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Lecture 16

Lecture 16 – Archaeomagnetism, Obsidian Hydration, Amino Acid Racemization.docx

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Anthropology 2229F/G
Christopher Ellis

Lecture 16 – Archaeomagnetism, Obsidian Hydration, Amino Acid Racemization  Archaeomagnetism o Done through paleoorientation o Magnetic field of the Earth has varied over time  Location of magnetic north is not always the same  E.g. magnetite in Atlantic seafloor spreading o Strength/intensity of magnetism has also varied over time o Clay or clay soils are heated to certain temperatures  Naturally contain iron oxides  Acquire a weak permanent magnetism when heated  Iron aligns to where magnetic north is at the time, reflects the direction/location of magnetic north  Also reflects the intensity  Point downwards, determined by strength o At any one point of magnetic north and intensity of the magnetic field reflects a specific/unique point in time o Best in locations like the southwest where hearths are often lined with clay, clay pottery, ovens, kilns, etc.  Will preserve magnetism o Do have to know over time where magnetic north was; need a master chronology to compare it to  Similar to dendrochronology o Can get a very accurate date, within 10-15 years  Obsidian Hydration o Obsidian – volcanic glass  Formed when lava cools very quickly, minerals are quenched and crystals don’t have time to form/grow  Creates very sharp edges; good for cutting/scraping tools, etc. o Hydration rind/layers form on the surface from the reaction with the obsidian with the air  Rind measured in microns  Long it is exposed to moisture in the air, the thicker the rind will be  Called the hydration layer; water penetrates/diffuses into the surface  Can provide a date when it was flaked  Assumes that rind develops at a consistent rate over time  Example o Hydration rate is 4 microns per 1000 years o Layer is 2 microns thick, therefore is 500 years old  Thickness of layer is directly linked t
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