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Quaternary Chronometry ***Absolute Dating***

Quaternary Chronometry ***Absolute Dating***. Carbon-14. Carbon-bearing Material Bones Wood Shell Charcoal Animal Droppings OM in Water 100-70,000 years Parent : N-14 ( t 1/2 = 5730 y ) Daughter: C-14. Advantages Abundance of datable material Low cost

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Quaternary Chronometry ***Absolute Dating***

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  1. Quaternary Chronometry***Absolute Dating***

  2. Carbon-14 Carbon-bearing Material • Bones • Wood • Shell • Charcoal • Animal Droppings • OM in Water 100-70,000 years Parent: N-14 (t 1/2 = 5730 y) Daughter: C-14

  3. Advantages Abundance of datable material Low cost Readily-accessible facilities Can directly compare with known ages (e.g. tree rings) to correct for reservoir effects Reservoir effects = atmospheric and hydrologic processes that give an older date Disadvantages Materials dated by C-14 typically quite porous (easily contaminated by old/young carbon) Must be very careful with pretreatments and sample selection (“correct” pretreatments still debated) - Some labs unreliable (must pick lab with good reputation) C-14 Dating

  4. Uranium Series http://www.gly.uga.edu/railsback/speleoatlas/SAimage0004.html Carbonate - U substitutes for Ca - “clean” = little detritus Dating of Corals: 234U/238U, 231Pa Speleothems: 234U/238U Must correct for Th (230Th/232Th) in “dirty” carbonates

  5. Advantages - Precise ages (low error) - Ages can be used to correct for C14 reservoir effects - Technologic advances allow more materials to be dated (carbonate, lava rock, soil carbonate, water, etc.) Disadvantages Methods extremely specialized, time-intensive, expensive - “Dirty” cave speleothems cannot be dated accurately. Uranium Series

  6. Cosmogenic Isotopes Cosmogenic radionuclides (galactic cosmic rays) are produced when cosmic rays bombard the Earth’s atmosphere and surface Examples: 26Al from Si 10Be from O 14C from N

  7. Advantages Allows glacial moraines and other terrestrial features that can’t otherwise be dated to be dated. - Disadvantages Assume sediment quickly buried. - Cosmogenic Dating

  8. Trapped Charge Dating: TL, OSL, ESR All methods depend on time-dependent radiation to and subsequent damage of crystal lattice. Naturally-occurring radioactive isotopes (U, Th, and K) emit a variety of radiation. Methods and Materials: ESR : tooth enamel TL : sediments and burnt flint OSL: sediments http://wwwrses.anu.edu.au/environment/eePages/eeDating/QuaternaryGeochronology/TCD.html

  9. Advantages Accuracy can be tested against radiocarbon and uranium dating methods. Inexpensive Disadvantages Several unknowns can affect ages (e.g. soil moisture, concentration of radioactive elements, etc.) High error TL, OSL, ESR dating

  10. Datable Materials

  11. Uncertainties

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