The potassium–argon (K–Ar) geochronological method is one of the oldest absolute dating methods and is based upon the occurrence of a radioactive isotope of potassium (40K), which naturally decays to a stable daughter isotope of argon (radiogenic 40Ar, also known as 40Ar*).

What dating technique does potassium-argon dating?

Potassium-argon 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 potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.