Deck 11: Earths Interior

Question 1

Our knowledge of Earth's interior is based on the travel times of seismic body waves.

Answer 1

True

Question 2

The velocities of P- and S-waves depend on the density and elasticity of the rocks through which they travel.

Answer 2

True

Question 3

All else being equal, wave velocities decrease with increasing elasticity.

Answer 3

False

Question 4

P-wave rays are most commonly reflected while S-wave rays are refracted.

Question 5

The S-wave shadow zone is evidence that the outer core is liquid.

Question 6

The mantle's density is uniform with depth at any given level.

Question 7

Seismic tomography uses seismic waves to get a more accurate measurement of Earth's surface shape.

Question 8

The mantle is more dense than the outer core because the latter is liquid.

Question 9

With increasing depth and pressure pyroxene changes to peridotite.

Question 10

A low velocity zone in the mantle indicates that rocks are less elastic due to partial melting.

Question 11

Increasing pressure with depth causes P-wave velocities to continuously increase into Earth's interior though at different rates.

Question 12

Kimberlite pipes are composed of materials intruded from as deep as the molten outer core.

Question 13

Seismic tomography uses X ray waves to analyze Earth's interior.

Question 14

Gravitational attraction is the same everywhere on Earth's surface.

Question 15

The geothermal gradient is about 25 C/km near the surface but is higher in areas with recent volcanism.

Question 16

Isostatic rebound is an alternative explanation for earthquakes.

Question 17

According the principle of isostasy, a higher mountain range has a deeper root.

Question 18

If correct, the principle of isostasy implies that mantle behaves as a fluid.

Question 19

Positive magnetic anomalies are evidence that the subsurface might locally contain iron-bearing minerals.

Question 20

When a magnetic field reversal occurs, geographic North and South poles also reverse.

Question 21

Rocks on Earth's surface all have normal polarity.

Question 22

Geomagnetic reversals are rare events in geological history.

Question 23

The deepest drill holes extend to approximately

A) 0.15 km
B) 1.5 km
C) 15 km
D) 150 km

Question 24

At a boundary between materials of different density and elasticity, P- and S-waves are

A) reflected
B) refracted
C) reflected and refracted
D) not affected

Question 25

Seismic discontinuities permit

A) the recognition of petroleum and ore deposits.
B) the identification of interior structural layers.
C) the identification of differing compositions and properties.
D) B and C
E) all of the above

Question 26

Which of the following is NOT a method by which the density and composition of the core is estimated?

A) the discovery of ultramafic rocks from kimberlite deposits
B) compositions of meteorites
C) experimental behavior of mixtures of various potential elements under high pressures and temperatures
D) the behavior and velocity of P- and S-waves in solids and liquids
E) calculations based on known whole-Earth and crustal-mantle densities

Question 27

The S-wave shadow zone exists because

A) S waves weaken substantially as they travel through liquids
B) S waves are reflected off liquids
C) S waves do not travel through liquids
D) S waves only travel to a certain depth

Question 28

The low-velocity zone is important because

A) the rigid lithosphere is buoyed by it.
B) magmas originate in this zone.
C) it flows and so carries the plates above.
D) A and C
E) all of the above

Question 29

Which of the following is NOT a method of inferring the composition of the mantle?

A) calculations based on color density values obtained from seismic studies
B) experiments on olivine and pyroxene stabilities at high pressures and temperatures
C) laboratory experiments on the seismic and other physical properties of peridotite
D) peridotite samples from basal oceanic crust and kimberlite pipe deposits
E) laboratory experiments on peridotite's behavior under high pressures and temperatures

Question 30

The thickness of Earth's crust varies because of

A) variations in composition
B) variations in density
C) variations in temperature
D) A and B
E) all of the above

Question 31

P-wave velocities in continental crust are __________in oceanic crust.

A) faster than
B) slower than
C) the same as

Question 32

The geothermal gradient, about 25°C/km, is generally valid for which of the following situations or uses?

A) to determine the depth at which the rock melts to form the outer core
B) to illustrate that variations in the temperature of the crust are minimal
C) to approximate near surface temperatures
D) to validate models showing increasing wave ray velocities with depth

Question 33

Given two objects of the same mass, one at sea level, and the other atop Mount Everest, which has the greater weight?

A) the object on Mount Everest because the distance to the center of Earth, and therefore, the mass of Earth is locally greater
B) the object at sea level because the distance to the center of Earth is least from this elevation
C) the object at sea level because the centrifugal force is greatest at sea level
D) the object on Mount Everest because centrifugal force increases with distance from the center of gravity
E) the object on Mount Everest because the Coriolis effect is strongest at high altitudes

Question 34

Gravitational attraction is variable around the Earth because

A) centrifugal force resulting from rotation varies
B) distribution of earth materials of different densities varies
C) elevation varies
D) A and B
E) all of the above

Question 35

Departures from Earth's expected gravitational attraction would NOT be due to

A) subsurface hydrocarbon resources
B) subsurface metal ore bodies
C) differences in geographic location
D) differences in surface temperature
E) all of the above

Question 36

Magnetometers measure the

A) declination of the magnetic field
B) inclination of the magnetic field
C) polarity of the magnetic field
D) strength of the magnetic field

Question 37

Positive magnetic anomalies may result from

A) subsurface iron-bearing deposits
B) extensive basaltic volcanism
C) subsurface salt domes
D) A and B
E) all of the above

Question 38

Iron-bearing minerals align with the magnetic field when they

A) crystallize from magma
B) cool through the Curie point
C) adjust to plate tectonic movement
D) A and B
E) all of the above

Question 39

Departures from the normal strength of Earth's expected magnetic field would NOT be due to

A) variations in iron content of ore bodies
B) lateral variations in rock type
C) differences in surface temperatures
D) buried geologic structures such as salt domes
E) none of the above

Question 40

With___________ , a pro propagating wave is bent; with___________ , the wave is bounced back toward the surface.

Question 41

A boundary marking a significant change in Earth materials or their properties is called a___________.

Question 42

The___________ - ___________boundary is a discontinuity that occurs at a depth of 2,900 km below Earth's surface?

Question 43

The P-wave velocity abruptly ___________at the core-mantle boundary and S-wave velocity goes to zero.

Question 44

The igneous rock___________ is considered the most likely candidate for representing the composition of the mantle.

Question 45

The___________ consists of crust and the upper mantle above the low-velocity zone.

Question 46

Continental crust is generally ___________in composition, while the oceanic crust is generally ___________.

Question 47

Continental crust has a mineral composition like that of ___________and is known as granitic crust.

Question 48

P-wave velocities in both continental and oceanic crust abruptly (decrease/increase)___________at their bases, a boundary also known as the___________ ___________.

Question 49

The of ancient rocks records the strength and direction of Earth's magnetic field at the time of the rocks' formation.

Question 50

Velocities of P- and S-waves are determined by which two physical properties of the material through which they pass? Explain.

Question 51

Discuss the contributions of seismic studies to our knowledge of different aspects of geology.

Question 52

What are two important and very useful differences between P-waves and S-waves? How are they useful?

Question 53

Why is the core not composed of minerals common on Earth's surface?

Question 54

How is Earth's magnetism used to explore for natural resources?

Question 55

Why are science fiction tales of subterranean journeys, such as Jules Verne's A Journey to the Center of Earth, impossible?

Question 56

Which structural layer of Earth comprises the greatest volume of Earth?

Question 57

Which structural layer of Earth is the thinnest and least voluminous?

Question 58

Which structural layer of Earth is liquid?

Question 59

What are possible rock compositions for the 3 major internal divisions or layers of Earth?

Question 60

What is the major source of information used in developing this model of Earth's interior?

Question 61

What are two ways in which the direction of travel of seismic waves can be changed as they travel through different materials?

Question 62

How are discontinuities located?

Question 63

Briefly explain why the outer core can be liquid at temperatures of 3,500 - 5,000 °C while the inner core is solid.

Question 64

What are the major elements comprising Earth's core?

Question 65

What significant boundary occurs at a depth of approximately 30 km beneath Earth's surface?

Question 66

How does the depth to the Mohorovicic discontinuity vary?

Question 67

What does the P- and S-wave low-velocity zone in the upper part of the mantle correspond to closely?

Question 68

What is the asthenosphere?

Question 69

How do the low-velocity zone and the asthenosphere differ?

Question 70

What do discontinuities below the low-velocity zone appear to represent?

Question 71

What is the transition zone within the mantle?

Question 72

What are the major minerals which comprise peridotite?

Question 73

Is Earth's mantle entirely molten? What evidence is there?

Question 74

What is Earth's mantle?

Question 75

Why do geophysicists believe the outer core is liquid?

Question 76

Where is the continental crust thickest?

Question 77

Where is the continental crust thinnest?

Question 78

Where is the oceanic crust thinnest?

Question 79

What is the geothermal gradient?

Question 80

What is the average geothermal gradient near the surface?