High Quality Content by WIKIPEDIA articles! Potassium-argon dating or K-Ar dating is a radiometric dating method used in geochronology and archeology It is based on measurement of the product of the radioactive decay of an isotope of potassium (K), which is a common element found in many materials, such as micas, clay minerals, tephra, and evaporites, ожнъл into argon In these materials, the decay product 40Ar is not trapped by the rock while it is liquid (molten), but starts to accumulate when the rock solidifies (recrystallises) Time since recrystallization is calculated by measuring the ratio of the amount of 40Ar accumulated to the amount of 40K remaining The long half-life of 40K allows the method to be used to calculate the absolute age of samples older than a few thousand years.  Полтавскую2010 г Мягкая обложка, 84 стр ISBN 6130500084.