Physical Geology - Chapter 12 Test Bank

79. What sort of geothermal gradient is consistent with having convection in the mantle? A) 0.5°C/km B) 2.5°C/km C) 25°C/km D) 250°C/km

A) 0.5°C/km

53. Exploring Earth's interior using seismic tomography is analogous to exploring the human body using a(n) A) CAT scanner. B) MRI machine. C) stethoscope. D) fMRI machine.

A) CAT scanner.

81. William Gilbert, the physician of Queen Elizabeth I, was the first to suggest that A) Earth had a dipole magnetic field. B) gravity varied over the surface of Earth. C) isostacy worked for the crust. D) oceanic depth was related to seafloor age.

A) Earth had a dipole magnetic field.

5. Which of the following seismic waves will arrive at a seismograph first? A) P B) S C) PP D) SS

A) P

46. Which of the following statements is false? A) S waves slow down as they travel through the mantle. B) P waves slow down in the outer core. C) S waves cannot transmit through the outer core. D) P waves travel through the inner core.

A) S waves slow down as they travel through the mantle.

19. How thick is average lithosphere? A) 25 km B) 100 km C) 250 km D) 1000 km

B) 100 km

72. The P wave shadow extends from roughly ___ to roughly ____ distance from an earthquake's focus. A) 60°; 100° B) 100°; 140° C) 140°; 180° D) 180°; 220°

B) 100°; 140°

78. In a deep mine, temperatures increase at the rate of approximately ______ per kilometer. A) 2.5°C B) 25°C C) 250°C D) 2500°C

B) 25°C

39. Above what temperature do materials lose their permanent magnetism? A) 100°C B) 500°C C) 1000°C D) 5000°C

B) 500°C

2. How fast do P waves travel through granite? A) 4 kilometers per second B) 6 kilometers per second C) 8 kilometers per second D) 12 kilometers per second

B) 6 kilometers per second

48. A P wave that travels from the earthquake focus through the mantle, outer core, back through the mantle, and to Earth's surface is labeled a= A) PcP wave. B) PKP wave. C) PKS wave. D) PcS wave.

B) PKP wave.

50. How many mineralogical phase changes do scientists interpret to occur in the mantle based on the jumps in S-wave speeds? A) one B) two C) three D) four

B) two

58. Evidence for the internal structure of Earth is mostly based on A) heat flow measurements. B) waves generated by earthquakes. C) existence of a magnetic field. D) deep mines and drilling.

B) waves generated by earthquakes.

60. The P wave shadow extends from roughly __________ to 142° distance from an earthquake's focus. A) 25° B) 50° C) 100° D) 125°

C) 100°

3. The S-wave shadow zone extends from ____ to 180° angular distance from the earthquake focus. A) 45° B) 75° C) 105° D) 145°

C) 105°

59. The P wave shadow extends from 105° to roughly __________distance from an earthquake's focus. A) 120° B) 130° C) 140° D) 160°

C) 140°

21. The boundary between the mantle and the core lies at a depth of approximately A) 300 kilometers. B) 1000 kilometers. C) 3000 kilometers. D) 10,000 kilometers.

C) 3000 kilometers.

1. What is the approximate distance from the surface to the center of Earth? A) 700 km B) 2900 km C) 6400 km D) 24,000 km

C) 6400 km

8. Continental crust beneath mountains can be up to ___ kilometers thick. A) 10 B) 40 C) 70 D) 100

C) 70

76. Which portion of the mantle is relatively free of seismic discontinuities? A) 30 to 100 km B) 100 to 400 km C) 400 to 1000 km D) 1000 to 2500 km

D) 1000 to 2500 km

32. The temperature at the center of Earth is approximately A) 200°C. B) 500°C. C) 2000°C. D) 5000°C.

D) 5000°C.

41. How much of Earth's magnetic field can be described by a simple dipole? A) 10% B) 25% C) 75% D) 90%

D) 90%

12. Which of the following statements about the Mohorovičić discontinuity (Moho) is false? A) The Moho marks the top of a partially molten layer. B) The Moho separates denser rocks below from less dense rocks above. C) The Moho separates the crust from the mantle. D) The speed of seismic waves increases as they pass down through the Moho.

A) The Moho marks the top of a partially molten layer.

24. At what depth does the transition from the upper mantle to the lower mantle occur? A) approximately 100 kilometers B) approximately 3000 kilometers C) approximately 700 kilometers D) approximately 5000 kilometers

A) approximately 100 kilometers

9. How thick is the oceanic crust? A) approximately 7 km B) approximately 70 km C) approximately 35 km D) approximately 240 km

A) approximately 7 km

28. The mechanical transfer of heat by vibration of atoms and molecules is called A) conduction. B) convection. C) magnetism. D) radiation.

A) conduction

62. As seismic waves travel through Earth, they generally A) curve upward. B) travel in straight lines. C) curve downward. D) travel along irregular paths.

A) curve upward.

25. What element makes up most of Earth's core? A) iron B) oxygen C) magnesium D) silicon

A) iron

17. After melting of a continental ice cap, the surface of the continent will tend to A) rise. B) sink. C) rise or sink depending on the thickness of the ice cap. D) remain the same.

A) rise.

65. Calculations suggest that the inner core A) spins at a faster rate than the rest of Earth. B) spins in the opposite direction of the rest of Earth. C) spins at the same rate as Earth. D) does not spin at all.

A) spins at a faster rate than the rest of Earth

44. When was there a 35-million-year period during which Earth's magnetic field did not undergo reversals? A) the Cretaceous B) the Eocene C) the Miocene D) the Pliocene-Pleistocene

A) the Cretaceous

22. Which of the following regions is the source of most basaltic magma? A) the asthenosphere B) the lithosphere C) the lower mantle D) the outer core

A) the asthenosphere

51. Using a compositional model of pure iron-nickel alloy for the inner core renders the inner core ________ to match the data for the outer core. A) too dense B) not dense enough C) too magnetic D) not magnetic enough

A) too dense

36. What cause large-scale variations in Earth's geoid? A) variations in gravity B) variations in radioactivity C) variations in magnetism D) variations in solar energy

A) variations in gravity

73. Let's assume that the inner core was liquid and the outer core was solid. What would one expect to see in terms of P and S wave shadows in terms of distance from an earthquake focus? A) P-wave and S-wave shadows would be the same size. B) S-wave shadow would start where the P-wave shadow ends. C) P-wave shadow would start where the S-wave shadow ends. D) There would only be a P-wave shadow.

B) S-wave shadow would start where the P-wave shadow ends.

54. Seismic tomography has revealed a superplume rising from the core-mantle boundary below A) Iceland. B) South Africa. C) the Himalayas. D) Mount St. Helens.

B) South Africa.

20. Which of the following statements about the asthenosphere is false? A) The asthenosphere lies beneath the lithosphere. B) The asthenosphere is stronger than the lithosphere. C) The asthenosphere rises close to the surface beneath mid-ocean ridges. D) The asthenosphere is partially molten.

B) The asthenosphere is stronger than the lithosphere.

13. Which of the following statements is false? A) P waves travel slower in the crust than in the mantle. B) The crust is denser than the mantle. C) The crust-mantle boundary is called the Mohorovičić discontinuity. D) The oceanic crust consists of basalt and gabbro.

B) The crust is denser than the mantle.

67. Geologists have formulated a simple mathematical equation that can predict the depth of oceans. According to their equation, on what does the water depth primarily depend? A) distance from shore B) age of the seafloor C) distance from the nearest mid-ocean ridge D) none of the above

B) age of the seafloor

14. Which of the following marks the boundary between the crust and the mantle? A) a decrease in P-wave velocity and a change in rock type B) an increase in P-wave velocity and a change in rock type C) a decrease in P-wave velocity, but no change in rock type D) an increase in P-wave velocity, but no change in rock type

B) an increase in P-wave velocity and a change in rock type

16. Why is the average elevation of the continents higher than the average elevation of the seafloor? A) because melting of large ice caps has caused isostatic rebound of the continents B) because oceanic crust is composed of denser rocks than the continental crust C) because the continents are supported by upwelling mantle currents D) because subduction pulls down the seafloor

B) because oceanic crust is composed of denser rocks than the continental crust

23. What causes the sharp increases in the velocity of S waves at a depth of 400 and 660 km in the mantle? A) changes in the composition of the mantle B) changes in the mineral structures C) changes in the pressure of the mantle D) changes in the temperature of the mantle

B) changes in the mineral structures

71. According to the principle of isostasy A) oceanic crust should stand higher than continental crust. B) continental crust should be thinner than oceanic crust. C) crustal thickness is directly related to surface elevation. D) elevation is independent of crust type.

B) continental crust should be thinner than oceanic crust.

83. If Earth's magnetic field disappeared, then A) seafloor spreading would cease. B) continental drift would stop. C) the atmosphere would be blown away by the solar wind. D) volcanic activity would increase.

B) continental drift would stop.

30. Over geologic time, most of the heat lost from Earth's interior has been transported by A) conduction. B) convection. C) radioactive decay. D) solar radiation.

B) convection.

80. Geologists have discovered a simple mathematical equation that relates the depth of the seafloor to crustal age. This relationship implies that the oceanic lithosphere A) floats on the asthenosphere. B) cools by conduction. C) cools by convection. D) is rigid.

B) cools by conduction.

75. The base of transition zone layer marks the beginning of the A) outer core. B) inner core. C) lower mantle. D) upper mantle.

B) inner core.

15. What principle is based on the continents being less dense than the underlying mantle? A) epeirogeny B) isostasy C) superposition D) tomography

B) isostasy

10. The oceanic crust consists mostly of A) felsic rocks. B) mafic rocks. C) sedimentary rocks. D) ultramafic rocks.

B) mafic rocks.

55. Earth's magnetic field shields the surface of Earth from A) asteroids. B) solar winds. C) intergalactic radio waves. D) geotherms.

B) solar winds.

26. According to a recent hypothesis, mantle plumes that feed hot spots originate from A) the asthenosphere-lithosphere boundary. B) the core-mantle boundary. C) the crust-mantle boundary. D) the inner core-outer core boundary.

B) the core-mantle boundary.

31. Which of the following regions is hottest? A) the crust B) the inner core C) the mantle D) the outer core

B) the inner core

74. Between 410 and 670 km depths, S-waves show several jumps attributed to phase changes in the upper mantle. What do geophysicists call this region? A) the seismic jump region B) the sudden change zone C) the low-velocity zone D) the transition zone

B) the sudden change zone

18. Which of the following regions in Earth consists primarily of olivine and pyroxene? A) the crust B) the upper mantle C) the lower mantle D) the inner core

B) the upper mantle

49. An S wave that is reflected once off the surface of Earth is labeled an ______ wave. A) SR B) SP C) SS D) SK

C) SS

57. What do sound, light, and seismic waves have in common? A) They can travel trough all types of materials. B) They travel at the same speeds. C) Their speed depends on the materials they travel through. D) Their speeds are independent of the material they travel through.

C) Their speed depends on the materials they travel through.

77. Where, inside Earth, is the largest change in material density? A) base of the crust B) base of the lithosphere C) core-mantle boundary D) outer core-inner core boundary

C) core-mantle boundary

40. Approximately how often does Earth's magnetic field reverse itself? A) every 50 years B) every 5000 years C) every 500,000 years D) every 50,000,000 years

C) every 500,000 years

82. What process generates Earth's magnetic field? A) Earth's rotation B) the magnetic stripes on the seafloor when it moves C) flow in the outer core D) movement of the continents that drag the magnetic poles with it

C) flow in the outer core

7. Where do P waves travel fastest? A) in the upper mantle B) in the outer core C) in the lower mantle D) in the inner core

C) in the lower mantle

38. Where is Earth's magnetic field generated? A) in the crust B) in the mantle C) in the outer core D) in the inner core

C) in the outer core

33. Seismic wave speeds increase with A) decreasing density and temperature. B) decreasing density and increasing temperature. C) increasing density and decreasing temperature. D) increasing density and temperature.

C) increasing density and decreasing temperature.

68. Recently scientists have suggested that __________, thus acting like a "planet within a planet." A) mantle spins faster than the core B) outer core spins faster than the mantle C) inner core spins faster than the mantle D) lower mantle spins faster than the outer core

C) inner core spins faster than the mantle

61. Which of the following layers will not transmit S waves? A) crust B) mantle C) outer core D) inner core

C) outer core

64. Which of the following foods would best serve a proxy for Earth's layering? A) apple B) orange C) peach D) onion

C) peach

45. Seismic waves that bounce off a boundary between two different materials are said to be ________, whereas seismic waves that cross the boundary and are bent are said to be ________. A) refracted; reflected B) reflected; transmitted C) reflected; refracted D) refracted; transmitted

C) reflected; refracted

34. Seismic tomography has revealed that seismic waves in the uppermost mantle are relatively A) fast beneath both mid-ocean ridges and subduction zones. B) fast beneath mid-ocean ridges and slow beneath subduction zones. C) slow beneath mid-ocean ridges and fast beneath subduction zones. D) slow beneath both mid-ocean ridges and subduction zones.

C) slow beneath mid-ocean ridges and fast beneath subduction zones.

42. Which of the following Earth systems powers Earth's magnetic field? A) the climate system B) the plate tectonic system C) the geodynamo system D) all of the above

C) the geodynamo system

35. Based on seismic tomographic images, how deep do subducting slabs extend? A) to the crust-mantle boundary B) to the upper mantle-lower mantle boundary C) to the core-mantle boundary D) to the inner core-outer core boundary

C) to the core-mantle boundary

69. Given that the P wave velocities are related to rock density, choose the sequence that shows the rocks in terms of increasing P wave speeds. Rock densities are: rock I = 2.9 gm/cc, rock II = 2.6 gm/cc, and rock III = 3.3 gm/cc. A) I, II, III B) II, III, I C) I, III, II D) II, I, III

D) II, I, III

63. Earth's inner core was discovered by seismologist A) Beno Gutenberg. B) Andrija Mohorovičić. C) Hugo Benioff. D) Inge Lehmann.

D) Inge Lehmann.

4. Which of the following statements is true? A) Liquids do not transmit P waves. B) P-wave velocities are greater in the core than in the mantle. C) Seismic waves follow straight paths through the interior of Earth. D) The S-wave shadow zone is larger than the P-wave shadow zone.

D) The S-wave shadow zone is larger than the P-wave shadow zone.

27. Which of the following statements about Earth's core is true? A) The inner core and the outer core are both liquid. B) The inner core and the outer core are both solid. C) The inner core is liquid and the outer core is solid. D) The inner core is solid and the outer core is liquid.

D) The inner core is solid and the outer core is liquid.

52. The graphical curve that describes how temperature changes with depth in Earth is called the A) tempotherm. B) heating gradient. C) geoid gradient. D) geotherm.

D) geotherm.

66. Over time, the size of the inner core will __________ and the size of the outer core will __________. A) grow; grow B) shrink; shrink C) shrink; grow D) grow; shrink

D) grow; shrink

70. Assume you are astronaut geophysicist working on Titan (Moon of Saturn) and measure a P-wave velocity of 8 km for the moon's crust. Assuming what you know from Earth, what kind of rock is this surface made of? A) granite B) basalt C) gabbro D) peridotite

D) peridotite

47. The area on the surface of Earth where P waves and S waves are not recorded by seimograms following an earthquake event are referred to as A) reflection zones. B) aseismic areas. C) geoid highs. D) shadow zones.

D) shadow zones.

6. Which layer in Earth does not transmit S waves? A) the crust B) the inner core C) the mantle D) the outer core

D) the outer core

84. Earth's magnetic field would disappear if A) Earth stopped rotating. B) the outer core grew larger. C) plate tectonics stopped. D) the outer core solidified.

D) the outer core solidified.

29. What drives plate tectonics? A) erosion B) solar energy C) thermal conduction D) thermal convection

D) thermal convection

43. Which of the following processes is responsible for the recording of the magnetic reversals on the seafloor? A) depositional remanent magnetism B) tectonosilicate magnetism C) metamorphic magnetism D) thermoremanent magnetism

D) thermoremanent magnetism

56. Variations in the pull of gravity at the surface of Earth are linked to A) variations in latitude. B) variations in the liquid outer core. C) variations in lithospheric densities. D) variations in the mantle temperature.

D) variations in the mantle temperature.