Introduction to Archaeological Dating Techniques

Dating TechniquesTwo major categories:

Relative DatingOrders items from oldest to youngestDoes not give a specific date

Absolute DatingAlso called chronometric datingGives a date in terms of calendar year

Relative DatingAnalysis during Excavation: 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

Relative Dating

Seriation: Linking Artifact Typologies with Temporal Associations

•Qualitative (changes in types of artifacts through time) or Quantitative (changes in the amount of different artifacts through time)

Relative Dating

Seriation

•Very important to 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

Relative Dating

One more Relative 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

Absolute Dating

Many different types:

•Dendrochronology—tree ring dating•Radiometric techniques—based on principles of radioactive decay•And more!

Dendrochronology

•Earliest form of absolute dating•First used in the American Southwest

Dendrochronology• Based on the 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

Absolute Dating

Radiometric Dating Techniques

•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

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•14C is an unstable carbon isotope; 12C is a stable carbon isotope•When organism dies, only the 14C begins to decay•Half-life of 14C (after death of organism) is approximately 5,730 years—meaning after 5,730 years, half of the 14C in the living organism is gone

Radiometric Dating

Radiocarbon Dating: Issues•Amount of 14C 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 14C left to measure

Radiometric Dating

Other Radiometric Dating 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