Uranium-Lead Chronology of Chrondritic Meteorites

Abstract

MODERN radiometric estimates of the age of the Earth are at present inseparably bound up with the classic works of Patterson and his colleagues^1–3 on the isotopic composition of lead in the triolite phase of iron meteorites and in bulk samples of chondritic meteorites. But it is not widely appreciated, outside the ranks of those who work directly in geochronology or meteoritics, that, judged by modern standards, the meteorite lead-lead isochron is very poorly established. Anders, has pointed out many times (see for example ref. 4) that the available evidence on uranium, thorium and lead abundances in meteorites^5–8 shows that for the majority of measured chondrites there is insufficient uranium and thorium to explain the observed development of radiogenic lead. This fact was recognized by Murthy and Patterson⁹ who, in constructing the meteoritic lead-lead isochron, rejected most of the available data on this ground. Only for three meteorites (Beardsley, Nuevo Laredo and Richardton) are the lead and uranium data known to be in tolerable agreement.