Excavation Techniques and Analysis
- 1. Excavation Techniques and Analysis Recovering Fossil Forms
- 2. Fundamentals of Archaeology Site discovery and selection Excavation of artifacts, ecofacts, and features Analysis for dates, attributes, and environment
- 3. How are Sites Formed? Taphonomy: Study of how lifeforms or artifacts wound up at a particular location Fossils: Remains of life form from the past Petrification: replacement of bone with mineral or stone
- 4. How are Items Preserved? Some materials resist deterioration: Bone: Skulls and teeth Stone or Metal (tools, ornaments) Seeds, with protective covers Others may be preserved by Arid climates (Peruvian coast) Water: Planks in Lakes in France Peat moss: the “Bog People”
- 5. More Examples of Preservation Waterlogged Sites: Bog People, Denmark Arid Sites: Puruchucho-Huaqerones Mummies, Peru Cold Sites: The Iceman, Italian Alps Volcanic Ash, Cerén, El Salvador
- 6. Site Discovery Lucky finds Consulting available sources: studies, records, even older informants Maps and aerial photographs Geographical Information Systems/Remote Sensing
- 7. Site Selection Learning everything possible about each site Selecting as large and representative a site as possible Preliminary work: surface finds, features, perhaps test pits or trenches Problem-Oriented Research and Deliberate Surveys: Hadar, Ethiopia
- 8. Survey: Mapping, Part 1: General First principle: Digging is destructive--record everything! Mapping Latitude, longitude, and elevation Benchmarks or features Measurements Horizontal Vertical
- 9. Survey: Mapping Part 2: Horizontal Measurement Select and draw west-east (X-axis) and north-south (Y-axis) baselines from primary site datum Mark off intervals at meters and centimeters from baselines Label the intervals along axes of the grid by letters, numbers, or both Adapt procedure according to topographical or archaeological features
- 10. Survey: Mapping Part 3: Vertical Measurements Surveying using transit or alidade and measuring rod Vertical base: benchmark or permanent feature of known elevation Convert measures to meters above sea level.
- 11. Survey: Test pits and trenches Test pits provide sample of site stratigraphy Stratigraphy: profile of two or more layers of Natural sediment Human remains and artifacts Test pits provide sample of overall site Test Trenches reveal stratigraphy
- 12. Tools for Excavation Dental picks or paint brushes Ice picks Tweezers (fragile objects) Trowels (pointed and square) Shovels (pointed and square-nosed) Heavy equipment (backhoes) Buckets and Screens
- 13. Vertical Excavation: Some “Laws” Law of Association: Artifacts found at the same stratum (layer) are in association with one another Artifacts found at different strata are not in association with one another Law of Superposition: Geological layers are stratified one upon another Lower strata are older than higher ones Uniformitarianism: Geological processes similar throughout time
- 14. Vertical Excavation: Stratigraphy Layer deposited in chronological order: lowest layer is oldest and so on. Disturbances can change stratigraphy Erosion from hillside: oldest is top layer Structure foundation disturbs layers Burrowing animals may move objects Then there are golddiggers and pothunters
- 15. Vertical Excavation: Procedure: Each artifact is recorded and removed Photographed, sketched, or described Vertical and horizontal position Soils analyzed for chemistry, pollen, etc Associations between artifacts are recorded Assumption: artifacts found at same layer occurred at same time period
- 16. Vertical Excavation: Proveniencing Definition: recording artifacts in three-dimensional space Transit and stadia rod: record is set from a secondary datum point Theodolite: records the position of an artifact using a laser bouncing off a prism of known height
- 17. Horizontal Excavation: Procedure As each layer or stratum is excavated, it is removed Same procedure of excavation is repeated for next layer One or two layers: prefer horizontal excavation to get lay of the site Different samples are taken for different layers: soil, pollen, charcoal, bone Some layers may be left for control
- 18. Analysis: Aims and Objectives Dating Artifact: classification Bone analysis Paleobotany Palynology (pollen analysis) Paleozoology Structures Other features
- 19. Overview of Dating Unifomitarianism Relative Dating Stratigraphy Association Absolute Dating Calendrical Natural Features Isotopic
- 20. Dating: Uniformitarianism Uniformitarianism vs. Catastrophism Uniformitarianism: All geological processes--erosion, weathering--observable today have always been present and at the same rate Uniformitarianism is the basis of dating. Catastrophism: Changes have been sudden and have occurred at different rates in the past from those of the present.
- 21. Relative Dating Stratigraphy: Establishment of sequences by soil strata Exceptions: soil disturbance, erosion. Law of Association: Dating of finds within a stratum
- 22. Chronometric Associations: Relative and Absolute Dating Combined? Basic principle: Materials associated with other materials of known age are the same age range Bottle styles and clay pipes . Gravestones in Stoneham, MA (Deetz)
- 23. Absolute Dating: Calendrical Entails use of traditional calendars Mayan Long Count: Beginning date fixed at 3113 BC Calendar Rounds: 260- and 365-day calendars Egyptians: 332 BC Conquest by Alexander the Great Traced back through recorded dynasties Astronomical events checked by present data Others: Chinese, Romans, Greeks
- 24. Absolute Dating: Natural Features Dendrochronology: Tree ring dating Tree rings vary from year to year Local stumps or timber compared with master sequence (e.g., Univ. of Arizona) Varve analysis: Clay deposits in lakes from melting ice. Patterns also differ yearly Likewise compared with master chart.
- 25. Absolute Dating: Isotopic Techniques Common Principles Isotopes: Radioactive variants of elements (e.g. carbon, potassium) Isotopes decay from radioactive to nonradioactive element They do so at a constant rate Half Life: The period in which radioactivity rate reaches half the original rate.
- 26. Isotopic Techniques: Radiocarbon Dating Carbon is found in all lifeforms Carbon 12 is the stable element All living things accumulate Carbon 14 At death, carbon 14 decays at a constant rate to Carbon 12 It reaches half the rate of original radioactivity in 5730 years At 11460 years, radioactivity is half the second rate--and so on
- 27. Isotopic Techniques: Accelerator Mass Spectrometry In dating, a sample is cleaned then burned to produce gas Proportion of C14 to C12 is then counted using Geiger counter Several grams are required for the count Accelerated Mass Spectrometer: counts individual molecules Advantage: High accuracy, less material
- 28. Isotopic Techniques: Radiopotassium Dating Half life: 1.3 billion years Potassium is found in granite, basalt, clay Potassium 40 decays to a gas, Argon 40 Argon 40 accumulate when a rock is formed Disadvantage: materials less than 500,000 years old cannot be dated
- 29. Other Absolute Dating Techniques Electronic Spin Resonance: Accumulation of unpaired electrons in crystals in tooth enamel and other items with calcium (inaccurate in bone) Geomagnetism: Alignment of particles on magnetic rock; this is approximate and there are few labs Obsidian Hydration: Reaction with water; measured by thickness of accretion.
- 30. Conclusion: Dating All techniques are problematic Appropriate labs may be rare Analyzable material must be present: no volcanic rock, no radiopotassium dates Inherent problems: radiocarbon dating may be off by centuries Best strategy: use several techniques e.g. dendrochronology with radiocarbon.