or common-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 с 4.6 billion years. This figure is in good agreement with the age of meteorites and the age of the Moon as determined independently.