Potassium-Argon Dating
Potassium-argon (K-Ar) dating is a radiometric technique that determines the age of volcanic rocks and minerals from the slow radioactive decay of potassium-40 to argon-40. Potassium is abundant in many rock-forming minerals, and a fixed fraction of its naturally radioactive isotope decays to argon gas at a precisely known rate, so the amount of argon trapped inside a crystal is a clock that starts when the mineral cools below its argon-retention temperature. By measuring how much radiogenic argon has accumulated relative to the remaining potassium, the analyst inverts the decay equation to obtain the time elapsed since crystallization. Because potassium-40 has a half-life of about 1.25 billion years, the method reaches far beyond the radiocarbon range and became the workhorse for dating the volcanic deposits that bracket Plio-Pleistocene hominin fossils at sites such as Olduvai Gorge.
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- McDougall, I., & Harrison, T. M. (1999). Geochronology and Thermochronology by the 40Ar/39Ar Method (2nd ed.). Oxford University Press. · ISBN 9780195109207
- Renfrew, C., & Bahn, P. (2016). Archaeology: Theories, Methods, and Practice (7th ed.). Thames & Hudson. · ISBN 9780500292105
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