Nuclear Power, as Mother Nature Intended

Natural nuclear fission reactor : There is apparently a uranium ore deposit in Africa that had a naturally-occurring nuclear reaction some time ago.

At the only known location, three ore deposits at Oklo in Gabon, sixteen sites have been discovered at which self-sustaining nuclear fission reactions took place approximately 2 billion years ago, and ran for a few hundred thousand years, averaging 100 kW of power output during that time.