Humanity’s ability to conduct nuclear fission is both one of the greatest and most dangerous discoveries in the history of science. The build up of WMDs during the Cold War created almost palpable tension between the USSR and the USA and ironically these ridiculously dangerous nuclear weapons may have been been the reason the Cold War remained cold. Without the mutually assured destruction (MAD) between the two super powers, who knows were we’d be now.

However, it seems that Earth had already beaten us to the punch and figured out nuclear fission two billion years earlier. In 1972 a worker at a French nuclear fuel processing plant noticed something strange in the ore he was analyzing. The ore in question was from the Oklo uranium mines in the small African country of Gabon. He had noticed that the anticipated levels of Uranium 235 in the ore was .003% less than what they should have been. This seemingly small difference meant that there was about 200 kilograms of uranium missing, possibly enough to build one of those aforementioned WMDs. The cause of the missing uranium remained a mystery to the scientific community until somebody remembered a prediction published 19 years prior by George Wetherill of UCLA and Mark Inghram of the University of Chicago that explored the possibility of naturally occurring nuclear fission reactors. Like the scientific community always does, scientists from all around the world started to explore what the conditions for such a thing would need to be. Paul Kuroda, a chemist from the Univeristy of Arkansas, calculated the exact conditions needed for natural fission to have occurred.

1.The size of the uranium deposit needed to be longer than the average length that a fission-inducing needs to travel (about 2/3 of a meter).

2. Uranium 235 must have accounted for at least 3% of the deposit’s total composition.

3. There needed to be a whats known as a “moderator” to slow the neutrons given off by fission enough for them to react with other uranium 235 nuclei.

All previous information courtesy of Scientific American

In an amazing display of nature, these conditions came together 2 billion years ago in 16 different locations in Oklo. It was determined that groundwater had flooded the uranium rich deposits. The water served as a catalyst for fission and the energy released by the ensuing nuclear reaction would then heat the water until it boiled off. When the deposits eventually cooled down, groundwater would again flood the area, restarting the process. Experts examined the levels of xenon isotopes (a byproduct of nuclear fission) found in the surrounding rocks and in doing so were able to determine that these reactions would occur about every two and a half hours. Scientists estimate that this process went on for hundreds of thousands of years until the uranium 235 was depleted to the level it is at today.   Information courtesy of Atlas Obscura

If you find things like this interesting (I sure do) you should really check out SciShow’s YouTube channel. I mentioned them in my initial blog post and they continue to be one of my favorite media sources. They actually have a fantastic video explaining the Oklo phenomenon. Check it out!

Who knows what else our planet is capable of. Something like this also serves to remind us that there are many things about science and the natural world that we are still ignorant of. The process of scientific discovery will continue to be a global effort to answer the questions we don’t have answers to… yet.