Is it possible all life on earth is descended from aliens?

The Church of Scientology believes that is the case. They state that Earth was once inhabited by aliens that evolved into all life forms in the five kingdoms today. To me, that sounds no more outlandish than the idea of creationism, but that is another story. After watching several episodes of Star Trek, I noticed that Spock and Data meet the criteria of someone on the autistic spectrum. I, myself, have Asperger's. Unlike all the self-professed "experts" like Jenny McCarthy, Denis Leary, and Michael Savage, I do not perceive my cirstance as an impediment. Our brains are just hardwired more differently. We function like the rational beings such as the Vulcans. We also cherish honor and loyalty like the Klingons do. Perhaps as we advance more, we will become like them. Moreover, I foresee the autistic spectrum as evolution. Through the process of natural selection, our genes have enhanced our versatility. Our ingenuity and creativity have enabled civilizations to advance. Perhaps one day, we will develop the wherewithal to discover extraterrestrial life and ascertain how much we are like them. Does anyone believe it is possible that all lifeforms on earth descended from aliens? Do you suppose there is extraterrestrial life within the earth's surface like that in War of the Worlds? Or are you too skeptical to conceive any of these theories?