Although it is not abundant in igneous rocks, it is sufficiently common to be used for the purposes of radiometric dating.It has two properties which make it useful for this purpose.The energies involved are so large, and the nucleus is so small that physical conditions in the Earth (i.e. The rate of decay or rate of change of the number N of particles is proportional to the number present at any time, i.e.
These minerals often produce lower precision ages than igneous and metamorphic minerals traditionally used for age dating, but are more common in the geologic record.Corfu described in the Pb, can also be measured.) “These twin decay systems, running at different speeds, allow an immediate verification of the validity of their ages, which must be concordant to be considered valid, although under favorable circumstances, discordant data can be extrapolated to the correct age.” Since uranium is often locked in tightly-bound minerals called zircons, from which parent and daughter product are locked in, the method is thought by modern geologists to provide a reliable clock. Krogh: “Only one answer is the right one, and only that one is good enough.” The progress in developments of the U-Pb method is both a history of technical discoveries and advances, as well as a history of a long struggle toward concordance, toward an understanding of the causes of discordance, and toward ways to eliminate it.In “A century of U-Pb geochronology: The long quest towards concordance,” Corfu, a geologist at the University of Oslo, described geologists’ frustration at persistent discordance between the two methods. Still, he finds it troubling that there should be discordance if the same physical processes are operating for the same amount of time. Despite the enormous progress achieved in this field, the problems of U-Pb discordance have not yet been completely resolved and will be one of the main hurdles to overcome in the future.Therefore we can assume that the entire lead content of the zircon is radiogenic.Where this is not the case, a correction must be applied.Uranium-lead dating is usually performed on the mineral zircon (Zr Si O), though it can be used on other minerals.Zircon incorporates uranium and thorium atoms into its crystalline structure, but strongly rejects lead.The paper is technical, so detailed evaluation of the contents should be left to geophysicists.The following quotes give a sense of the kinds of problems Corfu discussed, and their implications.Now lead and uranium are particularly susceptible to such shuffling in the event of even mild metamorphism.The other problem is that uranium is particularly susceptible to weathering.