uranium-thorium-lead dating

Method of dating very old rocks by means of the amount of common lead they contain. Common lead is any lead from a rock or mineral that contains a large amount of lead and a small amount of the radioactive precursors of lead (i.e., the isotopes uranium-235, uranium-238, and thorium-232). By this method, the age of the Earth has been estimated to be c. 4.6 billion years. This figure is in good agreement with the age of meteorites and the age of the Moon as determined independently.