SYNONYMS OR RELATED TERMS: K-A dating; potassium argon dating; radiopotassium dating CATEGORY: technique DEFINITION: An isotopic method of dating the age of a rock or mineral by measuring the rate at which potassium-40, a radioactive form of this element, decays into argon.

Though 89% decays to Calcium 40, it is not suitable for measurement since most rocks contain Calcium 40 as a primary element, and the amount caused by the decay of K 40 cannot be determined.

The remaining 11% decays into the gas Argon 40, and this can be measured, along with the amount of potassium in the sample, to get a date.

Dates produced by using this technique have been checked by .

The technique is best used on material more than 100,000 years old -- such as the dating of layers associated with the earliest remains of hominids, notably in the Olduvai Gorge.

Other methods include: coin dating, seriation, and amino-acid racemization.

The methods have varying applications, accuracy, range, and cost.

Many new techniques are being developed and tested.

Lava flows embedded with the deposits containing archaeological material have been dated.

SYNONYMS OR RELATED TERMS: chronology CATEGORY: technique DEFINITION: The process by which an archaeologist determines dates for objects, deposits, buildings, etc., in an attempt to situate a given phenomenon in time.