Questions

Review Questions

  1. Describe the various ways in which Earth is unique among the planets of our solar system.

  2. Describe the various ways in which Earth’s surface is reshaped over time.

  3. Why are typical rocks found on Earth’s surface much younger than Earth itself?

  1. What is convection? What causes convection in Earth’s atmosphere?

  2. Consider a variation of the pot of water in Figure 9-5. If the source of heat were placed at the top of the pot (instead of the bottom), would convection currents flow in the opposite direction? Explain your answer.

  3. Describe how energy is transferred from Earth’s surface to the atmosphere by both convection and radiation.

  4. If heat flows to Earth’s surface from both the Sun and Earth’s interior, why do we say that the motions of the atmosphere are powered by the Sun?

  1. How does solar energy help power the motion of water in Earth’s oceans?

  2. How does the greenhouse effect influence the temperature of the atmosphere? Which properties of greenhouse gases in the atmosphere cause this effect?

  1. How do we know that Earth was once entirely molten?

  2. What are the different types of seismic waves? Why are seismic waves useful for probing Earth’s interior structure?

  3. Describe the interior structure of Earth.

  1. What is a plastic material? Which parts of Earth’s interior are described as being plastic?

  2. The deepest wells and mines go down only a few kilometers. What then is the evidence that iron is abundant in Earth’s core? That Earth’s outer core is molten but the inner core is solid?

  3. The inner core of Earth is at a higher temperature than the outer core. Why, then, is the inner core solid and the outer core molten instead of the other way around?

  4. Describe the process of plate tectonics. Give specific examples of geographic features created by plate tectonics.

  5. Explain how convection in Earth’s interior drives the process of plate tectonics.

  6. Why do you suppose that active volcanoes, such as Mount St. Helens in Washington State, are usually located in mountain ranges that border on subduction zones?

  7. What is the difference between a rock and a mineral?

  8. What are the differences among igneous, sedimentary, and metamorphic rocks? What do these rocks tell us about the sites at which they are found?

  9. Why do geologists suspect that Pangaea was the most recent in a succession of supercontinents?

  10. Why do geologists think that Earth’s magnetic field is produced in the liquid outer core rather than in the mantle?

  11. Describe Earth’s magnetosphere. If Earth did not have a magnetic field, do you think aurorae would be more common or less common than they are today?

  12. What are the Van Allen belts?

  13. Explain how magnetic stripes are created around a rift on the ocean seafloor.

  14. If the seafloor spreads from a rift at a speed of 2.5 cm/yr and a magnetic stripe is produced that is 20 km wide, for how many years is Earth’s magnetic field in the same orientation without flipping?

  15. Summarize the history of Earth’s atmosphere. What role has biological activity played in this evolution?

  16. Ozone and carbon dioxide each make up only a fraction of a percent of our atmosphere. Why, then, should we be concerned about small increases or decreases in the atmospheric abundance of these gases?

  17. How are scientists able to measure what the atmospheric CO2 concentration and average surface temperature were in the distant past?

  18. Does global warming increase the surface temperature of all parts of Earth by equal amounts or by different amounts? What consequences does this have?

Advanced Questions

Problem-solving tips and tools

You can find most of the Earth data that you need in Table 9-1 and Table 9-3. You will need to know that a sphere has surface area 4πr2 and volume 4πr3/3, where r is the sphere’s radius. You may have to consult an atlas to examine the geography of the South Atlantic. Also, remember that the average density of an object is its mass divided by its volume. Section 5-3 and Section 5-4 and Box 5-2 describe how to solve problems involving blackbody radiation, Section 2-6 discusses precession, and Section 4-4 describes the properties of elliptical orbits.

  1. The total power in sunlight that reaches the top of our atmosphere is 1.75 × 1017 W. (a) How many watts of power are reflected back into space due to Earth’s albedo? (b) If Earth had no atmosphere, all of the solar power that was not reflected would be absorbed by Earth’s surface. In equilibrium, the heated surface would act as a blackbody that radiates as much power as it absorbs from the Sun. How much power would the entire Earth radiate? (c) How much power would one square meter of the surface radiate? (d) What would be the average temperature of the surface? Give your answer in both the Kelvin and Celsius scales. (e) Why is Earth’s actual average temperature higher than the value you calculated in (d)?

  2. On average, the temperature beneath Earth’s crust increases at a rate of 20°C per kilometer. At what depth would water boil? (Assume the surface temperature is 20°C and ignore the effect of the pressure of overlying rock on the boiling point of water.)

  3. What fractions of Earth’s total volume are occupied by the core, the mantle, and the crust?

  4. What fraction of the total mass of Earth lies within the inner core?

  5. (a) Using the mass and diameter of Earth listed in Table 9-1, verify that the average density of Earth is 5500 kg/m3. (b) Assuming that the average density of material in Earth’s mantle is about 3500 kg/m3, what must the average density of the core be? Is your answer consistent with the values given in Table 9-3?

  6. Identical fossils of the reptile Mesosaurus, which lived 300 million years ago, are found in eastern South America and western Africa and nowhere else in the world. Explain how these fossils provide evidence for the theory of plate tectonics.

  7. Measurements of the sea floor show that the Eurasian and North American plates have moved 60 km apart in the past 3.3 million years. How far apart (in millimeters) do they move in one year? (By comparison, your fingernails grow at a rate of about 50 mm/year.)

  8. The oldest rocks found on the continents are about 4 billion years old. By contrast, the oldest rocks found on the ocean floor are only about 200 million years old. Explain why there is such a large difference in ages.

  9. It was stated in Section 7-7 that iron loses its magnetism at temperatures above 770°C. Use this fact and Figure 9-10 to explain why Earth’s magnetic field cannot be due to a magnetized solid core, but must instead be caused by the motion of electrically conducting material in the liquid core.

  10. Most auroral displays (like those shown in Figure 9-20c) have a green color dominated by emission from oxygen atoms at a wavelength of 557.7 nm. (a) What minimum energy (in electron volts) must be imparted to an oxygen atom to make it emit this wavelength? (b) Why is your answer in (a) a minimum value?

  11. Describe how the present-day atmosphere and surface temperature of Earth might be different (a) if carbon dioxide had never been released into the atmosphere; (b) if carbon dioxide had been released, but life had never evolved on Earth.

  12. The photograph below shows the soil at Bryce Canyon National Park, Utah. The color of the whitish layer is due to a lack of iron oxide. More recent soils typically contain iron oxide and have a darker color. Explain what this tells us about the history of Earth’s atmosphere.

    R I V U X G
    (Frank Vetere/Alamy)
  13. Earth’s atmospheric pressure decreases by a factor of one-half for every 5.5-km increase in altitude above sea level. Construct a plot of pressure versus altitude, assuming the pressure at sea level is 1 atmosphere (1 atm). Discuss the characteristics of your graph. At what altitude is the atmospheric pressure equal to 0.001 atm?

  14. Earth is at perihelion on January 3 and at aphelion on July 4. Because of precession, in 15,000 a.d. the amount of sunlight in summer will be more than at present in the northern hemisphere but less than at present in the southern hemisphere. Explain why.

  15. Antarctica has an area of 13 million square kilometers and is covered by an ice cap that varies in thickness from 300 meters near the coast to 1800 meters in the interior. Estimate the volume of this ice cap. Assuming that water and ice have roughly the same density, estimate the amount by which the water level of the world’s oceans would rise if Antarctica’s ice were to melt completely (see Figure 9-33). What portions of Earth’s surface would be inundated by such a deluge?

Discussion Questions

  1. The human population on Earth is currently doubling about every 30 years. Describe the various pressures placed on Earth by uncontrolled human population growth. Can such growth continue indefinitely? If not, what natural and human controls might arise to curb this growth? It has been suggested that overpopulation problems could be solved by colonizing the Moon or Mars. Do you think this is a reasonable solution? Explain your answer.

  2. In order to alleviate global warming, it will be necessary to dramatically reduce the amount of carbon dioxide that we release into the atmosphere by burning petroleum. What changes in technology and society do you think will be needed to bring this about?

Web/eBook Question

  1. Search the World Wide Web for information about Rodinia, the supercontinent that predated Pangaea. When did this supercontinent form? When did it break apart? Do we have any evidence of supercontinents that predated Rodinia? Why or why not?

  2. Because of plate tectonics, the arrangement of continents in the future will be different from today. Search the World Wide Web for information about “Pangaea Ultima,” a supercontinent that may form in the distant future. When is it predicted to form? How will it compare to the supercontinent that existed 200 million years ago (see Figure 9-12a)?

  3. Use the World Wide Web to investigate the current status of the Antarctic ozone hole. Is the situation getting better or worse? Is there a comparable hole over the north pole? Why do most scientists blame the chemicals called CFCs for the existence of the ozone hole?

  4. Use the World Wide Web to research predictions of Earth’s future surface temperature. What are some predictions for the surface temperature in 2050? In 2100? What effects may the increased temperature have on human health?

  5. The Kyoto Protocol is an agreement made by a number of nations around the world to reduce their production of greenhouse gases. Use the World Wide Web to investigate the status of the Kyoto Protocol. How many nations have signed the protocol? What fraction of the world’s greenhouse gas production comes from these nations? Have any developed nations failed to sign? How effective has the protocol been?

  6. Observing Mountain Range Formation. Access the two animations “The Collision of Two Plates: South America” and “The Collision of Two Plates: The Himalayas” in Chapter 9 of the Universe Web site or eBook. (a) In which case are the mountains formed by tectonic uplift? In which case are the mountains formed by volcanoes from rising lava? (b) For each animation, describe which plate is moving in which direction.