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Archaeological dating techniques
- 1. Introduction to Archaeological DatingTechniques
- 2. Dating Techniques Two majorcategories: Relative Dating Orders items from oldest to youngest Does not give a specific date Absolute Dating Also called chronometric dating Gives a date in terms of calendar year
- 3. Relative Dating Analysis duringExcavation: Stratigraphy (layers of deposits, natural and human made) Law of Superposition •Older materials are typically on the bottom, younger materials on the top •Except when they are not!—sometimes old material is dug up and reused, natural formation processes redeposit materials, etc. •Why context is so important
- 4. Relative Dating Seriation: Linking ArtifactTypologies with Temporal Associations •Qualitative (changes in types of artifacts through time) or Quantitative (changes in the amount of different artifacts through time)
- 5. Relative Dating Seriation •Very importantto maintain context, understand relative frequency of artifacts •Charting time-sensitive artifacts forms “Battleship Curves” •Shows change in relative frequency of styles of artifact through time
- 6. Relative Dating One moreRelative dating technique: FUN Dating (Fluorine, Uranium and Nitrogen) •Buried bones slowly lose nitrogen and absorb fluorine and uranium through time •Amount of these elements in bones can be compared to see which were buried longer •Rates of absorption are locally specific, cannot compare bones from different regions
- 7. Absolute Dating Many differenttypes: •Dendrochronology—tree ring dating •Radiometric techniques—based on principles of radioactive decay •And more!
- 8. Dendrochronology •Earliest form ofabsolute dating •First used in the American Southwest
- 9. Dendrochronology • Based onthe annual growth of trees, each ring representing a new year of growth • Rings vary in thickness according to the year, over time will have a distinct pattern of rings • Patterns of rings are matched from newer to older trees • Limited to areas where trees preserve, only goes back a limited time, less than 10,000 years
- 10. Absolute Dating Radiometric DatingTechniques •Based on principles of atomic decay, where radioactive parent isotopes decay into daughter elements •Rate of decay is known and is measurable •When decay began is known
- 11. Radiometric Dating Radiocarbon Dating:most common •Must use organic materials, such as charcoal, bone, or plant matter •All organic life takes in carbon from their surroundings •14 C is an unstable carbon isotope; 12 C is a stable carbon isotope •When organism dies, only the 14 C begins to decay •Half-life of 14 C (after death of organism) is approximately 5,730 years—meaning after 5,730 years, half of the 14 C in the living organism is gone
- 12. Radiometric Dating Radiocarbon Dating:Issues •Amount of 14 C in the atmosphere has changed in the past! •Dates must be calibrated to reflect true date •Must have adequate amount of sample material, avoid contamination •Older techniques needed 10-20 grams, newer AMS technique need very small sample •Technique limited to dates from 500 to 50,000 years—after 50,000 years, there’s not enough 14 C left to measure
- 13. Radiometric Dating Other RadiometricDating Techniques (see your textbook) •Potassium-Argon: good for much older samples, dates into the billions of years, uses volcanic material •Uranium: dates limestone cave deposits, useful for “in-between” dates •Fission-track: uses volcanic rocks or glass, typically older dates •Thermoluminescence: pottery and burned clay