Question:
Why are we looking for carbon in outer space to determine
if life exists there? I know carbon composes all life on earth, but isn't
it at all possible for there to be a completely different set of elements
on other planets?
Replies:
It's possible. We don't claim to know everything. However, the types of
molecules that make up living things - polymers such as proteins,
carbohydrates, and nucleic acids - all require large, well-defined
molecules. So far, all types of chemical "functional groups" we know of
that canform such molecules contain carbon. The only element that even
comes close is silicon, but silicon-containing polymers do not have the
broad range of chemical reactivity as carbon-containing compounds. In
fact, basically all of the silicon-containing polymers known that behave as
discrete molecules (as opposed to being rocks) contain about twice as many
carbon atoms as silicon atoms.
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