The key to why the Oklo reactor was possible was not that a natural process separated U-235 from U-238 from a Uranium ore, but that the reactor existed 1.7 bill

The key to why the Oklo reactor was possible was not that a natural process separated U-235 from U-238 from a Uranium ore, but that the reactor existed 1.7 billion years ago. U-235 has a half life of about 700 million years so the ratio of U-235 to U-238 in naturally occuring Uranium decreases over time. U-235 was about 3.1% of Uranium in ores 1.7 billion years ago and is what can be used in some reactors today. Uranium ore today has only about %0.72, so an Oklo type natural reactor could not form on today's Earth. See [1] for a good description; the atlasobscura article is poor and factually incorrect in places. [1]https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...