Earth West 247,830,855 is a Joker, where the Earth is actually a moon which orbited a rocky world that had no counterpart on other Earths. This moon world was geologically active, and held complex life like creatures that look like pterodactyls.
This Earth-moon is described as a mix between Datum Earth and Io, one of Jupiter's moons.
Lights can be seen on the surface of this Earth's primary, indicating that there may be a civilization of some sort there.
After some scientists and some of the most adventurous crewmembers put together a petition, they left a small group there to explore this world further and moved on.
On their way back, the group left behind was nowhere to be found. Not having enough supplies to investigate and not wanting to risk leaving a search party behind, they left supplies and headed back to Datum Earth.