Variations in the Relative Abundances of the Isotopes of Common Lead

Abstract
Mass spectrometer measurements of the relative isotopic abundances of samples of lead ores from Archeantype rocks showed larger variations than reported by Nier. The isotopic constitution of one lead was within the limits calculated by Holmes and by Bullard and Stanley. From the new measurements combined with existing data estimates of the time of formation of the earth's crust of 3.5 billion years and of a maximum time of formation of the elements of 5.5 billion years have been calculated. These values are in reasonable agreement with previous estimates.