The application of physical and chemical methods to geochronology

Abstract

Methods used for measuring the age of rocks are based on the decay of the long-lived radioactive isotopes K40, Rb87, U238 and Th232. Analyses by isotope dilution have been developed to a high degree of accuracy and sensitivity for this purpose. Uncertainties in the decay constants are now comparable with or less than the analytical uncertainties inherent in this method. Recent events ({most positive}105 years) can be investigated using C14, Th230 and P231. The history of meteorites is studied by examining radioactive and stable nuclides produced by cosmic rays. Low-level counting techniques have been improved for this purpose, and gas mass spectrometers of very high sensitivity have been built. The age of the earth and meteorites is thought to be 4550 million years. The oldest identifiable fossil remains are ca. 600 million years old, while the oldest known rocks are 3500 million years old. Show more