radiometric dating

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radiometric dating

(ray-dee-oh-met -rik) The dating of rocks (and also fossils and archeological remains) by the accurate determination of the quantities of a long-lived radioactive isotope and its stable decay product in a sample. Assuming that the parent radioisotope was present at the time of formation of the rock, etc., then the number of daughter isotopes produced by radioactive decay of the parent depends only on the half-life of the parent and the age of the sample. Half-lives must therefore be known with great accuracy for precise dating and should range from about 105 to about 1010 years. In addition, there should be no loss or gain of parent or daughter isotope during the time the ‘radioactive clock’ is operating; if this condition is only partly satisfied, allowances must be made. The decay of radioisotopes can be used not only to date material but also to time very slow processes, such as the evolution of the Earth's atmosphere.

Pairs of isotopes used in radiometric dating include potassium–40 which decays to argon–40 with a half-life of 1.25 × 109 years, and rubidium–87 which decays to strontium–87 with a half-life of 4.88 × 1010 years.

radiometric dating

[‚rād·ē·ə‚me·trik ′dād·iŋ]
(archeology)
A dating method that utilizes the radioactive decay of certain long-lived, naturally occurring parent isotopes to stable daughter isotopes.
(nucleonics)
A technique for measuring the age of an object or sample of material by determining the ratio of the concentration of a radioisotope to that of a stable isotope in it; for example, the ratio of carbon-14 to carbon-12 reveals the approximate age of bones, pieces of wood, and other archeological specimens. Also known as isotopic age determination; nuclear age determination; radioactive age determination; radioactive dating; radiogenic age determination; radiogenic dating.