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Is that because of evolution? Does it have something to do with its amount in the universe? Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars as I know.

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  • $\begingroup$ related post $\endgroup$ – WYSIWYG Jun 26 '14 at 6:18
  • $\begingroup$ The definition of life as of now requires carbon based compounds(proteins,DNA etc). It's almost essential to the definition of life as of now. If there are other forms of life(possible) based on other macro molecules built using a different element from the periodic table, we could understand better why we are carbon based. Right now people say its because carbon can form chains to form proteins, but why do that? Is there no other alternative? If you think about it, the current(no consensus) definition of life is based upon the fact that we are carbon based. $\endgroup$ – user6417 Jun 26 '14 at 10:27
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We are carbon-based because carbon is the only molecule that is able to form the long, long chains of hundreds of molecules that are required to from proteins, DNA, etc. Absolutely no other molecule will do it. (Whatever you may have heard on Star Trek about Silicon-based life, Silicon doesn't form chains anywhere near as long.) Plus it's very handy in that its oxide is carbon dioxide, which is a gas, so using it and oxygen (another gas) as the end-points of respiration is very handy, you can get rid of a lot of gas very quickly. Silicon's oxide is, well, glass.

If you want to know why only carbon forms long chains, it's because of its size (not too large like silicon), its medium electronegativity (it's in a middle column of the periodic table, so it forms what are called "covalent bonds" very easily, especially with hydrogen, the #1 element in the universe by far; covalent bonds are easy to form and easy to break) and its valence (again, because of its position on the periodic table -- it forms four bonds, the maximum for a smallish molecule, giving it the geometry to form long chains).

For life to be based on anything but carbon, it would have to be made only of smaller molecules, which to our knowledge isn't very likely. Our DNA molecule is made up of billions of atoms; it's difficult to conceive how heredity could work on a small scale.

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  • $\begingroup$ would be nice if you bothered to give references to your answers by which people interested to get more info could read full articles. $\endgroup$ – The Last Word Jun 26 '14 at 4:44
  • $\begingroup$ Another factor is relative abundances of different elements in the universe. $\endgroup$ – WYSIWYG Jun 26 '14 at 6:19
  • $\begingroup$ @The Last Word, all of that stuff is pretty easy to find via google (once you know what terms to look for), I'm sorry, I don't have the references handy, it's all pretty basic background knowledge to people who are familiar with these things. I took time out of my life to answer a question, I'm sorry if you feel I didn't do enough. $\endgroup$ – prooffreader Jun 26 '14 at 15:09
  • $\begingroup$ @WYSIWYG, you are absolutely correct in that if carbon were not so abundant, there would be no life as we know it! $\endgroup$ – prooffreader Jun 26 '14 at 15:10
  • $\begingroup$ I just pointed out something that you do on stackexchange to validate answers. Everyone does it and Iam in no way belittling your effort. I noticed that you do most of ur answers without references and if u feel Iam being overbearing I take it back $\endgroup$ – The Last Word Jun 26 '14 at 15:18
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Too long for a comment. Just extending the answer from @prooffreader slightly.

It's true that long carbon chains are present in lipids, but in proteins and nucleic acids there are chains of carbon atoms interspersed with other atoms:

nucleic acids: -C[3']-O-P-O-C[5']-C-C[3']-

protein:       -C[alpha]-C-N-C(alpha)-

So the ability of C to form stable bonds with N and O (and S) is also important. It is also important that these bonds with heteroatoms are not too stable, thus allowing for making and breaking bonds at physiological temperatures. Then add to this the fact that most carbon atoms in biomolecules are tetravalent so that even when they are part of a chain they can be linked to other functional groups 'hanging off' the chain (such as amino acid side chains).

This combination of properties is unique to carbon.

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  • $\begingroup$ Thanks for pointing that out, I wasn't clear in my resonse, I didn't mean carbons form long chains just with each other, but every long biomolecule chain involves carbon, there's no other element that's in every biomolecule chain bond). $\endgroup$ – prooffreader Jun 26 '14 at 15:13

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