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Name: Katie
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 1999 - 2000

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?

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.

Richard Barrans Jr., Ph.D.

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