This collection of chapters from the Treatise on Geochemistry displays the range of radioactive geochronometric studies that have been addressed by researchers in various fields of Earth science. These range from the age of Earth and the Solar System to the dating of the history of Earth that assists us in defining the major events in Earth history. In addition the use of radioactive geochronometry in describing rates of Earth surface processes including the climate history recorded in ocean sediments an the patterns of circulation of the fluid Earth has extended the range of utility of radioactive isotopes as chronometric and tracer tools.