Deck 3: Drifting Continents and Spreading Seas

Question 1

Mid-ocean ridges tend to be

A) associated with the margins of continents.
B) roughly symmetrical about the ridge axis.
C) topographic lows on the ocean floor.
D) difficult to discern from the abyssal plains.

Answer 1

B

Question 2

Wegener's idea of continental drift was rejected by American geologists because

A) his English was too poor to be understood by them.
B) he could not conceive of a valid mechanism that would cause continents to shift positions.
C) he had relatively little evidence supporting the existence of a supercontinent.
D) the apparent fit of continental coastlines is blurred when the margins are defined by the edges of continental shelves rather than by sea level.

Answer 2

B

Question 3

Evidence that glaciers once covered an area might include

A) till and striations.
B) backwash and striations.
C) till and grabens.
D) backwash and grabens.

Answer 3

A

Question 4

Consult the figure below.Abundant swamps led to the formation of coal during the Late Paleozoic in which of the following places?

A) India
B) Southern Africa
C) North America
D) Antarctica

Question 5

If we mentally align the continents to fit Wegener's concept of Pangaea,evidence of Late Paleozoic glacial deposits

A) is more difficult to explain than in the modern continental configuration.
B) is much more readily explained than in the modern continental configuration.
C) makes very little sense in either the Pangaea configuration or the modern configuration.
D) is unchanged from the modern continental configuration.

Question 6

Wegener's proposal that the continents had once fit together as a single supercontinent was rejected by geologists at the time because

A) Wegener could not provide a driving force strong enough.
B) the continents did not fit together tightly enough.
C) the fossil evidence was inconclusive.
D) the distribution of climatic belts did not make sense in that configuration.

Question 7

Evidence that the South American and African continents were once joined includes evidence from their coastlines such as

A) shared anthropological evidence.
B) identical volcanic systems.
C) symmetrical earthquake patterns.
D) matching fossil distributions.

Question 8

As shown below,Wegener proposed continental drift after he observed evidence from fossils,glacial deposits,and the fit of the continents that suggested all of the continents were once

A) aligned north to south along the prime meridian.
B) aligned east to west along the equator.
C) combined to form a supercontinent he termed Rodinia.
D) combined to form a supercontinent he termed Pangaea.

Question 9

In Wegener's evidence for continental drift,continents were proposed to fit together,such as the east coast of South America with the

A) west coast of Europe.
B) east coast of Africa.
C) west coast of Greenland.
D) lower west coast of Africa.

Question 10

The broad flat regions that occupy most of the ocean floor are

A) abyssal plains.
B) continental rises.
C) fracture zones.
D) seamounts.

Question 11

Wegener saw Pangaea as a jigsaw puzzle,where the puzzle pieces were

A) oceans.
B) continents.
C) mid-ocean ridges.
D) plate tectonics.

Question 12

The term and concept of seafloor spreading was developed by

A) Hess and Dietz.
B) Hess and Wegener.
C) Wegener and Dietz.
D) Wegener.

Question 13

________ proposed the continental-drift hypothesis,suggesting that the arrangement of continents on the planet has changed over geologic time.

A) Harry Hess
B) Robert Dietz
C) Alfred Wegener
D) Harry Hess and Robert Dietz

Question 14

Which of these is NOT the result of plate tectonics?

A) continental movement
B) seafloor spreading
C) subduction
D) convection in the outer core

Question 15

Wegener's evidence for a united Pangaea comes from the fossil record of which type of organisms?

A) plant pollen
B) plankton
C) marine animals
D) land animals

Question 16

Distinctive rock sequences on South America terminate at the Atlantic Ocean but reappear on the continent of

A) Africa.
B) Europe.
C) North America.
D) Australia.

Question 17

Currently,most geologists

A) continue to reject continental drift.
B) agree that continental drift occurs,but they still do not understand why it occurs.
C) agree that continental drift occurs due to mechanisms at work in the ocean basins and upper mantle.
D) agree that continental drift occurs due to mechanisms at work in the lower mantle and outer core.

Question 18

Limestone reefs and salt deposits are important in the reconstruction of the Earth's history because they

A) can be used to infer the ancient climate of the Earth; they are deposited in environments that are restricted to warm climates.
B) automatically provide age information; all such deposits occurred between 200 and
400 million years ago.
C) are deposited in warm climates today,but there is good reason to think that they were deposited in cold climates millions of years ago.
D) pinpoint the locations of old subduction zones.

Question 19

Late Paleozoic glacial deposits are NOT found in which of the following places?

A) India
B) Southern Africa
C) North America
D) South America

Question 20

If a geologist discovered coal in a modern-day cold,snowy location,he or she could conclude that

A) a meteorite must have struck the area.
B) the area was once covered with swamps and/or jungles.
C) the area was once covered with an ocean.
D) this discovery was anomalous.

Question 21

Volcanoes that are submerged beneath the surface of the sea are termed

A) abyssal plains.
B) mid-ocean ridges.
C) fracture zones.
D) seamounts.

Question 22

Within the seafloor,the rate of geothermal heat flow is greatest

A) along mid-ocean ridges.
B) along fracture zones.
C) at the edges of ocean basins.
D) in the center of abyssal plains.

Question 23

If you were using both a compass and a map marked with latitude and longitude to navigate,you might note the angle difference between your compass and what is marked on the map,called

A) magnetic inclination.
B) magnetic declination.
C) magnetic dipole.
D) magnetic reversal.

Question 24

According to the figure below,what can be said about the ocean sediments at location B relative to location D?

A) They are thicker and younger.
B) They are thicker and older.
C) They are thinner and younger.
D) They are thinner and older.

Question 25

The majority of new oceanic crust is created

A) at subduction zones.
B) along fracture zones.
C) at mid-ocean ridges.
D) by ocean island volcanism.

Question 26

Deep-ocean trenches are found predominantly along the perimeter of the

A) Indian Ocean.
B) Pacific Ocean.
C) Atlantic Ocean.
D) Arctic Ocean.

Question 27

Beneath a blanket of sediments,oceanic crust is primarily composed of

A) granite.
B) basalt.
C) limestone.
D) coal.

Question 28

The thickness of clay and planktonic microskeletons is greatest

A) along mid-ocean ridges.
B) along fracture zones.
C) at the edges of ocean basins.
D) in the center of abyssal plains.

Question 29

The map below depicts earthquakes,which on the ocean floor coincide most often with

A) abyssal plains.
B) guyots.
C) mid-ocean ridges.
D) seamounts.

Question 30

The apparent tendency of the north (or south)magnetic pole to vary in position over time is termed

A) dipole.
B) magnetic declination.
C) magnetic inclination.
D) polar wander.

Question 31

Which of the following best describes the distribution of earthquakes?

A) They tend to occur randomly on the continents.
B) They tend to occur randomly in the ocean basins.
C) They tend to occur randomly both on the continents and in ocean basins.
D) They occur in distinct zones.

Question 32

Seafloor spreading occurs

A) along deep ocean trenches.
B) at mid-ocean ridges.
C) along fracture zones.
D) at subduction zones.

Question 33

The rate of seafloor spreading exactly matches the rate of

A) subduction.
B) ocean subsidence.
C) seafloor erosion.
D) magnetic declination.

Question 34

The polarity of the Earth's magnetic field in the geologic past is

A) unknown,but is assumed to have been identical to today's.
B) known to have stayed constant through geologic time,as shown by remnant magnetization of iron-rich minerals in rocks.
C) known to have experienced numerous reversals,as shown by remnant magnetization of iron-rich minerals in rocks.
D) known to have stayed constant through time,based on theoretical calculations.

Question 35

Continents passively move apart as a result of __________,and they passively move together as a result of __________.

A) subduction; seafloor spreading
B) declination; subduction
C) seafloor spreading; declination
D) seafloor spreading; subduction

Question 36

All deep-sea trenches border

A) fracture zones.
B) mid-ocean ridges.
C) volcanic arcs.
D) seamounts.

Question 37

Seafloor spreading is driven by volcanic activity

A) in the middle of abyssal plains.
B) along mid-ocean ridges.
C) at the edges of continental shelves.
D) along fracture zones.

Question 38

A great boost in seafloor exploration and a greater understanding of seafloor bathymetry were a result of

A) scientific advances in the 1950s.
B) scientific advances in the 1920s.
C) military needs during World War I.
D) military needs during World War II.

Question 39

With increasing distance from a mid-ocean ridge,the age of oceanic crust

A) increases.
B) decreases.
C) stays constant.
D) varies randomly.

Question 40

What is most likely to be found at fracture zones?

A) newly erupted oceanic crust
B) broad,flat,nearly featureless plains
C) broken-up rocks and vertical cracks
D) eroded remains of volcanic islands

Question 41

How do magnetic anomaly patterns on the ocean floor best serve as evidence for seafloor spreading?

A) The symmetry on either side of mid-ocean ridges shows that new crust is created and then split apart.
B) Their patterns prove that the Earth's magnetic field reverses every few hundred years.
C) They show that island arc volcanism creates new oceanic crust at the mid-ocean ridges.
D) The symmetry on either side of mid-ocean ridges shows that transform boundaries are sliding boundaries.

Question 42

Marine magnetic anomalies result from seafloor spreading in conjunction with

A) global warming.
B) magnetic storms on the surface of the Sun.
C) magnetic polarity reversals.
D) apparent wander of the magnetic poles.

Question 43

What evidence did Alfred Wegener use to support his continental-drift hypothesis? Was the evidence compelling? Why or why not?

Question 44

Regions of the sea floor with negative magnetic anomalies were formed during times when the Earth's magnetic field

A) was exceptionally strong.
B) was exceptionally weak.
C) had normal polarity.
D) had reversed polarity.

Question 45

Describe the process of seafloor spreading,making sure to address why the diameter of the Earth is not growing.

Question 46

What is paleomagnetism? How did the discovery of apparent polar-wander paths serve as a proof that continents move?

Question 47

Evidence of paleomagnetism can be found in

A) basaltic rocks.
B) ocean floor sediments.
C) continental sediments.
D) all rocks and minerals.

Question 48

Do earthquakes occur randomly? What bathometric features coincide with seismic activity?

Question 49

How does the observed pattern of marine magnetic anomalies form,and how does its existence help prove plate tectonics?

Question 50

Sketch a simplified cross-section of the ocean floor for both the Pacific and Atlantic Oceans.Be sure to label the mid-ocean ridge,abyssal plains,and deep-sea trenches.How are the Atlantic and Pacific Oceans different with regard to seafloor spreading? What tectonic process dominates in each ocean basin?

Question 51

What was Alfred Wegener's continental-drift hypothesis? What does this have to do with Pangaea?

Question 52

What does an ordinary compass indicate?

A) magnetic inclination
B) magnetic declination
C) magnetic north
D) true north

Question 53

What is a magnetic anomaly? What is the difference between a positive and negative anomaly?

Question 54

Marine magnetic anomaly belts run parallel to

A) mid-ocean ridges.
B) fracture zones.
C) continental coastlines.
D) continental shelves.

Question 55

Why wasn't Wegener's theory of continental drift originally accepted by geologists of his time?

Question 56

Describe patterns of sedimentation on the seafloor.What can be learned from this?

Question 57

According to the figure below,marine magnetic anomalies lay roughly ________ to mid-ocean ridges.

A) perpendicular
B) parallel
C) adjacent
D) at an obtuse angle

Question 58

The discovery that each continent had different and separate apparent polar-wander paths,such as those in the figure below,proved that

A) the continents move.
B) the poles move.
C) both the poles and continents move,but only one at a time.
D) both the poles and continents move,and do so together.

Question 59

According to the figure below,the Earth's magnetic poles move constantly.About how far from the geographic poles do the magnetic poles move?

A) They move as far south as the equator.
B) They move as far south as the tropics.
C) They remain in the high latitudes.
D) They remain less than a kilometer from the geographic poles.

Question 60

Regions of the sea floor with positive magnetic anomalies were formed during times when the Earth's magnetic field

A) was exceptionally strong.
B) was exceptionally weak.
C) had normal polarity.
D) had reversed polarity.