Answers to Chapter 3 Review Questions

1. Stony meteorites are similar in composition to Earth’s mantle, while iron meteorites are similar to the core.

2. Compare your answer to Figure 3.4.

3. P-waves can pass through a liquid, and travel approximately twice as fast as S-waves (which cannot pass through a liquid).

4. P-wave velocity decreases at the core-mantle boundary because the outer core is liquid.

5. The mantle gets increasingly dense and strong with depth because of the increasing pressure. This difference affects both P-wave and S-wave velocities, and they are refracted toward the lower density mantle material (meaning they are bent out toward Earth’s surface).

6. The key evidence for mantle convection is that the rate of temperature increase with depth within the mantle is less than expected. This can only be explained by a mantle that is mixing by convection. The mechanism for convection is the transfer of heat from the core to the mantle, causing the to mantle flow.

7. Earth’s magnetic field is generated within the liquid outer core because liquid metal is convecting.

8. The last two reversals of Earth’s magnetic field were at the beginning of the present Brunhes normal chron (0.78 Ma), and at the end of the Jaramillo normal subchron (0.90 Ma). 

9. The isostatic relationship between the crust and the mantle is dependent on the fact that over very long timescales, the mantle deforms by flowing.

10. In the area of the Rocky Mountains the crust is thickened and pushed down into the mantle. In Saskatchewan the crust is thinner and does not extend as far into the mantle.

11. During the Pleistocene glaciation, British Columbia was pushed down by glacial ice. Mantle rock flowed slowly out from under the weighted-down crust and toward the ocean floor. Now that the land area is rebounding, that mantle rock is flowing back and the offshore areas are subsiding.