Allende meteorite—old age but normal isotopic composition of potassium

Abstract

The extensive investigation of the Allende meteorite has provided much new information on the early history of our Solar System. The findings include small but significant anomalies of the isotopic composition for several elements which are clearly not due to any of the processes hitherto known to cause such variations (see ref. 1 for review). These anomalies seem to confirm the reality of astrophysical concepts developed since the classical paper of Burbidge et al.² on the different modes of origin of the nuclei. Evidence has also been found which points to the possible presence in Allende of pre-solar condensates. Jessberger and Dominik³ have presented data to support an earlier result⁴ according to which the ⁴⁰Ar gas retention ages of some white inclusions from Allende exceed the canonical age of the Solar System. These gas retention ages were obtained by ⁴⁰Ar–³⁹Ar dating, however, and are therefore based on the assumption that the ³⁹K/⁴⁰K ratio in the inclusions is identical to that used in the reference standard. In view of the far-reaching implications of finding in meteorites solid matter pre-dating by roughly 500 Myr the condensation of the Solar System we have attempted to verify this assumption. This is especially important because the Allende inclusions contain elements with an anomalous isotopic composition.