I agree, the Earth being in the far future seems likely. I'm wondering if it's possible the first exit from Earth was similar to the Cylons leaving for their new homeworld. The 13th tribe could have returned to a devastated Earth renewed by time. The may have prospered or failed. The Earth could be a palace of wonder or virgin territory. Wasn't there talk of a fallen one? Maybe, the 13th tribe were led back to Earth and self-destructed under their rule.