K/Ar and 40Ar/39Ar Isotopic Dating Techniques as Applied to Young Volcanic Rocks, Particularly Those Associated with Hominin Localities

The K/Ar and the closely related ⁴⁰Ar/³⁹Ar dating techniques, especially the latter, yield numerical ages on igneous rocks that are commonly precise to 1% or better in the range of 0.1Ma or younger to much older ages. The younger limit is dependent on detecting radiogenic argon above an atmospheric argon component mainly from the sample itself. After outlining the basis for these techniques, the means by which fossils in sedimentary sequences are assigned numerical ages by interpolation between dated volcanically derived beds is illustrated by examples from the hominin-bearing sequences in East Africa. In recent decades, the ⁴⁰Ar/³⁹Ar technique has been continually refined, and generally the results of dating by this approach are now well accepted by the geological and paleoanthropological communities.