 potassiumargon dating

/peuh tas"ee euhm ahr'gon/, Geol.a method for estimating the age of a mineral or rock, based on measurement of the rate of decay of radioactive potassium into argon.[196570]
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Method for determining the age of igneous rocks based on the amount of argon40 in the rock.Radioactive potassium40 decays to argon40 with a halflife of about 1.3 billion years, making this method useful for dating rocks that are billions of years old. A more sophisticated method, called argonargon dating, provides a more accurate estimate of the original potassium40 content by means of the ratio of argon40 to argon39 in the rock, thus yielding a more accurate age determination. See also dating.* * *
method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock. This dating method is based upon the decay of radioactive potassium40 to radioactive argon40 in minerals and rocks; potassium40 also decays to calcium40. Thus, the ratio of argon40 and potassium40 and radiogenic calcium40 to potassium40 in a mineral or rock is a measure of the age of the sample. The calciumpotassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium. On the other hand, the abundance of argon in the Earth is relatively small because of its escape to the atmosphere during processes associated with volcanism.The potassiumargon dating method has been used to measure a wide variety of ages. The potassiumargon age of some meteorites is as old as 4,500,000,000 years, and volcanic rocks as young as 20,000 years old have been measured by this method.* * *
Universalium. 2010.