 Over a period of four decades, "both released more than 200 million curies of radioactive isotopes into the surrounding environment -- twice the amount expelled in the Chernobyl disaster in each instance".The majority of plutonium isotopes are short-lived on a geological timescale, though it has been argued that traces of the long-lived 244Pu isotope still exist in nature.This isotope has been found in lunar soil, meteorites, and in the Oklo natural reactor.