Fossils Lecture
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Transcript

  • 1. Fossils Chapter 21
  • 2. Fossils
    • Remains or traces of once living organisms
    • Tells scientists when, where and how organism lived
    • Formation
      • Normal- Organism decays (deer on road)
      • MUST keep organism from rotting
        • Quick burial (sand, mud, tree sap, etc)
        • Hard parts (bones, wood, etc)
  • 3. Types
  • 4. Petrified Remains
    • Hard, rock-like parts replaced by mineral (calcium)
    • Bones, Tree trunks
  • 5. Carbonaceous Film
    • Carbon Deposits
    • Coal, oil, Natural gas
  • 6. Molds and Casts
    • Remains Covered
    • Sediments Harden
    • Water dissolves object
    • Mold Remains
    • Cast- Sediment fills mold and hardens
  • 7. Original Remains
    • Entire (or part) of organism is preserved
    • Amber (Tree Sap), Ice, Bog (swamp)
  • 8. Trace Fossils
    • Not actually the remains of the organism, but evidence it has been there
    • Footprints, Burroughs, etc
  • 9. How do we figure out age??
    • Absolute Age- Exact age
      • Example 3412 years old or 15 years old
    • Relative Age- Approximate Age
  • 10. Relative Age
    • Best guess of age
    • Index Fossils- Fossils from species that lived for short periods of time and were wide spread across the world
    • Rock Layers-
      • Law of Superposition- “above position”
        • In UNDISTURBED layers of rocks, the oldest layers are on the bottom and younger layers on top
        • Think about a clothes hamper
  • 11. Geode
  • 12. Absolute Dating
    • True Age
    • Radioactive Decay- Breakdown of unstable isotopes into stable atoms
    • Isotope- Variation in number of neutrons in an atom’s nucleus
    • Carbon- 2 isotopes
      • C 12 - 6p and 6 n=12
      • C 14 - 6p and 8n=14
      • C 14 is unstable
  • 13. Radiation
    • Alpha ( α )- blocked by newspaper
      • 2(p + )&2n=mass# decrease by 4, atomic # decrease by 2
    • Beta ( β )- Blocked by brick wall
      • 1 e -= no change in mass #
      • Electron is from neutron (p& e - )causing Atomic # to increase by 1
    • Gamma ( γ ) Blocked only by lead!
      • Photon
  • 14. Isotopes
    • Unstable- Parent isotope
    • Stable- Daughter
  • 15. Half-Life
    • Amount of time needed to breakdown half of the parent material into daughter material
    • Carbon 14- 5730 years
    • Uranium- 4.5 billion years
    • Potassium 40- 1.3 billion years
    • Which would you use to date the planet?