also be a problem that NH3 is a gas, while H2O is a liquid. The courses the reactions would have to take would be very different when you're looking at solid-gas reactions. I feel like water (or some liquid) would be necessary at some point before you start forming really complex compounds like amino acids, or some form of them anyway.
  4. Dec 9, 2009 #3
    Ah thanks for pointing that out, I forgot to add ammonia (the water replacement(I should have said that x.x)) this should do the job;
    2NH3(l) + Si3H4(s) → 3Si(NH)2(s) + H8(g)

    The main objection is that the liquid range of ammonia is -44 degrees centigrade and that that is too low for any life to thrive. This true but the liquid range is specified by the pressure of the planet which on earth is 1atm but for example on Jupiter or Venus where the pressure is 60atm the boiling point is ammonia becomes 98 degrees centigrade instead of minus -33 giving it a liquid range of 175 degrees

    So that shouldn't give a problem, how much weaker is SI tho?
    According to my chem teacher it can replace the C in all Organic substances.
    And it doen't need to be able to form over C just form instead of C because the planet is too hostile for C-life.

    Maybe I should post my entire draft so it will be easier to find the flaws?
  5. Dec 24, 2009 #4


    User Avatar

    I feel I should point out a flaw in the idea of silicon based life. The reason why life as we do know it is "carbon based" is because of carbon's exceptional ability to catenate (i.e. to make long chains with itself). This is how large organic molecules can form with ease. For example, the rings of C-C bonds in all the residues in the amino acids that form proteins, and all fatty material. From what I remember, it's far less thermodynamically stable for silicon to catenate - the highest possible chain for silicon is only about 11 or 12 Si - Si bonds long, although even the disilane, Si2H6 is difficult to obtain.

    (Above figures taken from Main Group Chemistry by A.G. Massey)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook