EXTRATERRESTRIAL RADIOACTIVITY

Until recently, scientists believed that the chemical elements were sy nthesized only in stars. The discovery of the Oklo Phenomenon in 1972 has revealed, however, that a nuclear ''fire'' had existed in terrestr ial uranium ore deposits about two billion years ago. The discovery of Pu-244 fission xenon in extraterrestrial samples, such as the Moon an d the meteorites, on the other band, has demonstrated that the transur anium elements were synthesized in exploding stars (supernovae).