When we generally think of nuclear reactors, we think of the ones created by humans to make atomic bombs or generate clean energy. However, French scientists working in the central African country of Gabon in 1972 discovered the Oklo-reactor — a naturally-formed reactor that was formed by a rare and unique set of geological circumstances.

When the scientists took an ore sample from a mine in the Oklo region of Gabon to test its uranium contents, they expected to find around 0.72% of the radioactive uranium-235 isotope. Instead, they found 0.717%, which meant that some of the uranium-235 had been depleted through nuclear fission — a process once thought to be exclusively man-made.

The Oklo-reactor formed about 2 billion years ago, when high oxygen levels and rock weathering patterns in the area created concentrations of uranium that were large enough for nuclear chain reactions to occur in them. Groundwater combated the heat given off by the reactions, allowing them to continue for hundreds of thousands of years.

The decay of uranium in the Oklo-reactor produced large quantities of radioactive plutonium and cesium, but miraculously these harmful substances never leaked into the surrounding environment. Studying this as a feasible application to nuclear waste disposal today could help us use nuclear energy as safely as possible until cleaner forms of energy can be implemented.