In 1960, physicist John H. Reynolds discovered that certain meteorites contained an isotopic anomaly in the form of an overabundance of Xe. He inferred that this must be a decay product of long-decayed radioactive I. This isotope is produced in quantity in nature only in supernova explosions. As the half-life of I is comparatively short in astronomical terms, this demonstrated that only a short time had passed between the supernova and the time the meteorites had solidified and trapped the I. These two events (supernova and solidification of gas cloud) were inferred to have happened during the early history of the Solar System, as the I isotope was likely generated before the Solar System was formed, but not long before, and seeded the solar gas cloud isotopes with isotopes from a second source. This supernova source may also have caused collapse of the solar gas cloud.