time marches on

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Across
  1. 2. four billion years ago the fist single celled organisms existed during the _____ periode
  2. 4. a subdivision of a geologic period
  3. 6. ______ are four hundred million years old and are also called phacops
  4. 7. age of the dinosaurs and the first flowering plants
  5. 10. measuring the age of an event or object in years
  6. 12. determining weather a object is older or younger than others
  7. 16. an arrangement of rock layers in which the older rocks are at the bottom
  8. 22. death of every member of a species
  9. 24. fossil that is found in only one geologic age
  10. 25. ______ states that geological processes happen over time
  11. 26. _______ states that geological processes happen suddenly
  12. 27. fossilized mark formed in soft sediment
  13. 28. fossil that forms when mold is filled
  14. 29. the scientific study of fossils
Down
  1. 1. ____ _____ created the theory of evolution
  2. 3. one continent forms called pangaea
  3. 5. _____ appear 8 million years ago as australopithecus
  4. 8. life moved on land as fish evolved into tetrapods
  5. 9. the first uniformitarianism
  6. 11. a unit of geologic time that includes multiple periods
  7. 13. the age of the mammals prevails after the dinosaurs go extinct
  8. 14. largest division of geologic time
  9. 15. the ice age comes and the first humans appear
  10. 17. coal that we burn today comes from this once luscious forest
  11. 18. cavity made in object by shell or other body
  12. 19. a break in the geologic record created when rock layers are eroded or sediment is not deposited over a long time
  13. 20. _______ states that younger rocks lie on older rocks
  14. 21. remains of an organism that lived long ago
  15. 23. after the precambrian life covered the sea floor
  16. 29. unit of geologic time into which eras are divided