Chronometric dating method
Argon, a noble gas, is not commonly incorporated into such samples except when produced in situ through radioactive decay.
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.
Thermoluminescence testing also dates items to the last time they were heated.
Absolute dating is the process of determining an age on a specified chronology in archaeology and geology.
Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy.
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.
Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.
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.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.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.After another 5,730 years only one-quarter of the original carbon-14 will remain.
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Thus dating that particular tree does not necessarily indicate when the fire burned or the structure was built.