Geological Time

    Philosophical significance of "deep time"-The discovery of time.

    1. Biblical chronology: Bishop Ussher. (Ireland; 1664)
      • Typifies the use of the bible for reconstructing the history of the earth-counting up time in patriarchal genealogies..
      • Date and time of the creation: 9:30 AM October 29, 4004 BC
      • Did not fool with fossils
    2. James Hutton (1726-1797)
      1. Expounded the principle of uniformitarianism
        • Present day processes can explain the past
        • Big features formed a little at a time
        • The earth is very old.
      2. Exemplified the principle by describing how an unconformity was created.
    1. Charles Lyell (1797-1875)
      1. Published principles of geology (1833)
      2. Espoused the principle of uniformitarianism
    2. Charles Darwin (1809-1882)
      1. Accepted the principle of uniformitariansism
      2. Used the ancient age of the earth to accommodate the evolution of species.

    Telling time

    1. Relative dating: how to tell what is older or younger
      1. Superposition: oldest is on the bottom
      1. Cross cutting relationships: something has to exist before it is cut
      1. Inclusions: the sedimentary particles are older than the pile of sediment.
    1. How to correlate between different locations
      1. Original horizontality: sedimentary layers (beds) are laid down nearly flat; if they are not flat, they were later disrupted

        2.  
      2. Lateral continuity: sedimentary layers are laterally continuous, so you can connect beds across gaps, or unknown areas.
      1. Faunal succession.
        • Species have a time of origination and a time of extinction.
        • Because of this, different times have different fauna and flora.
        • If sedimentary rocks from different places contain the same fossils, then they were deposited at the same time.

      1. Event Beds
        1. Volcanic ash falls
          1. example from Lexington
        2. Impact fallout
        3. Storms
        4. Turbidity currents
        5. Earthquake disruptions
          1. example from Lexington

    The (relative) geological time scale (better, see book, page 10).

    another geological time scale
    Geological Society of America timescale
    1. Precambrian
      1. Azoic
      2. Proterozoic
      3. Paleozoic
        1. Cambrian
        2. Ordovician
        3. Silurian
        4. Devonian
        5. Carboniferous
          1. Mississippian
          2. Pennsylvanian
        6. Permian
      4. Mesozoic
        1. Triassic
        2. Jurassic
        3. Cretaceous
      5. Cenozoic
      6. Tertiary
        1. Paleocene
        2. Eocene
        3. Oligocene
        4. Miocene
        5. Pliocene
      7. Quaternary
        1. Pleistocene
        2. Recent

    Absolute ages

    1. The Rotational Clock.
      1. Having to do with the orbit or with the rotation of the earth
      2. They can tell us durations some times, but not always how long ago:
        1. Growth lines (on shells, tree rings etc.)
        2. Lake Varves
    1. Hourglass Clocks.
      1. Lord Kelvin (1824-1907) and the Cooling Earth
        • assumed originally molten state
        • Knew temperature of melting for rocks.
        • Knew size of the earth.
        • measured current heat loss.
        • Calculated how long earth took to cool from molten state. 20 m.y, to 100 m.y.
        • claimed to have overthrown uniformitarianism.
      2. John Joly and the salt in the oceans
      3. Rates of sediment accumulation and thickness of known sediments
    2. Radiometric Clocks
      1. Structure of the Atom
        1. Role of Protons and Neutrons
        2. The Mass Number
      2. Isotopes
        1. Stable
        2. Unstable
          1. Parent and Daughter
      3. Half life
      4. Dating Rocks.
      5. Discussion of isotopes
        • Uranium - Lead
        • Thorium - Lead
        • Rubidium - strontium
        • Potassium - Argon
        • Carbon 14

    Putting it all together