Radiometric dating - (n.)
Besides radiocarbon (see entry above), other radioactive isotopes used for dating are isotopes of uranium (U-238, U-235, with half-lives of 4.5 billion yr and 0.7 billion yr, respectively) beryllium (10Be, with a half-life of 2.5 million yr) and potassium (40K, some of which decays to argon-40 and has a half-life of 1.24 billion yr). The long-lived radioisotopes are mainly of interest to geochemists, but can also serve to date long-term climatic trends and events.