Unit 4 Lesson 1-4 (ESS4)

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Across
  1. 4. era when dinosaurs roamed the earth and went extinct
  2. 5. the study of the origin, history, structure, and processes of Earth
  3. 7. this sample can be used to tell about ancient climate
  4. 10. law that states the present is the key to the past
  5. 14. person who studies fossils
  6. 16. dating that gives the absolute age of the rock by looking at its chemical composition
  7. 20. Era when Pangaea formed
  8. 21. provides the history of life on Earth
  9. 22. type of fossil that was only in existence for a short time period
  10. 23. the age of the ______ is 4.6 billion years old
  11. 24. When the age of rocks is determined by looking at a comparison of other rock layers
  12. 27. The law of _____ is when anything cuts across a rock layer - its younger than the layer it cut across
  13. 29. animals
  14. 30. earliest fossil
Down
  1. 1. remains, imprints, or traces of prehistoric plants or animals
  2. 2. divides earth's history into time intervals
  3. 3. law that states oldest rocks are on the bottom and youngest rocks are at the top
  4. 6. cause of missing rock layers
  5. 8. sudden change on earth
  6. 9. fossilized tracks
  7. 11. space rock used to help determine the age of the Earth
  8. 12. current epoch
  9. 13. The time needed for half of a sample of rock to undergo radioactive decay
  10. 15. era when earth formed into a planet
  11. 17. genetic code
  12. 18. current era, polar ice caps form
  13. 19. changes in the geologic time scale are based on changes in _________
  14. 25. missing rock layers = missing time
  15. 26. the precise (exact) age of a rock or rock layer
  16. 28. pieces of rock found in other layers are always older than the rock layer