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.

What is the most stable isotope of argon?

40Ar Argon is a noble gas. The main isotopes of argon in terrestrial systems are 40Ar (99.6%), 36Ar (0.337%), and 38Ar (0.063%) .Related Links•Periodic Table•Fundamentals of Stable Isotope Geochemistry•General References•Isotope Publications