Lecture 08 Dating Methods

Lecture 08 Dating Methods - Dating Methods-Lecture Outline...

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Unformatted text preview: Dating Methods-Lecture Outline Dating Methods Archaeological Age Determination Geological and Geochemical Age Determination Faunal and Floral Age Determination Radiometric Age Determination Geochronology, Varves, Obsidian Hydration Varves, Faunal Association, Dendrochronology, Bone Age Determination Dendrochronology, Radiocarbon, Uranium Series, Potassium-Argon, Fission PotassiumStratigraphy, Seriation Archaeomagnetic Age Determination Calendrical Age Determination Experimental Methods Aspartic Acid Raceminzation, Thermoluminescence, Electron Spin Raceminzation, Thermoluminescence, Ways of Measuring Time Earliest Method - counting annual passage of seasons Today - for prehistory, radioactive clocks are most important Neutral international system of dating Scientists using radioactive clocks have chosen to count back from before present (BP). The fixed date selected was "1950" - the approximate date when radiocarbon dating first established. Age Determination Direct analysis of artifacts, ecofacts, or feature itself Indirect analysis of material associated with the data 1 Archaeological Age Determination Techniques Relative Age Relative Methods Evaluate age of one Stratigraphy piece of data to another Seriation Sequence Comparison Geochronology Absolute or Bone Age Chronometric Place age of material on absolute time scale Calendrical B.P. Typological Sequences: Changes in Style or Design through Time. Absolute or Chronometric Methods Varves Obsidian Hydration Dendrochronology Radiocarbon Potassium-argon PotassiumArgon-argon ArgonUranium series Fission track Archaeomagnetic Calendrical Stratigraphy Archaeological Interpretation Behavioral Processes Natural Processes Stratigraphy: Near Eastern Tel 2 Seriation Seeks to order artifacts "in series" series" More similar than members further away Reflects passage of time on classes Two applications: Stylistic Seriation Frequency Seriation Stylistic Seriation: Seriation: Sir Flinders Petrie Pioneered by Sir Flinders Petrie in the Late 19th C. Orders artifacts and attributes according to similarity in style Frequency Seriation Relies mostly on measuring changes in the proportional abundance or frequency of design changes through time. Frequency Seriation: Battleship Curves Battleship curves are Characteristic of Frequency Seriation Studies. 3 Sequence Comparison: Cross-Dating CrossComparative Method Compares well documented sequences from nearby sites Places artifact classes into a temporal order based on the established sequences Geological and Geochemical Age Determination Assessed by association with geological deposits or formations Rules of superposition Radiometric or other techniques also used Allows approximate dates of artifacts Indirect Geochronology Long-term geological Longprocesses Glacial advance Land and sea levels Varve Accumulation Baron Gerard de Geer (late 1870's) 1870' Layers of outwash deposited in glacial lakes Alternation between deposits from summer to winter Sequences of erosion and deposition are dated Artifacts dated by association Heidelberg jaw-'Mauer Sands" Interglacial Period- 500,000 y.a. 4 Obsidian Hydration Friedman and Smith (1960) Cumulative hydration by obsidian Deep penetration layer through time=thickness of layer age of time surface has been exposed Faunal and Floral Age Determination Faunal and Floral Associations Index Species Life of Individual Organism Dendrochronology Fluorine dating Faunal and Floral Associations Faunal Associations Index Species Faunal restrictive existence in time and space Individual Faunal or Floral Specimens Dendrochronology Counting the annual growth rings observable in the cross-section of cut crosstrees The Basics (A.E.Douglass 1930s) (A.E.Douglass Floral Associations Pollen Climatic conditions Indicators of temperature and humidity 5 Tree-Ring Dating Tree Method -limited use proper kind of tree must be presentspecies must produce well defined annual rings and be sensitive to minute variations in climatic cycles. the ring growth variation must depend primarily on one environmental factor, such as temperature or soil humidity. The prehistoric population must have made extensive use of wood, especially in construction. cultural and environmental conditions must allow for good archaeological preservation of tree segments. Bone Age Determination Techniques date (Relative*) Bone ecofacts Human skeletal material Bone artifacts Premise Bone will loose organic components (Nitrogen) and gain inorganic (Flourine (Flourine and Uranium) Same rate as bones buried in same deposit Pueblo Bonito, NM (*Radiocarbon on bone collagen) Radiometric Age Determination Exploit the principle of radioactive decay Libby, Anderson and Arnold (1949) Relies on 3 Factors Original amount of radioactive isotope present at the onset of decay decay Amount now present Rate of decay (half-life) (half- Radiocarbon Age Determination 3 heavy isotope of carbon 12C and 13C Stable Both used to reconstruct ancient diets 14C Period required for of the unstable atoms to disintegrate and form the stable daughter isotope Unstable Decays at known rate 6 Radiocarbon Dating Radioactive Clocks based on radioactive decay. 14C is best known and useful for archaeologists (+50,000 years) Poor sampling & careless interpretation = errors Willard Libby 1949 devised use of Geiger counter to measure emissions of decaying beta particles Conventional (10 20 gr) vs Accelerator gr) Mass Spectrometry (AMS = 5 10 mg samples) counts atoms directly -Carbon 14 is produced in the atmosphere and absorbed by plants through carbon dioxide -animals absorb 14C by eating plants. -Uptake of 14C ceases when plant or animal die. 14C decays at known known rate (50% after 5730 years). -Measurement of amount left in sample gives date. Calibrating 14C Dates with the Dendrochronological record * Establishing absolute dates for radiocarbon determinations Radiocarbon date = 2200 +/- 100 BP On-line Calibration programs http://depts.washington.edu/qil/calib/index.html CALIB Radiocarbon Calibration M. Stuiver, P.J. Reimer, and R. Reimer HTML version 4.2 Execute at University of Washington Execute at Queen's University of Belfast OXCAL Radiocarbon Calibration Oxford Radiocarbon Accelerator Unit Research Laboratory for Archaeology and The History of Art 7 Archaeomagnetic Age Determination Earth's magnetic field Earth' varies through time Location of magnetic north pole changes positions Detection of this shift in artifacts Declination Dip angle Calendrical Age Determination Not always absolute Lack `zero point' point' Dependent on: Regional Magnetic variation calibrations Undisturbed fired clay samples Often associated with cultures that used writing systems Maya Long Count Egyptian Historical Chronology: Based on King List Note: Until this chronology was liked to our calendar, it was `floating.' floating.' 8 Experimental Methods Aspartic Acid Racemization Bone 5000-100,000 5000- Thermoluminscence Ceramics and glass Measures accumulated energy from the last time the pottery was heated above critical temperature. 400C-500C (ceramics) 400C- Electron Spin Resonance Measures electrons within shell and bone Magnetic field 9 ...
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This note was uploaded on 11/02/2008 for the course BILD 1 taught by Professor Unk during the Spring '08 term at UCSB.

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