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Relative and absolute dating, potassium-argon dating, early hominin skulls.docx

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ANTH 1120

Relative and absolute dating, potassium- argon dating, early hominin skulls Relative and Absolute Dating: A chronology developed on the basis of relations between entities, sometimes precise and imprecise. Useful when a particular object is not directly datable. Not a direct date Relative Dating Methods: Stratigraphy Law of Superposition Faunal evolution Seriation Artifact cross-dating Absolute Dating Provides a calendar date that is determmined through direct analysis of an entity Often radiometric chronometry May include an uncertainty factor Absolute Dating Methods: Dendrochronology Radiocarbon 14C Potassium-Argon Paleomagnetism Fission-Track Luminescence Radiometric chronometry Using decay rates radioactive isotopes to measure time Time measurement is based on an isotope’s “half life” Decay rate is unaffected by environment Need an event that “sets the clock back to zero” Potassium-Argon Dating Radioactive Potassium 40K occurs naturally in many rocks 40K slowly decays to a stable Argon-40 High temperatures during volcanic activity release all the Argon in the molten rock, (reset) Once cooled, the 40K decays. All 40Ar in that rock was produced since the volcanic event. 40K to 40Ar ratio indicates the time lapse since the rock cooled The half-life of 40K is 1.25B years. It can date material between 100k and 4-5 billion years old. Potassium-Argon Dating K/Ar dates of the
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