Some speculation that came to me in the Praetorian Timeline thread-
What if it was Prometheus' arrival on Primal Earth, millenia ago, and his subsequent mucking about with the Well of Humanity and/or gifting Humanity with his Flames that caused the Earth to split into all of the various different alternate Earths that we know exist in the CoH universe? (ie, Praetorian, Rikti, Reichsman, etc.)
Perhaps prior to that point, there was only one singular Earth. Perhaps that was the crime for which Zeus summarily punished Prometheus?
(If nothing else, it might solve some of the weird wonkiness that surrounds the whole notion of the apparently singular Well existing in both Primal and Praetorian Earth and the way it chose Tyrant as its primary avatar towards the end there.)