BTW, humans did not come from Earth. Everyone came from Kobol, the 13th tribe was a tribe of Cylons the Kobol people made, they settled the "Earth" we saw, the other 12 races were Humas and settled the 12 colonies.
I said this before, and I stand by it: the whole repeating history thing doesn't preclude there being a pre-Kobol iteration that started on our Earth, in our future.
One other 'fringe' possibility I pondered is if it's actually set in the distant past, and the whole dinosaur/fossil thing is either a Cylon trick (or will be totally ignored) or that they'll end up 'seeding' Earth with the building blocks for human-Cylon hybrid life to eventually 'evolve' back to a familiar human shape, but I don't think that's going to be the case. It's a bit too Star Trekkie for today's Ron Moore!