plate tectonics

3. ocean ridge-When does sea floor spreading begin?
4. As the plates move what do they do?
8. boundaries- what boundaries is two plates that move slowly away from each other?
9. drift-Wegener's idea that continents slowly moved over Earth's surface became known as?
10. boundaries- What boundaries is where two plates slip past each other,moving past each other?
11. was the name of the scientist?
14. its when wegener made a what about the continents were once joined together in a single landmass and have since drifted apart?
17. valley-where peices of Earth's crust diverge on land,a deep valley called a ?
18. supercontinent,or single landmass,about 300 million years ago.
19. is any trace of any trace of an ancient organism that has been preserved in rock.

1. and shape-the processes of subduction and sea floor spreading can change what?
2. the process by which the ocean floor sinks beneath a deep ocean trench and back into a mantle is called?
4. these pieces became the what?
5. thing did wegener infer lived on a single landmass
6. floor- part of what sinks back into the mantle at deep ocean trench?
7. did scientist mapped mid ocean ridges using?
12. floor spreading-what adds more crust to the ocean floor?
13. boundaries-What boundaries is where two plates collide?
15. ocean trench-At what trench does the oceanic crust bend downward?
16. oceans- what ocean is expanding?