I don't assume that it's our Earth. I assume that it's a fictional universe in which the writers have borrowed various elements of the real world and changed around others, just like Lord of the Rings, or, say, the alt-version of Earth in Independence Day, where there was a President Whitmore and aliens attacked us in 1996. Every work of fiction should have *internal* logical consistency, but I don't demand that it be consistent with the real world.
Well thats not what I said, I said it is not our civilisation
it is clear the planet in question is supposed to be our Earth, but the implication is not that the Cylon civilisation is our civilisation.
RDM is not as much of a hack writer as to do "this is our Earth but loads of stuff is different" - at least not unless it is a key part of the story in a "Watchmen" style.
As for Independence Day it is not in an alternate universe, it is a work of fiction set in ours, and as it is fiction they can have a fictional president. It does seem to be set in the near future after all.
At the moment, I'm just taking the show at face value, that life originated on Kobol, and so the show is not congruent with the real world, where we have pretty solid evidence that life evolved here on Earth. That discrepancy is fine by me, as it's just a fictional world that we're talking about. If Moore wants to change it around in the last episode, to make it more consistent with the real world, then that's OK.....but I won't be the least bit bothered if he doesn't.
I'm pretty certain the show will not conclude with life originating on Kobol, and that is not second guessing the show. I'd go as far as to say the reveal of where life came from will come in the same scene as the reveal of who is pulling everyone's strings.
I think the cycle has gone on far, far longer than any of the characters currently suspects.