230Th

Thorium-230 (230Th) is a radioactive isotope of thorium with atomic number 90 and a mass number of 230. It is a long-lived alpha emitter with a half-life of about 75,380 years. In nature it occurs as part of the uranium-238 decay chain, where it is produced by alpha decay of 234U and itself decays by alpha emission to 226Ra. The decay chain continues to stable 206Pb.

230Th is typically found in minerals and rocks that contain uranium, and its production and decay are used to study geochronology and radiometric dating. Because thorium is relatively immobile in many environments, 230Th accumulates in calcium carbonate materials synthesized by organisms or in precipitated carbonate minerals. This property underpins its use in dating carbonate records.

In practice, 230Th dating is a component of uranium-thorium (U-Th) dating, a method used to determine the ages of carbonate materials such as corals, cave deposits (speleothems), and carbonate sediments. The method relies on measuring the activities of 238U, 234U, 230Th, and 232Th in a sample and solving for age under assumptions of closed-system behavior since formation. Initial 230Th is typically negligible or accounted for by correcting with the 232Th (detrital thorium) component, which helps remove non-radiogenic contributions.

Applications of 230Th dating extend the ability to reconstruct paleoclimate and environmental changes over the late Quaternary, often up to several hundred thousand years, with typical uncertainties of a few percent to tens of thousands of years depending on sample quality and age.