Deck 2: The Way the Earth Works: Plate Tectonics

Question 1

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

A)his research background in meteorology and glaciology disqualified him to study geology.
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 sea level.

Answer 1

B

Question 2

The discovery of seafloor spreading finally provided a mechanism for

A)subduction zones.
B)continental drift.
C)transgressions.
D)normal faulting.

Answer 2

B

Question 3

Which of the following was NOT used as evidence by Alfred Wegener to support his theory of continental drift?

A)fossils
B)matching mountain ranges
C)seismic waves
D)the "fit" of the continents

Answer 3

C

Question 4

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 5

Younger oceanic crust will have __________ ocean sediments, whereas older oceanic crust will have __________ oceanic sediments.

A)older; younger
B)carbonate; silicic
C)thicker; thinner
D)thinner; thicker

Question 6

Evidence that glaciers once covered an area might include

A)glacial striations.
B)glacial piles.
C)remnants of ice.
D)well-sorted sediment.

Question 7

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

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

Question 8

In the geologic past, the polarity of Earth's magnetic field is

A)unknown, but it 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 9

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 10

Which of the following is MOST true of the lithosphere?

A)It is composed of the crust and uppermost part of the mantle.
B)It is the same thing as the crust.
C)It is a very ductile layer in the upper part of the mantle.
D)It is the layer of the mantle directly below the asthenosphere.

Question 11

Marine magnetic anomalies can be used to estimate the

A)rate of seafloor spreading.
B)rate of seafloor subsidence.
C)age of the seafloor sediments.
D)rate of Earth's expansion.

Question 12

Late Paleozoic glacial deposits are NOT found in

A)India.
B)southern Africa.
C)North America.
D)South America.

Question 13

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)northeast coast of Africa.
C)west coast of Greenland.
D)southern west coast of Africa.

Question 14

Seafloor spreading occurs at __________ boundaries.

A)divergent
B)convergent
C)transform
D)transvergent

Question 15

Subduction zones occur at

A)hot spots.
B)divergent boundaries.
C)transform boundaries.
D)convergent boundaries

Question 16

Seafloor spreading

A)recycles old oceanic crust.
B)closes ocean basins.
C)creates new continental crust.
D)creates new oceanic crust.

Question 17

The Himalayan Mountains are the result of

A) subduction.
B) continental rifting.
C)continental collision.
D)hot spot activity.

Question 18

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 19

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 20

Globally, the rate of seafloor spreading takes place at the same rate as

A)ocean subsidence.
B)transgression.
C)subduction.
D)erosion of the seafloor.

Question 21

Deformed (bent, stretched, or cracked) lithosphere occurs

A)randomly over the surface of Earth.
B)primarily within the interiors of tectonic plates.
C)primarily on the margins of tectonic plates.
D)primarily at hot spots.

Question 22

Continental coastlines that occur within the interior of a tectonic plate are called __________ margins.

A)internal
B)passive
C)active
D)inert

Question 23

Using the image below, which marine magnetic anomalies show a reversed polarity?

A)A; D; E
B)A; B; F
C)B; C; F
D)C; D; F

Question 24

Compared with typical oceanic lithosphere, the thickness of continental lithosphere is

A)less.
B)greater.
C)approximately the same.
D)There is not a consistent pattern of lithospheric thickness.

Question 25

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

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

Question 26

Under the theory of plate tectonics, the plates themselves are

A)discrete pieces of lithosphere at the surface of the solid Earth that move with respect to one another.
B)discrete layers of lithosphere that are vertically stacked one atop the other.
C)composed only of continental rocks that plow through the weaker oceanic rocks.
D)very thick (approximately one-quarter of Earth's radius).

Question 27

Which of the following was NOT used as evidence for seafloor spreading?

A)high heat flow at mid-ocean ridges
B)jigsaw puzzle fit of the continents
C)progressive change in age of crust
D)changes in thickness of sediments

Question 28

The primary difference between lithospheric and asthenospheric mantle that gives rise to numerous different patterns of physical behavior is

A)physical state: the lithosphere is solid; the asthenosphere is liquid.
B)chemical composition: the lithosphere is mafic; the asthenosphere is felsic.
C)temperature: the lithosphere is cooler than the asthenosphere.
D)chemical composition: the lithosphere is felsic; the asthenosphere is mafic.

Question 29

Unlike the lithosphere, the asthenosphere

A) is able to flow over long periods.
B) has a density similar to the core.
C)varies in thickness from place to place.
D)is relatively cool.

Question 30

The theory of __________ states that the lithosphere is broken into a series of plates that move relative to each other.

A)plate drift
B)seafloor spreading
C)continental drift
D)plate tectonics

Question 31

Slab pull occurs because subducting slabs are __________ and therefore __________ than surrounding asthenosphere.

A)less mafic; less dense
B)cooler; more dense
C)hotter; more dense
D)cooler; less dense

Question 32

The distribution of __________ across the globe provides the primary indicator of boundaries between all tectonic plates.

A)mountain ranges
B)volcanoes
C)mid-ocean ridges
D)earthquakes

Question 33

A geologist aboard a deep-sea research vessel has collected several drill cores of oceanic crust from the bottom of the ocean. The cores are collected in order from east to west along the bottom of the basin and are labeled A1, B1, C1, and D1, respectively. Core A1 has 2.88 meters (m) of clay and siliceous ooze covering 4.86 m of pillow basalt. Core B1 has 2.37 m of muddy, clay ooze covering 3.57 m of basalt. Core C1 has 2.11 m of clay and siliceous ooze above 3.2 m of basalt. Core D1 has 1.87 m of siliceous ooze over 2.54 m of basalt. Which core is closest to the mid-ocean ridge?

A)A1
B)B1
C)C1
D)D1

Question 34

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

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

Question 35

At a subduction zone, the down-going (subducting) plate

A)is always composed of continental lithosphere.
B)is always composed of oceanic lithosphere.
C)may be composed of either oceanic or continental lithosphere.
D)is composed entirely of asthenosphere.

Question 36

The thickness of oceanic lithosphere is

A)nearly uniformly 100 km.
B)greatest at the geographic poles and least near the equator.
C)greatest near the mid-ocean ridges and thins out away from the ridges.
D)least near the mid-ocean ridges and thickens away from the ridges.

Question 37

The discovery of marine magnetic anomalies was so important to the theory of seafloor spreading because they

A)showed a record of marine fossils, which can be linked to geologic time.
B)proved that Earth's magnetic field reverses polarity throughout history.
C)showed an accurate record of the creation and movement of oceanic crust.
D)allowed geologists to record the amount of oceanic crust formed.

Question 38

According to the image below, where is new oceanic crust being formed?

A) A
B) B
C)C
D)D

Question 39

Which of these parts of the deep-ocean floor is flat and nearly featureless?

A)ridge axis
B)abyssal plain
C)guyot
D)trench

Question 40

Transform boundaries occur MOST commonly perpendicular to __________ boundaries in order to break the __________ into segments so as to accommodate motion on a sphere.

A)convergent; accretionary prisms
B)convergent; deep ocean trenches
C)divergent; mid-ocean ridges
D)divergent; magnetic anomalies

Question 41

The image below shows a view of a typical segmented mid-ocean ridge. Which letter below marks the location of the active transform fault?

A) A
B) B
C)C
D)D

Question 42

What happens when a continental plate meets an oceanic plate at a convergent boundary?

Question 43

Which basic type of plate boundary is shown in the image below?

A)divergent
B)convergent
C)transvergent
D)transform

Question 44

The rate of motion of a lithospheric plate with respect to a stationary location inside Earth is termed __________ plate velocity, whereas the motion of a plate with respect to another is termed __________ plate velocity.

A)absolute; relative
B)relative; absolute
C) Both absolute and relative plate velocity are measures of absolute velocity.
D) Both absolute and relative plate velocity are measures of relative velocity.

Question 45

What would happen if the rate of seafloor spreading was faster than the rate of subduction?

A) Arc volcanoes would not form.
B) The ocean basins would shrink.
C)The Earth would become smaller.
D)The Earth would grow larger.

Question 46

The mid-ocean ridges are elevated above the surrounding seafloor because

A)ridge rocks are hot and therefore have relatively low density.
B)the lithosphere is thickest at the ridges so they stand up taller.
C)rising ocean currents create a vacuum that pulls ridges up.
D)ridge rocks are mafic, which are less dense than ultramafic ocean basin rock.

Question 47

Consult the figure below. Hawaii is an example of

A)hot-spot volcanism.
B)mid-ocean ridge volcanism.
C)a volcanic island arc formed by subduction.
D)transform margin.

Question 48

Are ocean floors uniformly flat? Explain why or why not.

Question 49

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

Question 50

Compare the oceanic crust to the continental crust with respect to age. Why is this so?

Question 51

Which basic type of plate boundary is shown in the image below?

A)divergent
B)convergent
C)transvergent
D)transform

Question 52

Explain why Wegener's theory of continental drift was not originally accepted by geologists of his time.

Question 53

Seafloor spreading is MOST likely to occur at

A) convergent boundaries.
B) transform boundaries.
C)divergent boundaries.
D)hot spots.

Question 54

Discuss why transform boundaries are found in conjunction with divergent boundaries.

Question 55

At transform plate boundaries,

A)earthquakes are common but volcanoes are absent.
B)volcanoes are common but earthquakes do not occur.
C)both earthquakes and volcanoes are common.
D)neither earthquakes nor volcanoes are common.

Question 56

Hot spots can occur

A) only within continental plates.
B) only within oceanic plates.
C)within either continental or oceanic plates.
D)only when the thickness of the crust is less than 10 km.

Question 57

How can hotspot volcanoes be used to measure past plate velocities?

Question 58

Compare and contrast the lithospheric mantle and the asthenosphere compositionally and behaviorally. Why is this so?

Question 59

Plate tectonics theory is often referred to as the "unifying" theory in geology. Explain why plate tectonics is such an important theory to the study of Earth.