Anthropology 2: Archaeology and Prehistory
Review Sheet #4:
Two primary dating methods -- Relative dating and Absolute (chronometric) dating
1) Relative dating
- based on stratigraphy and law of superposition on one hand and artifact classification and typology
- establish one artifact, stratigraphic level, or site is older than another by their relative position
- once relative chronology is established at one loci, it can be used to date other adjacent sites cross-dating
- a way to establish general chronological correlations between sites in an area or between areas
- technique that uses artifacts of known age (e.g., coins, pottery, glass beads) to date sites or associated artifacts type - a class of artifacts defined by their shared attributes typology
- the study and classification of artifacts into meaningful units of analysis
- Sir Flinders Petrie , Egyptologist, first to use typology to order Egyptian tombs
- typologies are based on different artifact attributes, e.g.,
- morphology traits (i.e., shape and size)
- stylistic traits (i.e., color, pattern, decoration, etc.)
- functional traits (e.g., cultural use or function) seriation
- relative dating technique, objects are arranged in series based on styles, and the series are then compared
- seriation is based on the assumption that popularity for any artifact or culture trait is transient
- popularity distribution = battleship curve -a lens-shaped graph representing changes in artifact type frequencies through time, from origin to expanding popularity, decline, and finally disappearance
- seriation assumes that for a group of sites in a region, styles that appear at more than one site were popular at the same time
- assumes that by tracing the rise and fall of the popularity of artifacts and styles on several sites, a chronological sequence ranking the sites can be established
2) absolute or chronometric dating
- determination of age on specific time-scale, as in years before present or according to a fixed calendrical system dendrochronology = tree ring dating
- A. E. Douglas, absolute dating based on recording the annual growth rings in trees
- study of tree-ring patterns which are linked to form a continuous sequence
- each year trees form a double ring of new growth, no two years are ever the same
- working back from modern trees, an increasingly long sequence of rings can be established potassium-argon dating
- geological dating method of volcanic rocks
- provides oldest dates, i.e., from 4 or 5 billion to 100,000 ybp; used to date our earliest relatives
- compares the amount of radioactive potassium to argon gas in volcanic rocks
- potassium (K) has same amount of potassium 40 atoms which decay to form agron-40 an inactive gas
- for every 100 K-40 atoms which decay 11 change into agron-40
- when rock is formed the clock is set to zero radiocarbon dating
- J. B. Arnold and W. F. Libby (1949) developed technique
- most important development in archaeology, limited to past 70,000 Y. B. P.
- a radiometric dating technique based on measuring the decay of the radioactive, i.e., a radioactive counting method isotopes (i.e., C14 into stable nitrogen
- isotopes are atoms who’s nuclei have the same numbers of protons, but different numbers of neutrons
- cosmic radiation produces neutrons that enter the earth’s atomosphere and react w/ nitrogen to form carbon14 isotopes (i.e., it has 8 neutrons instead of 6 in nuclei = radioactive)
- carbon14 acts like regular carbon 12 and enters the carbon-dioxide in the atmosphere
- plants and animals take it in
- when they die the process of decay begins, half-life = 5568 yrs.
- dates any material w/ organic constituents (e.g., bone, wood, shell, seeds, grains, hair, etc.)

AMS dating – highly refined method using accelerator spectrometry
- AMS dating actually counts the proportion of carbon 14 isotopes directly, rather than counting radioactive disintegration (Geiger counter method), distinguishing between carbon 12 and carbon 14 and other ions through mass and energy characteristics
- requires very small quantities of organic material obsidian hydration dating
- Irving Friedman and Robert Smith
- both absolute and relative dating applications
- absorption of water on exposed surface of obsidian which forms a hydration ban (human hair is c. 100 microns)
- microscopic measurement of the width of the hydration ban provides a relative indicator of age
- using radiocarbon dates to calibrate hydration bans absolute dates can be established
- prone to a number of limitations, e.g., effects of chemical constituents, exposure to different temperatures and weathering
- each obsidian source must be calibrated individually thermoluminescence
- dates to past 100,000 Y. B. P.
- pottery is most abundant kind of artifact found in archaeological contexts, thermoluminescence is designed to date pottery and other fired clay object (e.g., dates heat altered stone-tool, hearths)
- radioactive materials in clay, which decay at a known and steady rate, knock electrons into the clay’s crystalline lattice, which ‘traps’ them
- when the clay is rapidly heated to 500 degrees C (932 degrees F) or above, the trapped electrons are released and the pot glows, this glow is known as thermoluminescence, the older the pottery, the greater the glow