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	Potassium-Argon Dating	Bayesian Chronological Modeling
分野	考古学	考古学
系統	Regression model	Regression model
提唱年	1999	2009
提唱者	Developed from 1940s-1950s radiometric work; codified for the 40Ar/39Ar successor by McDougall and Harrison	Christopher Bronk Ramsey (OxCal); Caitlin Buck and colleagues (Bayesian framework)
種類	Radiometric dating clock based on radioactive decay of potassium-40 to argon-40	Bayesian statistical model combining dates with prior archaeological information
原典	McDougall, I., & Harrison, T. M. (1999). Geochronology and Thermochronology by the 40Ar/39Ar Method (2nd ed.). Oxford University Press. ISBN: 9780195109207	Bronk Ramsey, C. (2009). Bayesian Analysis of Radiocarbon Dates. Radiocarbon, 51(1), 337-360.
別名	K-Ar Dating, Potassium-Argon Geochronology, K-Ar Radiometric Dating, Potassium-Argon Method	Bayesian Radiocarbon Modeling, OxCal Bayesian Chronology, Bayesian Phase Modeling, Chronological Bayesian Modeling
関連	3	3
概要	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.	Bayesian chronological modeling refines archaeological chronologies by combining the calibrated probability distributions of individual radiocarbon dates with prior archaeological knowledge — most importantly the stratigraphic order of samples and their grouping into phases — within a single Bayesian model. Rather than treating each date in isolation, the method asks what calendar ages are jointly consistent with all the dates and all the ordering constraints at once, and returns sharpened posterior distributions for each date plus estimates of the start, end, and duration of phases and the timing of events. Formalized by Caitlin Buck and colleagues and made widely usable through Christopher Bronk Ramsey's OxCal software, with the international IntCal calibration curve as input, it has become the standard framework for high-precision archaeological dating.