Chapter 21 Plate Tectonics and Earth's Interior
21.1 Seismic Waves
1) The speed of a seismic wave depends on
A) the type of material it travels through.
B) how far it has to travel.
C) its amplitude.
D) its frequency.
Answer: A
2) Seismic waves are classified as body waves and surface waves. An example of a body wave is
a
A) Primary wave (P-wave).
B) Love wave.
C) Rayleigh wave.
D) Tertiary wave (T-wave).
Answer: A
3) Motion in a P-wave is
A) side to side.
B) transverse.
C) longitudinal.
D) up and down.
Answer: C
4) The fastest seismic wave is a
A) Primary wave.
B) Secondary wave.
C) Tertiary wave.
D) Rayleigh wave.
Answer: A
5) Earthquake P-waves
A) travel in straight lines through Earth's core.
B) cannot propagate through Earth's core.
C) are transverse vibrations similar to sound waves.
D) are longitudinal vibrations similar to sound waves.
Answer: D
6) A seismograph
A) predicts earthquakes.
B) measures ground movement.
C) helps prevent earthquakes.
D) measures fault displacement.
Answer: B
7) Secondary waves can travel through all areas of Earth except the
A) surface.
B) outer core.
C) inner core.
D) mantle.
Answer: B
8) The propagation of seismic waves through Earth's interior provides evidence of internal
layering. The first boundary discovered was between the
A) upper and lower mantle.
B) inner and outer core.
C) outer core and the mantle.
D) mantle and the crust.
Answer: D
9) An Earthquake occurs as
A) seismic waves travel to Earth's surface.
B) energy released from Earth's interior travels to Earth's surface.
C) energy released at Earth's surface travels to Earth's interior.
D) seismic waves travel to Earth's interior.
E) energy released from Earth's interior travels in the form of seismic waves to Earth's surface.
Answer: E
10) Earth's internal layers were discovered by studying
A) seismic waves.
B) the Mohorovicic discontinuity.
C) Rayleigh and Love waves.
D) convection cells.
Answer: A
11) Earth's internal layers were discovered by studying the propagation of P- and S- waves
through Earth's interior. In comparison to S-waves, the movement of P-waves is
A) fast, compressing and expanding the rock as they move through it.
B) fast, vibrating the rock particles up and down and side-to-side.
C) slower and can travel through solid granite, magma, water or air;
D) slower and can travel only through solids, not liquids.
Answer: A
12) Earth's internal layers were discovered by studying the propagation of P- and S- waves
through Earth's interior. In comparison to P-waves, the movement of S-waves are
A) faster and compresses and expands the rock as they move through it.
B) faster and vibrates rock particles up and down and side-to-side.
C) slower and can travel through solid granite, magma, water or air;
D) slower and they can only travel through solids, not liquids.
Answer: D
13) In comparison to P-waves, S-waves
A) compress and expand the rock as they move through it.
B) can travel through all mediums–solid granite, magma, water and/or air.
C) can travel only through solids—not in fluids.
D) are fast and the first to register on a seismograph.
Answer: C
14) In comparison to S-waves, P-waves
A) vibrate the particles of their medium up and down and side-to-side.
B) can travel through solid granite, magma, water and/or air.
C) can travel only through solids, not through fluids.
D) are the second seismic wave to register on a seismograph.
Answer: B
15) In comparison to S-waves, P-waves
A) cannot travel through solids, they only travel through fluids.
B) are the fastest of all seismic waves and the first to register on a seismograph.
C) are the second to register on a seismograph.
D) all of the above.
Answer: B
16) How can the location and the strength of an earthquake be determined?
Answer: The location and strength of an earthquake can be determined by comparing the
different types and arrival times of seismic waves recorded on a seismograph. Better accuracy is
achieved when several seismograph stations are used.
17) What are the two major kinds of waves an earthquake produces?
Answer: Body waves and surface waves. Body waves travel through Earth's interior and surface
waves travel on Earth's surface.
18) Body waves can be divided into two types–primary waves and secondary waves. What is the
difference between these two types of body waves?
Answer: Primary waves, as their name suggests, are the first to register on a seismograph. Pwaves are fast, longitudinal waves that move out in all directions from their source. Because both
solids and liquids respond to compressional/expansional movement, P-waves can travel through
any type of material. Secondary waves are slower than P-waves; as such they are the second to
register on a seismograph. S-waves are transverse; they vibrate in an up-down, side-to-side
fashion. Because liquids cannot support this type of movement, S-waves cannot travel through
liquids.
19) Compare the relative speeds of primary and secondary seismic waves, and relate speeds of
travel to the medium in which the waves travel.
Answer: The speed of a wave depends on the type of material it travels through. P-waves
(primary waves) are the fastest seismic waves and travel through all mediums: air, solids, and
fluids. The denser the material, the faster the movement. S-waves (secondary waves) are slower
and can only travel through solids.
21.2 Earth's Internal Layers
1) Which seismic waves produce a wave shadow?
A) P-waves.
B) Love waves.
C) S-waves.
D) P- and S- waves
Answer: D
2) P-waves travel faster through the inner core than the outer core because the inner core is
A) hotter than the outer core.
B) the same as the outer core.
C) rock.
D) solid.
Answer: D
3) The Mohorovicic discontinuity marks the change in rock density elasticity between the
A) inner and outer core.
B) core and the mantle.
C) mantle and the crustal surface.
D) asthenosphere and lithosphere.
Answer: C
4) Because S-waves do not travel through Earth's outer core, scientists inferred that the outer
core is
A) impenetrable.
B) molten liquid.
C) solid.
D) very dense.
Answer: B
5) Evidence to support the fact that Earth's central core is solid can be attributed to
A) a decrease in S-wave velocity as they encounter and move through the inner core.
B) an increase in P-wave velocity as they encounter and move through the inner core.
C) a decrease in P-wave velocity as they encounter and move through the inner core.
D) an increase in S-wave velocity as they encounter and move through the inner core.
Answer: B
6) The Earth's magnetic field is attributed to the
A) flow of molten liquid in Earth's inner core.
B) flow of molten fluid in Earth's outer core.
C) movement of lithospheric plates in the outer mantle.
D) movement of lithospheric plates at Earth's surface.
Answer: B
7) Earth's magnetic field is not stable; throughout geologic time it has changed direction. This
change is attributed to
A) changes in the direction of fluid flow in the molten outer core of Earth.
B) magnetic pole reversals.
C) fluctuations in the time / space continuum.
D) changes in the direction of fluid flow in the molten inner core of Earth.
Answer: A
8) The outer core is
A) rock.
B) plastic.
C) liquid.
D) the source for volcanoes.
Answer: C
9) The asthenosphere is part of the
A) crust.
B) lithosphere.
C) mantle.
D) outer core.
Answer: C
10) Continental crust is
A) thinner than oceanic crust.
B) less dense than oceanic crust.
C) more dense than oceanic crust.
D) thinner and more dense than oceanic crust.
Answer: B
11) The mantle can be separated into two different portions: the lower mantle and the upper
mantle. The lower mantle is
A) completely solid due to extreme pressure that prevents iron-rich silica rocks from melting.
B) composed of silly putty that flows like molasses.
C) rigid and has no capability of flow.
D) predominantly liquid silica.
Answer: A
12) The upper mantle can be divided into two portions, the
A) asthenosphere (lower zone of the upper mantle) and part of the lithosphere (the top zone of
the upper mantle).
B) asthenosphere (top zone of the upper mantle) and the lithosphere (the lower upper mantle).
C) Moho and the lithosphere.
D) continental mantle and the oceanic mantle.
Answer: A
13) We can say that Earth's crust floats on the mantle because
A) the mantle is very hot and flows from internal convection.
B) part of the mantle is hot enough to flow as a plastic solid.
C) the continental crust floats on the oceanic crust.
D) the mantle is below the crust.
Answer: B
14) Continental crust extends farther down into the mantle than oceanic crust because
A) it is thicker than oceanic crust.
B) oceanic crust is buoyant and rides atop the mantle.
C) it is heavier than oceanic crust.
D) it sinks into the mantle and asthenosphere.
Answer: A
15) The lithosphere includes
A) continental and oceanic crust.
B) the crust and the upper part of the mantle.
C) part of the mantle and the crust.
D) continental and oceanic crust and the upper part of the mantle.
Answer: D
16) The lithosphere rides on top of the asthenosphere. Lithospheric movement causes
A) earthquakes, volcanic activity, and mountain building activity.
B) the subduction of continental crust under oceanic crust.
C) hot-spot activity as found in Hawaii.
D) widespread destruction.
Answer: A
17) The thickness of Earth's crust
A) varies from 10 km under the continents to 60 km under the oceans.
B) on average is about 10 km.
C) on average is about 60 km.
D) varies from 10 km under the oceans to 60 km under the continents.
Answer: D
18) The Mohorovicic discontinuity was discovered by observing
A) earthquake movement at Earth's surface.
B) seismograms of an earthquake.
C) changes in rock density.
D) all of these
Answer: B
19) The Mohorovicic discontinuity occurs because of a
A) change in temperature with depth.
B) shift in the density of minerals with the same composition.
C) change in the composition of rocks on both sides of the boundary.
D) density change in rocks of the same composition on both sides of the boundary.
Answer: C
20) The outer core
A) has a plasticlike flow.
B) flows fast enough to power Earth's magnetic field.
C) is solid as a rock.
D) transmits S-waves.
Answer: B
21) The Earth's layer with plastic-like behavior is the
A) mantle.
B) crust.
C) inner core.
D) outer core.
Answer: A
22) Earth's core is probably composed of
A) silicate minerals.
B) aluminum oxides.
C) an iron-nickel alloy.
D) calcium magnesium sulfate.
Answer: C
23) Evidence to support that the inner core is solid and the outer core is liquid comes from
A) refraction of seismic waves as they encounter different mediums.
B) the wave shadow effect of P- and S-waves as they encounter the solid and liquid core.
C) the wave shadow effect of P- and S-waves, and the increase in velocity of P-waves as they
encounter the solid inner core.
D) the inner core is not solid, but is liquid.
Answer: C
24) The inner core is solid because
A) it is composed of iron and nickel.
B) the surrounding outer layers act as a blanket to insulate the core.
C) pressure from the weight of the surrounding layers prevents the inner core from melting.
D) none of these, for the inner core is not solid, but is liquid
Answer: C
25) The outer core is liquid because
A) it is magnetically charged, and, like a magnet, energy flows from one region to another.
B) the inner core is solid.
C) there is less weight, and thus less pressure on it.
D) it is composed of molten iron.
Answer: C
26) The outer core is thought to be molten because it
A) is denser than the inner core.
B) will not transmit P-waves.
C) is made of iron and nickel.
D) will not transmit S-waves.
Answer: D
27) The primary evidence that the outer core is molten is an abrupt
A) increase in the velocity of P-waves, but no increase in S-waves.
B) increase in the velocity of L-waves.
C) stop of S-wave propagation, and a decrease in P-wave velocity.
D) stop of P-wave propagation, and a decrease in S-wave velocity.
Answer: C
28) The Earth's magnetic field is generated in
A) outer space.
B) the crust.
C) the mantle.
D) the outer core.
Answer: D
29) The mantle is composed of
A) iron and nickel.
B) iron-rich silicate rocks.
C) half liquid and half rocky material.
D) solid rock.
Answer: B
30) The upper mantle is the region known as the
A) asthenosphere.
B) lithosphere.
C) mohorovicic.
D) centrosphere.
Answer: A
31) Thermal convection movement in the upper mantle
A) generates the electric current that powers Earth's magnetic field.
B) greatly influences Earth's surface features.
C) heats Earth's core by frictional forces.
D) is usually negligible.
Answer: B
32) The crustal surface and the uppermost part of the mantle is called the
A) asthenosphere.
B) lithosphere.
C) mohorovicic.
D) centrosphere.
Answer: B
33) The lithosphere floats atop the
A) mantle.
B) crust.
C) asthenosphere.
D) mohorovicic.
Answer: C
34) Movement of the lithosphere
A) has a plasticlike flow.
B) causes earthquakes and volcanic activity.
C) has a leisurely pace and allows the formation of gentle rolling hills.
D) is intermittent.
Answer: B
35) The top of the mantle is the same as the
A) base of the core.
B) base of the lithosphere.
C) top of the asthenosphere.
D) base of the crust.
Answer: D
36) The Earth's lithosphere
A) is the same as the crust.
B) consists of the crust and the asthenosphere.
C) is the same as the mantle.
D) consists of the crust and the uppermost part of the mantle.
Answer: D
37) Isostasy is
A) crustal equilibrium relative to the mantle.
B) the buoyant force exerted on the mantle by oceanic crust.
C) the buoyant force exerted on the mantle by continental crust.
D) crustal equilibrium relative to Earth's surface.
Answer: A
38) Compared with oceanic crust, continental crust is very buoyant because it is
A) composed of basaltic rock that contains air bubbles from successive lava flows.
B) composed of granitic rocks whereas oceanic crust is composed of basaltic rocks.
C) thinner and forms a thin upper skin on the oceanic crust below.
D) very young and fresh.
Answer: B
39) The crustal surface varies in
A) composition, density, and thickness.
B) isostasy, density, and rock competence.
C) thickness–the oceanic crust is thinner than the continental crust.
D) density–the oceanic crust is heavier than the continental crust.
Answer: A
40) What is the evidence for Earth's central core being solid?
Answer: Earth's solid central core is revealed by the differences in P- and S-wave propagation
through Earth's interior. As these waves encounter the boundary at 2900 km, a very pronounced
wave shadow develops. P-waves are both reflected and refracted at the boundary, but S-waves
are only reflected. S-waves cannot travel through liquids, implying a liquid outer core. As Pwaves move through the outer core, there is a depth at which there is a sudden increase in speed.
The faster traveling wave indicates a solid inner core.
41) Does the fact that the mantle is beneath the crust necessarily mean that the mantle is denser
than the crust? Explain.
Answer: The differential separation of elements during Earth's formation resulted in heavier
elements migrating toward the center of the planet and lighter elements floating to the surface.
So yes, the greater density of the mantle contributes to its position beneath the crust.
42) What is the principle of isostasy, and what evidence supports it?
Answer: The principle of isostasy is the state of equilibrium between the buoyant force of the
asthenosphere and the downward force of gravity. The lithosphere floats on the denser mantle.
Because the pressure exerted on the mantle by the lithosphere must be the same at any given
depth, the lithosphere adjusts its position until a state of equilibrium is achieved. The thicker (but
less dense) continents stand higher on Earth's surface and extend deeper into the mantle than the
thinner (but more dense) ocean basins. Seismic waves reveal the extension of continental and
oceanic crust into the mantle.
43) How does erosion and wearing away of a mountain affect the depth to which the crust
extends into the asthenosphere?
Answer: Just as shaving off the top of an iceberg would lighten the iceberg, and cause it to float
higher, the erosion and wearing away of mountains lightens them and causes them to float higher
on the asthenosphere.
21.3 Continental Drift–An Idea Before It's Time
1) The theory of continental drift is supported by paleoclimate data, paleontology, and
A) paleomagnetic data.
B) seafloor spreading.
C) transform boundaries.
D) the jig-saw fit of the continents at their continental margins.
Answer: D
2) In a reconstruction of Earth's geologic past, the continents of Africa and South America fit
best along the
A) shorelines.
B) continental shelves.
C) continental slopes.
D) ocean floors.
Answer: B
3) Which of the following did Alfred Wegener NOT use to support his theory of continental
drift?
A) Paleoclimate data.
B) Similar fossils on widely separated continents.
C) Paleomagnetic data.
D) Similar rocks on widely separated continents.
Answer: C
4) The theory of continental drift is attributed to
A) H.H. Hess.
B) Alfred Wegener.
C) W. Loma Prieta.
D) Simon Tectonic.
Answer: B
5) Wegener's theory of continental drift
A) was first considered a monumental breakthrough in science.
B) was not accepted by the scientific community of the early 1900's.
C) proved that heat flows convectively below Earth's surface .
D) has been proved wrong.
Answer: B
6) Alfred Wegener supported his theory of continental drift by
A) fitting together the shorelines of the African and South American continents.
B) using paleoclimatic data–evidence of glaciers in the Northern Hemisphere.
C) paleomagnetic data.
D) making a connection between rocks, rock structures, and plant and animal fossils found in
both Africa and South America.
Answer: D
7) The theory of continental drift is supported by paleoclimatic data, the jig-saw fit of the
continents
A) paleontology, and paleomagnetic data.
B) and seafloor spreading.
C) transform boundaries, and paleontology.
D) at their continental margins, and paleontology.
Answer: D
8) What evidence did Wegener use to support his hypothesis of continental drift?
A) sea-floor spreading
B) paleoclimatic data
C) polar reversals
D) transform fault boundaries
Answer: B
9) How did plant and animal fossils influence the theory of continental drift?
Answer: Similar plant and animal fossils found in both South America and Africa provided
evidence that the two continents had at one time been connected together. This is especially true
of the fossil plant Glossopteris, which had very large seeds, too large to be distributed by winds.
10) Describe the theory of continental drift.
Answer: Continental drift proposed that continental land was not static–the continents moved.
The theory was well supported by the jig-saw fit of continental land masses at their margins, and
by data in paleo-climatology and paleontology. Although the evidence was quite remarkable, a
suitable driving mechanism to produce such crustal movement was lacking.
21.4 Acceptance of Continental Drift
1) Detailed mapping of the ocean floors revealed
A) huge mountain ranges beneath the oceans.
B) deep trenches near some of the continents.
C) that the oceans are equally deep at all locations.
D) huge mountain ranges on the ocean floor, and deep trenches near some of the continents.
Answer: D
2) Paleomagnetism from a rock gives information on the
A) direction from the rock to the North Pole.
B) present-day magnetic field.
C) amount of iron in the rock.
D) magnetic field at the time the rock was formed.
Answer: D
3) In the 1950s a plot of the position of the magnetic north pole through time revealed that
A) either the magnetic poles had migrated through time or the continents had moved.
B) polar magnetization varied from pole to pole.
C) over the past 500 million years the geographic poles changed position at least once or twice.
D) all of the above.
Answer: A
4) According to the theory of seafloor spreading, molten rock is rising up along
A) the mid-ocean ridges.
B) trenches that border continental margins.
C) islands surrounding the Pacific volcanic rim.
D) areas of sinking seafloor.
Answer: A
5) When the magnetic field of Earth is reversed,
A) Earth flips over in its orbit.
B) Earth's rotation is also reversed.
C) newly formed mineral grains on the ocean floor are magnetized according to the new
orientation of the magnetic field.
Answer: C
6) The ocean crust
A) becomes progressively younger away from the mid-ocean ridges.
B) is the same age worldwide.
C) becomes progressively older away from the mid-ocean ridge.
D) ranges in age, the oldest ocean crust is in the Atlantic and the youngest is in the Arctic.
Answer: C
7) The theory of seafloor spreading is supported by
A) geological, biological, and climatological data.
B) paleomagnetic analysis of the ocean's floor.
C) the change in Earth's polarity.
D) none of these
Answer: B
8) The Earth's magnetic field
A) never appreciably changes.
B) has reversed itself many times.
C) is centered at Earth's core.
D) both B and C
Answer: B
9) Oceans are about four times as deep as mountains are high. At the bottom of the ocean are
A) towering mountains, deep valleys, and deep trenches near the continental borders.
B) thick layers of basaltic crust at midocean ridges that gradually thins near deep ocean trenches.
C) towering plutonic mountains created from volcanoes and fissures at oceanic ridge areas.
D) all of these
Answer: A
10) The rate of seafloor spreading can be calculated by
A) the magnetic pattern generated at the ocean floor.
B) knowing the dates for magnetic pole reversals, and the distance from the location of a known
reversal site to the ocean ridge.
C) looking at the magnetic tape recording of the ocean floor.
D) the rate of seafloor spreading cannot be calculated.
Answer: B
11) If the path of polar wandering found from two continents are not the same, then we can say
that
A) Earth's magnetic history has been very complex.
B) at least one of the continents has moved.
C) our radioactive dating techniques have been inaccurate.
D) the continents have always been widely separated.
Answer: B
12) Magnetic surveys of the ocean floors reveal
A) alternating stripes of normal and reversed polarity paralleling the mid-Atlantic ridge.
B) thin oceanic crust composed of basaltic rocks.
C) that reversed polarity is rare.
D) all of the above.
Answer: A
13) The theory of seafloor spreading is attributed to
A) Harry Hess.
B) Marie Tharp.
C) Alfred Wegener.
D) Richard Oldham
Answer: A
14) The main idea of seafloor spreading is that
A) lithosphere floats on the asthenosphere.
B) new crust forms at a spreading center and old crust is recycled at a subduction zone.
C) new crust is magnetized according to the existing magnetic field.
D) the seafloor never stops growing.
Answer: B
15) How did seafloor spreading suggest a driving force for continental drift?
A) Youngest seafloor is found near continents.
B) Seafloor spreading pushes continents.
C) Mantle convection causes irreversible slippage.
D) Subduction creates the youngest seafloor.
Answer: B
16) What evidence was used to support magnetic pole reversals?
A) Apparent polar wandering and alternating magnetic stripe patterns on the ocean floor.
B) Paleomagnetism.
C) Normal and reverse polarity.
D) Continental drift and seafloor spreading.
Answer: A
17) Why was it so important to survey the ocean floors?
A) People had a general curiosity of our planet.
B) To get a better understanding of polar wandering.
C) To know the topography and possible hiding places for submarines.
D) To find pirate treasure.
Answer: C
18) Describe the seafloor spreading theory.
Answer: The seafloor spreading theory states that ocean basins spread apart as the ocean crust
grows at the mid-ocean ridges.
19) Describe how the different paths of polar wandering helped establish that continents move
over geologic time.
Answer: A plot of the apparent path of polar wandering from North American rocks does not
match the path from European rocks. If one were to move North America and Europe back
together, then the paths of polar wandering would overlie one another.
20) What are the eight major plates according to the theory of plate tectonics?
Answer: Eurasian Plate, Indo-Australian Plate, Pacific Plate, North American Plate, South
American Plate, Nazca Plate, African Plate, and the Antarctic Plate.
21.5 The Theory of Plate Tectonics
1) Plate tectonics differs from continental drift because it
A) provides a credible driving force.
B) did not explain the fit between South America and Africa.
C) showed that ancient ice sheets did not exist.
D) showed that Pangaea broke up much later than predicted.
Answer: A
2) Lithospheric plates move in response to
A) convection in Earth's interior.
B) upper mantle convection cells.
C) gravity and heat flow in the mantle.
D) convection cells generated by gravity and heat flow in the mantle.
Answer: D
3) As hot mantle rock rises, it expands. As it expands it cools. This cooler rock is
A) less dense so it keeps rising to form underwater volcanoes.
B) more dense so it sinks. This contributes to the heat flow convection process.
C) ocean crust.
D) unstable and explodes in a volcano.
Answer: B
4) Convection in Earth's mantle is attributed to
A) sinking cold oceanic crust.
B) gravity and heat flow.
C) conduction of heat from Earth's core.
D) temperature differences between continental and oceanic crust.
Answer: B
5) The concept of seafloor spreading states that
A) Earth is expanding.
B) seafloor is created at mid-ocean ridges and destroyed at deep ocean trenches.
C) sea level is rising.
D) earthquakes occur underwater.
Answer: B
6) Tectonic plates are composed of the
A) crust and mantle.
B) lithosphere.
C) lithosphere and the asthenosphere.
D) crust.
Answer: B
7) Plate tectonics states that
A) the continents move through Earth's crust like an icebreaker through ice.
B) earthquakes occur because tectonic plates break like a dropped dinner plate.
C) tectonic plates have not moved since Pangaea broke up.
D) tectonic plates are in slow, but constant motion.
Answer: D
8) If seafloor spreading creates new lithosphere, does the size of Earth change?
A) Yes, Earth is getting larger.
B) No, the extra crust is crumpled up to form mountains.
C) No, older crust is recycled back into the asthenosphere.
D) Yes, the Earth is shrinking because it is cooling.
Answer: C
9) Mountains tend to form in long narrow ranges because
A) of plate convergence–plates coming together.
B) pluton formation tends to develop in an elongate pattern rather than a bubble-like pattern.
C) of plate divergence–plates squeezing together.
D) they form next to oceanic boundaries.
Answer: A
10) Transform faults are areas of crustal
A) formation.
B) destruction.
C) subduction.
D) accommodation and plate movement.
Answer: D
11) Two boundaries associated with seafloor spreading centers are
A) convergent boundaries and transform fault boundaries.
B) divergent boundaries and transform fault boundaries.
C) oceanic-oceanic boundaries and divergent boundaries.
D) divergent boundaries and convergent boundaries.
Answer: B
12) The theory of plate tectonics states that
A) the lithosphere is broken up into several plates that move about as a result of convective
motion in the asthenosphere.
B) earthquakes and volcanic activity result from convection motion in the lithosphere.
C) buoyant lithospheric plates float on top of the rigid asthenosphere.
D) the plates move in conveyor-belt fashion as new crust is generated at the continental margins
and destroyed at the mid-ocean ridges.
Answer: A
13) Regions in which earthquakes are common are also regions in which
A) hurricanes are common.
B) volcanoes are common.
C) the geomagnetic force is strong.
D) many fossils are found.
Answer: B
14) Most of Earth's seismic activity, volcanism, and mountain building occur along
A) convergent boundaries.
B) divergent boundaries.
C) plate boundaries.
D) transform fault boundaries.
Answer: C
15) The oldest rocks are found
A) at convergent boundaries.
B) at divergent boundaries.
C) in the ocean basins.
D) on continental land.
Answer: D
16) The longest mountain chain in the world is the
A) mid-ocean ridge.
B) Himalayas.
C) Appalachians.
D) Sierra Nevada.
Answer: A
17) Divergent boundaries are areas of
A) tensional forces that stretch the crust and generate a spreading center.
B) compressional forces that crunch the crust and generate a spreading center.
C) compressional forces that crunch and shorten the crust by folding and faulting.
D) plate collision.
Answer: A
18) Divergent boundaries are areas of
A) crustal formation.
B) crustal destruction.
C) continuous, high magnitude earthquakes.
D) intense compressional forces.
Answer: A
19) Spreading centers occur along
A) trenches.
B) transform faults.
C) mid-ocean ridges.
D) the northern and western margins of the Juan de Fuca Plate.
Answer: C
20) Which one of the following is NOT a type of plate collision?
A) Continental divergence.
B) Oceanic-continental.
C) Continental-continental.
D) Oceanic-oceanic.
Answer: A
21) Convergent boundaries are areas of
A) compressional forces that crunch the crust and generate a spreading center.
B) tensional forces that stretch the crust and generate a spreading center.
C) crustal formation.
D) plate collision.
Answer: D
22) Convergent boundaries are regions of
A) great mountain building.
B) plate subduction.
C) plate collision.
D) plate collision, subduction, and mountain building.
Answer: D
23) Another term for a spreading center is
A) convergent boundary.
B) divergent boundary.
C) transform fault boundary.
D) none of the above.
Answer: B
24) Transform faults are areas of crustal
A) formation.
B) destruction.
C) subduction.
D) accommodation and plate movement.
Answer: D
25) The process in which one plate bends and descends beneath another plate is called
A) subduction.
B) seduction.
C) segregation.
D) sinking.
Answer: A
26) Subduction occurs as a result of
A) slab pull–gravity pulls older and denser lithosphere downward.
B) horizontal plate accommodation.
C) upwelling of hot mantle material along the trench.
D) lubrication from the generation of andesitic magma.
Answer: A
27) The dominant force at divergent boundaries is
A) compression.
B) tension.
C) shearing.
D) similar to that in reverse faulting.
Answer: B
28) The dominant force at convergent boundaries is
A) compression.
B) tension.
C) shearing.
D) similar to that in normal faulting.
Answer: A
29) Magma is generated at all of these plate boundaries EXCEPT
A) divergent boundaries.
B) oceanic-oceanic convergent boundaries.
C) oceanic-continental convergent boundaries.
D) continental-continental convergent boundaries.
Answer: D
30) Convection in the mantle is caused primarily by
A) heat moving from the crust to the core.
B) conduction.
C) gravity and temperature differences.
D) friction of overlying lithosphere.
Answer: C
31) The occurrence of earthquakes in the absence of seafloor spreading, oceanic trenches, or
volcanic activity is a characteristic feature of
A) convergent boundaries between plates.
B) divergent boundaries between plates.
C) subduction zones.
D) transform fault boundaries between plates.
Answer: D
32) The San Andreas fault
A) stretches from the Gulf of California to Cape Mendocino, California, and separates the Pacific
Plate from the North American Plate.
B) accommodates all the motion between the Pacific Plate and the North American Plate.
C) is presently inactive.
D) all of the above
Answer: A
33) According to plate tectonic theory, the San Andreas fault is a
A) convergence zone.
B) divergence zone.
C) subduction zone.
D) transform fault.
Answer: D
34) Briefly describe the different types of plate boundaries.
Answer: Divergent boundaries, produced by tensional stress, are areas of crustal formation.
Convergent boundaries, produced by compressional stress, are areas of crustal destruction.
Transform fault boundaries, produced by shear stress, are areas where plates slide past one
another.
35) and destroyed (subduction zones). At transform boundaries, plates slide horizontally past
each other.
Answer: The lithosphere is broken up into about a dozen rigid moving plates that move in
response to convection cycles within the planet's interior. Two types of boundaries between these
plates–divergent and convergent–are the sites where crust is formed (seafloor spreading
36) Why is it that the most ancient rocks are found on the continents, and not on the ocean floor?
Answer: The ocean floors are sites of crustal formation. New crust generated at a spreading
center, pushes older crust away. In general, continental crust does not get subducted because of
its low density. Older oceanic crust has been subducted, while older continental crust has not.
37) plates are touching–plate boundaries. When the stress reaches a critical threshold, rocks
break, slide past each other, and earthquakes are generated.
Answer: Stress builds up in lithospheric plates where two (or three
38) What kind of plate boundary separates the South American Plate from the African Plate?
Answer: A divergent boundary. The Mid-Atlantic Ridge, a spreading center in the Atlantic
Ocean, separates the two continents.
39) Subduction is the process of one lithospheric plate descending beneath another. Why does
the oceanic portion of the lithosphere undergo subduction while the continental portion does not?
Answer: Oceanic crust is more dense than continental crust, so buoyancy inhibits the subduction
of continental crust.
40) What is the major source of energy responsible for earthquakes in southern California?
Answer: Horizontal sliding movement between the northwest moving Pacific Plate and the
southeast moving North American Plate.
41) How old is the Atlantic Ocean? For how many years has magma been extruding in the midAtlantic?
Answer: The Mid-Atlantic Ridge is a spreading center that has been extruding magma for 160
million years, long enough to produce the Atlantic Ocean floor. With production of lithosphere at
the ridges, the ocean floor grew and the continents drifted apart. The spreading rate has been
slow, about 2 cm each year, but over 160 million years it adds up to 3200 km–the width of the
Atlantic Ocean. So, It has taken 160 million years for a mere fracture in an ancient continent to
turn into the Atlantic Ocean.
21.6 Continental Evidence for Plate Tectonics
1) In a folded sequence of rocks we find younger rocks at the axis of the fold and older rocks
away from the fold axis. The fold is
A) called a syncline.
B) called an anticline.
C) plunging.
D) tilted.
Answer: A
2) In a folded sequence of rocks we find older rocks at the axis of the fold and younger rocks
away from the fold axis. The fold is
A) called a syncline.
B) called an anticline.
C) plunging.
D) tilted.
Answer: B
3) In an undeformed sequence of rocks, the youngest rocks are found
A) at the bottom of the rock sequence.
B) as an eroded bed.
C) at the top of the rock sequence.
D) in the core of an anticline.
Answer: C
4) Each step of 1 on the Richter scale corresponds to a change in energy release of
A) 2.
B) 30.
C) 100.
D) 1000.
Answer: B
5) An anticline is a fold in which the limbs bend
A) downward.
B) upward.
Answer: A
6) When you stretch a rubber band, you are applying
A) compressional stress.
B) tensional stress.
C) shear stress.
D) simple stress.
Answer: B
7) The stress that occurs when material is pulled apart is called
A) compressional stress.
B) tensional stress.
C) shear stress.
D) simple stress.
Answer: B
8) Compression cannot produce
A) anticlines.
B) synclines.
C) normal faults.
D) reverse faults.
Answer: C
9) When rock is subjected to compressive force, it may fault. If rocks in the hanging wall are
pushed up over rocks in the footwall, it is called a
A) reverse fault.
B) strike slip fault.
C) normal fault.
D) none of the above.
Answer: A
10) Most of the state of Nevada is in the Basin and Range Province. The predominant active fault
for this region is
A) thrust faulting.
B) reverse faulting.
C) normal faulting.
D) none of the above.
Answer: C
11) The San Andreas fault in California is a
A) thrust fault.
B) strike slip fault.
C) normal fault.
D) reverse fault.
Answer: B
12) The Richter scale measures an earthquake's
A) frequency.
B) magnitude.
C) damage.
D) all of the above.
Answer: B
13) The Mercalli scale measures an earthquake's
A) effects.
B) damage.
C) intensity.
D) intensity, damage, and overall effect.
Answer: D
14) The San Andreas fault is a
A) normal fault.
B) thrust fault.
C) reverse fault.
D) transform fault.
Answer: D
15) A fault in which the footwall has moved down relative to the hanging wall is called a
A) normal fault.
B) reverse fault.
C) transform fault.
D) horizontal fault.
Answer: A
16) Compressive forces cause the crust to
A) buckle and fold, thereby shortening the crustal surface.
B) buckle and fold, thereby lengthening the crustal surface.
C) stretch and pull, thereby shortening the crustal surface.
D) break and fracture, thereby lengthening the crustal surface.
Answer: A
17) Tensional forces cause the crust to
A) buckle and fold, thereby shortening the crustal surface.
B) buckle and fold, thereby lengthening the crustal surface.
C) stretch and pull, thereby shortening the crustal surface.
D) break and fracture, thereby lengthening the crustal surface.
Answer: D
18) Rocks in the core of an anticline are than rocks away from the core.
A) higher
B) lower
C) older
D) younger
Answer: C
19) Reverse faults are the result of
A) tension.
B) compression.
C) divergence.
D) heat.
Answer: B
20) When stress exceeds a rock's elastic limit, the rock
A) permanently loses its original form.
B) can either break or flow.
C) becomes plastic.
D) can lose its original form and either break or flow.
Answer: D
21) The energy in an earthquake is released
A) all at once.
B) before the quake, after the quake, and during the quake.
C) as an epicenter focus.
D) in unconsolidated rock.
Answer: B
22) Tsunami are correctly referred to as
A) seismic sea waves.
B) tidal waves
C) energy waves.
D) mega waves.
Answer: A
23) The majority of earthquakes occur where
A) lithospheric plates meet.
B) the asthenosphere touches the lithosphere.
C) the land surface is made of unconsolidated sediments.
D) narrow zones of land touch.
Answer: A
24) Rocks begin to deform when they are stressed. Near Earth's surface, when stress is severe,
the rock
A) behaves plastically–it folds and flows.
B) Is brittle–it breaks producing faults and fractures.
C) has brittle deformation–it folds and flows.
D) has plastic deformation–it faults and fractures.
Answer: D
25) Compressive stress causes rocks to buckle and fold. In a syncline fold, the rocks at the fold
axis (the core) are
A) younger than those away from the axis.
B) older than those away from the axis.
C) more deformed than those away from the core.
D) less deformed than those away from the core.
Answer: A
26) Damage from an earthquake is most severe when the
A) epicenter is close to the surface.
B) surface material is composed of unconsolidated sediments.
C) buildings and structures are poorly constructed.
D) epicenter close to surface which is composed of unconsolidated sediments and the building
are all of the above.
Answer: D
27) A tsunami is unlike most other water waves mainly because it
A) is stronger.
B) has a very long wavelength.
C) moves very fast.
D) is energetic.
Answer: B
28) Earthquakes are caused by the
A) friction between diverging plates.
B) sudden release of energy that is stored elastically in deforming rocks.
C) expansion of Earth's crust.
D) combined motion of tectonic plates.
Answer: B
29) Transform-fault boundaries usually form
A) between two segments of a mid-ocean ridge.
B) between two other transform-fault boundaries.
C) between a mid-ocean ridge and a subduction zone.
D) in the rift of a mid-ocean ridge.
Answer: A
30) The Himalayan Mountains formed at which type of plate boundary?
A) Transform-fault boundary.
B) Oceanic-continental convergent boundary.
C) Divergent boundary.
D) Continental-continental convergent boundary.
Answer: D
31) Volcanoes do not form at which type of convergent plate boundary?
A) Oceanic—oceanic boundaries.
B) Oceanic—convergent boundaries.
C) Continental—continental convergent boundaries.
Answer: C
32) Where does a tsunami usually occur?
A) Transform-fault boundary.
B) Underwater reverse fault.
C) Divergent boundary.
D) Continental-continental convergent boundary.
Answer: B
33) How are tensional and compressional forces related to faulting and folding?
Answer: Faulting: Tensional forces pull rocks apart, normal faults are produced by tensional
forces. Compressional forces push rocks together, reverse faults are produced by compressional
forces. Folding: most folding is a result of compressional force.
34) Distinguish between anticlines and synclines.
Answer: Anticlines are upward arched structures; the rocks in an anticline are oldest at the core
and grow progressively younger away from the axis. Synclines are downward sag structures; the
rocks in a syncline are youngest at the core, and as you move horizontally away from the axis,
the rocks get older.
35) How does movement in a normal fault differ from that in a reverse fault?
Answer: In a normal fault, movement along the fault is caused by tensional stress in the crust;
this causes the hanging wall to move downward with respect to the footwall. In a reverse fault,
movement along the fault is caused by compressional stress in the crust; this causes the hanging
wall to move upward with respect to the footwall.
36) What geologic features are explained by plate tectonics?
Answer: Mountain ranges, volcanoes, plutonic rocks, metamorphic rocks, folded and faulted
rocks are all explained by plate tectonics. Virtually all geologic processes can be tied back to
plate tectonics.
22.7 The Theory That Explains the Geosphere
1) Granite does not readily form near oceanic-oceanic convergent boundaries because
A) granite forms from granitic magma and most oceanic material is basaltic in origin.
B) the magma formed at this type of boundary is not conducive to producing granitic type rocks.
C) oceanic-oceanic convergence often results in the eruption of andesitic lavas.
D) all of the above.
Answer: D
2) At divergent boundaries the dominant rock type is
A) basalt.
B) granite.
C) andesite.
D) basalt, granite, and andesite.
Answer: A
3) Volcanic activity is associated with
A) divergent, convergent, and transform boundaries.
B) convergent and transform boundaries.
C) divergent and convergent boundaries.
D) divergent, convergent, and plate tectonic boundaries.
Answer: C
4) Earthquake activity is associated with
A) divergent, convergent, and transform plate boundaries.
B) convergent and transform plate boundaries.
C) divergent and convergent boundaries.
D) transform plate boundaries.
Answer: A
5) Water causes partial melting of the mantle at which type of plate boundary?
A) Convergent boundaries.
B) Divergent boundaries.
C) Transform-fault boundaries.
Answer: A
6) Tectonic interaction between plate boundaries does NOT explain
A) magma production and the variety of igneous rocks.
B) mountain building.
C) polar wandering.
D) global distribution of earthquakes and volcanoes.
Answer: C
Test Bank for Conceptual Physical Science
Paul Hewitt, John Suchocki, Leslie Hewitt
9780321752932, 9780134060491
