radiometric dating
radiometric dating(radioactive dating) The most precise method of dating rocks, in which the relative percentages of ‘parent’ and ‘daughter’ isotopes of a given radioactive element are estimated. Early methods relied on uranium and thorium minerals, but potassium–argon, rubidium–strontium, samarium–neodymium, and carbon14–carbon12 are now of considerable importance. Uranium238 decays to lead206 with a halflife of 4.5 billion (10^{9}) years, rubidium87 decays to strontium87 with a halflife of 50.0 billion years, and potassium40 decays to argon40 with a halflife of 1.5 billion years. For carbon14 the halflife is a mere 5730 ± 30 years (see radiocarbon dating). It is important that the radioactive isotope be contained within the sample being dated. Carbon14 is contained within plant material, but potassium40, argon40, and uranium238 are contained satisfactorily only within crystals. Igneous rocks are the most suitable for dating. Fossils occur mostly in sedimentary rocks, however, so absolute dates can be calculated for them less commonly than might be supposed. The only exceptions are fossils occurring in glauconite, a clay mineral containing potassium and argon which forms authigenically on the bottom of shelf seas.
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"radiometric dating." A Dictionary of Ecology. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.
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radiometric dating
radiometric dating (radioactive dating) The most precise method of dating rocks, in which the relative percentages of ‘parent’ and ‘daughter’ isotopes of a given radioactive element are estimated. Early methods relied on uranium and thorium minerals (see URANIUMLEAD DATING), but potassiumargon, rubidiumstrontium, samariumneodymium, and carbon14—carbon12 are now of considerable importance. Uranium238 decays to lead206 with a halflife of 4.5 billion (10^{9}) years, rubidium87 decays to strontium87 with a halflife of 50.0 billion years, and potassium40 decays to argon40 with a halflife of 1.5 billion years. For carbon14 the halflife is a mere 5730 ± 30 years (see RADIOCARBON DATING), and beyond about 70 000 years the amount of carbon14 remaining in organic matter is beyond accurate measurement. Compare INITIAL STRONTIUM RATIO.
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"radiometric dating." A Dictionary of Earth Sciences. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.
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dating, radioactive
dating, radioactive (radiometric dating) Any of several methods using radioactive decay to assess the ages of archaeological remains, fossils and rocks. The specimens must contain a very longlived radioisotope of known halflife (time taken for one half of its nuclei to decay), which, with a measurement of the ratio of radioisotope to a stable isotope (usually the decay product), gives the age. In potassiumargon dating, the ratio of potassium40 to its stable decay product argon40 gives ages more than 10 million years. In rubidiumstrontium dating, the ratio of rubidium87 to its stable product strontium87 gives ages to several thousand million years. In carbon dating, the proportion of carbon14 (halflife 5730 years) to stable carbon12 absorbed into onceliving matter gives ages to several thousand years.
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radiometric dating
radiometric dating (radioactive dating) See dating techniques; radioactive age.
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"radiometric dating." A Dictionary of Biology. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.
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radioactive dating
radioactive dating See radiometric dating.
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radioactive dating
radioactive dating: see dating.
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"radioactive dating." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.
"radioactive dating." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (August 21, 2017). http://www.encyclopedia.com/reference/encyclopediasalmanacstranscriptsandmaps/radioactivedating
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