Geological History Crossword

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Across
  1. 3. fossil that forms when minerals are deposited in molds
  2. 4. unit of time in an era
  3. 6. a species that no longer exists and will never exist again
  4. 8. the number of years since a rock formed
  5. 10. a substance made up of only one kind of atom
  6. 13. element used for dating younger organisms and rocks; half-life is 5,730 years
  7. 14. type of fossil that forms when minerals replace part or all of an organism
  8. 19. The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations
  9. 21. the breakdown of a radioactive element, releasing energy and particles
  10. 23. longest period of geologic time scale
  11. 26. smallest unit of matter
  12. 27. the preserved remains or traces of an organism
  13. 28. a long period in geologic history with a distinct characteristic or feature
  14. 29. In horizontal sedimentary rocks, the oldest layer is at the bottom and the newest layer is on the top.
  15. 30. time scale established by geologists to reflect a sequence of historical period
  16. 32. scientist who studies fossils
  17. 33. element used to date very old rocks; half-life is 1.3 billion years
  18. 34. fossils that were around for a short time, but were widespread. Useful for dating rock layers
Down
  1. 1. the age of a rock compared to the rocks around it
  2. 2. a break in Earth's crust
  3. 5. lava that hardens in the racks of existing rocks below the surface
  4. 7. chronological collection of life's remains in sedimentary rock layers
  5. 9. time it takes for half of the radioactive atoms to decay in a substance
  6. 11. smallest unit of geologic time
  7. 12. a place where and old rock layer is in contact with a newer one
  8. 15. imprint left by an organism
  9. 16. type of rock that forms from compressed layers of sediment
  10. 17. type of fossil that has a thin coating of carbon
  11. 18. type of rock that has been changed by heat and pressure
  12. 20. scientist who studies rocks
  13. 22. type of rock that forms when magma cools and hardens at or below the surface
  14. 24. a hollow area in sediment that is the shape of an organism
  15. 25. the gradual change in species over time
  16. 31. lava that hardens on the surface