Radiogenic isotope dating

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.Ra) in natural waters are discussed in this chapter.Methods of dating surface waters, groundwaters, closed reservoirs and bottom sediments are analysed.Other notable nuclides that are partly radiogenic are argon-40, formed from radioactive potassium, and nitrogen-14, which is formed by the decay of carbon-14.Other important examples of radiogenic elements are radon and helium, both of which form during the decay of heavier elements in bedrock.

It may itself be radioactive (a radionuclide) or stable (a stable nuclide).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.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.

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