Plate tectonics

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Across
  1. 4. A freshwater animal
  2. 5. the solid bulk of Earth's interior
  3. 6. the outermost shell of a terrestrial planet
Down
  1. 1. Broken pieces of the lithosphere
  2. 2. chains separated by a central valley.
  3. 3. an object that's reduced to liquid form by heating
  4. 5. ridge two parallel