geologic Time Scale

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Across
  1. 2. the amount of time it take for one-half of the original parent isotope to decay
  2. 4. matching rock outcrops or fossils exposed in one area to similar fossils and outcrops in another
  3. 7. smallest division of time
  4. 8. eon with the most fossils
  5. 9. the fragment in a rock layer must be older than the rock layer that contains them
  6. 11. remains and traces or imprints of ancient organisms
  7. 14. oldest 3 eons that make up 90% of geologic time
  8. 15. largest of the time units
  9. 17. a fossil used to determine a relative age of a rock
  10. 18. a type of fossil that is just evidence of an organism like a footprint
  11. 19. organism is buried in sediments then decays and leaves a hallow space
  12. 22. used to date rocks less than 60,000 years old
  13. 23. when scientists date an object using radioactive isotopes
  14. 24. second largest unit of time
  15. 27. a record of Earth's history from its origin 4.6 billion years ago to present
  16. 28. sedimentary rocks are deposited in horizontal layers
  17. 29. buried surfaces of erosion
Down
  1. 1. middle life
  2. 3. an index fossil for the paleozoic era
  3. 4. the mold left by an organism is filled by new material and sediments
  4. 5. the process of determining the numerical age of rocks and other objects
  5. 6. recent life
  6. 10. in an undisturbed rock sequence the oldest rocks are at the bottom and younger at top
  7. 12. an intrusion or fault is younger than the rock it cuts across
  8. 13. unstable elements that emit particle called radiation
  9. 16. geological processes occurring today have been occurring since Earth formed
  10. 20. third largest unit of time
  11. 21. old life
  12. 25. type of organisms that were most prevalent during the paleozoic era.
  13. 26. the process of studying the order in which the geologic events occurred