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1. plate tectonics

   Theory that Earth's crust is made of moving plates

2. tectonic plate

   Huge slab of lithosphere that moves

3. continental drift

   Idea that continents slowly move over time

4. Pangaea

   Supercontinent that formed long ago

5. convergent

   Plate boundary where plates push together

6. divergent

   Plate boundary where plates move apart

7. transform

   Plate boundary where plates slide past each other

8. subduction

   One plate sinking under another

9. fault

   Break in the crust where rock moves

10. epicenter

    Spot on the surface above an earthquake's start

11. focus

    Point underground where an earthquake begins

12. seismic waves

    Energy waves sent out by an earthquake

13. seismograph

    Instrument that records ground shaking

14. magnitude

    Measure of an earthquake's energy

15. tsunami

    Giant wave caused by an undersea earthquake

16. vent

    Opening where magma escapes a volcano

17. mid-ocean ridge

    Underwater mountain chain where plates split

18. hot spot

    Place where magma rises in the middle of a plate

19. lithosphere

    Rigid outer layer of crust and upper mantle

20. mantle

    Thick hot layer of rock below the crust