Chapter 12 Earth's Interior
Earth: An Introduction to Physical Geology, 9e (Tarbuck/Lutgens)
12.1 Multiple-Choice Questions
1) The P-wave shadow zone is largely the result of ________.
A) reflection of P waves from the inner core-outer core boundary
B) lower P-wave velocities in the mantle than in the crust
C) refraction of P waves crossing the mantle-outer core boundary
D) reflection of P waves at the boundary between the inner and outer cores
Answer: C
Diff: 1
2) Which one of the following statements concerning Earth's magnetic field is true?
A) At high latitudes, the force lines intersect Earth's surface at steep angles.
B) Magnetic poles are not fixed and move freely across the Earth.
C) Generated by magnetic, crystalline, iron grains in the outer core.
D) Dipolar with the two poles centered near the equator.
Answer: A
Diff: 1
3) ________ are thought to be similar in composition to Earth's mantle.
A) Shooting stars
B) Metallic meteorites
C) Cosmic gas clouds
D) Stony meteorites
Answer: D
Diff: 1
4) The Earth's magnetic field originates by ________.
A) weak electrical currents associated with hot, rising, mantle plumes
B) magnetic mineral grains in the inner core
C) weak electrical currents associated with fluid motions in the outer core
D) magnetization of oxygen and nitrogen atoms in the atmospheric ozone layer by solar
radiation
Answer: C
Diff: 1
5) The Earth's magnetic field ________.
A) is a self-generating and self-reversing dynamo in the outer core
B) is a high temperature superconductor in the inner core
C) results from self-induction of rising magmas in the asthenosphere
D) is a permanent field due to magnetized, iron-rich, mineral grains in the oceanic
lithosphere
Answer: A
Diff: 1
1
For the following question(s), match the layers of the Earth with the appropriate description.
A. inner core
B. mantle
C. crust
D. outer core
6) ________ upper part of the lithosphere includes this layer
Answer: C
Diff: 1
7) ________ very dense, solidified, iron-rich alloy
Answer: A
Diff: 1
8) ________ Earth's magnetic field originates in this layer
Answer: D
Diff: 1
9) ________ transmits P waves but not S waves
Answer: D
Diff: 1
10) ________ the top of this layer is marked by the Mohorovicic discontinuity
Answer: B
Diff: 1
11) ________ includes the asthenosphere
Answer: B
Diff: 1
12) ________ includes large percentages of feldspars and quartz
Answer: C
Diff: 1
13) Which of the following best characterizes how the diameter of Earth's core and the nature of
the outer core were discovered?
A) Crystalline iron was found in lavas erupted from the deepest known hot spots.
B) By analysis of the P-wave and S-wave shadow zones.
C) Because P-wave speeds are higher in the outer core than in the lower mantle.
D) By using the ratio of iron meteorites to stony meteorites to deduce the relative
diameters of the core and mantle.
Answer: B
Diff: 1
14) ________ discovered the crust-mantle seismic discontinuity in ________.
A) Beno Gutenberg; 1936
B) Petrovich Divacs; 1914
C) Charles Richter; 1888
D) Andrija Mohorovicic; 1909
Answer: D
Diff: 1
2
15) The fact that ________ is good evidence for a solidified, inner core.
A) S waves do not pass directly through the core
B) P waves are faster in the inner core than in the outer core
C) S waves are slower in the inner core than in the outer core
D) S waves are focused at the center of the P-wave shadow zone
Answer: B
Diff: 1
16) Dense forms of ________ are probably major components of the inner core.
A) solid iron silicates and magnesium silicates
B) crystalline iron and nickel
C) liquid iron-nickel-sulfur alloy
D) solidified uranium and other very heavy elements
Answer: B
Diff: 1
17) The ________ of the Earth does not transmit S waves.
A) outer mantle
B) inner crust
C) outer core
D) deep mantle
Answer: C
Diff: 1
18) The ________ is the seismic discontinuity that forms the boundary between the crust and
mantle.
A) Mojo
B) Moto
C) Mogo
D) Moho
Answer: D
Diff: 1
19) The ________ of the Earth has the smallest volume.
A) crust
B) outer core
C) mantle
D) inner core
Answer: A
Diff: 1
20) The ________ of the Earth is enriched in the elements silicon, potassium, sodium, and
aluminum compared to the most common types of stony meteorites.
A) inner core
B) outer core
C) mantle
D) crust
Answer: D
Diff: 1
3
21) ________ are much more abundant in mantle rocks than in crustal rocks.
A) Potassium aluminum silicates
B) Quartz and calcite
C) Magnesium silicates
D) Hydrous minerals like micas and clays
Answer: C
Diff: 1
22) A mixture of ________ represents the average chemical composition of the continental crust.
A) quartz and calcite
B) average shale and andesite
C) olivine and peridotite
D) basalt and metallic iron
Answer: B
Diff: 1
23) ________ is probably closest in chemical composition to the upper mantle.
A) Granite
B) Shale
C) Andesite
D) Peridotite
Answer: D
Diff: 1
24) ________ are closest to the average chemical composition of the oceanic crust.
A) Basalt and gabbro
B) Granite and limestone
C) Andesite and granite
D) Rhyolite and diorite
Answer: A
Diff: 1
25) Which one of the following best characterizes the asthenosphere?
A) a layer of soft, solid, magnesium silicates and molten iron droplets at the base of the
mantle
B) a zone of hardened, silicate rock at the base of the oceanic crust
C) a zone of softened peridotite in the upper mantle
D) the zone in the mantle from which hot-spot magmas are melted
Answer: C
Diff: 1
26) A shallow-focus earthquake occurs directly under the South Pole. A seismic station at the
North Pole would receive ________.
A) S waves from this quake but not P waves
B) both P and S waves from this quake separated in arrival times by two minutes
C) neither P waves nor S waves from the quake
D) P waves from this quake, but no S waves would be detected
Answer: D
Diff: 1
4
27) Convection in the mantle causes ________.
A) warm rock to rise as narrow pipe-like plumes
B) warm rock to rise as tabular sheets
C) cool rock to rise as vertical, pipe-like masses
D) cool rock to rise as tabular sheets
Answer: A
Diff: 1
For the following question(s), match the phrases with the appropriate descriptions.
A. the "D" layer
B. the low-velocity zone
C. the mesosphere
D. the 660-km-depth discontinuity
28) ________ zone of incipient partial melting in the upper mantle
Answer: B
Diff: 1
29) ________ most of the lower mantle; more rigid than the asthenosphere
Answer: C
Diff: 1
30) ________ caused by the transition from the spinel to the perovskite mineral structure
Answer: D
Diff: 1
31) ________ implicated in the upward flow of warmed mantle from near the core-mantle
boundary
Answer: A
Diff: 1
12.2 Word Analysis Questions
Examine the words and/or phrases for each question below and determine the relationship among the
majority of words/phrases. Choose the option which does not fit the pattern.
1) A) crust
B) lithosphere
C) core
D) mantle
Answer: lithosphere
Diff: 1
2) A) core
Answer: core
B) asthenosphere
C) mesosphere
D) lithosphere
B) peridotite
C) perovskite
D) granodiorite
Diff: 1
3) A) kimberlite
Answer: granodiorite
Diff: 1
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12.3 True/False Questions
1) Oceanic crust is mainly basaltic in composition; the mantle is more like the igneous rock
peridotite in chemical composition.
Answer: TRUE
Diff: 1
2) The inner core is probably mainly liquid iron because it has the characteristics of a
permanent magnet.
Answer: FALSE
Diff: 1
3) Continental crust has an average chemical composition much like the igneous rock andesite;
the oceanic crust is basaltic in composition.
Answer: TRUE
Diff: 1
4) On the basis of seismic evidence, the outer core is believed to be liquid.
Answer: TRUE
Diff: 1
5) The crust and mantle are solids; the inner core is thought to be solid.
Answer: TRUE
Diff: 1
6) The mantle is composed mainly of iron with small amounts of magnesium silicate minerals.
Answer: FALSE
Diff: 1
7) The S-wave shadow zone exists because S waves cannot pass through the outer core.
Answer: TRUE
Diff: 1
8) Continental crust is generally thicker than oceanic crust.
Answer: TRUE
Diff: 1
9) The Milankovitch discontinuity separates Earth's mantle and outer core.
Answer: FALSE
Diff: 1
10) P waves are faster than S waves; S waves are faster than refracted P waves.
Answer: FALSE
Diff: 1
11) High rock temperatures enhance plastic deformation and flow in the asthenosphere and
inhibit brittle fracturing.
Answer: TRUE
Diff: 1
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12) As P waves pass from the mantle into the outer core, velocities drop abruptly.
Answer: TRUE
Diff: 1
13) Stony and iron meteorites are thought to provide samples of the materials from which Earth
originally formed.
Answer: TRUE
Diff: 1
12.4 Short Answer Questions
1) ________ are not transmitted through the outer core.
Answer: S waves
Diff: 1
2) The ________ discontinuity marks the boundary between the crust and mantle.
Answer: Mohorovicic
Diff: 1
3) What is thought to be the material state (liquid, solid, gas) and elemental composition of
Earth's outer core?
Answer: liquid iron
Diff: 1
4) ________ is the cool, brittle, outer layer of Earth that includes the crust and uppermost
mantle.
Answer: Lithosphere
Diff: 1
5) The chemical and mineralogical composition of the upper oceanic crust are essentially the
same as the aphanitic, igneous rock ________.
Answer: andesite
Diff: 1
6) ________ is the layer of warm rock below the crust and uppermost mantle that readily
deforms and flows plastically.
Answer: Asthenosphere
Diff: 1
7) ________ is thought to be the major component of the inner and outer core.
Answer: Iron
Diff: 1
8) The ________ core is probably solidified.
Answer: inner
Diff: 1
9) The upper mantle is very close in chemical and mineralogical composition to ________.
Answer: peridotite
Diff: 1
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12.5 Critical Thinking Questions
Use complete sentences, correct spelling, and the information presented in Chapter 12 to answer the
questions below
1) Since much of our knowledge of Earth's interior is inferred from the behavior of seismic
waves and not actual samples, what are some of the assumptions that are made in order for
our models to be correct? (Hint think of earth materials, physical and chemical parameters,
etc.)
Diff: 3
2) Given the similarities between Earth and the other Terrestrial planets in our solar system,
would you expect similar interior structures on Venus or Mars? What major geological
processes on those planets should be similar to those on Earth?
Diff: 3
3) Briefly discuss the distribution of elements (silicate minerals verses metallic phases) within
Earth. Does this distribution make sense, given the most popular explanations for Earth's
origin? How so?
Diff: 3
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12.6 Visualization Questions
1) On the blank spaces provided in the illustration below, fill in the names of the layers of
Earth's interior that are labeled.
Answer: a) base of lithosphere or top of asthenosphere (top of low velocity zone)
b) inner core c) lower mantle (mesosphere) d) asthenosphere
Diff: 1
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2) Carefully examine the illustration below, which shows how P-waves are transmitted
through the Earth. Also note the letters A, B, and C.
Which level indicates the P-wave shadow zone? a) ________
Which level indicates the zone where no direct P-waves are received? b) ________
Which level indicates the zone where direct P-waves are received? c) ________
Answer: a) B b) A c) C
Diff: 1
10
3) What is the belt where seismic waves are blocked by the outer core in the diagram below?
Answer: S-wave shadow zone
Diff: 1
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