chapter 7

Chapter 7: Plate Tectonics

Multiple Choice

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1. The man who pioneered the continental drift hypothesis was ____________.

a. J. Tuzo Wilson b. Harry Hess c. D.H. Matthews d. Fred Vine e. Alfred Wegener

2. Which one of the following was not evidence used by early supporters of the continental drift hypothesis?

a. fossils b. fit of the continents c. polar wandering d. rock type similarities on different continents e. ancient glacial features

3. The formation of the Hawaiian Islands is associated with ____________.

a. divergent boundaries b. convergent boundaries c. transform fault boundaries d. no plate boundary of any kind e. both divergent boundaries and convergent

boundaries

4. Pangaea is ____________. a. another name given the Alaskan earthquake

of 1964 b. a portion of the mid-Atlantic ridge c. a German word for "plate tectonics" d. a name of a fossil found in both Africa and

South America that led scientists to believe these continents were once connected

e. the name of a supercontinent

5. The asthenosphere is ____________. a. a cool, rigid zone directly above the

lithosphere b. the name given to the molten outer core c. a source of magma at divergent boun-

daries d. none of these

6. Geomagnetic reversals ____________. a. provided strong evidence for seafloor

spreading b. revealed that polar wandering may have

occurred c. were discovered by the Deep Sea Drilling

Project d. confirmed the existence of subduction zones e. cause the movements of plates

7. Plates move apart, leaving a gap at ____________. a. divergent plate boundaries b. convergent plate boundaries c. transform fault boundaries d. all of these e. none of these

8. Plates move together along ____________. a. divergent plate boundaries b. convergent plate boundaries c. transform fault boundaries d. all of these e. none of these

9. New oceanic crust forms at _________. a. divergent plate boundaries b. convergent plate boundaries c. transform fault boundaries

d. all of these e. none of these

10. Plates slide past one another at _________. a. divergent plate boundaries b. convergent plate boundaries c. transform fault boundaries d. all of these e. none of these

11. Oceanic crust is destroyed along _______. a. divergent plate boundaries b. convergent plate boundaries c. transform fault boundaries d. all of these e. none of these

12. Oceanic crust is neither created nor destroyed along this type of boundary.

a. divergent plate boundaries b. convergent plate boundaries c. transform fault boundaries d. all of these e. none of these

13. Volcanic island arcs are associated with ____________ boundaries.

a. divergent b. convergent (oceanic-oceanic) c. convergent (continental-continental) d. convergent (oceanic-continental) e. transform fault

14. The Red Sea was formed along a(n) ____________ boundary.


15. Mount St. Helens is associated with a(n) ____________ boundary.


16. The Himalayan mountains were produced along a(n) ____________ boundary.

a. divergent b. convergent (oceanic-oceanic) c. convergent (continental-continental) d. convergent (oceanic-continental)

e. transform fault

17. San Andreas fault exemplifies this type of plate boundary.

a. divergent boundary b. convergent (oceanic-oceanic) boundary c. convergent (continental-continental) bound-

ary d. convergent (oceanic-continental) boundary e. transform fault boundary

18. Iceland is located along a(n) _________ boundary. a. divergent b. convergent (oceanic-oceanic) c. convergent (continental-continental) d. convergent (oceanic-continental)

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e. transform fault

19. Japan is associated with this type of plate bound-ary.

a. divergent boundary b. convergent (oceanic-oceanic) boundary c. convergent (continental-continental)

boundary d. convergent (oceanic-continental)

boundary e. transform fault boundary

20. The Mid-Atlantic Ridge is an example of a(n) ____________ boundary.


21. The Aleutian Islands are the result of plate inter-action at which type of plate boundary?

a. divergent boundary b. convergent (oceanic-oceanic) boundary c. convergent (continental-continental)

boundary

d. convergent (oceanic-continental) boundary e. transform fault boundary

22. The African rift valleys are associated with a(n) ____________ boundary.


23. The Andes mountains were generated at a(n) ____________ boundary.


24. The Ural mountains were produced along a(n) ____________ boundary.


25. Convergent boundaries are zones where plates ____________.

a. slide past each other b. move together c. move apart, leaving a gap d. cause seafloor spreading e. none of these

26. Divergent boundaries are zones where plates ____________.

a. move together b. move apart c. slide past each other d. move obliquely to each other e. move together, then apart

27. It was learned from the Deep Sea Drilling Project that the oceans are ____________.

a. Precambrian age in the oldest regions b. Pleistocene age in the oldest regions c. about the same age as the continents d. much older than the continents e. oldest adjacent to the continents and

youngest at the ridges

28. The continents fit together best in the Pangaea configuration when _________.

a. the present shorelines are matched b. shorelines that existed in the distant past

are matched c. the outer edges of the continental

shelves are matched d. earthquake zones are matched e. the mid-oceanic ridges are matched

29. Wegener's suggestion that tidal forces might cause continental drift was untenable when it was shown that ____________.

a. Earth's magnetic field was too strong b. the tidal forces required to move the

continents would stop Earth's rotation in a matter of years

c. the Americas were drifting westward, whereas Wegener's mechanism would have them going eastward

d. the Moon's gravity could not affect continental material as far away as Earth

e. Earth's density was too low

30. Late Paleozoic continental glaciation provided important evidence favoring continental drift. This evidence was gathered from ____________.

a. all the continents b. North America and Europe c. Greenland, North America, and Asia d. South America, Africa, Antarctica, and

India e. North America and South America

31. The true margin of a continent is _______. a. the shoreline b. the outer edge of the continental shelf c. at a depth of 100 fathoms d. the edge of the ocean floor e. the mid-ocean ridge

32. The island of Hawaii experiences volcanism because it is located __________.

a. above an active mid-oceanic ridge b. above a hot spot c. above a subduction zone d. along a transform fault e. at a site where two plates are colliding

33. If you wanted to draw the boundaries of active lithospheric plates on a globe, which of the following maps would give you the most complete information? A map showing ____________.

a. active volcanoes b. mid-oceanic ridges c. earthquake distribution d. the edges of continental shelves e. the global distribution of hot spots

34. Mountains formed by the collision between continents are the ____________.

a. Cascades b. Himalayas

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c. Appalachians d. Cascades and Himalayas e. Himalayas and Appalachians

35. The asthenosphere ____________. a. will not transmit P waves b. occurs only in the vicinity of subduction

zones c. permits plate motion d. is a layer of great strength within the mantle e. produces Earth's magnetic field

36. The pattern of magnetic anomalies on the sea floor most resembles ____________.

a. stripes on a zebra b. spots on a leopard c. splotches on a giraffe d. warts on a toad

37. When a deep oceanic trench is located ad-jacent to a continent, we would likely find active volcanoes ____________.

a. seaward from the trench b. landward from the trench c. along the axis of the trench d. at the extremities of the trench

38. The Hawaiian Islands are located where the Pacific plate is ____________.

a. diving under the North American plate b. being thrust over the North American plate c. separating from the North American plate d. migrating over a hot spot e. diving under Japan

39. Hot spots are believed to originate ______. a. when rock is subducted b. because of concentrations of radioactive

material in the upper mantle c. as columns of hot material rising

through the deep mantled. during magnetic reversals e. by chemical reactions in the asthenosphere

40. The geographic distribution of Mesosaurus, a small swimming reptile that lived during the late Paleozoic, provides evidence that ____________.

a. England was covered by a shallow sea during the late Paleozoic

b. migration between North America and England was possible

c. South America and Africa were once joined

d. a land bridge existed between Australia and India

e. the Pacific Ocean did not exist during this time period

41. Lithospheric plates are about ________ km thick. a. 1 b. 10 c. 100 d. 1000 e. 10,000

42. Deep ocean trenches are associated with ____________.

a. rifting b. sub-oceanic erosion c. subduction zones

d. transform fault offsets e. submarine extension

43. The energy that causes plates to move is derived from ____________.

a. tidal forces b. solar energy c. Earth's internal heat d. gravitational energy e. magnetic energy

44. If Earth's magnetic field did not occasionally reverse polarity ____________.

a. polar wandering curves would not exist b. compasses would not work c. the sea floor would not produce mag-

netic strips d. paleomagnetic analysis of a rock would not

give the direction to the pole e. continental drift would not have occurred

45. In the plate tectonics model, Earth's outer shell consists of about ____________ individual plates.

a. 3 b. 5 c. 20 d. 50 e. 100

46. Much of the evidence in support of plate tectonics has come from ____________.

a. oil wells b. the Deep Sea Drilling Project c. mapping of the major river systems d. the Intercontinental Drilling Project e. Project Mohole

47. How did the opponents of the continental drift hypothesis account for the existence of similar life forms on widely separated landmasses?

a. parallel evolution b. cross-pollination c. migration across land bridges d. oceanic currents e. migration of the zygote stage

48. Alfred Wegener's now famous book was first written under the title ____________.

a. Plate Tectonics b. Continental Drift with Supporting Evidence c. The Origin of Continents and Oceans d. Pangaea e. Our Wandering Continents

49. How many years passed from the time con-tinental drift was first formally proposed until the concept was widely accepted?

a. less than 10 b. about 20 c. about 50 d. over 100 e. over 200

50. When an iron-bearing mineral is heated above a certain temperature, it loses its magnetism. This temperature is about ____________.

a. 110˚C b. 220˚C c. 340˚C d. 580˚C e. 1200˚C

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51. When a rock is heated above a certain tem-perature, called the ____________, it loses its magnetism.

a. Curie Point b. magnetic position c. critical temperature d. isopoint

52. Subduction zones are associated with ____________.

a. divergent plate boundaries b. convergent plate boundaries c. transform fault boundaries d. all of these e. none of these

53. Deep-ocean trenches are associated with ____________.

a. divergent plate boundaries b. convergent plate boundaries c. transform fault boundaries d. all of these

e. none of these

54. Most of the world's deep-ocean trenches are located within the ____________.

a. Atlantic Ocean b. Pacific Ocean c. Indian Ocean d. Antarctic Ocean e. small ocean basins, such as the Gulf of

Mexico

55. Seafloor spreading goes through various stages. Which of the sequences below correctly places these locations in order so that the initial stage is depicted first and followed by more advanced stages of development?

a. Red Sea, Atlantic Ocean, African Rift Valley b. Red Sea, African Rift Valley, Atlantic Ocean c. Atlantic Ocean, African Rift Valley, Red Sea d. Atlantic Ocean, Red Sea, African Rift Valley e. African Rift Valley, Red Sea, Atlantic

Ocean

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Completion:

74. In the continental drift hypothesis, a supercontinent called PANGAEA was proposed.

75. Instruments which measure Earth's magnetic field are called MAGNETOMETERS.

76. Earth's present magnetic field is said to possess NORMAL polarity.

77. At numerous times in the past, Earth possessed a magnetic field opposite of that observed today. Rocks which exhibit this magnetism are said to have REVERSE polarity.

78. The hypothesis, which proposed that sea floor was continually forming at the mid-ocean ridges while older sea floor was being destroyed at the trenches, was later termed SEAFLOOR SPREADING

79. The idea that the magnetic poles migrated through time became known as polar wandering.

80. Iron bearing rocks that formed in the distant past and retain the magnetic alignment at the time of their origin are said to possess PALEOMAGNETISM/FOSSIL MAGNETISM

81. The man given credit for developing the continental drift hypothesis was ALFRED WEGENER

82. When a rock is heated above a certain temperature, called the CURIE POINT, it loses its magnetism.

83. The concept of the magnetic poles changing polarity through geologic time became known as MAGNETIC REVERSAL

84. The theory of plate tectonics states that Earth's rigid outer shell consists of several individual segments. These segments are known as PLATES.

85. During the breakup of a continent along a divergent plate boundary, large downfaulted valleys are generated. These valleys are called RIFTS OR RIFT VALLEYS

86. The vessel that operated during the 1970s and early 1980s as part of the Deep Sea Drilling Project to provide evidence for plate tectonics was called the GLOMAR CHALLENGER

87. Plumes of molten rock originating deep within the mantle are known as HOT SPOTS

88. The Aleutian, Mariana, and Tonga islands all contain active volcanoes and are examples of VOLCANIC ISLAND ARCS

89. What feature would you expect to find adjacent to a volcanic island arc such as the Aleutian Islands? TRENCH

90. The San Andreas fault is an example of which type of plate boundary?TRANSFROM FAULT

91. The true nature of transform faults was provided by J TUZO WILSON

92. The island of Hawaii experiences volcanism because it is located above a(n) HOT SPOT

93. The magma which generates new sea floor originated from the partial melting of the rock PERITODITE.

94. If the present plate movements persist along the western margin of North America, Los Angeles and San Francisco will pass each other in about TEN million years.

95. The true outer boundary of the continents is the _CONTINENTAL SHELF

96. The theory of PLATE TECTONICS holds that Earth's outer shell consists of about twenty rigid slabs called plates.

97. Earth's rigid outer shell is called the LITHOSPHERE

98. Because each plate moves as a distinct unit, all major interactions between plates occur along plate BOUNDARIES

99. The breakup of Pangaea began about 200 million years ago.

100. The CONVECTION current hypothesis for the driving mechanism of plate tectonics suggests that large

currents within the mantle drive plate motion.

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1. Alfred Wegener is credited with developing the continental drift hypothesis.

2. The puzzle-like fit of the continents, especially Africa and South America.

3. Pangaea, the supercontinent named by Alfred Wegener, is thought to have begun to break apart about 200 million years ago, the fragments eventually forming the present continents.

4. Wegener and his associates found that the fit of the continents, fossil evidence, paleoclimatic evidence, and similarities in rock type and structural features all seemed to bridge together the now-separated continental landmasses.

5. If Mesosaurus was able to swim well enough to cross the vast ocean currently separating Africa and South America, its remains should also be found on other continents. Since this is not the case, we conclude that South America and Africa were joined during the time period that these animals existed.

6. Early in this century, migration of land animals was thought to have occurred via land bridges. According to this view, these land bridges were recently submerged as sea level rose following the last glacial event.

7. First, it is difficult to explain, by assuming that a general cooling trend occurred, why late Paleozoic glaciation was essentially confined to the Southern Hemisphere. This and other paleoclimatic data can best be reconciled by assuming that the continents were located at different latitudes from where they are today. Second, glacial striations in some locations indicate that the ice movement was from areas presently occupied by water. We know, however, that thick accumulations of ice can form only on land.

8. The first approximations of plate boundaries were made on the basis of earthquake and volcanic activity.

9. Divergent boundaries - where plates are moving apartConvergent boundaries - where plates are moving togetherTransform fault boundaries - where plates slide past one another along faults

10. Sea-floor spreading refers to the creation of new sea floor at the oceanic ridges along with its conveyor belt movement away from the ridge crests. Sea-floor spreading occurs today along the oceanic ridges.

11. Subduction zones occur in the deep-ocean trenches where slabs of oceanic crust are descending into the mantle. Subduction zones are associated with convergent plate boundaries.

12. Lithosphere is being consumed at convergent boundaries where a slab of oceanic crust plunges into the asthenosphere. The production and destruction of the lithosphere must take place at about the same rate because Earth is neither growing nor shrinking in size.

13. The Himalayan Mountains formed as a result of a collision between the Indian landmass and the Asian continent.

14. Transform fault boundaries, like the San Andreas fault, represent areas where plates slip past one another. Lithosphere is neither produced (as along divergent boundaries) nor destroyed (as along convergent boundaries) along transform faults.

15. If the movement along the San Andreas fault continues in its present manner, the part of Cali fornia west of the fault will indeed slide out to sea, eventually becoming an island off the west coast of the United States and Canada. This, however, will take millions of years.

16. Paleomagnetism is the natural magnetism in rock bodies, which was acquired from Earth's magnetic field at the time when the rock formed.

17. Evidence from studies of paleomagnetism indicates that Earth's magnetic poles have migrated during the past 500 million years. This apparent migration can also be explained if the magnetic poles remained stationary while the landmasses moved. Thus, continental drift does in fact account for the apparent wandering of Earth's magnetic poles.

18. Shallow-focus earthquakes occur in trench areas where the oceanic plate is bent. Intermediate- and deep-focus quakes occur close to the continents. The depth of earthquake activity is associated with the position of the descending plate. As the slab descends, deeper focus earthquakes are generated.

19. The age of the oldest sediments recovered by deep-ocean drilling is about 160 million years. Some continental crust has been dated at 3.9 billion years.

20. Hot spots are relatively stationary plumes of molten rock rising from Earth's mantle. According to the plate tectonics theory, as a plate moves over a hot spot, magma often penetrates the surface, thereby generating a volcanic structure. In the case of the Hawaiian Islands, as the Pacific plate moved over a hot spot, the associated

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igneous activity produced a chain of five major volcanoes. The oldest of the Hawaiian Islands is Kauai. The youngest, and only active volcanic island in the chain is the island of Hawaii.

21. Himalayas: convergent (continent-continent)Aleutian Islands: convergent (ocean-ocean)Red Sea: divergentAndes Mountains: convergent (ocean-continent)San Andreas fault: transform faultIceland: divergentJapan: convergent (ocean-ocean)Mount St. Helens: convergent (ocean-continent)

22. The three models proposed to explain mantle convection are a shallower, two layer convective model, a whole mantle convective model, and a deeper layer model. The shallow, two layer model envisions a thin convective layer above 660 kilometers and a deeper layer below. The whole mantle model proposes a single convective cell where rising, hot mantle plumes originate near the core-mantle boundary and subducted lithosphere descends into the lower mantle. The deeper, layered model has two layers that swell and shrink in the lower mantle without substantial mixing. None of the models fit all of the available data, thus the exact nature of the convective flow in the mantle remains unknown.

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chapter 7

Documents

african rift

outer shell

hawaii experiences

san andreas

north american

transform

volcanic island

divergent