ATH 242-01

Dating the past: relative & absolute methods

  • we date almost anything to some level of precision, using relative or absolute dating
    • direct dating: an analysis of the artifact, feature of ecofact itself to arrive at its age
    • indirect dating: an analysis of material in association with the artifact, feature or eco fact being studied
  • can we date an idea or style? yes

Dating techniques

  • relative dating: determining a chronological sequence without reference to a fixed time scale
  • absolute/chronometric dating: determination of age using a specific scale, as in years before present or according to a fixed calendar
  • relative dating: seriation
    • technique used to order materials in a  relative sequence
    • adjacent items in the sequence are more similar to each other than to items farther apart in the series
    • first used by Sir Flinders Petrie to order EG ceramics
    • there are different methods of seriation
    • occurrence seriation: deals with the presence or absence of objects/traits
    • frequency seriation: artifacts or other archaeological data are chronologically ordered by ranking their relative frequencies
      • “battleship-shaped curves”
    • types based on style and form will vary in popularity and abundance over time
    • types go thru stages:
      • intro
      • peak of popularity
      • disuse
    • can be applied to order many things in everyday life
    • Deetz & Dethlefsen: studied tombstone motifs in colonial New England
    • cheap & successful way to order things
      • requires no fancy technology, inexpensive
      • capable of great precision
      • requires large sets of data
    • it actually works!
      • works well when:
    • we have large data sets
    • the focus is on traits/objects that are fairly close in time and space
    • we have many variables to look at
    • we have comparable, complete data
    • variables we are looking at are sensitive to time
  • Absolute dating:  dendrochronology
    • based on tree-ring growth and matching
    • provides very specific dates (even up to specific year)
    • useful for precise reconstructions of prehistoric environment
    • context: are we sure that we’re dating the right event?
    • only applicable in specific regions
  • absolute dating: radiocarbon
    • invented in 1947 by Willard Libby (won Nobel Prize in chem for it)
    • primary way to date archaeological materials
      • can be applied anywhere on a variety of materials
      • has to be done in laboratory controlled conditions
      • date must be interpreted by archaeologist
    • requires careful consideration of both context and composition to be accurate
    • only works on organic materials such as bone, wood, shell, cloth etc
    • some materials are preferable to others
    • cannot be used on stone/fossils
      • fossils cannot be dated because the organic material has been replaced with minerals and they are usually far too old
    • due to C-14 half-life, cannot date objects older than 60k years
    • ratio of C-12 to C-14 in the atmosphere has not been constant through time
      • calibration curves are used to correct “radiocarbon years” into real years
    • calibration curves are made by comparison with dendrochronology, thorium dating and uranium dating back to about 30k years
  • old wood problems
      • expensive
      • easily contaminated
      • multiple dates are needed for each stratigraphic level or component
      • sample size used to be an issue, but not so much with AMS method
      • Interpretation
      • radiocarbon dates/years are given with the suffix b.p. (before present)
      • “present” means AD 1950
      • after conversion to “real years” the suffix changes to B.P.
      • theoretically it is difficult to date anything after 1950
        • atmospheric nuclear testing, etc
        • radiocarbon dates are given as a statistical statement with a mean date and range

      range increases with older samples

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