Tectonic plates.

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Across
  1. 4. The type of boundary where plates collide
  2. 7. The gradual movement of continents over time
  3. 8. The semi-fluid layer of the mantle that plates glide upon
  4. 10. A deep valley formed where two plates move apart.
  5. 11. An undersea mountain chain where new seafloor is created
  6. 14. A long, narrow, deep depression on the ocean floor
  7. 16. A major, volcanic, horseshoe-shaped belt around the Pacific Ocean
  8. 18. Type of boundary where plates move apart
  9. 19. Molten rock beneath Earth's surface
  10. 20. The rigid outer layer of Earth, broken into plates
Down
  1. 1. The process where one plate sinks beneath another
  2. 2. The type of crust that forms the ocean floor
  3. 3. The force driving plate movement, often occurring in the mantle
  4. 5. A mountain that forms where magma erupts
  5. 6. A deep valley formed where two plates move apart
  6. 9. The scientist who proposed Continental Drift
  7. 12. Type of plate boundary where plates slide past each other
  8. 13. A supercontinent that existed 200 million years ago
  9. 15. The shaking of the ground caused by plate movement
  10. 17. The type of crust that forms the continents