GEO 101 Actual Exam study set with
Questions and correct/verified Answers
In what ways does continental crust differ from oceanic crust? - ANSWER-Continental crust differs from
oceanic crust in all of the following ways: its thicker, less dense, more buoyant, richer in light elements
like Na, K, and Si, and poorer in dense elements like Fe and Mg relative to oceanic crust
Earth's interior is hot because - ANSWER-Earth's interior is hot because the process that formed Earth
(accretion) generated large amounts of heat. Additional heat has been added through geologic time by
radioactive decay of unstable isotopes (heat is a byproduct of the decay process). Molten rock or magma
is actually rare in earth's interior - only the outer core is hot enough to be above the melting point for
material of that composition under that amount of pressure.
Tectonic plates of rigid and brittle __________ move over a softer and ductile ___________ below. -
ANSWER-lithosphere; asthenosphere
The layer of the Earth that is thought to be a liquid is the: - ANSWER-Outer core
How does the lithosphere differ from the asthenosphere? - ANSWER-The lithosphere is a rigid and brittle
solid while the asthenosphere is a soft and ductile solid. (The terms crust and mantle are used to denote
differences in chemical composition; while the terms lithosphere and asthenosphere are used to denote
differences in physical state (for example, rigid, brittle solid vs.. soft, ductile solid). Because the
boundaries between layers with different chemical compositions do not occur at the same depth as
boundaries between layers with different physical properties, lithosphere cannot be considered
synonymous with crust, not can asthenosphere be considered synonymous with mantle. For example, a
large change in chemical composition occurs as you move from crust to mantle. However, there is no
change in physical properties at boundary between crust and mantle because uppermost mantle is still
cold enough relative to its melting point to behave in the same manner as the crust- as a rigid brittle
solid. The transition to a soft ductile solid- the asthenosphere- does not occur until we get further down
into the upper mantle - where temperature approaches the melting point of the mantle at that depth.)
Describe the Earth's internal structure in terms of both chemical composition and physical properties. -
ANSWER-The earth is divided into three layers, a crust, a mantle and a core, that differ in their chemical
composition. The crust is the thin outer layer, consisting primarily of oxygen, silicon and aluminum. It is
further subdivided into continental and oceanic crust. The oceanic crust is thinner and denser, and is
similar in composition to basalt (Si, O, Ca, Mg, and Fe). The continental crust is thicker and less dense,
and is similar to granite in composition (Si, O, Al, K, and Na). The mantle is made of magnesium, iron and
silicon. The core is almost exclusively iron and nickel. The outer core is liquid iron and the inner core is
solid iron. The mantle and crust are further divided into the lithosphere, asthenosphere and
mesosphere, depending on their physical properties, namely how close the material is to its melting
point. The lithosphere is cold and rigid and includes the curst and uppermost part of the mantle where
rocks are far below their melting point. Further down in the mantle is the asthenosphere where rocks
are weak and can flow because they are close to their melting point. The deepest part of the mantle is
the mesosphere where rocks are gain strong and below their melting point due to the high pressure.
, The division of Earth's interior into core, mantle, and crust is used to describe differences in - ANSWER-
Composition. (We use the crust-mantle-core terminology to describe differences in chemical
composition in Earth's interior. We use the lithosphere- asthenosphere terminology to describe
differences the physical state and behavior. Note that the boundaries between layers with different
compositions do not occur at the same depths as the boundaries between layers with different physical
properties. For example, there is a change in composition when passing from crust into mantle. But
there is no change in physical state or behavior at this boundary- the uppermost part of the mantle
behaves in the same way that the crust does because it is still far enough below its melting temperature
to be a rigid, brittle solid. The transition to a softer, more pliable solid occurs further down within the
mantle and this change in behavior occurs with no change in composition.)
Because earth is a closed system: - ANSWER-Both A and B: there is a finite supply of resources and all
waste and pollutants generated on Earth stay on Earth
Explain why geologists believe that the Earth's core is made mostly of iron. - ANSWER-The average
density of the Earth, as shown by its gravitational field, is significantly higher than the density of the
mantle, which is known from a few direct observations of materials erupted from volcanoes and
exposures of mantle rock at the surface. This is despite the fact that the mantle makes up most of the
earth by volume. Therefore, the core must be very dense to explain the earth's average density. Iron is
one element that would provide the needed density, and iron is known to be abundant in the solar
system from studies of meteorites, making iron a likely candidate for the composition of the core.
Which of the following are a result of planetary differentiation? - ANSWER-All of the above: Light
elements rose to form the crust; Heavy elements sank to form the core; Light lithosphere floating on
denser asthenosphere
Earth's atmosphere was once very similar in composition to the atmosphere of - ANSWER-Both B and C:
Venus and Mars
Which choice best describes the age distribution of oceanic crust? - ANSWER-oceanic crust is youngest at
the ridge and gets older with increasing distance from the ridge
How did seafloor spreading revive Alfred Wegener's ideas about continental drift? - ANSWER-sea floor
spreading provided a viable mechanism for moving the continents
At a passive continental margin the primary geologic process occuring is - ANSWER-sedimentation
(Passive continental margins are places where the crust changes from thick continental crust to thin
oceanic crust, but functioning as one plate- moving at the same direction and speed - and as such do not
coincide with a plate boundary. When that area of continental crust first started breaking up by
continental rifting, it was at a new divergent boundary, but is now far from the plate boundary due to
addition of new oceanic crust to the edge of each plate by seafloor spreading- with the plate boundary
remaining at the ocean ridge. As the edge of the continental crust gets further and further from the
divergent plate boundary where hot mantle rock is rising, the continental crust cools and subsides
(having been heated and elevated during the rifting stage). Since the crust was also thinned by the rifting
process, its not as thick as it once was and drops below sea level as it cools, forming a broad continental
Questions and correct/verified Answers
In what ways does continental crust differ from oceanic crust? - ANSWER-Continental crust differs from
oceanic crust in all of the following ways: its thicker, less dense, more buoyant, richer in light elements
like Na, K, and Si, and poorer in dense elements like Fe and Mg relative to oceanic crust
Earth's interior is hot because - ANSWER-Earth's interior is hot because the process that formed Earth
(accretion) generated large amounts of heat. Additional heat has been added through geologic time by
radioactive decay of unstable isotopes (heat is a byproduct of the decay process). Molten rock or magma
is actually rare in earth's interior - only the outer core is hot enough to be above the melting point for
material of that composition under that amount of pressure.
Tectonic plates of rigid and brittle __________ move over a softer and ductile ___________ below. -
ANSWER-lithosphere; asthenosphere
The layer of the Earth that is thought to be a liquid is the: - ANSWER-Outer core
How does the lithosphere differ from the asthenosphere? - ANSWER-The lithosphere is a rigid and brittle
solid while the asthenosphere is a soft and ductile solid. (The terms crust and mantle are used to denote
differences in chemical composition; while the terms lithosphere and asthenosphere are used to denote
differences in physical state (for example, rigid, brittle solid vs.. soft, ductile solid). Because the
boundaries between layers with different chemical compositions do not occur at the same depth as
boundaries between layers with different physical properties, lithosphere cannot be considered
synonymous with crust, not can asthenosphere be considered synonymous with mantle. For example, a
large change in chemical composition occurs as you move from crust to mantle. However, there is no
change in physical properties at boundary between crust and mantle because uppermost mantle is still
cold enough relative to its melting point to behave in the same manner as the crust- as a rigid brittle
solid. The transition to a soft ductile solid- the asthenosphere- does not occur until we get further down
into the upper mantle - where temperature approaches the melting point of the mantle at that depth.)
Describe the Earth's internal structure in terms of both chemical composition and physical properties. -
ANSWER-The earth is divided into three layers, a crust, a mantle and a core, that differ in their chemical
composition. The crust is the thin outer layer, consisting primarily of oxygen, silicon and aluminum. It is
further subdivided into continental and oceanic crust. The oceanic crust is thinner and denser, and is
similar in composition to basalt (Si, O, Ca, Mg, and Fe). The continental crust is thicker and less dense,
and is similar to granite in composition (Si, O, Al, K, and Na). The mantle is made of magnesium, iron and
silicon. The core is almost exclusively iron and nickel. The outer core is liquid iron and the inner core is
solid iron. The mantle and crust are further divided into the lithosphere, asthenosphere and
mesosphere, depending on their physical properties, namely how close the material is to its melting
point. The lithosphere is cold and rigid and includes the curst and uppermost part of the mantle where
rocks are far below their melting point. Further down in the mantle is the asthenosphere where rocks
are weak and can flow because they are close to their melting point. The deepest part of the mantle is
the mesosphere where rocks are gain strong and below their melting point due to the high pressure.
, The division of Earth's interior into core, mantle, and crust is used to describe differences in - ANSWER-
Composition. (We use the crust-mantle-core terminology to describe differences in chemical
composition in Earth's interior. We use the lithosphere- asthenosphere terminology to describe
differences the physical state and behavior. Note that the boundaries between layers with different
compositions do not occur at the same depths as the boundaries between layers with different physical
properties. For example, there is a change in composition when passing from crust into mantle. But
there is no change in physical state or behavior at this boundary- the uppermost part of the mantle
behaves in the same way that the crust does because it is still far enough below its melting temperature
to be a rigid, brittle solid. The transition to a softer, more pliable solid occurs further down within the
mantle and this change in behavior occurs with no change in composition.)
Because earth is a closed system: - ANSWER-Both A and B: there is a finite supply of resources and all
waste and pollutants generated on Earth stay on Earth
Explain why geologists believe that the Earth's core is made mostly of iron. - ANSWER-The average
density of the Earth, as shown by its gravitational field, is significantly higher than the density of the
mantle, which is known from a few direct observations of materials erupted from volcanoes and
exposures of mantle rock at the surface. This is despite the fact that the mantle makes up most of the
earth by volume. Therefore, the core must be very dense to explain the earth's average density. Iron is
one element that would provide the needed density, and iron is known to be abundant in the solar
system from studies of meteorites, making iron a likely candidate for the composition of the core.
Which of the following are a result of planetary differentiation? - ANSWER-All of the above: Light
elements rose to form the crust; Heavy elements sank to form the core; Light lithosphere floating on
denser asthenosphere
Earth's atmosphere was once very similar in composition to the atmosphere of - ANSWER-Both B and C:
Venus and Mars
Which choice best describes the age distribution of oceanic crust? - ANSWER-oceanic crust is youngest at
the ridge and gets older with increasing distance from the ridge
How did seafloor spreading revive Alfred Wegener's ideas about continental drift? - ANSWER-sea floor
spreading provided a viable mechanism for moving the continents
At a passive continental margin the primary geologic process occuring is - ANSWER-sedimentation
(Passive continental margins are places where the crust changes from thick continental crust to thin
oceanic crust, but functioning as one plate- moving at the same direction and speed - and as such do not
coincide with a plate boundary. When that area of continental crust first started breaking up by
continental rifting, it was at a new divergent boundary, but is now far from the plate boundary due to
addition of new oceanic crust to the edge of each plate by seafloor spreading- with the plate boundary
remaining at the ocean ridge. As the edge of the continental crust gets further and further from the
divergent plate boundary where hot mantle rock is rising, the continental crust cools and subsides
(having been heated and elevated during the rifting stage). Since the crust was also thinned by the rifting
process, its not as thick as it once was and drops below sea level as it cools, forming a broad continental
