There's a site near Oklo, Gabon where groundwater seeped into uranium deposits, causing a self-sustaining nuclear fission reaction that ran for hundreds of thousands of years. It's the only known case of a naturally formed nuclear reactor.

There's a site near Oklo, Gabon where groundwater seeped into uranium deposits, causing a self-sustaining nuclear fission reaction that ran for hundreds of thousands of years. It's the only known case of a naturally formed nuclear reactor.