How would the existence of extraterrestrial life affect Christianity?

i don't think it would affect it at all. there's nothing saying that earth is the end all and be all of intelligent life. i'd say you're pretty close minded to say that it is. as far as single-celled organisms, i've never heard that scientists believe that life on other planets would be single-celled, but i know they test for bacteria first, because it is capable of living in harsh environments, and if bacteria can't survive there, nothing else can either.