Not exactly atomic bombs, but we do have evidence of naturally occurring, self sustaining nuclear reactors having operated for potentially hundreds of thousands of years in Earth's past (https://www.wikiwand.com/en/Natural_nuclear_fission_reactor)
That's a fair point, I just thought the natural fission reactors were cool while completely forgetting the one in the sky responsible for my ability to think that haha
I'm suggesting we know enough to rule out the spontaneous self assembly of nuclear bombs. And there's probably a few other things we can rule out by the same logic.