GEOLOGY3140 THE CHANGING EARTH 5TH EDATION MONROE TEST BANK CHAPTER2
The Changing Earth: Exploring Geology and Evolution, 5e Test
Bank
Chapter 2: Test Bank
Note: Questions with an asterisk (*) denote appearance in web quiz (Tutorial Quiz)
Short Answer Essay Questions
1. What were the major lines of evidence for continental drift as presented by Wegener in the early 20 th
century?
Answer: The glaciations on the Gondwana continents could only have occurred if the continents were
joined since the centers of the glaciers would have been in the ocean if they were not. Also, the
continents, such as South America and Africa, match like a jigsaw puzzle. Similar fossil plant and
animals are separated by oceans leading to the assumption that they must have lived in adjacent regions
when they were alive. Finally, similar rock sequences and mountain ranges could be connected across
oceans. [pp. 31-35]
2. Explain how mountain ranges can be used as evidence to support continental drift.
Answer: A mountain range forms under the same geological conditions along its length. This means
that the same or nearly the same rock types are found along the range’s length in the same or nearly the
same sequence. The processes that form mountain ranges tend to create somewhat linear, elevated
features. So a mountain range that has been split, even if it has been separated by an ocean, is fairly
easy to recognize. [p. 32]
3. How does fossil evidence support continental drift?
Answer: The distribution of fossils is such that it would be impossible for the plants and animals not
to have lived in contiguous land areas. Glossopteris seeds are too heavy to be dispersed by wind and
would not have remained viable if they had traveled far across the oceans. The plants associated with
Glossopteris do not match the climate zones the fossils are found in. As for the animals, it’s hard to
imagine a freshwater reptile like Mesosaurus swimming across the Atlantic. And the land-dwelling
reptiles, Lystrosaurus and Cynognatuus, could not have swum at all! [p. 33]
4. What was the principal reason why Wegener's theory of continental drift was rejected?
Answer: Wegener lacked a plausible mechanism to explain how continental crust could move through
the sea floor. [p. 35]
5. Why were glacially deposited strata important in the development of continental drift theory?
Answer: The glacial deposits indicated that all southern continents must have been contiguous and
closer to the South Pole. Glaciers cannot form in the middle of an ocean, which is where they would
have originated if the continents were not together. [p. 33]
6. What are the three possible explanations for the distribution of paleomagnetic data?
Answer: (1) The continent remained fixed and the north magnetic pole moved; (2) the north magnetic
pole stayed still and the continent moved; (3) both the continent and north magnetic pole moved.
[p. 36]
11
,Chapter 2: Plate Tectonics: A Unifying Theme
7. Briefly explain why apparent polar wandering is "apparent."
Answer: Paleomagnetic studies of ancient rocks point to different locations for the North Pole at
different times. When this is mapped out, it makes the pole appear to wander over time. The
alternative to a wandering magnetic pole, for which there is no other evidence at all, is that the
continents move and with them the rocks that contain the paleomagnetic data. [p. 36]
8. Briefly explain why the movement of continents over geologic time was the best explanation for
polar wandering.
Answer: Since the Earth has only one magnetic north pole now, it was extremely unlikely that
there would have been more than one in the past, though this would have been required to explain
the different polar wander paths of the different continents. The only other possible explanation is
that the continents were once joined and have since moved apart. [p. 36]
9. What evidence is there that ocean basins are young and old oceanic crust must be destroyed?
Answer: The maximum age for oceanic crust is 180 million years, but the continents contain
rocks both younger and much older than 180 million years, so the older oceanic crust must go
somewhere. [p. 38]
10. Briefly describe what happens when divergent plate boundaries form within a continent.
Answer: High heat flow elevates the continent and a rift valley forms, with normal faults and a
central valley called a graben. Magma is intruded into fractures. As the plates diverge, basalt
erupts in the rift, creating new ocean crust. Ultimately, as the plates continue to diverge, a new
ocean basin forms. [p. 40]
11. Describe how the two models for the driving force of plate motion are the same. How are they
different?
Answer: Both models involve thermal convection in the mantle. In both models, where two
adjacent convection cells have upwelling limbs, there is a divergent plate boundary. Where there is
a descending limb of a convection cell, there is a convergent boundary. The models differ in the
location of the convection cells. In one, the convection cells are restricted to the asthenosphere. In
the other, the convection cells take up the entire mantle. [p. 52]
12. What are the heat sources for each of the two mantle convection models for plate tectonics?
Answer: With whole mantle convection, the heat source is the core. With convection only in the
asthenosphere, the heat source is harder to identify. [p. 52]
13. How does seafloor spreading explain the movement of the continents?
Answer: With seafloor spreading, the continents and oceanic crust move together as part of large
plates. The plate is pushed by the formation of new ocean crust and pulled by the subduction of
old ocean crust. New crust forms due to seafloor spreading. [p. 52]
14. In what ways does plate tectonics theory have economic applications?
Answer: By understanding the geologic history of a region, geologists can predict whether it will
be a worthwhile place to search for petroleum or ore deposits. [pp. 53-54]
12
, The Changing Earth: Exploring Geology and Evolution, 5e Test
Bank
15. Briefly explain the roles of magma and hydrothermal activity in forming ore deposits along convergent
and divergent plate boundaries.
Answer: Magma contains valuable elements, some of which leave the magma in gases and fluids.
These substances transport the elements and facilitate their exchange for other elements in the
surrounding rock. The surrounding rock may then have enough of the valuable elements to become an
ore deposit. At convergent plate boundaries, partial melting at the subducting plate allows magma and
valuable minerals to rise up in fluids and erupt as volcanoes or cool beneath the surface as plutons. At
divergent plate boundaries, hydrothermal vents form. In these locations, seawater filters past hot
magma, picks up valuable elements, and then the hot fluids flow onto the seafloor and drop their
valuable elements. [pp. 53-54]
16. Draw a cross-section of an oceanic-oceanic convergent plate boundary. Show the directions of relative
plate motion. Put stars for the locations of earthquakes. Put triangles with smoke out the top for the
locations of volcanoes. Label the trench, back arc basin, and subduction complex.
Answer: See Figure 2.18a [p. 45]
17. What are four of the many things that plate tectonics theory explains?
Answer: Plate tectonics explains, at least to some extent, all of the following phenomena: the
distribution of earthquakes and volcanoes, the locations of ore deposits and mountain systems, climate
and ocean circulation patterns, and the geographic distribution, evolution, and extinction of life forms.
[p. 54]
18. Draw a cross-section of an ocean-continent convergent plate boundary. Show the directions of relative
plate motion. Put stars for the locations of earthquakes. Put triangles with smoke out the top for the
locations of volcanoes. Label the trench and subduction complex.
Answer: See Figure 2.18b [p. 45]
19. Draw a cross-section of a continental-continental convergent plate boundary. Show the directions of
relative plate motion. Put stars for the locations of earthquakes. Show the location of the mountain
range. Label the subduction complex.
Answer: See Figure 2.18c [p. 45]
20. Briefly explain how magnetic reversals in oceanic crust and fossils in ocean sediments are used to
construct a magnetic time scale.
Answer: A terrestrial sequence of magnetic reversal in volcanic deposits was dated radiometrically.
These dates were extrapolated to regions which were not dated, but showed the same pattern of normal
and reversed magnetic polarities. Ages of ocean-floor basalts lying within a zone of normal or reversed
polarity are dated by the ages of the fossils found in the sediments which directly overlie the basaltic
crust. These fossils have already been incorporated within a biostratigraphic zone. [p. 38]
21. Briefly explain how convection transfers heat.
Answer: When a material is heated, it expands, and its density decreases so it rises. After having risen
some distance, it begins to cool, contract, and become denser. Thus the material sinks and returns to
the original level where it will eventually be heated and rise again. [p. 51]
13
The Changing Earth: Exploring Geology and Evolution, 5e Test
Bank
Chapter 2: Test Bank
Note: Questions with an asterisk (*) denote appearance in web quiz (Tutorial Quiz)
Short Answer Essay Questions
1. What were the major lines of evidence for continental drift as presented by Wegener in the early 20 th
century?
Answer: The glaciations on the Gondwana continents could only have occurred if the continents were
joined since the centers of the glaciers would have been in the ocean if they were not. Also, the
continents, such as South America and Africa, match like a jigsaw puzzle. Similar fossil plant and
animals are separated by oceans leading to the assumption that they must have lived in adjacent regions
when they were alive. Finally, similar rock sequences and mountain ranges could be connected across
oceans. [pp. 31-35]
2. Explain how mountain ranges can be used as evidence to support continental drift.
Answer: A mountain range forms under the same geological conditions along its length. This means
that the same or nearly the same rock types are found along the range’s length in the same or nearly the
same sequence. The processes that form mountain ranges tend to create somewhat linear, elevated
features. So a mountain range that has been split, even if it has been separated by an ocean, is fairly
easy to recognize. [p. 32]
3. How does fossil evidence support continental drift?
Answer: The distribution of fossils is such that it would be impossible for the plants and animals not
to have lived in contiguous land areas. Glossopteris seeds are too heavy to be dispersed by wind and
would not have remained viable if they had traveled far across the oceans. The plants associated with
Glossopteris do not match the climate zones the fossils are found in. As for the animals, it’s hard to
imagine a freshwater reptile like Mesosaurus swimming across the Atlantic. And the land-dwelling
reptiles, Lystrosaurus and Cynognatuus, could not have swum at all! [p. 33]
4. What was the principal reason why Wegener's theory of continental drift was rejected?
Answer: Wegener lacked a plausible mechanism to explain how continental crust could move through
the sea floor. [p. 35]
5. Why were glacially deposited strata important in the development of continental drift theory?
Answer: The glacial deposits indicated that all southern continents must have been contiguous and
closer to the South Pole. Glaciers cannot form in the middle of an ocean, which is where they would
have originated if the continents were not together. [p. 33]
6. What are the three possible explanations for the distribution of paleomagnetic data?
Answer: (1) The continent remained fixed and the north magnetic pole moved; (2) the north magnetic
pole stayed still and the continent moved; (3) both the continent and north magnetic pole moved.
[p. 36]
11
,Chapter 2: Plate Tectonics: A Unifying Theme
7. Briefly explain why apparent polar wandering is "apparent."
Answer: Paleomagnetic studies of ancient rocks point to different locations for the North Pole at
different times. When this is mapped out, it makes the pole appear to wander over time. The
alternative to a wandering magnetic pole, for which there is no other evidence at all, is that the
continents move and with them the rocks that contain the paleomagnetic data. [p. 36]
8. Briefly explain why the movement of continents over geologic time was the best explanation for
polar wandering.
Answer: Since the Earth has only one magnetic north pole now, it was extremely unlikely that
there would have been more than one in the past, though this would have been required to explain
the different polar wander paths of the different continents. The only other possible explanation is
that the continents were once joined and have since moved apart. [p. 36]
9. What evidence is there that ocean basins are young and old oceanic crust must be destroyed?
Answer: The maximum age for oceanic crust is 180 million years, but the continents contain
rocks both younger and much older than 180 million years, so the older oceanic crust must go
somewhere. [p. 38]
10. Briefly describe what happens when divergent plate boundaries form within a continent.
Answer: High heat flow elevates the continent and a rift valley forms, with normal faults and a
central valley called a graben. Magma is intruded into fractures. As the plates diverge, basalt
erupts in the rift, creating new ocean crust. Ultimately, as the plates continue to diverge, a new
ocean basin forms. [p. 40]
11. Describe how the two models for the driving force of plate motion are the same. How are they
different?
Answer: Both models involve thermal convection in the mantle. In both models, where two
adjacent convection cells have upwelling limbs, there is a divergent plate boundary. Where there is
a descending limb of a convection cell, there is a convergent boundary. The models differ in the
location of the convection cells. In one, the convection cells are restricted to the asthenosphere. In
the other, the convection cells take up the entire mantle. [p. 52]
12. What are the heat sources for each of the two mantle convection models for plate tectonics?
Answer: With whole mantle convection, the heat source is the core. With convection only in the
asthenosphere, the heat source is harder to identify. [p. 52]
13. How does seafloor spreading explain the movement of the continents?
Answer: With seafloor spreading, the continents and oceanic crust move together as part of large
plates. The plate is pushed by the formation of new ocean crust and pulled by the subduction of
old ocean crust. New crust forms due to seafloor spreading. [p. 52]
14. In what ways does plate tectonics theory have economic applications?
Answer: By understanding the geologic history of a region, geologists can predict whether it will
be a worthwhile place to search for petroleum or ore deposits. [pp. 53-54]
12
, The Changing Earth: Exploring Geology and Evolution, 5e Test
Bank
15. Briefly explain the roles of magma and hydrothermal activity in forming ore deposits along convergent
and divergent plate boundaries.
Answer: Magma contains valuable elements, some of which leave the magma in gases and fluids.
These substances transport the elements and facilitate their exchange for other elements in the
surrounding rock. The surrounding rock may then have enough of the valuable elements to become an
ore deposit. At convergent plate boundaries, partial melting at the subducting plate allows magma and
valuable minerals to rise up in fluids and erupt as volcanoes or cool beneath the surface as plutons. At
divergent plate boundaries, hydrothermal vents form. In these locations, seawater filters past hot
magma, picks up valuable elements, and then the hot fluids flow onto the seafloor and drop their
valuable elements. [pp. 53-54]
16. Draw a cross-section of an oceanic-oceanic convergent plate boundary. Show the directions of relative
plate motion. Put stars for the locations of earthquakes. Put triangles with smoke out the top for the
locations of volcanoes. Label the trench, back arc basin, and subduction complex.
Answer: See Figure 2.18a [p. 45]
17. What are four of the many things that plate tectonics theory explains?
Answer: Plate tectonics explains, at least to some extent, all of the following phenomena: the
distribution of earthquakes and volcanoes, the locations of ore deposits and mountain systems, climate
and ocean circulation patterns, and the geographic distribution, evolution, and extinction of life forms.
[p. 54]
18. Draw a cross-section of an ocean-continent convergent plate boundary. Show the directions of relative
plate motion. Put stars for the locations of earthquakes. Put triangles with smoke out the top for the
locations of volcanoes. Label the trench and subduction complex.
Answer: See Figure 2.18b [p. 45]
19. Draw a cross-section of a continental-continental convergent plate boundary. Show the directions of
relative plate motion. Put stars for the locations of earthquakes. Show the location of the mountain
range. Label the subduction complex.
Answer: See Figure 2.18c [p. 45]
20. Briefly explain how magnetic reversals in oceanic crust and fossils in ocean sediments are used to
construct a magnetic time scale.
Answer: A terrestrial sequence of magnetic reversal in volcanic deposits was dated radiometrically.
These dates were extrapolated to regions which were not dated, but showed the same pattern of normal
and reversed magnetic polarities. Ages of ocean-floor basalts lying within a zone of normal or reversed
polarity are dated by the ages of the fossils found in the sediments which directly overlie the basaltic
crust. These fossils have already been incorporated within a biostratigraphic zone. [p. 38]
21. Briefly explain how convection transfers heat.
Answer: When a material is heated, it expands, and its density decreases so it rises. After having risen
some distance, it begins to cool, contract, and become denser. Thus the material sinks and returns to
the original level where it will eventually be heated and rise again. [p. 51]
13
