No, science doesn't "believe" that. Science has concluded that based on the evidence. And while the evidence for universal common ancestry is good, it's not as good as the evidence for particular lines of descent.
The origin of life on earth is still an unknown, but there's a lot of interesting work that has gone on over the last 50 years. Whatever the origin of life on earth, evolution isn't effected by it in the least. Here's a thought experiment - I'll list three origins for life on earth. You tell me how, if at all, they would effect evolution.
1. abiogenesis
2. panspermia
3. creation by God