Question 1

A body of rock begins at location A in the figure below.The rock,over a period of time,moves to location B and begins to melt.This is an example of melting due to ________. 
A)fractional crystallization
B)heat transfer
C)addition of volatiles
D)decompression

Accepted Answer

The process described in the question involves a body of rock moving from one location to another and beginning to melt. This is typically the result of decompression, where the pressure on the rock decreases as it moves to a shallower depth, causing melting to occur. Fractional crystallization involves the removal of minerals from a melt as it cools, heat transfer involves the transfer of heat from one source to another, and the addition of volatiles can also lead to melting, but these are not applicable to the scenario described in the question.

Question 2

Decay of radioactive isotopes,differentiation of Earth's iron core,gravity-driven compression,and meteoric bombardment all caused early Earth to ________.
A)glow brighter than the Sun
B)be much cooler than at present
C)be much hotter than at present
D)be much more oblong than at present

Accepted Answer

The decay of radioactive isotopes, differentiation of Earth's iron core, and gravity-driven compression all generated heat, causing early Earth to be much hotter than at present. Meteoric bombardment also contributed to this heat, but it was not the primary cause. Therefore, choice C is the best answer.

Question 3

The difference between magma and lava is ________.
A)magma cools more rapidly than lava
B)magma is found at the surface,whereas lava is found below the surface
C)magma is found beneath the surface,whereas lava is found at the surface
D)There is no difference;the two terms mean the same thing.

Accepted Answer

Magma is molten rock beneath the surface of the Earth, while lava is molten rock that has erupted and is at the surface of the Earth. Therefore, magma is found beneath the surface and lava is found at the surface. The other options are incorrect.

Question 4

In general,if a body of igneous (source)rock is subjected to partial melting,the magma that is produced is expected to be ________.
A)identical in chemical composition to the source rock
B)more mafic than the source rock
C)more felsic than the source rock
D)The melt composition is not predictable.

Accepted Answer

When partial melting occurs, the melt that is produced typically has a higher silica content (making it more felsic) than the source rock. This is because minerals with a lower melting point, like quartz and feldspar, are more common in felsic rocks and will melt before the more mafic minerals. As a result, the melt will have a higher concentration of these minerals and a higher silica content overall.

Question 5

Injecting hot fudge into ice cream and causing the ice cream to melt is an appropriate analogy for which cause of magma melt?
A)melting due to a decrease in pressure
B)melting due to an addition of volatiles
C)melting due to heat transfer from rising magma
D)flux melting

Accepted Answer

Just like injecting hot fudge into ice cream causes it to melt, heat transfer from rising magma causes the surrounding rock to melt and form magma.

Question 6

Viscosity does NOT depend on ________.
A)temperature
B)volatile content
C)silica content
D)the total volume of the magma body

Accepted Answer

Viscosity is a measure of the magma's resistance to flow, which is primarily determined by the silica content and temperature. Volatile content can also affect viscosity, but to a lesser extent. The total volume of the magma body is not a factor in determining viscosity.

Question 7

The formation of magma within Earth is NOT caused by which of the following processes?
A)decompression (drop in pressure)
B)addition of volatiles
C)transfer of heat from adjacent magma or very hot rocks
D)loss of volatiles to the atmosphere

Accepted Answer

Loss of volatiles to the atmosphere actually causes the cooling and solidification of magma, rather than its formation.

Question 8

A majority of the melts in the Earth form through the partial melting of ultramafic mantle rock.These newly formed magmas are ________.
A)ultramafic
B)mafic
C)felsic
D)intermediate

Accepted Answer

When ultramafic mantle rock partially melts, the resulting magmas are typically mafic in composition.

Question 9

Important volatiles in magmas include ________.
A)mafic minerals,such as olivine
B)potassium and aluminum
C)water and carbon dioxide
D)silicon and iron

Accepted Answer

Important volatiles in magmas include water and carbon dioxide. These volatiles play a significant role in determining the viscosity and explosiveness of volcanic eruptions. Mafic minerals like olivine and elements like potassium and aluminum are not necessarily considered volatiles in magmas, and silicon and iron are components of the magma but not volatiles.

Question 10

When magma crystallizes,________ are formed.
A)intrusive igneous rocks
B)extrusive igneous rocks
C)volatiles
D)pyroclastic debris

Accepted Answer

When magma cools and solidifies underground, it forms intrusive igneous rocks such as granite, gabbro, and diorite. Extrusive igneous rocks form when lava cools and solidifies above the Earth's surface. Volatiles refer to gases and fluids contained within magma or lava, and pyroclastic debris refers to fragments of volcanic rock and ash that are ejected during explosive volcanic eruptions.

Question 11

Igneous rocks ________.
A)are formed through the freezing or crystallization of a melt
B)are formed by changing existing rock by the application of heat and pressure
C)are formed by depositing loose material into layers
D)form by chemically precipitating from solutions

Accepted Answer

Igneous rocks are formed through the freezing or crystallization of a melt, which can occur both below and above the Earth's surface. Magma and lava are common examples of molten materials that can solidify to form igneous rocks.

Question 12

In general,when rock is partially melted,the chemistry of the melt is ________.
A)more mafic than the original chemistry of the rock that was partially melted
B)more felsic than the original chemistry of the rock that was partially melted
C)identical to the original chemistry of the rock that was partially melted
D)completely unpredictable (it could be more mafic or more felsic)

Accepted Answer

When rock is partially melted, the melt tends to be more felsic than the original rock. This is because felsic minerals (rich in silica and aluminum) have lower melting points compared to mafic minerals (rich in magnesium and iron), and thus they melt first, leading to a melt that is more felsic in composition.

Question 13

Most commonly,felsic igneous rocks ________.
A)contain more iron and magnesium than intermediate rocks
B)are lighter in color than mafic rocks
C)are darker in color than mafic rocks
D)are found in oceanic crust

Accepted Answer

Felsic igneous rocks are typically composed of light-colored minerals such as quartz, feldspar, and muscovite, and have a lower density than mafic rocks, which are composed of darker minerals such as pyroxene and olivine. Therefore, felsic rocks are lighter in color than mafic rocks.

Question 14

Given the solidus and liquidus curves below,which location represents material that is partially melted? 
A)A
B)B
C)C
D)D

Accepted Answer

Material that is partially melted would have a composition that is in between the solidus and liquidus curves, meaning it is in a region where both solid and liquid phases are present. Point C is the only location that falls in this region, making it the best choice for the answer.

Question 15

Very early in Earth's history (during the Hadean Eon),the Earth ________.
A)was very cold,so no igneous rocks had yet formed
B)was so hot that it was,at times,completely molten
C)was entirely composed of loose material called regolith
D)had a similar diversity in rock types as seen today

Accepted Answer

During the Hadean Eon, the Earth was bombarded by asteroids and had a lot of heat energy that led to the complete melting of the Earth's surface. This is evidenced by the lack of remaining rocks from this period and the presence of ancient zircon crystals with ages up to 4.4 billion years old, which could only have formed in a completely molten Earth.

Question 16

If the volatile content of magma is increased,its viscosity will ________.
A)increase
B)decrease
C)stay the same
D)Volatile content has no effect on viscosity.

Accepted Answer

When the volatile content of magma is increased, it tends to decrease the viscosity. Volatiles, such as water vapor and carbon dioxide, help to break the chemical bonds within the magma, making it less viscous and more fluid.

Question 17

Volatiles refer to substances that ________.
A)crystallize most rapidly out of a melt
B)melt immediately upon contact with a hot body of magma
C)are highly flammable
D)have a tendency to evaporate into gases

Accepted Answer

Volatiles are substances with low boiling points, meaning they can evaporate easily into gases. Examples of volatiles include water vapor, carbon dioxide, and sulfur dioxide, which are commonly found in volcanic gases.

Question 18

The geotherm is the rate of change of ________.
A)pressure with depth in Earth's interior
B)temperature with depth in Earth's interior
C)temperature with altitude in Earth's atmosphere
D)temperature with latitude on Earth's surface

Accepted Answer

The geotherm is the rate of change of temperature with depth in Earth's interior.

Question 19

Which type of magma has the greatest silica content?
A)felsic
B)intermediate
C)mafic
D)ultramafic

Accepted Answer

Felsic magma has the greatest silica content, with typically over 65% silica. This high silica content results in a high viscosity and a tendency to erupt explosively, creating ash, pumice, and obsidian.

Question 20

As compared to mafic igneous rocks,all felsic igneous rocks ________.
A)cool and solidify more quickly
B)cool and solidify more slowly
C)solidify at higher temperatures
D)solidify at lower temperatures

Accepted Answer

Felsic igneous rocks have a higher silica content than mafic igneous rocks, which means they have a lower melting point and will solidify at lower temperatures. Therefore, they cool and solidify more quickly than mafic igneous rocks.

Quiz 6: Up From the Inferno: Magma and Igneous Rocks

Decay of radioactive isotopes,differentiation of Earth's iron core,gravity-driven compression,and meteoric bombardment all caused early Earth to ________.

The difference between magma and lava is ________.

In general,if a body of igneous (source) rock is subjected to partial melting,the magma that is produced is expected to be ________.

Injecting hot fudge into ice cream and causing the ice cream to melt is an appropriate analogy for which cause of magma melt?

Viscosity does NOT depend on ________.

The formation of magma within Earth is NOT caused by which of the following processes?

A majority of the melts in the Earth form through the partial melting of ultramafic mantle rock.These newly formed magmas are ________.

Important volatiles in magmas include ________.

When magma crystallizes,________ are formed.

Igneous rocks ________.

In general,when rock is partially melted,the chemistry of the melt is ________.

Most commonly,felsic igneous rocks ________.

Given the solidus and liquidus curves below,which location represents material that is partially melted?

Very early in Earth's history (during the Hadean Eon) ,the Earth ________.

If the volatile content of magma is increased,its viscosity will ________.

Volatiles refer to substances that ________.

The geotherm is the rate of change of ________.

Which type of magma has the greatest silica content?

As compared to mafic igneous rocks,all felsic igneous rocks ________.