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Relative & Absolute Dating
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Relative & Absolute Dating

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  • 1. Geologic Time and Earth History
  • 2. Two Conceptions of Earth History:
    • Catastrophism
    • Assumption: Great Effects Require Great Causes
    • Earth History Dominated by Violent Events
    • Uniformitarianism
    • Assumption: We Can Use Cause And Effect to Determine Causes of Past Events
    • Finding: Earth History Dominated by Small-scale Events Typical of the Present.
    • Catastrophes Do Happen But Are Uncommon
  • 3. Uniformitarianism
    • Continuity of Cause and Effect
    • Apply Cause and Effect to Future - Prediction
    • Apply Cause and Effect to Present - Technology
    • Apply Cause and Effect to Past – Uniformitarianism
    • The Present is the Key to the Past
  • 4. Ripple Marks, Bay Beach
  • 5. Fossil Ripple Marks, Baraboo Range
  • 6. Modern Mud Cracks
  • 7. Fossil Mud Cracks, Virginia
  • 8. Two Kinds of Ages
    • Relative - Know Order But Not Dates
    • Civil War Happened Before W.W.II
    • Bedrock in Wisconsin Formed Before The Glaciers Came
    • Absolute - Know Dates
    • Civil War 1861-1865
    • World War II 1939-1945
    • Glaciers Left Wisconsin About 11,000 Yrs Ago
  • 9. Superposition: Mindoro Cut, Wisconsin
  • 10. Geologic Map
  • 11. Fossils Remains of Ancient Plants And Animals, Evidence of Life
  • 12. Commonly Preserved:
    • Hard Parts of Organisms:
    • Bones
    • Shells
    • Hard Parts of Insects
    • Woody Material
  • 13. Rarely Preserved
    • Soft or Easily Decayed Parts of Organisms:
    • Internal Organs
    • Skin
    • Hair
    • Feathers
  • 14. Types of Fossils
    • Original Material
    • Casts & Molds
    • Replacement (Petrified Wood)
    • Carbonized Films (Leaves)
    • Footprints, Tracks, Etc.
      • “ Trace Fossils” – Our only preserved record of behavior of fossil organisms
  • 15. Dinosaur Tracks, Texas
  • 16. Where Fossils Occur
    • Almost Exclusively in Sedimentary Rocks
    • Heat of Melting or Metamorphism Would Destroy Almost Every Type of Fossil
    • Rare Exceptions :
      • Some Fossils in Low-grade Metamorphic Rocks
      • Trees Buried by Lava Flow
    • To Be Preserved, Organisms Have to Be:
    • Buried Rapidly After Death
    • Preserved From Decay
  • 17. Fossil Tree in Lava Flow, Hawaii
  • 18. Some Geologic Rates
    • Cutting of Grand Canyon
    • 2 km/3 m.y. = 1 cm/15 yr
    • Uplift of Alps
    • 5 km/10 m.y. = 1 cm/20 yr.
    • Opening of Atlantic
    • 5000 km/180 m.y. = 2.8 cm/yr.
    • Uplift of White Mtns. (N.H.) Granites
    • 8 km/150 m.y. = 1 cm/190 yr.
  • 19. Some Geologic Rates
    • Movement of San Andreas Fault
    • 5 cm/yr = 7 m/140 yr.
    • Growth of Mt. St. Helens
    • 3 km/30,000 yr = 10 cm/yr.
  • 20. The Fundamental Rule of Absolute Ages The Earth is older than everything on or in it -Except its atoms -All ages are minimum ages
  • 21. Radiometric Dating: Half-Life
  • 22.  
  • 23.
    • If I had a sharks tooth that I estimate to be 15,000 years old based on the sediments I found it in… what could I use to determine the absolute age? U 238 or C 14 ?
    • (*go back one slide to check your answer)
  • 24.
    • If I had a sharks tooth that I estimate to be 15,000 years old based on the sediments I found it in… what could I use to determine the absolute age? U 238 or C 14 ?
    • Carbon-14 Dating
    • (*go back one slide to check your answer)
  • 25.  

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