rubidium—strontium dating
rubidium—strontium dating A radiometric dating method based on the radioactive decay of ^{87}Rb to ^{87}Sr. Rubidium has two isotopes (^{85}Rb 72.15%, ^{87}Rb 27.85%), but only ^{87}Rb is radioactive. ^{87}Rb disintegrates in a single step to ^{87}Sr by the emission of a lowenergy beta particle (see BETA DECAY). Unfortunately this lowenergy disintegration makes it very difficult to assess the halflife (see DECAY CONSTANT) and two values (5.0 × 10^{10} years or 4.88 × 10^{10} years) have been in common use. When a mineral crystallizes, it will usually incorporate both rubidium and strontium ions and the ratio of Rb to Sr will vary depending on the mineral involved. This initial strontium in the mineral is known as ‘common strontium’ (see INITIAL STRONTIUM RATIO) and is normally in the proportion of ^{88}Sr 82.56%, ^{87}Sr 7.02%, ^{86}Sr 9.86%, and ^{84}Sr 0.56%. Using these proportions it is possible to identify the amount of radiogenic ^{87}Sr present. Originally the above proportions were assumed, but today it is more usual to plot ^{87}Sr:^{86}Sr against ^{87}Rb:^{86}Sr to produce a straightline isochron from which the age of the mineral can be determined. When using the ^{87}Rb:^{86}Sr method it is customary to use wholerock samples in the analysis, because although ^{87}Sr may leak from one mineral to adjacent minerals over time it usually remains in the system. Micas and potassium feldspars are the most suitable minerals for ^{87}Rb:^{87}Sr age determinations and the results can commonly be compared with ^{40}K:^{40}Ar age determinations from the same sample (see POTASSIUM—ARGON DATING). The method has particularly been applied to ancient metamorphic rocks.
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"rubidium—strontium dating." A Dictionary of Earth Sciences. . Encyclopedia.com. 29 Jul. 2017 <http://www.encyclopedia.com>.
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rubidium–strontium dating
rubidium–strontium dating A method of dating geological specimens based on the decay of the radioisotope rubidium–87 into the stable isotope strontium–87. Natural rubidium contains 27.85% of rubidium–87, which has a halflife of 4.7 × 10^{11} years. The ratio ^{87}Rb/^{87}Sr in a specimen gives an estimate of its age (up to several thousand million years).
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"rubidium–strontium dating." A Dictionary of Biology. . Encyclopedia.com. 29 Jul. 2017 <http://www.encyclopedia.com>.
"rubidium–strontium dating." A Dictionary of Biology. . Encyclopedia.com. (July 29, 2017). http://www.encyclopedia.com/science/dictionariesthesaurusespicturesandpressreleases/rubidiumstrontiumdating0
"rubidium–strontium dating." A Dictionary of Biology. . Retrieved July 29, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionariesthesaurusespicturesandpressreleases/rubidiumstrontiumdating0