Potassium-Argon (40K/40Ar) has a rate of decay of 1.25 billion years. Potassium is a radioactive isotope that decays into Argon. This method is useful for dating vocanic eruptions as heating during eruption removes all argon gas. As the material cools, the "clock" resets because there is no argon remaining and potassium stays in the system.


Potassium-Argon 

Thermoluminescence refers to the name for the light that a mineral produces  when heated. Thermoluminescence dating means when all buried material  are constantly exposed to radiation; a small portion is trapped as energy. The amount of time a crystal is underneath is recorded by amount of thermoluminescence accumulated. If heat is reapplied, the energy in the crystal is released as a form of light and the amount of thermoluminescence released can be measured to calculate how much time passed since the last heating. 

Thermoluminescence Dating

Arizona State University

Chronometric dating methods use chronological age estimates of the antiquity of an object in years before the present through physical and chemical measurements. This can tell anthropologists the time of occurance, creation of material, when used, or altered. 

Chronometric or Absolute Dating 

Absolute Dating Methods in Anthropology 

Isotopes differ based on anatomic weights and numbers of neutrons in the nucleus. They can be stable and unstable elements. 

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