Earth built nuclear reactors before humans

Around 2 billion years ago, Earth ran nuclear reactors.

Uranium deposits at Oklo, in what is now Gabon, sustained natural fission reactions—long before humans existed.

Actual drill-core pieces from the ancient natural nuclear reactors at Oklo — Naturhistorisches Museum Wien. Original Oklo drill-core specimen photograph resized; scale retained.

The geology supplied concentrated uranium. Groundwater slowed the neutrons, helping the chain reactions continue.

The right rock, water and ancient uranium composition came together naturally.

How concentrated uranium and groundwater supported natural nuclear fission — Pandi explanatory diagram based on the cited research. Schematic, not to scale.

The evidence was discovered in 1972. Scientists noticed unusual uranium isotope proportions and found traces left by fission.

These surviving rock samples preserve the story of a natural nuclear reactor.

Curator Ludovic Ferrière holding a surviving Oklo reactor specimen — L. Gil / IAEA. Ludovic Ferrière holding the Oklo specimen at the Vienna Natural History Museum.

Around 2 billion years ago, Earth ran nuclear reactors.

Uranium deposits at Oklo, in what is now Gabon, sustained natural fission reactions—long before humans existed.
The geology supplied concentrated uranium. Groundwater slowed the neutrons, helping the chain reactions continue.

The right rock, water and ancient uranium composition came together naturally.
The evidence was discovered in 1972. Scientists noticed unusual uranium isotope proportions and found traces left by fission.

These surviving rock samples preserve the story of a natural nuclear reactor.

Earth built nuclear reactors before humans

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