The only naturally occurring nuclear fission reactor was found to be in Oklo, Gabon in Central Africa and was thought to be active about 1.5 billion years ago.

The only naturally occurring nuclear fission reactor was found to be in Oklo, Gabon in Central Africa and was thought to be active about 1.5 billion years ago. https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...