Deck 11: The Earths Interior - Whats Going on Down There

Question 1

The discovery of the Mohorovišic´ discontinuity (the Moho) was prompted by the observation that:

A) seismic waves that traveled through the mantle reached a seismograph sooner than those that traveled only through the crust.
B) seismic waves that traveled through the mantle had to travel farther and arrived at a seismograph later than those that traveled only through the crust.
C) seismic waves can travel through the same medium at two different speeds.
D) seismic waves that were reflected off the mantle arrived at a seismograph sooner than those that were not reflected off the mantle.

Answer 1

A

Question 2

The experiment that best simulates pressures of the Earth's core was demonstrated by:

A) high velocity bullets shot into a thin iron film.
B) shock waves produced by chemical explosives.
C) a diamond- anvil high- pressure cell.
D) the hydraulic press.

Answer 2

A

Question 3

Heat at the Earth's surface is a function of:

A) amount of radioactivity in the crust.
B) thickness of oceanic crust above the mantle.
C) thickness of continental crust above the mantle.
D) all of the above.

Answer 3

D

Question 4

The mantle accounts for what percentage of the Earth's total volume?

A) 60%.
B) 70%.
C) 80%.
D) 90%.

Question 5

The asthenosphere is considered the low- velocity zone because:

A) seismic waves travel more slowly through it than through any other region in the Earth's interior.
B) seismic waves travel more slowly through it than through other parts of the mantle.
C) in this thin layer of mantle, P- wave velocity is slower than in the crust.
D) circulation of material within asthenosphere convection currents moves extremely slowly.

Question 6

Seismic tomography studies have revealed all of the following information about the Earth's interior EXCEPT:

A) topography of the core- mantle boundary.
B) regions of higher or lower heat values in the mantle.
C) composition of the mantle rocks.
D) evidence that subducting plates may descend to the core- mantle boundary.

Question 7

The North American mid- continent gravity high marks the location of an ancient:

A) concentration of metallic ore.
B) continental rift zone.
C) continental suture zone.
D) volcanic mountain range.

Question 8

Seismic waves travel in a straight line with constant velocity only when moving:

A) in a homogeneous medium at different temperatures and pressures.
B) in a homogenous medium at different temperatures but constant pressures.
C) in a homogenous medium at constant temperatures and pressures.
D) through media of various compositions at different temperatures and pressures.

Question 9

Which of the following descriptions of the behavior of seismic waves is NOT correct?

A) When seismic waves approach the boundary between two media at a relatively small angle, they may bounce, or reflect, off the surface.
B) Changes in material, temperature, pressure, and physical state can all affect the speed of a seismic wave.
C) Within the Earth, seismic wave speed tends to increase with depth.
D) When seismic waves pass through the boundary between two media, the waves tend to change speed and bend, or refract, in several directions.

Question 10

The mantle- core boundary has a dramatic effect on seismic waves in that:

A) S waves increase in speed and P waves vanish.
B) S waves decrease in speed and P waves vanish.
C) P waves decrease in speed and S waves vanish.
D) P waves increase in speed and S waves vanish.

Question 11

Knowing the exact depth of a point within the Earth's interior enables us to calculate:

A) density.
B) composition.
C) pressure.
D) temperature.

Question 12

Magnetism exists only in elements in which:

A) the electrons all tend to spin in one direction.
B) the electrons all tend to stay on one side of the nucleus.
C) the electrons all tend to orbit in the same plane.
D) the electrons all tend to maintain the same energy level.

Question 13

The P- wave shadow zone occurs for all of the following reasons EXCEPT:

A) reflection at the mantle- core boundary directs the P waves toward a different area.
B) the rigidity of the core prevents P waves from compressing the core material.
C) refraction at the mantle- core boundary directs the P waves toward a different area.
D) the difference in rigidity between the mantle and core changes the speed of P waves.

Question 14

The Earth's magnetism is caused by:

A) the movement of electrons in the outer core.
B) a concentration of iron magnetite in the inner core.
C) the release of electrons from radioactive isotopes.
D) the movement of electrons in the asthenosphere convection cells.

Question 15

Because of isostasy, all of the following are true EXCEPT:

A) melting of a continent- wide glacier removes weight from a landmass, causing it to rise.
B) the erosion of a mountain peak causes the mountain to rise.
C) a dense, massive lava flow causes a landmass to sink lower into the asthenosphere.
D) oceanic lithosphere sinks deeper into the asthenosphere than continental lithosphere.

Question 16

In North America, the thinnest crust is only:

A) 20- 30 kilometers thick.
B) 60 kilometers thick.
C) 70 kilometers thick.
D) 40- 50 kilometers thick.

Question 17

Seismic tomography studies detect warmer interior regions as indicated by which phenomenon?

A) Bending of seismic waves paths.
B) Lower seismic velocities.
C) Earlier seismic wave arrival times.
D) Higher seismic velocities.

Question 18

Which of the following statements about the continental crust is NOT true?

A) Continental crust is least dense near the surface and most dense near the base.
B) The smooth increase in the speed of P wave toward the base of the crust indicates that the composition of the crust is homogeneous.
C) The average speed of P waves through continental crust is 6 kilometers per second near the surface and 7 kilometers near the base.
D) P waves travel faster near the base of continental crust than they do near the surface, possibly because of a pressure- induced increase in rigidity.

Question 19

The Mohorovišic´ discontinuity (the Moho) is:

A) the boundary between sedimentary rocks on the Earth's surface and the deeper plutonic rocks.
B) the boundary between oceanic and continental crust.
C) the boundary between the crust and the mantle.
D) a region of low seismic velocity.

Question 20

All of the following gravity anomalies could be expected EXCEPT:

A) a negative gravity anomaly over an ocean trench.
B) a positive gravity anomaly over subsurface salt deposits.
C) a negative gravity anomaly at a continental mountain range.
D) a positive gravity anomaly over an ocean basin.

Question 21

To determine the melting temperature of a portion of the Earth's interior, a geologist needs to know the region's:

A) pressure and velocity of P waves.
B) velocity of P waves and composition.
C) density and velocity of P waves.
D) composition and pressure.

Question 22

Which of the following statements about the Earth's magnetic field is NOT true?

A) The lines of magnetic force are curved and intersect the Earth's surface at various angles.
B) Every cubic centimeter of the Earth has lines of magnetic force.
C) The magnetic force lines are perpendicular to the surface at the equator and parallel at the poles.
D) It completely surrounds the entire Earth and extends far into space.

Question 23

Which of the following is most likely to occur during a reversal of the Earth's normal magnetic field?

A) A decrease in solar radiation.
B) Metals and magnetic substances would be affected, but on living organisms, there would be no effect.
C) A reduction in the level of ultraviolet radiation.
D) An interval without any magnetic field.

Question 24

The pull of gravity at the top of a mountain is:

A) higher than at sea level because of the tremendous mass of the mountain.
B) higher than at sea level because of the thickness of the continental crust associated with mountains.
C) lower than at sea level because it is farther from the Earth's center.
D) lower than at sea level because the mass of the peak is less than the mass of the base of the mountain.

Question 25

Which of the following statements concerning S waves is NOT true?

A) S waves temporarily displace materials they pass through with a shearing stress.
B) The speed of an S wave depends on the elasticity of the media through which it travels.
C) S waves may change their direction of travel when they encounter a material of different rigidity.
D) S waves do not have enough energy and speed to pass through liquids or gases.

Question 26

The Earth has gained internal heat through all of the following ways EXCEPT:

A) absorption of solar radiation.
B) solidification of the outer core.
C) friction from plate motions.
D) the decay of radioactive isotopes.

Question 27

All of the following have a magnetic field EXCEPT:

A) Mercury.
B) the Moon.
C) Saturn.
D) Jupiter.

Question 28

A location that exhibits a positive gravity anomaly has:

A) a higher gravitational pull than expected after adjusting for its latitude and altitude.
B) a higher gravitational pull than average because of its latitude or altitude.
C) a higher gravitational pull than usual for that location.
D) a higher gravitational pull than most locations on Earth.

Question 29

Which of the following statements about the Earth's core is NOT true?

A) The entire core may once have been liquid.
B) The core may still be undergoing differentiation because of dissimilar densities of its components.
C) The core is slightly larger than the Moon.
D) Heat dominates the outer core, causing it to be molten, while pressure dominates the inner core, causing it to be solid.

Question 30

To generate a magnetic field, a planet must do all of the following EXCEPT:

A) concentrate conductive material in its interior.
B) maintain an atmosphere capable of supporting electrical energy.
C) spin on its axis.
D) maintain a flowing liquid layer in the core.

Question 31

Which of the following statements about the lower mantle is NOT true?

A) The rocks near the base of the lower mantle are more rigid than those near the top of the lower mantle.
B) P waves reach a velocity of 13.6 kilometers per second at the base of the mantle.
C) The rocks of the lower mantle are most likely magnesium silicates and oxides.
D) The lower mantle is solid because its temperatures are lower than those in the asthenosphere.

Question 32

Reversals in the Earth's magnetic field have probably been caused by:

A) reversals in the polarity of the Sun's magnetic field.
B) variations in convection currents in the outer core.
C) changes in the direction of tectonic plate movement.
D) reversals in the direction of the Earth's rotational axis.

Question 33

The deepest drill hole, located in northern Russia, extends how far into the crust?

A) 7 kilometers.
B) 11 kilometers.
C) 13 kilometers.
D) 15 kilometers.

Question 34

The location of the thinnest continental crust in North America is located in:

A) Nevada.
B) California.
C) Iowa.
D) North Carolina.

Question 35

The transition zone between the upper and lower mantle is marked by:

A) abrupt changes in material rigidity 400 kilometers and 700 kilometers below the asthenosphere.
B) abrupt changes in temperature 400 kilometers and 700 kilometers below the Earth's surface.
C) abrupt changes in mineral structure 400 kilometers and 700 kilometers below the Earth's surface.
D) abrupt changes in pressure 400 kilometers and 700 kilometers below the lithosphere.

Question 36

The principles of paleomagnetism can be used to determine any of the following EXCEPT:

A) the ancient geographic arrangement of the Earth's landmasses.
B) the location of the Earth's magnetic poles during sediment deposition by an ancient river.
C) the location of the Earth's magnetic poles during an ancient volcanic eruption.
D) the alignment of the Earth's magnetic field during the formation of any region of the ocean floor.

Question 37

The principle of isostasy is used to describe:

A) changes in polarity of the Earth's magnetic field.
B) changes in seismic wave velocities relative to the density of the media through which they travel.
C) the buoyancy of portions of the Earth's crust as they float on the asthenosphere.
D) changes in gravitational attraction dependent on latitude and altitude.

Question 38

Formation of the oceanic crust involves all of the following processes EXCEPT:

A) deep- sea sedimentation.
B) intrusion of gabbro at divergent plate boundaries.
C) intrusion of granite at oceanic subduction zones.
D) effusive eruptions of basalt.

Question 39

Rocks from deep within the Earth have reached the surface by all of the following processes EXCEPT:

A) mantle rocks brought to the surface along rift zones.
B) volcanic eruption of deep- origin magmas containing unmelted subterranean rocks.
C) rocks found within kimberlite pipes produced by deep, explosive volcanism.
D) ultramafic mantle rocks brought up to the surface when continental plates collide.

Question 40

The S- wave shadow zone occurs because:

A) S waves cannot pass through the outer part of the core.
B) refraction at the mantle- core boundary bends the S waves 154° away from a straight path.
C) reflection at the mantle- core boundary directs the S waves at a 154° angle.
D) S waves cannot pass through solids with an extremely high density.

Question 41

What is meant by the "Mantle Flush"?

Question 42

Discuss how P- wave and S- wave shadow zones delineate the Earth's core.

Question 43

Briefly explain how we know the structure of the Earth's interior.

Question 44

Describe the principle of isostasy.

Question 45

What characteristics are necessary for a planet or a moon to generate a magnetic field?

Question 46

Discuss the relationships among depth, pressure, temperature, and physical state in the Earth's interior.

Question 47

Discuss how paleomagnetism can help geologists to reconstruct past geographic locations of the Earth's landmasses.

Question 48

How do geologists determine the Earth's interior temperatures?

Question 49

All of the following statements concerning mantle temperature are true EXCEPT:

A) lower concentrations of subsurface radioactive isotopes reduce the geothermal gradient.
B) higher concentrations of surface radioactive isotopes give a steeper geothermal gradient.
C) higher pressure at depth raises melting temperatures.
D) mantle rock melts at depths below 100 kilometers.

Question 50

How is gravity measured? What are gravity anomalies and what causes them?

Question 51

Magnetism is most closely associated with:

A) gravity and the ability of one mass to attract another mass.
B) the decay of radioactive atoms, which causes minerals to become magnetized.
C) chemical energy and the attraction of atoms during bonding.
D) electricity and the movement of electrons.

Question 52

Which of the following formulas describes the force of gravity?

A) Mass of A distance2/mass of B.
B) Mass of A mass of B2/distance.
C) Mass of A mass of B/distance².
D) Distance²/mass of A mass of B.

Question 53

Why do P waves travel at different speeds through different media? Why can S waves travel through only solids?

Question 54

The sample of mantle rock collected directly from the rifted Hess Deep valley was composed of:

A) granite.
B) gabbro.
C) peridotite.
D) basalt.