Deck 2: The Way the Earth Works: Plate Tectonics

Question 1

The age of oceanic crust ____________ with increasing distance from a mid-ocean ridge.

A) increases
B) decreases

Answer 1

A

Question 2

Wegener's evidence for a united Pangaea was so compelling that virtually all geologists agreed with the idea of continental drift during his lifetime.

Answer 2

False

Question 3

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 during the late Cenozoic
B) aligned east to west along the equator during the late Mesozoic through the Cenozoic
C) combined to form a supercontinent (he termed Rodinia) in the Proterozoic
D) combined to form a supercontinent (he termed Pangaea) in the late Paleozoic through the Mesozoic

Answer 3

D

Question 4

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; the mechanisms that drive drift are at work in the ocean basins and upper mantle and were unknown in Wegener's time
D) agree that continental drift occurs; the mechanisms that drive drift are at work in the lower mantle and outer core and were unknown in Wegener's time

Question 5

Within the sea floor,the rate of 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 6

Regions of the sea floor 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 7

Regions of the sea floor with negative 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

The apparent polar-wander paths for continents that were not connected over some span of geologic history will likely ____________ concerning the positions of the ancient magnetic pole.

A) agree
B) disagree

Question 9

Marine magnetic anomaly belts run parallel to ____________.

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

Question 10

The apparent polar-wander path obtained from magnetite crystals in basalts on the North American continent is now interpreted to be the result of ____________.

A) wandering of the geomagnetic north pole
B) drifting of the North American continent

Question 11

Which plant genus dominated glaciated regions during the late Paleozoic and early Mesozoic?

A) Ginkgo
B) Glossopteris
C) Neuropteris
D) Quercas

Question 12

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

Question 13

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 at sea level

Question 14

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 15

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 16

Sea-floor 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 17

Marine magnetic anomaly belts are widest when and where ____________.

A) continents are joined to form supercontinents
B) sea-floor spreading rates are relatively rapid
C) sea-floor spreading rates are relatively slow

Question 18

The magnetic field of Earth in the geologic past is ____________.

A) unknown, but it is assumed to have been identical to today's
B) known to have been constant through geologic time, due to remnant magnetization of iron-rich minerals in rocks
C) known to have experienced numerous polarity reversals, due to remnant magnetization of iron-rich minerals in rocks
D) known to have been constant through time, on the basis of theoretical calculations

Question 19

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 20

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 21

Beneath a blanket of sediments,oceanic crust is primarily composed of two rocks,____________.

A) granite and diorite
B) gabbro and basalt
C) sandstone and shale
D) slate and gneiss

Question 22

Broad,sediment-covered continental shelves are found along ____________.

A) active margins
B) passive margins

Question 23

Unlike the lithosphere,the asthenosphere ____________.

A) is relatively weak and flows readily
B) has a density similar to the core
C) varies in thickness from place to place
D) is relatively cool

Question 24

Marine magnetic anomalies result from sea-floor 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 25

Tectonic plates move at rates that are approximately ____________.

A) 1 to 5 cm every 1,000 years
B) 1 to 15 cm/year
C) 1 to 15 m/year
D) 10 to 100 m/year

Question 26

All basalts younger than 700,000 years old ____________.

A) have normal magnetic polarity
B) have reverse magnetic polarity
C) are found on the ocean floor very far from mid-ocean ridges
D) are found on the continents

Question 27

The thickness of oceanic lithosphere is ____________.

A) 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 28

Continental lithosphere ____________.

A) is thicker than oceanic lithosphere
B) contains more mafic rocks than oceanic lithosphere
C) is denser than oceanic lithosphere
D) contains no crustal material, consisting solely of lithified upper mantle

Question 29

The primary difference between lithospheric and asthenospheric mantle that gives rise to numerous divergent patterns of physical behavior,is ____________.

A) physical state (the lithosphere is solid, and the asthenosphere is liquid)
B) chemical composition (the lithosphere is mafic, and the asthenosphere is felsic)
C) temperature (the lithosphere is cooler than the asthenosphere)
D) chemical composition (the lithosphere is felsic, and the asthenosphere is mafic)

Question 30

The oldest sediments on the ocean floor are about ____________ years old.

A) 50 thousand
B) 4 billion
C) 200 million
D) 2.5 million

Question 31

Every plate boundary can be recognized by ____________.

A) the presence of active volcanoes
B) the presence of an earthquake belt
C) a deep chasm which can be seen from space
D) none of the above

Question 32

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

Question 33

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, which plow through the weaker oceanic rocks
D) very thick (approximately one-quarter of Earth's radius)

Question 34

At a divergent plate boundary,two opposed plates ____________.

A) move toward one another
B) move away from one another
C) slide past one another

Question 35

The deep ocean floor is flat and nearly featureless.

Question 36

Tectonic plates might consist of ____________.

A) continental lithosphere only
B) oceanic lithosphere only
C) oceanic or continental lithosphere or a combination of both
D) either oceanic or continental lithosphere, but not both

Question 37

The average thickness of continental lithosphere is about ____________.

A) 30 km
B) 60 km
C) 150 km
D) 10,000 km

Question 38

The theory of plate tectonics ____________.

A) incorporates continental drift but not sea-floor spreading
B) incorporates sea-floor spreading but not continental drift
C) incorporates and explains both sea-floor spreading and continental drift
D) does not incorporate sea-floor spreading or continental drift

Question 39

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

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

Question 40

In the terminology of plate tectonics,an active margin is ____________.

A) synonymous with "subduction zone"
B) a 5-mile radius surrounding an active volcano
C) a continental coastline that coincides with a plate boundary
D) anywhere on Earth where earthquakes are especially frequent

Question 41

A triple junction is a place on Earth's surface where ____________.

A) three volcanoes form a tight, triangular cluster
B) glacial ice, continental rocks, and the ocean can be found together
C) the boundaries of three lithospheric plates meet at a single point
D) the boundaries of three lithospheric plates meet to form an elongate surface

Question 42

The mid-ocean ridges are elevated above the surrounding sea floor because ____________.

A) ridge rocks are hot and therefore of relatively low density
B) the lithospheric plates are thickest at the ridges so they stand up taller
C) rising ocean currents leave a vacuum above the ridge
D) ridge rocks are mafic, whereas the ocean basin crust consists of ultramafic rock

Question 43

Most of the pulling force that drives plate motion is produced ____________.

A) at mid-ocean ridges
B) at subduction zones
C) at collision zones
D) in the interiors of continental plates

Question 44

At a subduction zone,the downgoing (subducting)plate ____________.

A) is always composed of continental lithosphere
B) is always composed of oceanic lithosphere
C) may be composed or either oceanic or continental lithosphere

Question 45

All lithospheric plates are approximately the same size and contain a combination of oceanic and continental crust.

Question 46

The Wadati-Benioff zone extends down within the mantle to a maximum depth of ____________.

A) 30 km
B) 150 km
C) 670 km
D) 990 km

Question 47

Oceanic lithosphere thickens away from the mid-ocean ridge primarily due to ____________.

A) the addition of new crust due to hot-spot volcanism
B) the addition of new crust due to sedimentation
C) the addition of new lithospheric mantle as a result of cooling
D) reasons that geologists cannot determine at present

Question 48

When two bodies of continental lithosphere are pushed together at a convergent boundary,the result is ____________.

A) subduction
B) collision and mountain formation

Question 49

At a subduction zone,the overriding 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

Question 50

At a transform plate boundary,two opposed plates ____________.

A) move toward one another
B) move away from one another
C) slide past one another

Question 51

Mid-ocean ridges are ____________.

A) convergent plate boundaries
B) divergent plate boundaries
C) transform plate boundaries

Question 52

Subduction zones are ____________.

A) convergent plate boundaries
B) divergent plate boundaries
C) transform plate boundaries

Question 53

The Wadati-Benioff zone is a belt of earthquakes found ____________.

A) within an otherwise stable continental interior
B) within an overriding plate at a subduction zone
C) within a downgoing plate at a subduction zone
D) along mid-ocean ridges

Question 54

Hawaii is an example of ____________.

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

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

Question 56

Segments of the mid-ocean ridge system are offset.Between the offset segments we observe ____________.

A) a second series of ridges, perpendicular to the main set
B) deep-ocean trenches
C) transform faults
D) None of the above is correct.

Question 57

As compared to a slowly spreading mid-ocean ridge,a rapidly spreading ridge is ____________.

A) wider
B) narrower
C) more silicic in lava composition

Question 58

Most of the pushing force that drives plate motion is produced ____________.

A) at mid-ocean ridges
B) at subduction zones
C) at collision zones
D) in the interiors of continental plates

Question 59

The youngest sea floor occurs ____________.

A) along passive margins
B) along active margins
C) along mid-ocean ridges
D) randomly over the entire ocean basin

Question 60

At a convergent plate boundary,two opposed plates ____________.

A) move toward one another
B) move away from one another
C) slide past one another