Week 4           Archaeology

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. The long half-life of 40K allows the method to be used to calculate the absolute age of samples older than a few thousand years.

Argon-argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede potassium-argon (K/Ar) dating in accuracy. The older method required two samples for dating while the newer method requires only one. This newer method converts a stable form of potassium (39K) into 39Ar while irradiated with neutrons in a nuclear reactor.