11/8/20171Course Business• Midterm 2: Tuesday, Nov. 14– 50 multiple choice questionsExam will cover:– Lectures: Weeks 6-10– Labs: 5 - 9– Text book: ch. 5 – 9• ALA#4 was skipped 211/8/20172Geology & the Context of Human Evolution3We have examined the evolutionary theory and the living laboratory…4…and now we can use the uniformitarian principle and theoretical guidance to apply these lessons to human evolutionary history.11/8/20173Topics for Today• How do we find fossils and their preserved behaviors?• Geoarchaeology (geology + archaeology)• Site formation processes• Dating techniques• How do we know the conditions of natural selection (and the other three forces of evolution) in the past? – Methods of paleoclimatic reconstruction.56Where does one find fossils and artifacts with which to reconstruct human evolution?611/8/201747Site Formation Processes1. Sediment Traps: Depositional environment to capture the behaviors in the past2. Stable environment that allows site preservation3. Opportunity for site discovery, often erosion or the intersection between our landscape and the past landscape.78Context!• What objects are found together: assemblages of fossils & artifacts• The association between what is dated and what we want to study.• Site location• Excavation is destruction!811/8/201759Extreme Preservation: extreme environments• Very Cold• Very Dry• Very Wet (anaerobic)Unfortunately, these types are irrelevant for paleoanthropology910Common good and bad contexts for preservation• Rapid burial• Fine grained sediment, airborne or from still water environments• Weathering (sunlight)• Consumption and trampling by animals• Acidic soil• Geologically active localitiesGoodBadFOSSILIZATION →(replacing bone tissue with stone)1011/8/2017611Volcanic Depositional Environments1112East African Rift Valley System:a natural sediment trap12Olduvai Gorge11/8/201771314Karstic Depositional Systems of South AfricaCross-sectionView from above1411/8/20178Sterkfontein Cave, South Africa1516Cave Depositional Systems (mostly Eurasia)1611/8/20179La Ferrassie Cave, France1718The drunk under the lamp post …1811/8/201710ALA #9a: If the tooth comb contains both the incisors and canines, the first tooth immediately behind the tooth comb is a(n) ________. a) Molarb) Caninec) Incisord) Premolare) Ribosome19Relative Dating Techniques• Stratigraphy: – Principle of Superposition– Stratigraphic Correlation: example of Bryce to Zion to Grand Canyon• Biostratigraphy2011/8/201711Relative Dating: Paleomagnetism21Absolute or Chronometric Dating TechniquesUsing radioactive decay as a clockPotassium– Argon (40K-40A) DatingDating volcanic sediments from 10,000 years to 4.5 billion years2211/8/201712Argon/Argon Dating(40Ar/39Ar, an advanced measurement of traditional K-Ar to date single grains)23• Materials: organic, living tissue that incorporates carbon.• Range: 200 years – 60,000 yearsAnother important chronometric dating technique: Radiocarbon2411/8/201713Radiocarbon is only a quasi-absolute technique until it can be calibrated to calendrical age25“Mind the Gap”: Other important chronometric dating techniques that fill in between the ranges of Ar/Ar and 14C techniques• Uranium/Thorium Dating: 238U to 230Th– range 1,000 years - 500,000 years, – Material: carbonate sediments like stalagmites and flowstone in caves, also bones & teeth.2611/8/201714Mind the Gap: “Archaeologically-relevant Dating Techniques for the Next Century. Small, hot and identified by acronyms” • The Electron Trap Techniques =– Thermoluminescence (TL)• Burned stone– Optically Stimulated Luminescence (OSL)• Quartz crystals27Chronometric Dating Techniques: Thermoluminscence (TL)Material: burnt stone toolsRange: 5,000 to 1,000,000 yearsEvent? The heating of the artifact, not the formation of the rock or its shaping by a hominin2811/8/201715Chronometric Dating Techniques:Thermoluminscence (TL)Age = Paleodose as TLAnnual dose rate29Chronometric Dating Techniques:Optically Stimulated Luminescence (OSL)Age = Paleodose as TLAnnual dose rate3011/8/20171631Take-Home Messages for How We Find Fossils 1.Paleoanthropological sites are rare because our landscape and any preserved prehistoric landscape only intersect in a few places.2.The context of what artifacts are found together provides the strength to give a date and meaning to any given fossil or artifact.3.Each dating technique has its own physical principles, materials, and dating range.
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