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19. The plate boundary associated with the formation of new crust 29. The idea of seafloor spreading along the Mid-Atlantic Ridge was
is called supported by evidence from
a. divergent. a. changes in magnetic patterns and ages of rocks moving away
b. convergent. from the ridge.
c. transform. b. faulting and volcanoes on the continents.
d. None of the above is correct. c. the observations that there was no relationship between one
20. The movement of one plate under another plate creates a continent and another.
a. divergent boundary. d. All of the above are correct.
b. ridge. 30. According to the plate tectonics theory, seafloor spreading takes
c. subduction zone. place at a
d. boundary zone. a. convergent boundary.
21. Transform boundaries occur when b. subduction zone.
a. two plates slide by each other without the formation or loss c. divergent boundary.
of crust. d. transform boundary.
b. two plates come together and “transform” each other. 31. The presence of an oceanic trench, a chain of volcanic mountains
c. one plate slides under another plate. along the continental edge, and deep-seated earthquakes is
d. ridges are formed. characteristic of a (an)
22. What is the current theory about why the plates move? a. ocean-ocean plate convergence.
a. Plates follow the rotation of Earth. b. ocean-continent plate convergence.
b. Convective cells move from the core to the lithosphere. c. continent-continent plate convergence.
c. Gravity. d. None of the above is correct.
d. Conduction cells move from the core to the lithosphere. 32. The presence of an oceanic trench with shallow earthquakes and
23. The seismic waves that cause the most damage during an island arcs with deep-seated earthquakes is characteristic of a (an)
earthquake are a. ocean-ocean plate convergence.
a. P-waves. b. ocean-continent plate convergence.
b. S-waves. c. continent-continent plate convergence.
c. surface waves. d. None of the above is correct.
d. P- and S-waves. 33. The ongoing occurrence of earthquakes without seafloor spreading,
24. Earth’s mantle has a chemical composition that agrees closely oceanic trenches, or volcanoes is most characteristic of a
with the composition of a. convergent boundary between plates.
a. basalt. b. subduction zone.
b. iron and nickel. c. divergent boundary between plates.
c. granite. d. transform boundary between plates.
d. gneiss. 34. The evidence that Earth’s core is part liquid or acts as a liquid
25. From seismological data, Earth’s shadow zone indicates that part comes from
of Earth’s interior must be a. the P-wave shadow zone.
a. liquid. b. the S-wave shadow zone.
b. solid throughout. c. meteorites.
c. plastic. d. All of the above are correct.
d. hollow. 35. The surfaces of early planets in our solar system were thought to
26. The Mohorovicic discontinuity is a change in seismic wave be formed from
velocity that is believed to take place because of a. melting by the Sun.
a. structural changes in minerals of the same composition. b. bombardment by dust and debris remaining from initial
b. changes in the composition on both sides of the boundary. planet formation.
c. a shift in the density of minerals of the same composition. c. nuclear decay processes.
d. changes in the temperature with depth. d. volcanic eruptions.
27. The oldest rocks are found in 36. The early Earth’s core is thought to have formed from the
a. continental crust. a. exterior melting from radioactive decay.
b. oceanic crust. b. gravitational pull of heavier materials to the center of Earth.
c. neither, since both are the same age. c. exterior melting from fusion reactions.
d. interior melting from lava.
28. The least dense rocks are found in
a. continental crust. 37. Indirect evidence that supports the theory of how Earth formed
b. oceanic crust. is not supported by the study of
c. neither, since both are the same density. a. vibrations in Earth.
b. Earth’s magnetic field.
c. heat flow.
d. samples from Earth’s core.

18-19 CHAPTER 18 Plate Tectonics 473