potassium-argon dating

a technique for determining the age of minerals based on the occurrence in natural potassium of a small fixed amount of radioisotope ⁴⁰ K that decays to the stable argon isotope ⁴⁰ Ar with a half-life of 1.28 × 10 ⁹ years. Measurement of the ratio of these isotopes thus gives the age of the mineral Compare radiocarbon dating rubidium-strontium dating

A method of radiometric dating, involving analysis of the ratio of potassium 40 (a radioactive isotope of potassium) to argon (the product of radioactive decay of potassium 40) in a given sample.