Potassium-argon dating
One of the most widely used is potassium–argon dating (K–Ar dating). Potassium-40 is a radioactive isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated.
absolute dating is based on calculations of the age of rock strata based on half lives of minerals, relative dating is based on the assumed age of fossils found in the strata and the laws of super imposition.
