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Lead is perhaps the best example of a partly radiogenic substance, as all four of its stable isotopes (Th.
Radiogenic nuclides (more commonly referred to as radiogenic isotopes) form some of the most important tools in geology.
They are used in two principal ways: Some naturally occurring isotopes are entirely radiogenic, but all these are isotopes that are radioactive, with half-lives too short to occur primordially.
Such nuclides are formed in supernovas, but are known as extinct radionuclides, since they are not seen directly on the Earth today.
An example of an extinct radionuclide is xenon-129, a stable isotope of xenon which appears as a relative excess against other xenon isotopes.
This latter ratio is known from extraterrestrial sources, such as some moon rocks and meteorites, which are relatively free of parental sources for helium-3 and helium-4.
As noted in the case of lead-204, a radiogenic nuclide is often not radioactive.
Iodine-129 was the first extinct radionuclide to be inferred, in 1960.
Others are aluminium-26 (also inferred from extra magnesium-26 found in meteorites), and iron-60.
Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.Tags: Adult Dating, affair dating, sex dating