Radiometric dating of potassium
The potassium-argon (K-Ar) isotopic dating method is especially useful for determining the age of lavas.Developed in the 1950s, it was important in developing the theory of plate tectonics and in calibrating the geologic time scale.
Then the gas sample is cleaned of all unwanted gasses such as H, nitrogen and so on until all that remains are the inert gasses, argon among them. 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.Thus, the ratio of argon-40 and potassium-40 and radiogenic calcium-40 to potassium-40 in a mineral or rock is a measure of the age of the sample.The Ar-Ar method is considered superior, but some of its problems are avoided in the older K-Ar method.Also, the cheaper K-Ar method can be used for screening or reconnaissance purposes, saving Ar-Ar for the most demanding or interesting problems.
Potassium occurs in two stable isotopes (Ar atoms trapped inside minerals.