The Geologic Time Scale

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Across
  1. 1. Groups of organisms rapidly diversified in the _______ explosion
  2. 3. The appearance of the first mammals
  3. 5. Extensive glaciation occured before the______
  4. 6. The meteorite that struck Earth in the Paleogene period caused a change in global _______
  5. 7. Era that means "recent life"
  6. 9. An event in which many species become extinct in a short time; they occur every 26 to 30 million years on average and are known as mass ___________
  7. 13. Earth's _________ was 4.6 billion years ago
  8. 14. By the end of the Carboniferous period, the first ____ began to roam the forests
  9. 16. Epoch in which humans began to form civilizations
  10. 17. The model that expresses the major geological and biological events in Earth's history is known as the ________ time scale
  11. 18. Number of eras in the Phanerozoic eon
Down
  1. 2. Cause of the mass extinction of the dinosaurs after the Cretaceous period
  2. 4. 90 percent of all history
  3. 8. Birds evolved from ________, who lived in the Mesozoic era
  4. 10. Movement of plate ________ that make up the surface of Earth
  5. 11. Largest division divides the scale into ______ parts
  6. 12. Element found in the K-T boundary that is not prevalent on Earth
  7. 15. The land mass that existed on Earth 225 million years ago