Plate tectonics crossword

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Across
  1. 3. boundary where 2 plates collide
  2. 5. a valley created through the divergent boundary
  3. 6. a zone created by different density of plates
  4. 8. a layer under Earth's crust
Down
  1. 1. boundary where 2 plates move away from eachother
  2. 2. currents found in the upper mantle.
  3. 4. pieces of Earth's crust
  4. 7. molten rock