Geochronology is the science that deals with determining the age of rocks, fossils, and other geological features. A geochronometer is a scientific instrument or method used to determine the age of objects or geological features. Synonyms for geochronometer include radiometric dating, isotopic dating, absolute dating, and chronometric dating. Radiometric dating is the most commonly used geochronometer, which involves measuring the decay of radioactive isotopes in rocks and minerals. Isotopic dating is another geochronometer that involves measuring the ratio of different isotopes in rocks, such as carbon or uranium-lead dating. Chronometric dating is used to establish the duration of geological events by measuring changes in the Earth's magnetic field or the compression of sedimentary rocks.