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Slide 1Slide 2How old is that rock?Determining Relative Geologic TimePrinciple of Original HorizontalitySlide 6Principle of SuperpositionSlide 8Principle of Cross-Cutting RelationshipsSlide 10Slide 11Order of Events?Slide 13Principle of Faunal (fossil) SuccessionIndex FossilsRelative Dating: UnconformitiesThe Great UnconformityTypes of UnconformitySlide 19Slide 20Relative Dating: CorrelationSlide 22Absolute Dating: Radioactive DecayRadioactive Half-LifeHalf-life ExampleYour Bank AccountIsotopes & Half LivesRadiometric DatingRadioactive Decay CurveCalculating Absolute AgeSlide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 42Slide 43Slide 44Slide 45Geologic TimeSlide 47Precambrian (4.6 Ga – 570 Ma)Paleozoic Era (570 Ma - 245 Ma)Mesozoic Era (245 Ma – 66 Ma)Cenozoic Era (66 Ma - present)Slide 52Slide 53Class 4: Stratigraphy & Age Class 4: Stratigraphy & Age DatingDatingGeologic History and Geologic History and ExtinctionsExtinctionsToday’s topics: Characterizing geologic time Relative ages (stratigraphy) Absolute ages (radioactive decay)Today’s topics: Earth History Mass Extinctions Geologic Time ScaleClass 4: Stratigraphy & Age Class 4: Stratigraphy & Age DatingDatingGeologic History and Geologic History and ExtinctionsExtinctionsClass updates: Reading: Section 4.0-4.6 Homework 1 due today Homework 2 online, due next Mon. Midterm practice online (website) Midterm review online (website) Midterm 1 on Feb. 28th (next Mon.)How old is that rock?Determining Relative Geologic Time1. Principle of Original Horizontality2. Principle of Superposition3. Principle of Cross-Cutting Relationship4. Principle of Faunal SuccessionPrinciple of Original HorizontalityPrinciple of Original HorizontalitySan Juan River, UtahSan Juan River, UtahCanadian Rockies, AlbertaCanadian Rockies, AlbertaPrinciple of SuperpositionPrinciple of SuperpositionPrinciple of Cross-Cutting RelationshipsFaulted rockFaulted rockIgneous intrusionIgneous intrusionPrinciple of Cross-Cutting RelationshipsPrinciple of Cross-Cutting RelationshipsGrand CanyonGrand CanyonOrder of Events?11223344Grand CanyonExampleOrder of Events?11223344Principle of Faunal (fossil) SuccessionIndex Fossils Def.: accurately indicate the ages of sedimentary rocks1) Abundantly preserved in rocks2) Geographically widespread3) Fast evolving - existed for a relatively short time4) Easily identifiedRelative Dating: UnconformitiescomformitycomformityunconformityunconformityThe Great UnconformityTypes of UnconformityTypes of UnconformityTypes of UnconformityRelative Dating: CorrelationHow old is that rock? Relative age: order of events Absolute age: age in yearsRelative dating tells us what order things happened, but not how many years ago they happened.Absolute Dating: Radioactive DecayRadioactive Half-LifeHalf-life Example•You start with $1000 in your bank account•Every week your spouse or boyfriend/girlfriend removes half of the money•The half-life of your account = 1 week1 weekYour Bank Account•Start: $1000•Week 1: $500 •Week 2: $250•Week 3: $125•Week 4: $62.50•Week 5: $31.25•Week 6: $15.63•Week 7: $7.81•Week 8: $3.90•Week 9: $1.95•Week 10: $0.98•Week 11: $0.49•Week 12: $0.24•Week 13: $0.12•Week 14: $0.06•Week 15: $0.03•Week: 16: $0.015 left in your bank account(1 half-life)Isotopes & Half LivesYoung thingsOld thingsRadiometric DatingRadioactive Decay CurveCalculating Absolute Age• Potassium-40 included in mineral (start clock)• Begins decaying to Argon-40• Brilliant scientists have told us the half-life of K-Ar is 1.3 billion yrs (Gyr)• We count # parents & daughters in sample• We find that our sample contains 50% K & 50% Ar• So 1/2 of our initial sample (K) has decayed• How old is it?• We find another sample that is 25% K & 75% Ar• How old is it?Mass ExtinctionsA Bad Day…. 65 Million Years AgoMass Extinctions:Extraterrestrial ImpactsFig. 4-2, p.75Mass Extinctions:Volcanic EruptionsFig. 4-2, p.75Example Eruptions:Mass Extinctions:Atmosphere-Ocean-Continent InteractionsEvolution of Earth AtmosphereNitrogenOxygenAll OthersFig. 4-2, p.75Mass Extinctions:Atmosphere-Ocean Interaction (1)Mass Extinctions:Atmosphere-Ocean Interaction (2)Mass Extinctions:Atmosphere-Ocean-Continent InteractionsMass Extinctions:Ocean-Continent InteractionGeologic Time & BiologyGeologic time (millions of years)Fig. 4-1b, p.74Geologic Time & BiologyGeologic time (millions of years)Geologic Time & BiologyGeologic time (millions of years)Geologic TimeMajor divisionsCenozoic: 66 - 2.5 m.y.aMesozoic: 245 - 66 m.y.a.Paleozoic: 544 - 245 m.y.a.Precambrian: pre-544 m.y.a. (proterozoic)Geologic TimePrecambrian (4.6 Ga – 570 Ma)Paleozoic Era (570 Ma - 245 Ma)Mesozoic Era (245 Ma – 66 Ma)Cenozoic Era (66 Ma - present)• Satellites 1 (Moon)• Size (radius) 6378 km• Bulk density 5.5 g/cm3 (4.1 g/cm3uncompressed)• Surface gravity 9.8 m/s2• Tectonism, volcanism yes (today)• Rotation 1 day• Orbit 365.25 days• Atmosphere 78% N2, 21% O2• Surface pressure 1 atm• Surface temperature 20°C (diurnal, seasonal changes)• Plate tectonics yes• Water


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UTEP GEOL 1312 - Class 4 Lecture Notes

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