Heating an item to 500 degrees Celsius or higher releases the trapped electrons, producing light.

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.

K–Ar dating was used to calibrate the geomagnetic polarity time scale.

Thermoluminescence testing also dates items to the last time they were heated.

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.

One of the most widely used and well-known absolute dating techniques is carbon-14 (or radiocarbon) dating, which is used to date organic remains.

The development of accelerator mass spectrometry (AMS) dating, which allows a date to be obtained from a very small sample, has been very useful in this regard.

Other radiometric dating techniques are available for earlier periods.

The relatively short half-life of carbon-14, 5,730 years, makes the reliable only up to about 50,000 years.

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.

Absolute dating is the process of determining an age on a specified chronology in archaeology and geology.