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GMATPrep EP2 :Scientists generally credit violent collisions

This topic has 4 expert replies and 5 member replies

GMATPrep EP2 :Scientists generally credit violent collisions

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Scientists generally credit violent collisions between tectonic plates, the mobile fragments of Earth’s rocky outer shell, with sculpting the planet’s surface, as, for example, when what is now the Indian subcontinent collided with Asia, producing the Himalayan Mountains. However, plate tectonics cannot fully explain certain massive surface features, such as the “superswell” of southern Africa, a vast plateau over 1,000 miles across and nearly a mile high. Geologic evidence shows that southern African has been slowly rising for the past 100 million years, yet it has not experienced a tectonic collision for nearly 400 million years. The explanation may be in Earth’s mantle, the layer of rock underlying the tectonic plates and extending down over 1,800 miles to the outer edge of Earth’s iron core.

Since the early twentieth century, geophysicists have understood that the mantle churns and roils like a thick soup. The relative low density of the hottest rock makes that material buoyant, so it slowly ascends, while cooler, denser rock sinks until heat escaping the molten core warms it enough to make it rise again. While this process of convection was known to enable the horizontal movement of tectonic plates, until recently geophysicists were skeptical of its ability to lift or lower the planet’s surface vertically. However, recent technological advances have allowed geophysicists to make three-dimensional “snapshots” of the mantle by measuring vibrations, or seismic waves, set in motion by earthquakes originating in the planet’s outer shell and recording the time it takes for them to travel from an earthquake’s epicenter to a particular recording station at the surface. Because geophysicists know that seismic waves become sluggish in hot, low-density rock, and speed up in colder, denser regions, they can now infer the temperatures and densities in a given segment of the interior. By compiling a map of seismic velocities from thousands of earthquakes across the globe, they can also begin to map temperatures and densities throughout the mantle.These methods have revealed some unexpectedly immense formations in the deepest parts of the mantle; the largest of these is a buoyant mass of hot rock directly below Africa’s southern tip. Dispelling researchers’ initial doubts, computer models have confirmed that this formation is buoyant enough to rise slowly within the mantle and strong enough to push Africa upward as it rises.

1) In the highlighted text( Himalayan Mountains), the author mentions the Himalayan Mountains most likely In order to

A) highlight certain similarities between the southern African superswell and other massive features on Earth's surface
B) identify a feature of Earth's surface that predates the origins of the southern African superswell
C) provide an example of a feature of Earth's surface that can be explained by plate tectonics
D) suggest that geophysicists are correct in attributing the sculpting of Earth's surface to violent collisions between tectonic plates
E) give an example of a feature of Earth's surface that scientists are unable to explain fully

OA:C

2) It can be Inferred from the passage that prior to the technological advances referred to In the highlighted text(recent technological advances), geophysicist were unable to

A) understand exactly how the collisions of tectonic plates created the Earth's mountains
B) establish that mantle material becomes more buoyant as it heats and more sluggish as it cools
C)start mapping the densities and temperatures of rock throughout the mantle
D) connect the phenomenon of convection within the mantle to the horizontal movement of tectonic plates E) prove that different types of rock within the mantle have different densities

OA:C


3) According to the passage, the process of convection mentioned in the highlighted text(this process of convection) was regarded until recently by geophysicists as

A) a process unlikely to occur deep within Earth's mantle
B) a probable explanation for the rising of the southern African plateau
C) an improbable explanation for the horizontal movement of tectonic plates
D) unlikely to account for the vertical rising or lowering of Earth's surface
E) unrelated to the creation of Earth's most massive surface features

OA: D

4) According to the passage, which of the following pieces of geological evidence makes plate tectonics an inadequate explanation for the existence of the superswell of southern Africa?

A) The depth of the mantle underlying the tectonic plates surrounding southern Africa
B) The absence of any significant mountain ranges in the vicinity of the superswell
C) The vast size of the plateau comprising the superswell's most visible feature
D) The rate at whit the superswell has been rising above sea level over the past 100 million years
E) The absence of any tectonic collisions in southern Africa for several hundred million years prior to the origin of the superswell

OA: E

Source: GMATPrep EP2

Got only first one right Sad

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This passage follows a very common structure for GMAT RC science passages:
- there's a prevailing theory / something most scientists believe
- however, new evidence shows that they were wrong / partially wrong / there's some aspect we haven't considered
- details about how evidence was gathered
- explanation about why it allows us to draw new conclusions


Quote:
1) In the highlighted text( Himalayan Mountains), the author mentions the Himalayan Mountains most likely In order to

A) highlight certain similarities between the southern African superswell and other massive features on Earth's surface
B) identify a feature of Earth's surface that predates the origins of the southern African superswell
C) provide an example of a feature of Earth's surface that can be explained by plate tectonics
D) suggest that geophysicists are correct in attributing the sculpting of Earth's surface to violent collisions between tectonic plates
E) give an example of a feature of Earth's surface that scientists are unable to explain fully
Whenever you have a question about something presented "in order to," think back to the general structure of the passage. Broadly speaking, anything mentioned in the passage can usually fall into one of the following categories:
- a theory
- evidence for a theory
- a counterexample to something previously mentioned
- a specific example of a general rule
etc.

In this passage, the thing that scientists generally believe is that collisions between tectonic plates sculpt the planet's surface. The Himalayan Mountains are given as an example of this prevailing theory.

A) Later in the passage it's suggested that the African superswell might be caused by similar processes, but that's not why the Himalayas are mentioned at this point.
B) Predating is irrelevant - we don't care when these processes happen in time.
C) Yes - this is the prevailing theory that we're providing an example of.
D) The next sentence says "plate tectonics cannot fully explain," so this is not correct.
E) The Himalayas are explained by plate tectonics. The African superswell is not.

The answer is C.

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EdM in Mind, Brain, and Education
Harvard Graduate School of Education


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Quote:
2) It can be Inferred from the passage that prior to the technological advances referred to In the highlighted text(recent technological advances), geophysicist were unable to

A) understand exactly how the collisions of tectonic plates created the Earth's mountains
B) establish that mantle material becomes more buoyant as it heats and more sluggish as it cools
C)start mapping the densities and temperatures of rock throughout the mantle
D) connect the phenomenon of convection within the mantle to the horizontal movement of tectonic plates
E) prove that different types of rock within the mantle have different densities
If "until recently geophysicists were skeptical of its ability to lift or lower the planet’s surface vertically," but recent advances "have allowed geophysicists to make three-dimensional “snapshots” of the mantle ," it can be inferred that they were unable to make these types of snapshots previously, and these new snapshots have allowed them to know about the ability to lift the planet's surface vertically.

Later, it says

A) We're talking about superswells, not mountains. Incorrect.
B) The beginning of the 2nd paragraph, it's implied that scientists already knew about heat = buoyancy. Incorrect.
C) These new snapshots are what allowed scientists to compile a map of seismic velocities. Correct.
D) These advances are all about tracking vertical movement, not horizontal movement. Incorrect.
E) The paragraph discusses rocks in general, but makes no distinctions between different types of rocks. Incorrect.

The answer is C.

_________________


Ceilidh Erickson
Manhattan Prep GMAT & GRE instructor
EdM in Mind, Brain, and Education
Harvard Graduate School of Education


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Quote:
3) According to the passage, the process of convection mentioned in the highlighted text(this process of convection) was regarded until recently by geophysicists as

A) a process unlikely to occur deep within Earth's mantle
B) a probable explanation for the rising of the southern African plateau
C) an improbable explanation for the horizontal movement of tectonic plates
D) unlikely to account for the vertical rising or lowering of Earth's surface
E) unrelated to the creation of Earth's most massive surface features
We're told that convection "was known to enable the horizontal movement of tectonic plates," but "until recently geophysicists were skeptical of its ability to lift or lower the planet’s surface vertically."

A) There is no mention of the depth at which convection occurs. Incorrect.
B) The African plateau is a feature that could not be explained by horizontal movement of plates. Incorrect.
C) That's the opposite of what the sentence says. Incorrect.
D) Since "geophysicists were skeptical of its ability to lift or lower the planet’s surface vertically," then this answer is a perfect fit.
E) No, because it explains horizontal movement of tectonic plates.

The answer is D.

_________________


Ceilidh Erickson
Manhattan Prep GMAT & GRE instructor
EdM in Mind, Brain, and Education
Harvard Graduate School of Education


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4) According to the passage, which of the following pieces of geological evidence makes plate tectonics an inadequate explanation for the existence of the superswell of southern Africa?

A) The depth of the mantle underlying the tectonic plates surrounding southern Africa
B) The absence of any significant mountain ranges in the vicinity of the superswell
C) The vast size of the plateau comprising the superswell's most visible feature
D) The rate at whit the superswell has been rising above sea level over the past 100 million years
E) The absence of any tectonic collisions in southern Africa for several hundred million years prior to the origin of the superswell
The passage says: "However, plate tectonics cannot fully explain certain massive surface features, such as the “superswell” of southern Africa, a vast plateau over 1,000 miles across and nearly a mile high. Geologic evidence shows that southern African has been slowly rising for the past 100 million years, yet it has not experienced a tectonic collision for nearly 400 million years."

Plate tectonics cannot explain the superswell because it has been rising long after its last tectonic collision; therefore something else must explain why it was rising 300 million years later.

A) depth of the mantle is irrelevant
B) this is not mentioned
C) the passage mentions that the superswell is vast, but this in itself is not evidence for why plate tectonics did not cause its rise.
D) the *fact* that it has risen long since a tectonic collision is relevant. The *rate* at which it has risen is not.
E) Correct - this is a perfect paraphrase of what the passage says.

The answer is E.

_________________


Ceilidh Erickson
Manhattan Prep GMAT & GRE instructor
EdM in Mind, Brain, and Education
Harvard Graduate School of Education


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Ceilidh, Thanks for your wonderful explanation Smile

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bobbymovie wrote:
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Awesome information dear. Thanks a lot for every thing.
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