A technique for the potassium-argon dating of high potassium feldspars of less than 50,000 years age is described. The technique is applied to the obtaining of high precision ages in the time-range 60,000-2,000,000 years. Sufficient data are presented to show that the time-scale of Plio-Pleistocene glaciations is greater than 10 years and that the time-scale of hominoids capable of fashioning tools by the working of stone is at least 1.75 10 years. Several other points on the time-scale of human evolution are presented. The time-scale of rift faulting in Kenya is established and the ages of several Italian volcanoes are presented.
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Evernden et al. (1965) studied this question.