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Thermoluminescence testing also dates items to the last time they were heated.
This technique is based on the principle that all objects absorb radiation from the environment.
It is possible, particularly in dry, desert climates, for organic materials such as from dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record.
Thus dating that particular tree does not necessarily indicate when the fire burned or the structure was built.
Particular isotopes are suitable for different applications due to the types of atoms present in the mineral or other material and its approximate age.
For example, techniques based on isotopes with half lives in the thousands of years, such as carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments.
This is a radiometric technique since it is based on radioactive decay.
Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.
Argon, a noble gas, is not commonly incorporated into such samples except when produced in situ through radioactive decay.
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.
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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.