I suspect the "seeding" was with one of two things.
Either with radiation degraded DNA, or with generic precursors of DNA. Either way Earth-compatible DNA was formed from those half-formed elements, and evolution started all over.
I my humble opinion: And from that we've evolved specific to this Earth and aren't leaving alive. There may be some future iteration of the Homo Sapien DNA which has better adaptive mechanisms but I'm afraid we're going to live and die here.
Arf
