6 The Dynamic Earth U2 L4 The Geological Time Scale

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Across
  1. 3. ____ formed and broke up at least twice during the Precambrian time
  2. 9. This era had the largest extinction event known
  3. 11. Limited photosynthesis would ____ plants causing the food chain to collapse
  4. 13. The atmosphere had no free ____ until cyanobacteria released it into the air through the process of photosynthesis
  5. 14. At the end of the Precambrian time, land was ____
  6. 15. The principle that geologic changes occur suddenly
  7. 17. Water was added to the atmosphere due to constant ____ activity
  8. 18. This is the scientific study of the origin, history and structure of Earth and the processes that shape it
  9. 22. The Geologic Time Scale divides Earth's history into ____ of time
  10. 23. water fell as rain and collected in basins to form ____
Down
  1. 1. These are sudden events that some people think how mountains and seas were formed
  2. 2. At least 5 divisions of time have ended in large mass ____ events
  3. 4. ____ time makes up almost 90% of Earth's history
  4. 5. ____ split apart during the Mesozoic
  5. 6. ____ means changes that occur gradually
  6. 7. According to the Geologic Time Clock, which era was the shortest
  7. 8. This is one of the four units of geologic time
  8. 10. This is the largest unit of geologic time
  9. 12. Scientists think that asteroids led to the extinction of ____
  10. 16. During Cambrian time, new species ____ rapidly in shallow seas
  11. 19. Scientists have found that huge craters caused by ancient ____ impact
  12. 20. These mountains formed during the Cenozoic Era
  13. 21. This era led to the extinction of Dinosaurs