History of the Earth VOCABULARY

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Across
  1. 4. An event where many living things go extinct at the same time.
  2. 6. Three long units of time.
  3. 8. time scale A record of the geologic events and the evolution of life forms shone in rocks and fossil records.
  4. 9. The preserved remains or traces of living things.
  5. 11. A rock's age compared to other rocks.
  6. 13. An animal with a backbone.
  7. 15. Geologists use it to determine the absolute ages of rocks.
Down
  1. 1. A gap in the geologic record.
  2. 2. Animals without backbones.
  3. 3. Geologist use it to determine the relative ages of sedimentary rock layers.
  4. 5. decay The process of atoms of one element bread down to form atoms of another element.
  5. 7. The number of years that have passed since the rock formed
  6. 10. An animal with scaly skin and lays eggs with tough, leathery shells.
  7. 12. Eras are subdivided into units of geologic times called ___
  8. 14. A vertabrate that controls its own body temperature and feeds milk to its young.
  9. 16. An animal that lives part of its life on land and part in water.