The measurement is based on an isotope of potassium that radioactively decays at a known rate into argon.K-Ar dating has been used to date lava flows above and below archaeological deposits that contain important hominid fossils in Africa's Olduvai Gorge.These grains absorb radiation over time from the surrounding sediments and the radiation (electrons) remain trapped within the mineral grain structure.
The method also assumes a 'zeroing' event in the life of the material, when it was either last heated or exposed to sunlight.
Nineteenth century geologists recognized that rocks formed slowly as mountains eroded and sediments settled on the ocean floor.
Optical dating, also known as optically stimulated luminescence (OSL), dates the last time mineral sediments (usually quartz or feldspar grains ) were exposed to sunlight.
In the Willandra area it is typically used on quartz sand grains which have been buried and have not been exposed to sunlight since burial.
Potassium-argon (K-Ar) dating is a radiometric technique that is used to determine the age of minerals that contain potassium, which include clay minerals and micas.