Evernden, G. Curtis, J. AAPG Bulletin ; 41 9 : — The solutions of a great many geological problems await only the accurate determinations of dates of some of the events or processes that are involved in them. Delays in obtaining such data have been due to the lack of a dating technique applicable to the large diversity of geological settings. One of the most recent and promising advances in the field of physical age determination is the use of the radioactive decay of potassium to argon

Isotopes of Potassium and Argon But, for the purposes of the KAr dating system​, the relative abundance of 40K is.

Paleolithic Archaeology Paleoanthropology. Dating Methods Used in Paleoanthropology. Radiopotassium, Argon-Argon dating Potassium-argon dating or K-Ar dating is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium K into argon Ar. Potassium is a common element found in many materials, such as micas, clay minerals, tephra, and evaporites.

In these materials, the decay product 40Ar is able to escape the liquid molten rock, but starts to accumulate when the rock solidifies recrystallizes. Time since recrystallization is calculated by measuring the ratio of the amount of 40Ar accumulated to the amount of 40K remaining.