science

2. ocean ridge the undersea mountain chain where new ocean floor is created
4. core dense ball of solid material at the center of the Earth a layer of molten iron and nickel that surrounds the inner core of the Earth
5. a break in the earth's lithosphere along which rocks moves
7. boundary a plate boundary where two plates move toward each other
8. thickest layer of the Earth
11. spreading the process by which molten material adds new crust to the ocean floor
12. a deep canyon on the ocean floor
14. current cause the plates to move; between the lithosphere and the asthenosphere
15. valley a deep valley where to plates move apart

1. rigid layer made up of the uppermost part of the mantle and the crust
3. drift Alfred Wegener's hypothesis that the continents were once one huge landmass
6. a soft layer of the mantle on which the lithosphere floats on
9. the name 0f a single landmass that broke apart about 255 million years ago
10. the layer of rock that forms the Earth's outer surface
13. boundary a plate boundary where two plates move away from each other