Lead has four stable isotopes: Pb, Pb, Pb, and Pb.
Lead is created in the Earth via decay of actinide elements, primarily uranium and thorium.
Lead isotope geochemistry is useful for providing isotopic dates on a variety of materials. Because the lead isotopes are created by decay of different transuranic elements, the ratios of the four lead isotopes to one another can be very useful in tracking the source of melts in igneous rocks, the source of sediments and even the origin of people via isotopic fingerprinting of their teeth, skin and bones.
It has been used to date ice cores from the Arctic shelf, and provides information on the source of atmospheric lead pollution.
Lead–lead isotopes has been successfully used in forensic science to fingerprint bullets, because each batch of ammunition has its own peculiar Pb/Pb vs Pb/Pb ratio.