Umm, what? I don't recall them showing continent shapes of charred Earth from space.
Final shot of "Crossroads" Part II

edit: Hmmmmm Battlestar wiki claims this is Second Earth even though it was season 3's finale. Not really sure how they got that.
edit2: OK now I see how, Kara's survey photos of First Earth.

edit3: How could anyone think that looked hospitable?