Chapter 9 Flashcards
What parts of Earth are most closely represented by typical stony meteorites and typical iron meteorites?
Typical stony meteorites are similar in composition to the Earth’s mantle, while typical iron meteorites are similar to the core.
Describe the important differences between P-waves and S-waves.
P-waves can pass through a liquid and travel approximately twice as fast as S-waves (which cannot pass through a liquid).
Why does P-wave velocity decrease dramatically at the core-mantle boundary?
P-wave velocity decreases at the core-mantle boundary because the outer core is liquid.
Why do both P-waves and S-waves gradually bend as they move through the mantle?
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).
What is the evidence for mantle convection, and what is the mechanism that causes it?
The key evidence for mantle convection is that the rate of temperature increase within the mantle is less than expected and 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.
Where and how is Earth’s magnetic field generated?
Earth’s magnetic field is generated within the liquid outer part of the core by the motion of the metallic core material.
When were the last two reversals of Earth’s magnetic field?
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).
What property of the mantle is essential for the isostatic relationship between the crust and the mantle?
e isostatic relationship between the crust and the mantle is dependent on the plastic nature of the mantle.
How would you expect the depth to the crust-mantle boundary in the area of the Rocky Mountains to differ from that in central Saskatchewan?
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.
British Columbia is still experiencing weak post-glacial isostatic uplift, especially in the interior, but also along the coast. Meanwhile offshore areas are experiencing weak isostatic subsidence. Why?
During the Pleistocene glaciation British Columbia was pushed down by glacial ice and mantle rock flowed slowly out beneath the ocean floor. Now that the land area is rebounding, that mantle rock is flowing back and the offshore areas are subsiding.
