Geologic time scale

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Across
  1. 3. any animal that lacks a vertebral column, or backbone,
  2. 7. divides up the history of the earth based on life-forms that have existed during specific times since the creation of the planet.
  3. 8. an investigative approach that involves sorting objects or events into groups or categories.
  4. 9. the preserved remains, or traces of remains, of ancient organisms.
Down
  1. 1. the age of a rock layer (or the fossils it contains) compared to other layers.
  2. 2. a very long span of geologic time;
  3. 3. any animal or plant preserved in the rock record of the Earth that is characteristic of a particular span of geologic time or environment.
  4. 4. unit of geological time during which a rock series is deposited.
  5. 5. a very large division of geologic time usually longer than an era.
  6. 6. A division of geologic time that is longer than an epoch and shorter than an era.