Exercises

Question 14.1

The velocity of compressional waves in the lower part of the oceanic crust averages about 7 km/s. What rock type is most consistent with this observation as well as with your other knowledge of the oceanic crust?

Question 14.2

What evidence suggests that the asthenosphere is partially molten?

Question 14.3

What evidence indicates that Earth’s outer core is molten and composed mostly of iron and nickel?

Question 14.4

What is the depth to the core, and how do we know it?

Question 14.5

What is the difference between conduction and convection? Which process is more efficient in transporting heat through the mantle?

Question 14.6

Would the temperature at the Moho beneath a continental craton be hotter or cooler than the temperature at the Moho beneath an ocean basin?

Question 14.7

How can features of mantle convection, such as rising and descending convection currents, be seen by seismic tomography?

Question 14.8

How can a mountain float on the mantle when both are composed of rock?

Question 14.9

How do igneous rocks become magnetized when they form? How does the magnetization of sedimentary rocks differ from this process?

Question 14.10

What evidence supports the hypothesis that Earth’s magnetic field is generated by a geodynamo in its outer core?

Question 14.11

Does the magnetic field change by an observable amount over the span of a human lifetime? What does the answer suggest about convective movements in the outer core?