Tectonic Plates

2. boundary the boundary between two colliding tectonic plates.
5. core the solid, dense center of the Earth.
6. the layer of Earth between the crust and the core.
9. A scientist who studies matter that constitutes the Earth and other terrestrial planets.
10. the central, spherical part of the Earth below the mantle.
13. zone the region where an oceanic plate sinks down into the asthenosphere.
15. tectonics the theory that the Earth's lithosphere is divided into tectonic plates that move around on top of the asthenosphere.
17. a break in the Earth's crust along which two blocks of the crust slide relative to one another.
18. boundary the boundary between two tectonic plates that are sliding past each other horizontally.
19. the soft layer of the mantle on which pieces of the lithosphere move.
20. spreading the process by which new oceanic lithosphere is created at mid-ocean ridges as older materials are pulled away from the ridge.

1. the "middle sphere," the strong, lower part of the mantle between the asthenosphere and the outer core.
3. the phenomena associated with volcanic activity.
4. the outermost, rigid layer of the Earth that consists of the crust and the rigid upper part of the mantle.
7. plate a piece of the lithosphere that moves around on top the asthenosphere.
8. boundary the boundary between two tectonic plates that are moving away from each other.
11. drift the theory that continents can drift apart from one another and have in the past.
12. core the liquid layer of the Earth's core that lies beneath the mantle and surrounds the inner core.
14. the thin, outermost layer of the Earth.
16. Wagener German polar researcher, geophysicist, and meteorologist.