Alien life may well have flourished many times around our galaxy, and even our solar system. Why haven't we found it, though? It probably lived and died long before we were around, and didn't last long enough to evolve into complex multicellular forms. A new study published by scientists and researchers at the Australian National University suggests that near-universal early extinction of other lifeforms in our universe — at a cellular and microbial level — is due to the relatively rapid change of the climates on planets like Venus and Mars.