The Potassium-Argon (K-Ar) dating method is the measurement of the accumulation of argon in a mineral. In contrast to a dating method such as C14 dating which measures the disappearance of a substance, K-Ar dating measure the accumulation of argon in a substance from the decomposition of potassium.

This is relatively easy because argon, being an inert gas, usually does not leech out of a mineral and is easy to measure in small samples. The actual date is comprised of the time it has been formed from molten/heated minerals. This method, therefore, is not very useful when dating the time a human bone has been in the ground, but it does help in giving the time of many of the artifacts that are often times found alongside burials.

If you were to take a piece of everyday rock, the K-Ar method would give you the date that piece of rock was "reset" by the changing of it's chemical structure. Many things can and do change the structure of rocks. Heating, weathering and many kinds of alterations will reset this time. Therefore, archaeologists can determine relatively accurately how long ago a heat treated projectile point was made, or a piece of pottery was last used to cook food.