They've now officially identified an amino acid, glycine, in the tail of Comet Wild-2. That's one small step for man, one giant leap towards figuring out where humans fall on the cosmic game of Life. It will be a while, I suppose, before we find more conclusive proof of life--or the absence of it--beyond Earth, but I'd like to ask what difference such a finding would make while there's still time to do it blind.
A lot of Christians have trouble reconciling a "jot and tittle literal" understanding of Genesis with the latest scientific evidence. One way to resolve the problem is to raise doubts about Darwin. Until we develop a time machine that can run the tape backwards, there's no way to prove God didn't create the heavens and the earth with an "apparent age" of "billions of years" even though they all came into being exactly 6,000 years (or so) ago.
Would single-celled life in outer space would shake Young Earth Creationism? I can't see why it should. The Bible says God created the heavens and the earth--it doesn't say anything about what He chose to do on other planets. Intelligent life on other planets would raise more interesting issues--but I'm persuaded by the Fermi Paradox that we won't discover intelligent life on other planets for a LONG time.
So I don't think finding single-celled life in outer space would shake a Young Earth Creationist one way or the other.
How about an ardent Darwinist? If we found life with a completely different chemical structure, the Darwinist could and should say that this disproves the Intelligent Design hypothesis. After all, if life can arise independently and repeatedly by chance, how hard can it be? The ID argument is that the statistical odds make it impossible to take "mere time and chance" seriously as an explanation for the appearance of biology.
If we found life in space with the same essential chemical structure that we find here on Earth, the Darwinist would have to do a little adjusting. Finding DNA-based life with left-handed amino acids in space would well-nigh prove that life as we know it didn't originate on Earth. I wouldn't expect that to fundamentally change the Darwinist paradigm, but I would hope some people would take back a few of the nasty things they've said about panspermia over the years. (I'm not holding my breath.)
What would really throw everybody for a loop would be finding pollen grains from flowering plants. There's a "jot and tittle literal" reading of Genesis 1 that predicts that, but it's so fantastically unlikely to be the case that I'm not even going to explain what it is. I'll just say that if we find pollen grains out past Pluto--past the heliopause, rather--then it will be time to read Genesis 1 in a whole new way.