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.
One of the most widely used is potassium–argon dating (K–Ar dating).
The date measured reveals the last time that the object was heated past the closure temperature at which the trapped argon can escape the lattice.
K–Ar dating was used to calibrate the geomagnetic polarity time scale.
In archaeology, absolute dating is usually based on the physical, chemical, and life properties of the materials of artifacts, buildings, or other items that have been modified by humans and by historical associations with materials with known dates (coins and written history).
Techniques include tree rings in timbers, radiocarbon dating of wood or bones, and trapped-charge dating methods such as thermoluminescence dating of glazed ceramics.