Two billion years ago, there was a nuclear reactor in what is now the African nation of Gabon.
No, it wasn't put there by aliens or an ancient civilization. It was created by circumstance: A combination of a large river, sandstone, siltstone, magmatic rocks, bacteria, and earthquakes.
Scientists discovered what was, in reality, a natural nuclear reactor in 1972 when they went to a uranium mine in Gabon and found some mined uranium with lower concentrations of the isotope uranium 235 than expected. But, the only way this could be true is if the uranium had been in a nuclear reaction.
And it had.
Scientists were astonished to conclude that there had been a nuclear reactor there. It was an entirely natural one, in a place called the Oklo-Formation. According to Forbes, bacteria in weathering magmatic rocks concentrated the uranium enough to start a nuclear chain reaction. At the same time, water filtered through the formation to allow sustained and stable nuclear fission. The reactor produced energy for hundreds of thousands of years. The toxic wastes of plutonium and cesium were surrounded by ruthenium, a rare inert metal, isolated from the environment, and are now harmless.
