some say that life arrived here in comets shorty after the earth cooled. tiny microscopic single celled organisims piggybacked in the ice of a comet Land into the ocean.

another theroy is that some of the basic needs for life were here. At the time most of the solar system was still chaotic, and a piece of mars that had broke off in another event slammed into the earth witch caused a catalismic(sp) explosion. Releasing new compounds into the air and water.