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This 5 page One Day of Notes was uploaded by Natalie Polinsky on Friday October 3, 2014. The One Day of Notes belongs to a course at a university taught by a professor in Fall. Since its upload, it has received 159 views.
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Lectures notes?? Yes please! Looking forward to the next set!
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Date Created: 10/03/14
Fossils 1 Paeontoogy the study of extinct organisms 2 Fossi the preserved remains of a once iving organism usually reserved for remains that have been lithified turned into stone a Fossil Skeleton i Usually bone is fossilzed because they are already 70 mineral ii Organic frantion is replaced by mineral salts carried in by groundwater iii Surrounding sandy sediment is also turned to stone b Complete animals are Rare i Most fossils are fragments especially of teeth ii Tooth enamel is 99 mineral already Dentin is ca 70 iii Can reconstruct type of animal size diet even social organization from teeth alone 1 This type of reconstruction started by Cuvier c How do you become a fossil i Have hard mineralized skeleton or shell ii Die iii Die in a good place for burial cave stream margin volcanic landscape iv Get buried protects body from ravaging by carnivores weather v Get buried in a good place for preservation dry not too acidic Avoid subsequent disturbance UNTIL 1 Erosion is necessary to re expose fossils a Map on presentation b Need to go to a place where fossil are accessible ie erosion has occurred 2 Sometimes fossils sealed in tree resin no decay d Different Fossils i Some fossils are actually impressions where the rock hardened around a soft leaf or body 1 The soft tissue then decayed and was filled in by minerals of a different color ii Fossil Footprints 1 Hollows in sand covered and filled in with another layer of ash or soil 2 Prints emerge when upper layer of a different color is carefully removed iii Fossil Poop 1 Can contain microorganisms 2 Male fertilizing element of plants 3 Can give info on environment and life 4 Can identify what kind of animal left it e Bias in the fossil record i Fossil record isn t a complete record of the history of organisms ever to exist on earth it s only a sample of the plants and animals that once lived ii Some environments promote fossilization more than others 1 Politics and other factors may also intervene a Don39t know much about N Korea Saudi Arabia S Asia iii Some skeletal parts preserve better than others 1 Bones shells and especially teeth f The Matrix stuff around fossil i Context is important ii Skeletons become fossils by absorbing minerals from surroundings Absorb isotopes and other matter iii The matrix composition is informative for analyzing fossils and its critical for g Dating fossils i Relative methods 1 2 Lithostratigraphy particular volcanic ash it s buried in ROCKS Biostratigraphy reies on assemblage of other animals found with your fossil ORGANISMS Geomagnetic poarity poarity of sediment which way was north when dirt formed around fossil a Take sample measure where north is now take to lab demagnetizes it b Because earth39s poles change sometimes READ BOOK When the earth39s magnetic field reverses the new direction is recorded in rocsk and sediments forming at that time ii Chronometric methods 1 Isotopicradiometric methods a 14Cdating carbon dating b K Ar dating PotassiumArgon c Uranium series dating Electron Trap methods a Thermoluminescence b Opticallystimulated luminescence c Electron spin resonance Stratigraphy a Nicholas Steno 16381686 i Studied shark teeth in old marine sediments ii Led to laws of superposition horizontality lateral continuity b William quotStrata Smith 17691839 i Principle of faunal succession Relative dating methods Scales a Establishes a broad geological contex i Uses principle of stratigraphy to establish the relative ages between localities and between fossils found in the localities b Principles of superposition Steno Other stratographic principles a Principle of original horizontality Steno rock layers are horizontal to start with non horizontaity is due to subsequent earth movement b Principle of crosscutting relationships Hutton uniformitarian if one layer cuts through another the one being cut through is older c Principle of faunal succession William Smith deeper fauna is older Layers have typical of index fossils A fossil that disappears goes extinct doesn39t come back later iii Deposition and Stratigraphy 1 Depositional Settings a Alluvial fan b Fluvial channel overbank c Lacustrine d Coastal e Aeolian f Cavefissure i Rock shelter 2 Heavier vs Lighter Sediments a Lakes heavy particles settle to the bottom first b Rivers heavier objects require stronger current to carry them and are carried less far in the same current than fine particles c Caves and sopes heavier objects may roll further downhill but lighter sediments more likely to be removed by slopewash 3 Volcanism Earthquakes a Vocano ash pumices lavas basalts obsidians i Datable ii Create changed landscapes open vegetation erosion iii Economic utility stone sources b Earth movements i Faults ii Upift exposes older layers to erosion iii Creates new topographies where water and sediments can accumulate iv Clocks 1 Radiometric best depend on atomic decay 2 Luminescencetrapped charge depend on regular absorption of atomic energy from soils v Isotopes are variations of the same element which differ in their molecular weight vi Radioactive decay 1 Half ife time for half of the radioactive isotope to decay 2 Logarithmic decay evend per unit of time decrease as concentration of radioactive element is reduced 3 67 half lives approach limits of detection lt1 of original amount of radioactive material remains vii Rock Shelter Site Formation 1 2 3 4 Freezethaw is a big factor in colder climates Generates debris or eboulis Stratigraphy can be complex In tropical climates viii Radiometric Potassium Argon 1 Uquot39gtS quot h Erasperiods Discovered in 1960s Decay of ca 105 of radioactive isotope of K40 to A40 in rocks Half life of 125 billion yrs Effective range 20007 billion years Requires starting point with no 140 usually need volcanics Radiogenic A trapped in crystal lattices eg feldspars hear to release and measure Step heating controls for diagenetic argon leakage or old argon Irradiate sample to convert of K39 to A39 which doesn39t exist in nature of A39 is proportional to of K allows direct measurement of A39A40 in same lab step instead of separate measurements of K and A Allows measurements of very small samples single crystals using mass spectrometer eliminate contaminated crystals i Ceonzoic 1 2 Radiometric Uranium Series a Uranium in newly formed rocks or absorbed into bones teeth after burial b Uranium decays to Pb over very long half life Big atom decays to daughter products first over shorter hair lives d U238 to U234 248 000 years to Thoruim230 752 thousand years e U235 to Protactinium231 343k years f Ombined age range ca 5 500k years Luminescence dating a Energy added from soil radiation moves electrons in crystal out of usual quantum level b Crystals contain imperfections that can trap superenergized electrons c Heating to above 300 degrees or sunlight can empty or zero the traps allow measurement of trapped charge d Determining annual dose of radiation from soil allows conversion of trapped charge to age Geiger counter of dosimeter Optically stimuated or thermo uminescence OSL or TL f Can date pots hearths burned flints sands g Limits determined by amount of soil radiation and number of traps in materia usuay around 1 200k years h Probems intermediate heating non homogenous materials changes in annual dose due to groundwater or leaching of U 3 Electron Spin Resonance a Developed to measure trapped charge in apatite heating converts apatite to carbonate b Measure differences in magnetic field created by trapped electrons c Used to date ii Pleistozoic 1 Interglacials 2 Thermometers climate a Oxygen isotopes i 18 b Soil features coldsolifluxion cryotubation or hot aridification laterites c Sea level changes d Fossil pollen palynology e Palaeontology especially micropaaeontoogy micromammals snails etc
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