Plate Tectonics

5. The way scientists mapped mid-ocean ridges in the mid-1900s.
6. The theory that pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle.
8. A deep valley that forms where two plates move apart.
10. German scientist who became curious about why some continents look as though they could fit together.
12. Reptile fossil that has been found in places now separated by oceans.
14. A plate boundary where two plates move away from each other.
15. The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.
17. Mid-Ocean ridges that are continually adding new material to the ocean floor.
19. A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.
20. A book published by Alfred Wegener.

1. A section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust.
2. Any trace of an ancient organism that has been preserved in rock.
3. Mountain ranges that run along the middle of some ocean floors.
4. Another reptile fossil that has been found in places now separated by oceans.
7. The theory that the continents slowly drifted over Earth's surface.
9. A break in Earth's crust along which rocks move.
11. A plate boundary where two plates move past each other in opposite directions.
13. A plate boundary where to plates move toward each other.
16. A fernlike plant that lived 250 million years ago.
18. A supercontinent or single landmass.