From what I understand, all life on earth is descendent from a common ancestor, which was probably a self replicating molecule that spontaneously formed billions of years ago. As I think I understand it this single molecule self replicated, and succesive generations of the replicated molecules mutated, etc. forming all of life today, and there for all living things are related. I've heared it hypothisised that this process might be common on plannets that are conducive to life. So, Ive been wondering if there is any evidence that this process might have occured several times on earth. Is there any evidence that there are organisms on earth that don't trace there lineage to the same origin as us? Should we expect that the process that started life to have happened more than a single time? Also would there be a way to tell if an organism was spawned from a seperate lineage?