Interestingly, given the right conditions, chain reactions can take place with very little effort. There is one known example of a natural nuclear reactor that was in operation for a few hundred thousand years (2 billion years ago). <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Natural_nuclear_fission_reactor" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Natural_nuclear_fission_reacto...</a>