6th Grade Study Guide Answer Key
April 29, 2014
Ch. 4 Test A
1. d
2. d
3. c
4. a
5. a
6. b
7. b
8. c
9. b
10. a
11. convection
12. sliding
13. asthenosphere
14. sea-floor spreading
15. continental drift
16. spreading
17. Pangaea
18. true
19. true
20. crust
21. The heating and cooking of a fluid, changes in the fluid’s density, and the
force of gravity combine to set convection currents in motion.
22. In sea-floor spreading, molten material arises from the mantle and erupts
through a mid-ocean ridge. The molten material then spreads out, pushing
older rock to both sides of the ridge. This process continually adds new
material to the ocean floor.
23. Crust, mantle, outer core, inner core.
24. You would draw the line in the mantle just below the crust, since the
lithosphere includes the crust and the top part of the mantle.
25. Layer 3, the outer core is molten, while layer 4, the inner core, is solid.
26. The plate boundary at A is a spreading boundary; the plate boundary at C is a
colliding boundary; a sliding boundary is not shown.
27. A spreading boundary on land would pull apart the land, creating a rift valley.
Eventually the rift valley may become deep enough for the sea to fill the
widening gap.
28. One kind is when two plates carrying oceanic crust collide. In this case, the
denser plate subducts below the less dense plate at a deep-ocean trench. A
second kind is when a plate carrying continental crust. In this case, the
oceanic plate plunges beneath the continental plate. In a third kind, two
plates carrying continental crust collide. In this case, neither plate is
subducted. Instead, the collision squeezes the crust into mountain ranges.
29. Scientists did not believe Wegener because he could not provide an
explanation for the force that moves continents. Scientist now know that
convection currents in the mantle cause the movements of plates on Earth’s
surface, and those plates carry the continents with them.
30. Oceanic crust is made mostly of basalt, while continental crust is made
mostly of granite. Since basalt is denser than granite, oceanic crust is denser
than continental crust.