chapter 9

  1. Geologic column
    an ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom.
  2. era
    a unit of geologic time that includes two or more periods.
  3. period
    a unit of geologic time that is longer than an epoch but  shorter than an era.
  4. epoch
    a subdivision of geologic time that is longer than an age but shorter than a period.
  5. evolution
    the process of change by which new species develop from preexisting species over time.
  6. paleozoic era
    the geologic era that followed Precambrian time and that lasted from 542 million to 251 million years ago
  7. Precambrian time
    the interval of time in the geologic time scale from Earth's formation to the beginning of the Paleozoic era, from 4.6 billion to 542 million years ago.
  8. mass extinction
    an episode during which large numbers of species become extinct
  9. Mesozoic Era
    the geologic era that lasted from 251 million to 65.5 million years ago
  10. Cenozoic era
    the current geologic era, which began 65.5 million years ago
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chapter 9
chapter 9