Following on the tail of the hit book The World Without Us by Alan Weisman, and the documentary Life After People, Hollywood seems determined to make scifi movies that explore the same theme. Certainly we've had "Earth without most of us" flicks like I Am Legend, but two movies that were on proud display at WonderCon, Wall-E and Journey to the Center of the Earth were literally about an Earth that has no humans at all. In Wall-E all the humans have flown off in spaceships, left the garbage bots to clean up their messes, and have never returned. In Journey, the main characters discover an "Earth" that has never evolved human life. Why are we so obsessed by alternative Earths without humans right now? I've got four reasons why.