The Solar System

CHAPTER 20 | EARTH: THE STANDARD OF COMPARATIVE PLANETOLOGY 441

Discussion Questions

1. If you orbited a planet in another solar system and discovered oxygen
   in its atmosphere, what might you expect to fi nd on its surface?


2. If liquid water is rare on the surface of planets, then most Terrestrial
   planets must have CO 2 -rich atmospheres. Correct? Why?

Problems

1. In Figure 20-3, the earthquake occurred 7440 km from the
   seismograph. How fast did the P waves travel in km/s? How fast did
   the S waves travel?


2. What percentage of Earth’s volume is taken up by its metallic core?


3. If the Atlantic seafl oor is spreading at 3 cm/year and is now 6400 km
   wide, how long ago were the continents in contact?


4. The Hawaiian-Emperor chain of undersea volcanoes is about 7500 km
   long, and the Pacifi c plate is moving 9.2 cm a year. How old is the
   oldest detectable volcano in the chain? What has happened to older
   volcanoes in the chain?


5. From Hawaii to the bend in the Hawaiian-Emperor chain is about
   4000 km. Use the speed of plate motion given in Problem 4 to
   estimate how long ago the direction of plate motion changed. (Note
   that the San Andreas fault in southern California became active at
   about the same time!)


6. Calculate the age of the Grand Canyon as a percent of Earth’s age.

Learning to Look

1. Look at the globe of Earth shown on page 435 and look for volcanoes
   scattered over the Pacifi c Ocean. What is producing these volcanoes?


2. In what ways is the photo
   at the right a typical view
   of the surface of planet
   Earth? How is it unusual
   among planets in general?


3. What do you see in this
   photo that suggests heat
   is fl owing out of Earth’s
   interior?

William K. Hartmann

USGS