Gabon

Sand is versatile. During the Chernobyl nuclear disaster, sand helped contain the fallout. Contrastingly in Oklo, Gabon, sand was part of triggering the world’s only known natural nuclear reactor. 

In the 70s scientists noticed uranium with abnormal % of the U-235 isotope in Oklo, Gabon. With it, they discovered the world’s only known natural nuclear reactors, a 2 billion-year-old one.

Uranium particles were deposited in the region in low concentration by water shortly after the bing bang.

Water kept depositing a massive amount of sand on top. When the uranium-rich sand deposits became flooded, a self-sustaining nuclear chain reaction was set off, lasting for a few hundred thousand years.