There is strong geochemical evidence that the Oklo uranium deposit behaved as a natural nuclear fission reactor in Precambrian times: some of the mined uranium was found to have a lower concentration of uranium-235 than expected, as if it had already been in a reactor.
Ada bukti geokimia kuat bahwa deposit uranium Oklo bekerja sebagai suatu reaktor nuklir alam pada zaman Prekambrium: sejumlah uranium yang diambil mempunyai konsentrasi uranium-235 lebih rendah dari yang diharapkan, seakan-akan sudah pernah dipakai di dalam reaktor.