We know that life exists on Earth. Does it exist elsewhere in the Universe? Are we even certain
what the question means? Would we recognize other life if we saw it?
The first question that we must address in considering whether life exists elsewhere in the Universe
is that of the biological and chemical basis for life on Earth. Since that is the only life that we
have to study, a reasonable assumption is that if other life exists it may have a chemistry and biology
that are at least related to our own.