Deck 8: The Theory of Plate Tectonics

Question 1

Reverse and normal magnetization of the seafloor was first discovered by British geophysicists in the __________.

A) Atlantic Ocean
B) Indian Ocean
C) Pacific Ocean
D) Gulf of Mexico

Answer 1

B

Question 2

Alfred Wegener envisioned a supercontinent of the past called

A) Laurasia.
B) Pangaea.
C) Gondwanaland.
D) Antarctica.

Answer 2

B

Question 3

In Hess's concept of plate tectonic movement, continental rifts were explained as the location of

A) former seamounts and guyots.
B) upwelling limbs of two adjacent convective cells in the mantle.
C) newly formed crust.
D) a descending conveyor belt-like feature.

Answer 3

B

Question 4

Lystrosaurus is an extinct, heavy-set, herbivorous animal with beak-like jaws that played a role in support of the contention that __________ was part of Gondwanaland.

A) Africa
B) Brazil
C) Antarctica
D) India

Question 5

What sort of fossil is Glossopteris?

A) Large reptile
B) Small reptile
C) Plant
D) Fungus

Question 6

In Hess's concept of plate tectonic movement, the deep furrow that runs along the center of the mid-ocean ridges represents

A) convective cells of the mantle.
B) the site of newly formed crust that is moving laterally in two directions.
C) the site of apparent polar wandering and deep mantle convection.
D) the effect of low-velocity earthquake waves.

Question 7

The theory of plate tectonics helps to explain why

A) Earth's ocean basins are among the oldest features of the planet.
B) most volcanoes occur along curved belts of seafloor.
C) mountain belts almost invariably occur near the centers of continents.
D) earthquakes are randomly distributed throughout Earth's crust.

Question 8

Today, Earth's magnetic pole has a declination of about __________ degrees from the geographic pole.

A) 0
B) 7
C) 14
D) 21

Question 9

The key to Harry Hess's initial understanding of the young age of the seafloor lay is in the measurement of

A) the rate of sediment deposition in the deep sea.
B) high rates of heat flow.
C) seismic waves from earthquakes.
D) the average thickness of sediment on the seafloor.

Question 10

The Gondwana sequence of Carboniferous tillites and interglacial coals, Permian dark shales, Triassic dune deposits, and Jurassic lava flows is best preserved in

A) Africa.
B) Brazil.
C) Antarctica.
D) India.

Question 11

A deep-focus earthquake originates more than __________ kilometers below Earth's surface.

A) 3000
B) 300
C) 30
D) 3

Question 12

Select the evidence NOT cited by Alexander Du Toit from the list below regarding evidences that have been cited in support of the former existence of Gondwanaland.

A) Age and distribution of Mesosaurus in Brazil and South Africa
B) Trans-Atlantic matching regional trends of rock deformation and mountain belts
C) Occurrence of Glossopteris beyond South America, South Africa, India, and Antarctica
D) Age and orientation of glacial scour features in South America and elsewhere

Question 13

Strong support for Hess's concept of widening seafloors came in the 1960s when it was recognized that the pattern of Late Cenozoic magnetic reversals determined in terrestrial rocks was also evident also in rock of the seafloor in the form of

A) guyots and seamounts, which tended to cluster around mid-ocean ridges.
B) symmetrical patterns of magnetic striping surrounding mid-ocean ridges.
C) normal magnetization of mid-ocean ridges and reverse magnetization of other seafloor.
D) a constant rate of seafloor spreading throughout the long span of geological time.

Question 14

The non-plate tectonics interpretation of paleomagnetic data referred to as ___________ eventually helped geophysicists conclude that continents had changed position over time.

A) apparent polar wander
B) declination and inclination
C) rock magnetism
D) geopoetry

Question 15

Before plate tectonics was accepted, some geologists invoked the concept of __________ to explain the similarities of some fossil plants and animals between and among continents, which were separated by oceans.

A) repositioning
B) continental drift
C) ancient land bridges
D) corridors of felsic rock

Question 16

Select the item below that was NOT cited by Hess cited in support for his concept of very young seafloors.

A) Deep-sea trenches
B) Truncation of seamounts on a descending conveyor belt
C) Relatively small number of volcanic seamounts on Earth
D) Paleomagnetic striping of the seafloor

Question 17

Studies of paleomagnetism are focused on

A) previous positions of Earth's magnetic pole.
B) the long-term stability of Earth's magnetic field.
C) magnetization of ancient rocks at the time of their formation.
D) the formation of guyots and seamounts.

Question 18

A guyot is a

A) convective cell in Earth's mantle.
B) furrow down the center of a mid-ocean ridge.
C) a flat-topped seamount on the deep-sea floor.
D) name for all kinds of volcanic seamounts.

Question 19

In Hess's model of plate tectonics, the moving seafloor is swallowed up again by the mantle along

A) guyots.
B) trenches.
C) ridges.
D) furrows.

Question 20

The difference in seismic velocity above versus below the Moho at a distance from the mid-ocean ridge that has a lower temperature and where most fractures have healed is __________ km/sec.

A) 2.4
B) 1.7
C) 1.4
D) 0.7

Question 21

The Hawaiian Islands owe their existence to the process of volcanism that is directly related to

A) plate tectonics.
B) subduction.
C) a hot spot.
D) transform faulting.

Question 22

In contrast to younger eras, the detailed history of plate tectonic movements is only moderately well known for

A) Cenozoic.
B) Cretaceous.
C) Jurassic.
D) Paleozoic.

Question 23

__________ is the name of the entire body of rocks formed by piling up along huge thrust faults at subduction zones.

A) Accretionary wedges
B) Forearc basins
C) Island arcs
D) Mélanges

Question 24

Faulting at the deep furrows along the crest of a mid-ocean ridge takes the form of a

A) graben.
B) strike-slip fault.
C) thrust fault.
D) transform fault.

Question 25

Slabs of descending plate that break away may descend eventually to a maximum depth within the Earth of the

A) base of the asthenosphere.
B) core-mantle boundary.
C) upper part of the outer core.
D) inner core.

Question 26

The Gauss interval (or chron) of Earth's magnetic history spans about __________ million years and consists of __________.

A) 1.0; normally magnetized rocks only
B) 1.0; mainly normally magnetized rocks but with a brief interval of reversed magnetization near the middle of the interval
C) 0.3; reversely magnetized rocks only
D) 0.3; mainly reversely magnetized rocks but with a brief interval of normal magnetization near the middle of the interval

Question 27

The sinking of the downgoing slab that is attached to the larger crustal plate causes

A) transform faults to form between plates.
B) convective motion in the asthenosphere.
C) dragging down of the rest of the plate.
D) the plate to be pushed apart in two opposite directions.

Question 28

Which of the following is NOT typically associated with a subduction zone?

A) Island arc
B) Mélange
C) Trench
D) Normal fault

Question 29

The difference in age between the northern Hawaiian island (Kauai) and the southern island (Hawaii) is at least __________ million years.

A) 5.6
B) 4.6
C) 3.6
D) 2.6

Question 30

__________ faults form because pressures are uneven along ridges and some segments of newly formed crust break away from others that move less rapidly away from the ridge axis.

A) Transform
B) Thrust
C) Normal
D) Strike-slip