Chapter 12 Earth's Interior

True or False? Oceanic crust is compositionally more similar to the mantle than to continental crust.

True

What is the average geothermal gradient in the crust? A) 20°C/km B) 30°C/km C) 45°C/km D) 100°C/km

B) 30°C/km

What is the average thickness of the oceanic crust? A) 4 km B) 7 km C) 40 km D) 70 km

B) 7 km

Which atom is easier to compress when pressure is squeezing a rock and why? A) Negative ion; it has more electrons and is "fluffier." B) Positive ion; it has fewer electrons and is already densely compact. C) Negative ion; electrons are easier to remove. D) Positive ion; it is less resistant and easier to compress.

A) Negative ion; it has more electrons and is "fluffier."

What is the dominant mineral in the lower mantle? A) Perovskite B) Olivine C) Quartz D) Pyroxene

A) Perovskite

What is the average density of oceanic crust? A) 2.7 g/cm3 B) 3.0 g/cm3 C) 3.3 g/cm3 D) 5.6 g/cm3

B) 3.0 g/cm3

As of 2015, what was the deepest drill core yet taken that allowed scientists to study the Earth's interior? A) 7.6 km B) 12.3 km C) 15 km D) 50.5 km

B) 12.3 km

What is the difference in densities between the upper mantle and the lower mantle? A) 2.7 & 3.0 g/cm3 B) 3.0 & 3.3 g/cm3 C) 3.3 &5.6 g/cm3 D) 10 & 12.1 g/cm3

C) 3.3 &5.6 g/cm3

Which layer is thought to be the birthplace of deep mantle plumes? A) Transition zone B) Outer core C) D" layer D) Shadow zone

C) D" layer

Which of the following factors contributed toward the early increase in temperature in the Earth's interior? A) Impact from planetesimals B) Friction between landmasses C) Friction between landmasses and radioactive decay D) Radioactive decay and impact from planetesimals

D) Radioactive decay and impact from planetesimals

________ is a technique to view three-dimensional changes in composition and density by using seismology. A) Magnetometry B) Paleomagnetism C) Chemical convection D) Seismic tomography

D) Seismic tomography

True or False? The inner core and the outer core are compositionally the same. The major difference between them is the states of matter in which they exist.

True

What is the average rate of temperature increase in the mantle? A) 0.3°C/km B) 0.7°C/km C) 1°C/km D) 1.3°C/km

A) 0.3°C/km

What is the average density of continental crust? A) 2.7 g/cm3 B) 3.0 g/cm3 C) 3.3 g/cm3 D) 5.6 g/cm3

A) 2.7 g/cm3

Where is oceanic crust generated? A) Along divergent plate boundaries B) Where volcanic lava meets the sea C) Where continents collide D) Where magma bodies are emplaced deep in the crust

A) Along divergent plate boundaries

Where is the highest rate of heat flow escaping the Earth's interior? A) At mid-ocean ridges B) At subduction zones C) At volcanoes D) At mountain ranges

A) At mid-ocean ridges

Which of the following material properties will not result in a seismic velocity anomaly when using seismic tomography? A) Confining pressure B) Composition C) Temperature D) Water content

A) Confining pressure

Which physical property is responsible for determining how Earth materials separate into interior layers? A) Density B) Color C) Molecular charge D) Tensile strength

A) Density

An earthquake occurs in California. What is the minimum magnitude an earthquake can have if it is to be picked up by seismographic networks around the world? A) M 5.5 B) M 7 C) M 8 D) M 9.5

A) M 5.5

Which of the following materials will allow for the fastest transmission of seismic waves? A) Rigid, less compressible material B) Material that has been slightly heated C) Partially molten material D) Molten material

A) Rigid, less compressible material

What will happen to a seismic wave when it is refracted? A) The wave will be bent when passing into a material of differing density. B) The wave will undulate. C) The wave will be bounced back toward its source. D) Nothing will change the wave.

A) The wave will be bent when passing into a material of differing density.

________ is the process where materials separate into different layers due to density. A) Shearing B) Differentiation C) Phase change D) Tensional stress

B) Differentiation

What materials make up Earth's core? A) Perovskite and silica B) Iron and nickel C) Olivine and pyroxene D) Sulfur and aluminum

B) Iron and nickel

If the outer core is cooler than the inner core, why is it in a liquid state? A) It has more radioactivity than in the inner core. B) It is under less pressure than the inner core. C) It has greater water content than the inner core. D) It has higher density materials than the inner core.

B) It is under less pressure than the inner core.

Which layer or layers of the interior are believed to have convection cells? A) Mantle B) Mantle and outer core C) Inner core D) Outer core and inner core

B) Mantle and outer core

Since humans cannot access the core, what objects do scientists use as a proxy to determine the composition of the inner and outer core? A) Volcanic rocks B) Meteorites C) Comets D) Glaciers

B) Meteorites

Which seismic wave(s) would be most useful in determining the extent and thickness of the Earth's interior layers? A) P waves B) P and S waves C) S waves D) Surface waves

B) P and S waves

Of the three mechanisms of heat transfer, which is the only one that does not operate in the interior of Earth? A) Convection B) Radiation C) Conduction

B) Radiation

Where is the thickest continental crust in North America? A) Appalachian Mountains B) Rocky Mountains C) Basin and Range region D) Great Basin

B) Rocky Mountains

Why might there be density changes between different parts of the same layer of the planet? A) Different materials make up different regions of the same layer. B) Some materials may compress when squeezed by overlying rock. C) Repelling forces may cause some atoms to expand. D) Differentiation is still separating materials into distinct interior layers.

B) Some materials may compress when squeezed by overlying rock.

The inner core is believed to rotate independently from the outer layers of Earth. Why is this possible? A) The immense interior pressures generate rotation. B) The inner core is separated from the mantle by the liquid outer core and can spin freely. C) Radioactive decay generates spin. D) Frictional drag pushes the inner core at a different rate than the rest of the planet.

B) The inner core is separated from the mantle by the liquid outer core and can spin freely.

Outside of the crust, the layer that scientists know the most about is the mantle. Other than via seismic waves, how else do geologists obtain information about the composition of the mantle? A) Drill cores B) Volcanoes C) Sonar D) Seismic waves

B) Volcanoes

A ________ occurs when an iron-rich fluid in the core is electrically charged and flowing, which generates a magnetic field. A) geotherm B) geodynamo C) geophysical anomaly D) geosyncline

B) geodynamo

The magnetic north pole is currently moving (toward /away from) the geographic North Pole, and the magnetic south pole is currently moving (toward /away from) the geographic South Pole. A) toward; toward B) toward; away from C) away from; toward D) away from; away from

B) toward; away from

P waves moving through the base of continents move at about ________ km/sec, but once they cross the Moho, the velocity changes to ________ km/sec. A) 8; 4 B) 2; 10 C) 6; 8 D) 3; 9

C. 6; 8

What is diffraction? A) A seismic wave is bounced back toward its source. B) A seismic wave is bent when moving from one material to another. C) A seismic wave is bent when it passes by a curved surface. D) Seismic waves are separated by liquids

C) A seismic wave is bent when it passes by a curved surface.

Where is the thinnest continental crust in North America? A) Appalachian Mountains B) Mississippi River Valley C) Basin and Range region D) Colorado Plateau

C) Basin and Range region

Which process is responsible for Earth's magnetic field? In which layer does this process occur? A) Radiation; upper mantle B) Subduction; lower mantle C) Convection; outer core D) Crystallization; inner core

C) Convection; outer core

What physical property of continents makes them difficult to subduct? A) Age B) Temperature C) Low density D) Thickness

C) Low density

Which one of the following is not one of the three compositionally distinct layers of the Earth's interior? A) Crust B) Mantle C) Lower mantle D) Core

C) Lower mantle

Which layer of Earth makes up more than 82 percent of the volume of the planet? A) Outer core B) Crust C) Mantle D) Inner core

C) Mantle

Why is conduction not an efficient way to move heat through most of the Earth? A) Radioactive decay generates too much heat. B) Molecules are too far apart to transfer heat via that method. C) Rocks are poor conductors of heat. D) Radiation is the most efficient way to move heat through the interior.

C) Rocks are poor conductors of heat.

________ are responsible for the heat generated in the interior today. A) Meteorite impacts B) Magma plutons C) Short-lived radioactive isotopes D) Nuclear reactions

C) Short-lived radioactive isotopes

How is the shape of Earth affected by its rotation? A) Earth is perfectly round. B) The poles are further from the center of Earth than the equator. C) The equator is further from the center of Earth than the poles.

C) The equator is further from the center of Earth than the poles.

What will happen to a seismic wave when it is reflected? A) The wave will be bent. B) The wave will undulate. C) The wave will be bounced back toward its source. D) Nothing will change the wave.

C) The wave will be bounced back toward its source.

Heat will transfer by ________ in the outer core. A) radiation B) convection C) conduction and convection D) conduction

C) conduction and convection

True or False? In the D" layer, the portion of the mantle closest to the core-mantle Boundary is hypothesized to be partially melted because the S-wave velocities decrease by 30% when passing through it.

True

The following choices contain densities of various materials. Based on this data, which will yield the fastest seismic velocity? A) 2.7 g/cm3 B) 3.0 g/cm3 C) 3.3 g/cm3 D) 5.6 g/cm3

D) 5.6 g/cm3

What is a mineral phase change? A) A mineral melts from a solid state to a liquid state. B) The exterior of a mineral weathers and changes color. C) A mineral changes density because of the addition of water. D) Atoms in a mineral are rearranged into a denser and more stable structure.

D) Atoms in a mineral are rearranged into a denser and more stable structure.

Which of the following materials would cause the greatest gravity anomaly? A) Quartz B) Water C) Granite D) Metallic ore

D) Metallic ore

The ________ is a seismic boundary between the crust and the mantle where there is a dramatic increase in seismic wave velocity. A) Schrodinger discontinuity B) Greenschist facies C) Low-velocity pathway D) Moho boundary

D) Moho boundary

What is the primary method scientists use to determine the layering of the interior of the Earth? A) Drill cores B) Volcanic rocks C) Sonar D) Seismic waves

D) Seismic waves

When olivine is undergoing a mineral phase change due to pressure, what mineral will it form? A) Perovskite B) Quartz C) Pyroxene D) Spinel

D) Spinel

How does water get from the surface to the middle of the mantle? A) Percolation via pores and fractures B) Subterranean streams C) Seawater seeping into the interior at mid-ocean rifts D) Subducting oceanic lithosphere

D) Subducting oceanic lithosphere

Why do seismic waves follow strongly curved paths as they move through the interior? A) Their paths are altered by changes in temperature. B) Their paths are altered by reflection off dense materials. C) Their velocities are altered by changes in chemistry. D) Their velocities are changed because of increasing pressure with depth.

D) Their velocities are changed because of increasing pressure with depth.

The composition of the upper mantle is defined by ________. A) granite B) quartz C) perovskite D) peridotite

D) peridotite

True or False? P waves cannot penetrate the outer core because it is liquid.

False

True or False? Seismic tomography requires only the data from one earthquake in order to "see" all parts of the Earth's interior.

False

True or False? The inner core is shrinking.

False

True or False? The mantle is composed of pure nickel and iron.

False