Fiendish Nuclear Quiz

Q4. When did the first uranium fission chain reaction occur on Earth?

Unlucky! It is 1.8 billion years ago!

Owing to radioactive decay, geological deposits of uranium now contain less of its fissile isotope (uranium-235) than they did billions of years ago. A uranium ore formation in Oklo, Gabon, was found to have acted as a natural nuclear reactor between 1.7 and 1.8 billion years ago, owing to the greater abundance of fissile uranium-235 and to groundwater seeping through the rocks, slowing neutrons to the right energy. This “natural experiment” gives us a wealth of information on the behaviour of fission products in the soil and on the value of important fundamental physical constants throughout time (much to our comfort, they seem to be in fact constant).