Chronometric dating method
This light can be measured to determine the last time the item was heated. Fluctuating levels can skew results – for example, if an item went through several high radiation eras, thermoluminescence will return an older date for the item.Many factors can spoil the sample before testing as well, exposing the sample to heat or direct light may cause some of the electrons to dissipate, causing the item to date younger.Cosmic radiation entering the earth’s atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide.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.Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.
One of the most widely used is potassium–argon dating (K–Ar dating).
This process frees electrons within minerals that remain caught within the item.
Heating an item to 500 degrees Celsius or higher releases the trapped electrons, producing light.
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.
The technique often cannot pinpoint the date of an archeological site better than historic records, but is highly effective for precise dates when calibrated with other dating techniques such as tree-ring dating.