In Gabon, Africa is a strange geologic phenomena. Approximately 1.7 billion years ago, a natural nuclear reactor formed without any human intervention at what is now the Oklo Mine.
It formed due in part to an unusually dense uranium deposit alongside a consistent supply of groundwater. Thus, for several hundred thousand years, a natural fission reaction took place.
This video, made by a geologist who is based in Arizona, will discuss this fascinating geologic oddity.