Vertaile menetelmiä

	Argon-Argon Dating	Amino Acid Racemization
Tieteenala	Arkeologia	Arkeologia
Menetelmäperhe	Regression model	Regression model
Syntyvuosi	1999	1997
Kehittäjä	Craig Merrihue and Grenville Turner (method, 1960s); synthesized by McDougall and Harrison	Reviewed for archaeology by Beverly Johnson and Gifford Miller
Tyyppi	Radiometric dating clock measuring argon isotope ratios after neutron irradiation	Chemical kinetic dating clock based on the racemization of amino acids in biogenic materials
Alkuperäislähde	McDougall, I., & Harrison, T. M. (1999). Geochronology and Thermochronology by the 40Ar/39Ar Method (2nd ed.). Oxford University Press. ISBN: 9780195109207	Johnson, B. J., & Miller, G. H. (1997). Archaeological Applications of Amino Acid Racemization. Archaeometry, 39(2), 265-287.
Rinnakkaisnimet	40Ar/39Ar Dating, Argon-Argon Geochronology, Single-Crystal Laser-Fusion Dating, Ar-Ar Step-Heating Dating	AAR Dating, Amino Acid Geochronology, Amino Acid Epimerization, D/L Ratio Dating
Liittyvät	3	3
Tiivistelmä	Argon-argon (40Ar/39Ar) dating is the modern, high-precision successor to conventional potassium-argon dating, in which the parent potassium is measured indirectly by converting it to a measurable argon isotope inside a nuclear reactor. A potassium-bearing sample is irradiated so that potassium-39 transmutes into argon-39, which then stands as a proxy for the parent potassium; both the radiogenic argon-40 daughter and this argon-39 proxy can be measured on the same aliquot by a single mass spectrometer, eliminating the sample-heterogeneity problem of the older method. Crucially, the gas can be released either by fusing a single crystal with a laser or by heating the sample in incremental steps, the latter producing an age spectrum that reveals argon loss, excess argon, and disturbance. Synthesized in McDougall and Harrison's monograph, the technique delivers the precise, internally checkable ages now standard for dating volcanic deposits at hominin and Palaeolithic sites.	Amino acid racemization (AAR) dating estimates the age of biogenic materials such as mollusc shell, ostrich eggshell, bone, and teeth from the slow chemical conversion of amino acids from one mirror-image form to the other after an organism dies. Living tissue builds proteins almost entirely from left-handed (L) amino acids, but after death these gradually interconvert toward an equilibrium mixture of left- and right-handed (D) forms, so the measured ratio of D to L rises predictably with time. Because the reaction is a temperature-dependent chemical process rather than a radioactive decay, AAR is fundamentally a kinetic clock that must be calibrated against an independently dated reference and corrected for the sample's thermal history. Reviewed for archaeology by Johnson and Miller and covered as a standard chronometric tool in Renfrew and Bahn's textbook, it offers a rapid, inexpensive way to date or correlate deposits across the Quaternary, well beyond the radiocarbon range.