ANTH 120 1nd Edition Lecture 12 Outline of Last Lecture I. Primate Locomotor DiversityOutline of Current Lecture II. The Geological Framework for EvolutionCurrent LectureThe Geological Framework for EvolutionThe Context for Darwin’s Hypothesis- Prior to the 1700’s- Young Earth ~6,000 years old- Life was static: created by God and had always existed in the same form as today1. Nicolaus Steno: 1669 Father of Sedimentologya. Used fossils to reconstruct history of the Earthb. Rocks that contain fossils are referred to as stratai. Sedimentary origin of rock strataii. Organic nature of fossils1. Shark Teeth, once living organismiii. Law of Superposition overlying rock layers are younger than those below, strata are deposited in chronological order; rocks are younger on topiv. Law of Horizontality strata are naturally deposited horizontallyv. Olduvai Gorge: 2 million years of prehistoryStratigraphy- Strata: a layer of rock or sediment- Stratigraphy: describing layers of rock or sediment- Example: Layers of rock in the grand canyonGeological TimeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Eras, Periods, & EpochsEras- Pre-Cambrian 4.6 Ba – 542 Ma- Paleozoic 542 – 252 Ma- Mesozoic 252—65 Ma- Cenozoic 65 MA – Present Mass extinction between Permian and Triassic periods Mass extinction KT boundary Cretaceous – Tertiary 65 MaIf we take Earth’s history and make it equivalent to one calendar year:- January-April No life- Early May Simple Life begins- Summer- Early Fall single celled organisms- Early November first multi-cellular life- Late November first vertebrates- Last Week of November first land plants- Early December First Reptiles- December 10th Dinosaurs dominate- December 15th first mammals- 5 p.m. NYE first bipedsEra: CanozoicPeriod:- Quaternary- Tertiaryo Epochs: Pliocene 2.6 mya First Bipedal Hominids Miocene OligoceneDating MethodsHow can you tell how old it is?1. Relative Dating Methoda. Not Exact Agei. Age of something (fossil, site, etc) Relative to something else (fossil, site, etc.)ii. Older, younger, same age2. Absolute dating methodsa. Exact age (in years)Relative Dating MethodsBiostratigraphy- Index fossilso Fossil Pig Molarso Irish Elk finding a bone lets you know the site is over 10,000 years oldo Different strata constrained sequences of fossilso Between site comparisons Compares site of unknown date to ‘reference’ siteFluorine Dating absorptions of chemicals by fossils, bones, 100kya- Within site comparison- Bone looses nitrogen and gains fluorine- Are fossils found together contemporaneous?- The older the remains are the fluorine content should increase- Different amounts of fluorine are not contemporaneouso Pilt Down Hoax -1953 Modern crania, ape like mandibleCultural Dating tracks artifacts change through time, artifacts, 2.5 mya- Tools from different periods- Changes in pipe technologyPaleomagnetism shifts in magnetic field and earth’s polarity, sedimentary rock- Reversals in earth’s magnetic field creates stratigraphic layerso Chrons: long periods of the same polarity Gilbert, gaues, etc.Subchrons: shorter reversals within the chronAbsolute Dating exact age of an object1. Methods use natural processes as ‘clocks’.2. ‘Radiometric Dating’a. Measures radioactive decay b. Measures accumulation of radiationDendrochronology tree growth Trees suspend growth in winter and resume growth in spring… forming tree-rings. Look at layers associated with archeological site Tree rings = how old the structure or tree isIsotopic (Radiometric) Methods tree growth Radioactive ‘parent’ decays into stable ‘daughter’ isotope Average rate of decay is always constant and predictable… half life Half-life: time necessary for half the radioactive atoms to decay Compare remaining parent with amount of daughter, get estimate of how long decayhas been going on Conditions:o Isotope must have a known half-lifeo At time of formation, only parent must be present (daughter: parent ration 0:1)o Must have a method for measuring the ratioAtoms: 1. Nucleus (central core)a. Protonsi. Positive chargeii. Has massb. Neutronsi. No charge ii. No mass2. Shells (surrounding nucleus)a. Electrons i. Negative chargeii. No discernable massIsotopes Same number of protons Different number of neutrons An atom with a variable number of neutrons Radioactive Isotopes are unstable; give off radiation (energy) to become stableRadiocarbon Dating carbon 14, organic material, <75
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