GEOS - 1. Geologic Time

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  1. Radioactive dating
    break the rock into ions and use mass spectrometer to measure the number of parent isotopes and the number of daughter isotopes in the rock
  2. Why are many rocks difficult to date?
    The age of the rock must be so that we have enough parent and daughter atoms to measure; it cannot be told old or too young. It also must have the right minerals that contain the right amount of parent isotopes
  3. Uniformitarianism
    The principle that states that geological processes causing change on the earth are gradual rather than catastrophic and are the same processes that can be observed today.
  4. Cross-bedding:
    near-horizontal units that are internally composed of inclined layers; the original depositional layering is tilted, not as a result of post-depositional deformation
  5. Sediment
    rock particles
  6. Original horizontality
    Sedimentary rock layers were originally horizontal when they were laid down and formed
  7. Superposition
    Younger layers were originally on top of older layers
  8. Cross-cutting relationships
    any rock that cuts across or penetrates a second rock body is younger than the rock it penetrates
  9. Give examples of processes that deform rocks
    • Rock can be broken - faulted
    • bent - folded
    • Eroded
    • liquid rock (magma) can push into (intrude) old rock
  10. Why are names used for relative timing instead of numbers?
    Numbers are only estimated
  11. What is the geologic time scale measured in?
    Millions of years
  12. How old are the oldest rocks we've touched?
    4.1 billion years old
  13. How old is the earth?
    4.6 billion years
  14. How old are the oldest fossil cells?
    3.5 billion years
  15. How old is the blue ridge?
    1.1 billion years
  16. How old are the Appalachians?
    3 billion years
  17. How old are the first shells?
    570 million years
  18. How old are the first land plants?
    400 million years
  19. How old are dinosaurs?
    65-250 million years
  20. When did homo sapiens first exist?
    0.5 million years ago
  21. When was the end of the last ice age?
    10 thousand years ago
  22. What is catastrophism?
    a belief that the earth's surface was generally a stable, nonchanging place that had remained quiescent except for violent upheavals during which mountains were thrust upward from the plains and canyons were formed as the earth's surface was ripped apart
  23. What did the theory of neptunism involve?
    the presence of a primordial ocean from which rocks at the earth's surface precipitated
  24. What are beds?
    Layers of rock that appear to be tilted or folded
  25. What is the principle of original continuity?
    accumulations of sediment are deposited in continuous sheets up to the point where they terminate against a solid surface
  26. Plutonism
    explains that the formation of igneous rocks by cooling from a hot, melted state rather than by precipitation from the ocean
  27. Unconformity:
    the surface separating two rock sequences
  28. Lithification:
    the process of beds near the base of the sequences becoming compacted and beginning the transformation from sedimentation into sedimentary rocks
  29. Magma
    a molten liquid that can later cool to form an igneous rock
  30. Metamorphic rock:
    a rock that has been changed to such a great degree by heat and pressure but not to the point of melting
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GEOS - 1. Geologic Time
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