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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.
By measuring the carbon-14 in organic material, scientists can determine the date of death of the organic matter in an artifact or ecofact.
The relatively short half-life of carbon-14, 5,730 years, makes dating reliable only up to about 50,000 years.
After another 5,730 years only one-quarter of the original carbon-14 will remain.
After yet another 5,730 years only one-eighth will be left.
Other radiometric dating techniques are available for earlier periods.
One of the most widely used is potassium–argon dating (K–Ar dating).
In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from very young (radiocarbon dating with Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes.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.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.An additional problem with carbon-14 dates from archeological sites is known as the "old wood" problem.