Absolute dating techniques notes
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.
It cannot be used to accurately date a site on its own.
However, it can be used to confirm the antiquity of an item.
Cosmic radiation entering the earth’s atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide.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.Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.Carbon-14 moves up the food chain as animals eat plants and as predators eat other animals. It takes 5,730 years for half the carbon-14 to change to nitrogen; this is the half-life of carbon-14.After another 5,730 years only one-quarter of the original carbon-14 will remain.