What is the Earth made of?

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Across
  1. 2. Parts or pieces that together form a whole.
  2. 5. The hard, rocky outer layer of the Earth.
  3. 6. To wear away slowly by wind, water, or ice.
  4. 10. To be made up of; to include or contain.
  5. 12. A scientist who studies rocks, layers of the Earth, and its history.
  6. 14. To hit or crash into each other with force.
  7. 15. Slowly over a long time; step by step.
  8. 17. An object that is perfectly round like a ball.
Down
  1. 1. A large amount or piece of something without a definite shape.
  2. 3. A thick, solid piece of something.
  3. 4. Very strong, extreme, or serious.
  4. 5. In a way that relates to chemistry or substances reacting.
  5. 7. The force created when pushing hard against something.
  6. 8. Extremely large; huge.
  7. 9. Relating to one of the Earth's main large landmasses (continents).
  8. 11. The thick layer of hot rock inside the Earth below the crust.
  9. 13. To suddenly explode and send out lava, ash, or steam.
  10. 16. An enclosed space or underground room (e.g., for magma). Clues