Dating and interpretation of geologic events in the history of the Earth. The classical technique of geochronology was stratigraphy, including faunal succession. Since the mid 20th century, radiometric dating has provided absolute age data to supplement the relative dates obtained from the fossil record. Radiometric dating is based on the principle that radioactive isotopes in geologic material decay at constant, known rates to daughter isotopes. See alsocarbon-14 dating.