It was "our" Earth, they showed what was left of some bridge in NYC. If you can't see that you haven't watched enough movies or need glasses, or both.
I loved how they did it, they all partied and such, the fleet in orbit as the sun rose, and then landing. Then the screen goes black and they are all sad, it was perfect, I loved it.
And I don't think this is Earth Earth, I think they need the final cylon in order to open something, much like what was needed with the arrow and the temple on Kobol or whatever the planet was called.