4.11.2: Chapter Questions

Study Questions

1. Describe the Earth’s mantle. How do we know what the mantle is made of and how it behaves?
2. What are the differences between continental crust and oceanic crust, and why are these differences important?
3. What is a hot-spot trail? How do hot-spot trails show that lithospheric plates move across the Earth’s surface?
4. What three types of motion occur at plate boundaries?
5. List the types of convergent plate boundaries. Describe the characteristics and locations of volcanoes associated with convergent plate boundaries. Why are there few or no volcanoes at convergent plate boundaries where two continents collide?
6. What processes occur at oceanic ridges to form their mountainous topography and the fracture zones that cut across them?
7. Describe the changes in seafloor depth and sediment cover with increasing distance from an oceanic ridge. What causes these changes?
8. Why are passive margins described as “passive”? What are their characteristics?
9. Distinguish between isostatic and eustatic processes that cause sea level to change. How do these processes complicate efforts to measure changes in global sea level by measuring sea-level heights at various coastlines?
10. If there were no ice cap on the Antarctic continent, which coast of the United States—the California coast, the Pacific Northwest coast, or the Mid-Atlantic coast—would the Antarctic coast and continental shelf resemble? Why?
11. Describe and explain the principal differences in geography and seafloor topography between the Atlantic Ocean and the Pacific Ocean. 

 

Critical Thinking Questions

1. The structure of the Earth and the processes of plate tectonics depend on the way that fluids and solids of different density interact. List examples of everyday situations in which the difference in density between substances or within a substance determine their behavior. One such example is oil floating on top of water.
2. If continental crust and oceanic crust were able to flow like the material in the asthenosphere, how might the Earth be different? How would the processes of plate tectonics be different?
3. Most ice ages in the Earth’s history have lasted about 50 million years. The most recent ice age began 2 to 3 million years ago. About 10,000 years ago, the glaciers that extended into much lower latitudes than they do today began to melt and the Earth’s climate warmed. Does this evidence indicate that the most recent ice age is over? Explain the reasons for your answer.
4. Is it possible that plate tectonic motions occur at present on any planet or moon in our solar system other than the Earth? Why or why not?
5. Are there planets or moons on which there were probably active plate tectonic motions in the past but not at present? If so, which planets or moons are the most likely to have had such motions? Why?
6. Using the surface topography maps of the planets and moons that are now available, how would you investigate whether, in fact, there had been plate tectonic activity on these planets? 
7. Volcanoes occur at intervals along the length of divergent plate boundaries, but not along the length of transform faults such as the San Andreas Fault. Why?
8. Evidence exists that there are extinct volcanoes in California arranged roughly parallel to the San Andreas Fault. What are the possible explanations for their origin? How would you determine which of the possible explanations was correct?
9. If the Atlantic Ocean stopped expanding and started to contract, what would happen to New York City? Where would it be located a few million years after this change of direction occurred? Would it still be on land? Where would the nearest mountains be? Where would the coastline be?
10. There have apparently been several spreading cycles in the Earth’s history. What might cause the continents to repeatedly collect together, then break apart, only to collect together again?
11. One of the hypothesized effects of the enhanced greenhouse effect is that sea level will rise. Will sea level rise, and if so, why? What will be the causes of sea-level change if climate changes? How many of these causal factors can you list? Which of these factors would be the most important? Would any of them tend to lower sea level? What effects would a sea-level rise of 1 m or 10 m have on humans?
12. In the 1995 movie Waterworld, melting of all the ice in glaciers and the polar ice caps caused the oceans to expand and cover all the land surface on the Earth except for a few small islands. Is this possible? Why or why not?