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40Ar/39Ar and K–Ar Geochronology

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Encyclopedia of Geoarchaeology

Part of the book series: Encyclopedia of Earth Sciences Series ((EESS))

Synonyms

Ar–Ar dating; Argon–argon dating; K–Ar dating

Definition

K–Ar geochronology. A geochronometer (geologic dating method) used to date potassium-bearing rocks, based on the decay of parent isotope 40K to daughter isotope 40Ar.

40Ar/39Ar geochronology. A variant of the K–Ar geochronometer, where 39Ar is measured as a proxy for the parent isotope 40K.

Introduction

The K–Ar method and its derivative, the 40Ar/39Ar method, are based on the radioactive decay of 40K to the noble gas 40Ar (sometimes symbolically indicated as 40Ar*, or radiogenic Ar). Potassium (K) is a major element in the Earth’s crust and is abundant in many rocks and minerals. It possesses two stable isotopes: 39K (93 %) and 41K (7 %). After some early indications that a radioactive isotope of potassium of mass 40 might exist (for details see McDougall and Harrison, 1999, and references therein), it was definitively identified by Nier (1935). It was not until later that rocks enriched in 40Ar were identified and the...

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Authors and Affiliations

  1. Scottish Universities Environmental Research Centre, G75 0QF, East Kilbride, UK

    Leah E. Morgan

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  1. Leah E. Morgan
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Correspondence to Leah E. Morgan .

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Editors and Affiliations

  1. Fordham University, Bronx, NY, USA

    Allan S. Gilbert

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Morgan, L.E. (2017). 40Ar/39Ar and K–Ar Geochronology. In: Gilbert, A.S. (eds) Encyclopedia of Geoarchaeology. Encyclopedia of Earth Sciences Series. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-4409-0_45

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