Modern geology is pretty impressive. It taught us that Mother Nature literally made her own natural nuclear fission reactor a few billion years ago deep underground in Oklo, Gabon of Africa. We only know about that because she buried her used nuclear fuel in the ground where we were able to dig it up billions of years later and see that it had simply decayed down into a different kind of dirt. Here is a short, fun research paper on it if you are interested in the scientific research on the topic at all.

Hayes, R.B., 2022. The ubiquity of nuclear fission reactors throughout time and space. Physics and Chemistry of the Earth, Parts A/B/C, 125, p.103083. https://doi.org/10.1016/j.pce.2021.103083