Reference Work Entry

Encyclopedia of Scientific Dating Methods

Part of the series Encyclopedia of Earth Sciences Series pp 848-857

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Uranium–Lead Dating

  • Randall ParrishAffiliated withDepartment of Geology, University of Leicester and NERC Isotope Geosciences Laboratory, British Geological Survey Keyworth Email author 

Definition

Uraniumlead dating is the geological age-determination method that uses the radioactive decay of uranium (U) isotopes (238U, 235U, and also in this entry 232Th) into stable isotopes of lead (Pb) (206Pb, 207Pb, and 208Pb, respectively). U–Pb geochronology is the science of both the methodology but also the application of these methods to geological problems.

U–Pb decay system and age calculations

The accumulation of Pb in U-bearing minerals according to known decay rates of radioactive parent isotopes of U and Th forms the basis of this dating method. One measures the amount of radiogenic (i.e., produced from radioactive decay) Pb relative to the amount of radioactive parent isotope. As there are three radioactive isotopes (238U, 235U, and 232Th) that decay into stable “daughter” isotopes of Pb, one can calculate three ages in this manner, two of which have the same (i.e., U and Pb) elements forming parent and daughter. The decay systems, decay constants (λ), and half-lives (T½

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