Life on earth, did it come from out there?

Not for the first time meteorites show signs of life. Or to be more precise they show signs of past life. Supposed micro-fossils of algae found in three meteorites seem to suggest that life is wide spread in the universe and it may even suggest that life on earth may have come from other parts of the universe.

Of course the claims are counter-claimed, suspected, scrutinised, disbelieved and generally treated with the utmost circumspection. After all, God forbid (!) that life on earth should be less unique than we hoped it would be.

On the other hand: can someone please explain to me why should life only exist on earth? I know, I know: There are lots of theories proving that the situation on earth has a <insert very big number here> to one chance of having occurred anywhere else but given that the universe is pretty damn large, the chance of it not having occurred elsewhere becomes remote again. So let's just say the chances in both camps even out which means that life on earth is just so-so unique and it is quite possible that life has developed on other planets in the universe.

Hopefully the extensive poring over rocks from outer space will one day give a conclusive answer to the controversial question: is there life somewhere out there in the universe? It would be great to put a definitive check-mark against that one so that we can all get on with our, well, life really.