These types of minerals often produce lower precision ages than igneous and metamorphic minerals traditionally used for age dating, but are more common in the geologic record.
During the alpha decay steps, the zircon crystal experiences radiation damage, associated with each alpha decay.
Finally, ages can also be determined from the U–Pb system by analysis of Pb isotope ratios alone. Clair Cameron Patterson, an American geochemist who pioneered studies of uranium–lead radiometric dating methods, is famous for having used it to obtain one of the earliest estimates of the age of the Earth.
Although zircon (Zr Si O) is most commonly used, other minerals such as monazite (see: monazite geochronology), titanite, and baddeleyite can also be used.
Where crystals such as zircon with uranium and thorium inclusions do not occur, a better, more inclusive, model of the data must be applied.
Uranium-lead dating techniques have also been applied to other minerals such as calcite/aragonite and other carbonate minerals.
A particular isotope of a particular element is called a nuclide. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide.
This transformation may be accomplished in a number of different ways, including alpha decay (emission of alpha particles) and beta decay (electron emission, positron emission, or electron capture).
Unraveling such complications (which, depending on their maximum lead-retention temperature, can also exist within other minerals) generally requires in situ micro-beam analysis via, say, ion microprobe (SIMS) or laser ICP-MS.The dating method is usually performed on the mineral zircon.The mineral incorporates uranium and thorium atoms into its crystal structure, but strongly rejects lead.Undamaged zircon retains the lead generated by radioactive decay of uranium and thorium until very high temperatures (about 900 °C), though accumulated radiation damage within zones of very high uranium can lower this temperature substantially.Zircon is very chemically inert and resistant to mechanical weathering—a mixed blessing for geochronologists, as zones or even whole crystals can survive melting of their parent rock with their original uranium-lead age intact.All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.Additionally, elements may exist in different isotopes, with each isotope of an element differing in the number of neutrons in the nucleus.Therefore, one can assume that the entire lead content of the zircon is radiogenic, i.e.it is produced solely by a process of radioactive decay after the formation of the mineral.Fission tracks and micro-cracks within the crystal will further extend this radiation damage network.These fission tracks inevitably act as conduits deep within the crystal, thereby providing a method of transport to facilitate the leaching of lead isotopes from the zircon crystal.