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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, but potassium–argon, rubidium–strontium, samarium–neodymium, and carbon-14–carbon-12 are now of considerable importance. Uranium-238 decays to lead-206 with a half-life of 4.5 billion (109) years, rubidium-87 decays to strontium-87 with a half-life of 50.0 billion years, and potassium-40 decays to argon-40 with a half-life of 1.5 billion years. For carbon-14 the half-life is a mere 5730 ± 30 years (see radiocarbon dating). It is important that the radioactive isotope be contained within the sample being dated. Carbon-14 is contained within plant material, but potassium-40, argon-40, and uranium-238 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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Cite this article
MICHAEL ALLABY. "radiometric dating." A Dictionary of Ecology. 2004. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "radiometric dating." A Dictionary of Ecology. 2004. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O14-radiometricdating.html MICHAEL ALLABY. "radiometric dating." A Dictionary of Ecology. 2004. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-radiometricdating.html |
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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 URANIUM-LEAD DATING), but potassium-argon, rubidium-strontium, samarium-neodymium, and carbon-14—carbon-12 are now of considerable importance. Uranium-238 decays to lead-206 with a half-life of 4.5 billion (109) years, rubidium-87 decays to strontium-87 with a half-life of 50.0 billion years, and potassium-40 decays to argon-40 with a half-life of 1.5 billion years. For carbon-14 the half-life is a mere 5730 ± 30 years (see RADIOCARBON DATING), and beyond about 70 000 years the amount of carbon-14 remaining in organic matter is beyond accurate measurement. Compare INITIAL STRONTIUM RATIO.
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AILSA ALLABY and MICHAEL ALLABY. "radiometric dating." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "radiometric dating." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O13-radiometricdating.html AILSA ALLABY and MICHAEL ALLABY. "radiometric dating." A Dictionary of Earth Sciences. 1999. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-radiometricdating.html |
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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 long-lived radioisotope of known half-life (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 potassium-argon dating, the ratio of potassium-40 to its stable decay product argon-40 gives ages more than 10 million years. In rubidium-strontium dating, the ratio of rubidium-87 to its stable product strontium-87 gives ages to several thousand million years. In carbon dating, the proportion of carbon-14 (half-life 5730 years) to stable carbon-12 absorbed into once-living matter gives ages to several thousand years.
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"dating, radioactive." World Encyclopedia. 2005. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "dating, radioactive." World Encyclopedia. 2005. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O142-datingradioactive.html "dating, radioactive." World Encyclopedia. 2005. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-datingradioactive.html |
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radioactive age dating
radioactive age dating A technique for measuring the ages of rocks and minerals from the decay of certain radioactive elements within them; also known as radiometric dating. The technique involves comparing the amount of a long-lived radioactive parent isotope in a sample with the amount of the daughter isotope into which it decays. Isotopes used in radioactive age dating include uranium-238, which decays to thorium-230 with a half-life of 4.5 × 109 years; uranium‐235, which decays to protactinium-231 with a half-life of 7.0 7times; 108 years; potassium-40, which decays to argon-40 with a half-life of 1.27 × 109 years; and rubidium-87, which decays to strontium-87 with a half-life of 4.88 × 1010 years.
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Cite this article
"radioactive age dating." A Dictionary of Astronomy. 1997. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "radioactive age dating." A Dictionary of Astronomy. 1997. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O80-radioactiveagedating.html "radioactive age dating." A Dictionary of Astronomy. 1997. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-radioactiveagedating.html |
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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. 2004. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "radiometric dating." A Dictionary of Biology. 2004. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O6-radiometricdating.html "radiometric dating." A Dictionary of Biology. 2004. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O6-radiometricdating.html |
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radiometric dating
radiometric dating Another name for radioactive age dating.
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Cite this article
"radiometric dating." A Dictionary of Astronomy. 1997. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "radiometric dating." A Dictionary of Astronomy. 1997. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O80-radiometricdating.html "radiometric dating." A Dictionary of Astronomy. 1997. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-radiometricdating.html |
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radioactive dating
radioactive dating See radiometric dating.
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Cite this article
MICHAEL ALLABY. "radioactive dating." A Dictionary of Ecology. 2004. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "radioactive dating." A Dictionary of Ecology. 2004. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1O14-radioactivedating.html MICHAEL ALLABY. "radioactive dating." A Dictionary of Ecology. 2004. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-radioactivedating.html |
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radioactive dating
radioactive dating see dating . |
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Cite this article
"radioactive dating." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. 10 Feb. 2012 <http://www.encyclopedia.com>. "radioactive dating." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. (February 10, 2012). http://www.encyclopedia.com/doc/1E1-X-radiodat.html "radioactive dating." The Columbia Encyclopedia, 6th ed.. 2008. Retrieved February 10, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-X-radiodat.html |
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