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3. rebound The sudden return of elastically deformed rock to its undeformed shape.
6. spreading The process by which new oceanic lithosphere forms when magma rises to earth’s surface at mid-ocean ridges and solidifies.
8. The soft layer of the mantle on which the tectonic plates move.
10. current Any movement of matter that results from differences in density.
13. boundary The boundary between tectonic plates that are sliding past each other horizontally
15. The bending, tilting, and breaking of Earth’s crust.
17. reversal The process by which Earth’s magnetic north pole and magnetic south pole switch positions periodically.
19. plate A block of lithosphere that consists of the crust and the rigid outermost part of the mantle.
20. The thin and solid outermost layer of earth above the mantle.
23. The strong lower part of the mantle between the asthenosphere and the outer core
24. The point of Earth's surface directly above an earthquake's starting point, or focus.

1. The process by which one lithospheric plate moves beneath another plate as a result of tectonic forces
2. A break in a body of rock along which one block moves relative to another.
4. tectonics The theory that Earth’s outer layer is made up of large, moving pieces called tectonic plates.
5. The solid outer layer of earth that consists of the crust and the rigid upper part of the mantle.
7. A system of Ideas that explains many related observations and is supported by a large body of evidence acquired through scientific investigation.
9. boundary The boundary between two tectonic plates that are moving away from each other.
11. The central part of earth below the mantle.
12. The layer of rock between earth’s crust and the core
14. drift The hypothesis that a single large landmass that broke into smaller land masses to form the continents, which then drifted to their present location
16. A movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move.
18. boundary The boundary between tectonic plates that are colliding.
21. plate boundary The edge between two or more plates classified as divergent, convergent, or transform by movement taking place between the plates.
22. The location within earth along a fault at which the first motion of an earthquake occurs.