It is a fundamental tenet of geophysics that the Earth’s magnetic fiel

Question

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Passage # 216, Date : 19-Jul-2019
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It is a fundamental tenet of geophysics that the Earth’s magnetic field can exist in either of two polarity states: a “normal” state, in which north-seeking compass needles point to the geographic north, and a “reverse” state, in which they point to the geographic south. Geological evidence shows that periodically the field’s polarity reverses, and that these reversals have been taking place at an increasing rate. Evidence also indicates that the field does not reverse instantaneously from one polarity state to another; rather, the process involves a transition period that typically spans a few thousand years.

Though this much is known, the underlying causes of the reversal phenomenon are not well understood. It is generally accepted that the magnetic field itself is generated by the motion of free electrons in the outer core, a slowly churning mass of molten metal sandwiched between the Earth’s mantle (the region of the Earth’s interior lying below the crust) and its solid inner core. In some way that is not completely understood, gravity and the Earth’s rotation, acting on temperature and density differences within the outer core fluid, provide the driving forces behind the generation of the field. The reversal phenomenon may be triggered when something disturbs the heat circulation pattern of the outer core fluid, and with it the magnetic field.

Several explanations for this phenomenon have been proposed. One proposal, the “heat-transfer hypothesis,” is that the triggering process is intimately related to the way the outer core vents its heat into the mantle.  For example, such heat transfer could create hotter (rising) or cooler (descending) blobs of material from the inner and outer boundaries of the fluid core, thereby perturbing the main heat-circulation pattern.  A more controversial alternative proposal is the asteroid-impact hypothesis. In this scenario an extended period of cold and darkness results from the impact of an asteroid large enough to send a great cloud of dust into the atmosphere. Following this climatic change, ocean temperatures drop and the polar ice caps grow, redistributing the Earth’s seawater. This redistribution increases the rotational acceleration of the mantle, causing friction and turbulence near the outer core-mantle boundary and initiating reversal of the magnetic field.

How well do these hypotheses account for such observations as the long-term increase in the frequency of reversal? In support of the asteroid-impact model, it had been argued that the gradual cooling of the average ocean temperature would enable progressively smaller asteroid impacts (which are known to occur more frequently than larger impacts) to cool the Earth’s climate sufficiently to induce ice-cap growth and reversals. But theories that depend on extraterrestrial intervention seem less convincing than theories like the first, which account for the phenomenon solely by means of the thermodynamic state of the outer core and its effect on the mantle.   1  
 OA:C 
 1.Which one of the following statements regarding the Earth’s outer core is best supported by information presented in the passage?

(A) Heat circulation in the outer core controls the growth and diminution of the polar ice caps.
(B) Impact of asteroids on the Earth’s surface alters the way in which the outer core vents its heat into the mantle.
(C) Motion of electrons within the metallic fluid in the outer core produces the Earth’s magnetic field.
(D) Friction and turbulence near the boundary between the outer core and the mantle are typically caused by asteroid impacts.
(E) Cessation of heat circulation within the outer core brings on multiple reversals in the Earth’s magnetic field.

2  
 OA:E 
 2.The author’s objection to the second hypothesis discussed in the passage is most applicable to which one of the following explanations concerning the extinction of the dinosaurs?

(A) The extinction of the dinosaurs was the result of gradual changes in the composition of the Earth’s atmosphere that occurred over millions of years.
(B) The dinosaurs became extinct when their food supply was disrupted following the emergence of mammals.
(C) The dinosaurs succumbed to the new, colder environment brought about by a buildup of volcanic ash in the atmosphere.
(D) After massively overpopulation the planet, dinosaurs disappeared due to widespread starvation and the rapid spread of disease.
(E) After radical climatic changes resulted from the impact of a comet, dinosaurs disappeared from the Earth.

3  
 OA:A 
 3.The author mentions the creation of blobs of different temperatures in the Earth’s outer core ( Highlighted ) primarily in order to

(A) present a way in which the venting of heat from the outer core might disturb the heat-circulation pattern within the outer core
(B) provide proof for the proposal that ventilation of heat from the outer core into the mantle triggers polarity reversal
(C) give an example of the way in which heat circulates between the Earth’s outer core and the Earth’s exterior
(D) describe how the outer core maintains its temperature by venting its excess heat into the Earth’s mantle
(E) argue in favor of the theory that heat circulation in the Earth’s interior produces the magnetic field

4 
 OA:B 
 4.Which one of the following statements regarding the polarity of the Earth’s magnetic field is best supported by information in the passage?

(A) Most, but not all, geophysicists agree that the Earth’s magnetic field may exist in two distinct polarity states.
(B) Changes in the polarity of the Earth’s magnetic field have occurred more often in the recent past that in the distant past.
(C) Heat transfer would cause reversals of the polarity of the Earth’s magnetic field to occur more quickly than would asteroid impact.
(D) Geophysicists’ understanding of the reversal of the Earth’s magnetic field has increased significantly since the introduction of the heat-transfer hypothesis.
(E) Friction near the boundary of the inner and outer cores brings on reversal of the polarity of the geomagnetic field.

5  
 OA:D 
 5.Which one of the following can be inferred regarding the two proposals discussed in the passage?

(A) Since their introduction they have sharply divided the scientific community.
(B) Both were formulated in order to explain changes in the frequency of polarity reversal.
(C) Although no firm conclusions regarding them have yet been reached, both have been extensively investigated.
(D) They are not the only proposals scientists have put forward to explain the phenomenon of polarity reversal.
(E) Both were introduced some time ago and have since fallen into disfavor among geophysicists.

6  
 OA:D 
 6.The author mentions each of the following as possible contributing causes to reversals of the Earth’s magnetic field EXCEPT

(A) changes in the way heat circulates within the outer core fluid
(B) extended periods of colder temperatures on the Earth’s surface
(C) the creation of circulation blobs of outer core material of different temperatures
(D) changes in circulation patterns in the Earth’s oceans
(E) clouding of the Earth’s atmosphere by a large amount of dust

Source:   LSAT Official PrepTest 14   ( February 1995 ) 
 Difficulty Level:   650

Skywalker18 · Accepted Answer

All correct except Q2(misread the question) in 11 mins, including almost 5 mins to read.
Para 1- Earth's magnetic field- periodic reversals
Para 2- causes not well understood, reversal phenomenon may be triggered when something disturbs the heat circulation pattern of the outer core fluid
Para 3- explanations- heat-transfer hypothesis and asteroid-impact hypothesis
Para 4- Do these hypothesis account for increase in frequency of reversals?

1.Which one of the following statements regarding the Earth’s outer core is best supported by information presented in the passage?

(C) Motion of electrons within the metallic fluid in the outer core produces the Earth’s magnetic field.
It is generally accepted that the magnetic field itself is generated by the motion of free electrons in the outer core

2.The author’s objection to the second hypothesis discussed in the passage is most applicable to which one of the following explanations concerning the extinction of the dinosaurs?

(E) After radical climatic changes resulted from the impact of a comet, dinosaurs disappeared from the Earth.- the impact of a comet is an extraterrestrial intervention and thus the cause is of the same type in option E
But theories that depend on extraterrestrial intervention seem less convincing than theories like the first, which account for the phenomenon solely by means of the thermodynamic state of the outer core and its effect on the mantle.

3.The author mentions the creation of blobs of different temperatures in the Earth’s outer core ( Highlighted ) primarily in order to

(A) present a way in which the venting of heat from the outer core might disturb the heat-circulation pattern within the outer core
One proposal, the “heat-transfer hypothesis,” is that the triggering process is intimately related to the way the outer core vents its heat into the mantle. For example, such heat transfer could create hotter (rising) or cooler (descending) blobs of material from the inner and outer boundaries of the fluid core, thereby perturbing the main heat-circulation pattern.

4.Which one of the following statements regarding the polarity of the Earth’s magnetic field is best supported by information in the passage? 
(B) Changes in the polarity of the Earth’s magnetic field have occurred more often in the recent past that in the distant past.
Geological evidence shows that periodically the field’s polarity reverses, and that these reversals have been taking place at an increasing rate

5.Which one of the following can be inferred regarding the two proposals discussed in the passage? 
(D) They are not the only proposals scientists have put forward to explain the phenomenon of polarity reversal.- Correct
Several explanations for this phenomenon have been proposed.

6.The author mentions each of the following as possible contributing causes to reversals of the Earth’s magnetic field EXCEPT

(A) changes in the way heat circulates within the outer core fluid- incorrect, “heat-transfer hypothesis,” is that the triggering process is intimately related to the way the outer core vents its heat into the mantle.
(B) extended periods of colder temperatures on the Earth’s surface- incorrect, Following this climatic change, ocean temperatures drop and the polar ice caps grow, redistributing the Earth’s seawater. This redistribution increases the rotational acceleration of the mantle, causing friction and turbulence near the outer core-mantle boundary and initiating reversal of the magnetic field.
(C) the creation of circulation blobs of outer core material of different temperatures- incorrect, For example, such heat transfer could create hotter (rising) or cooler (descending) blobs of material from the inner and outer boundaries of the fluid core, thereby perturbing the main heat-circulation pattern.
(D) changes in circulation patterns in the Earth’s oceans- Correct
(E) clouding of the Earth’s atmosphere by a large amount of dust- incorrect,
In this scenario an extended period of cold and darkness results from the impact of an asteroid large enough to send a great cloud of dust into the atmosphere.

masoomjnegi · Answer

1. “It is generally accepted that the magnetic field itself is generated by the motion of free electrons in the outer core, a slowly churning mass of molten metal sandwiched between the Earth’s mantle (the region of the Earth’s interior lying below the crust) and its solid inner core.” This statement from the second paragraph clearly supports the statement ‘c’. Hence, c is the answer.

masoomjnegi · Answer

2. The author stated that theories that depend on extraterrestrial intervention seem less convincing than theories which account for the phenomenon solely by means of the thermodynamic state of the outer core and its effect on the mantle. This shows that author is highly unlikely to support or admit any explanation given for the extinction of dinosaurs that is based on extraterrestrial interventions. Only option ‘e’ mentions of an extraterrestrial intervention of a comet. So, author’s objections to second hypothesis is most applicable to the explanation stated in option ‘e’. Hence, ‘e’ is the answer.

auradediligodo · Answer

Hi everyone,
Took 14:40 minutes and got 5/6 correct.

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P1

Paragraph one starts with presenting the subject at hand: the magnetic field and polarity.
We know that when conditions are normal the compass will point at north.
On the other hand, when the polarity is reversed the compass will point at south.
We are also given that this changes in polarity has been occurring at an increasing rate and that are not instantaneous.

Brief summary:  Polarity changes occur more and more but not instantaneous

P2

Paragraph 2 stresses the fact that the causes behind the change in polarity are not very well understood.
What we know is that the magnetic field is produced by the motion of free electrons in the outer core (outer core= zone between the mantle and its inner core).
What on the other hand we don't understand well is the role of heart's gravity and rotation, role that affects the temperature and the density of the fluids in the outer core.
The heat-fluid pattern of the outer core in fact might affect the magnetic field

Brief summary:  The magnetic field and causes behind the changes

P3

Paragraph 3 gives us 2 of the many explanation to this phenomenon.
The first one is the heat transfer hypothesis, according to which there is a creation of blobs (cold or warm) that affect the heat-fluid patterns of the outer core, impacting on the polarity change.
The second,  controversial , explanation is the asteroid impact one.
According to this theory an asteroid has an impact, its dust reaches the atmosphere, provoking the drop of the temperatures and consequently the increase of the ice caps. Such increase affects the rotational acceleration of the mantle, causing friction and possibly generating a change in polarity.

Brief summary:  Two explanation the the phenomenon

P4

Paragraph 4 evaluates the two theories in terms of accountability for the long term frequency increase.
The asteroid impact theory at first seems plausible because the temperature drop in the ocean would allow impacts from smaller asteroid to induce the ice caps growth and vice versa.
However the first theory is more credible since it relies solely on events which are earth based

Brief summary:  accountability of the 2 theories

Main point

The main point is to investigate the causes behind the shift in polarity

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1.Which one of the following statements regarding the Earth’s outer core is best supported by information presented in the passage?

Pre-thinking

Inference question

The earth outer core is described in P2. Outer core= area between the mantle and its inner core
 
(A) Heat circulation in the outer core controls the growth and diminution of the  polar ice caps. 
 ice caps are nominated in P3 but are out of context here

(B) Impact of asteroids on the Earth’s surface alters the way in which the outer  core vents its heat into the mantle. 
 the impact causes friction in the mantle

(C)   Motion of electrons within the metallic fluid in the outer core produces the Earth’s magnetic field.
 This statement seems more like a paraphrase of the information in P2

(D) Friction and turbulence near the boundary between the outer core and the mantle are  typically  caused by asteroid impacts.
 the asteroid impact is a theory not a proven fact

(E) Cessation of heat circulation within the outer core brings on multiple reversals in the Earth’s magnetic field.
 cannot be inferred

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2.The author’s objection to the second hypothesis discussed in the passage is most applicable to which one of the following explanations concerning the extinction of the dinosaurs?

Pre-thinking

Application question

The asteroid impact theory is rejected because it provides an explanation based on something that comes from space. So, what we are looking for is an explanation for the extinction of dinosaurs based on something coming from space
 
(A) The extinction of the dinosaurs was the result of gradual changes in the composition of the Earth’s atmosphere that occurred over millions of years.
 Not in line with pre-thinking

(B) The dinosaurs became extinct when their food supply was disrupted following the emergence of mammals.
 Not in line with pre-thinking

(C) The dinosaurs succumbed to the new, colder environment brought about by a buildup of volcanic ash in the atmosphere.
 Not in line with pre-thinking

(D) After massively overpopulation the planet, dinosaurs disappeared due to widespread starvation and the rapid spread of disease.
 Not in line with pre-thinking

(E)   After radical climatic changes resulted from the impact of a comet, dinosaurs disappeared from the Earth.
 in line with pre-thinking

------------------------------------------------------------------------------------------

3.The author mentions the creation of blobs of different temperatures in the Earth’s outer core (Highlighted) primarily in order to

Pre-thinking

Purpose question

The purpose is to give the reason for the change in polarity.
 
  (A)   present a way in which the venting of heat from the outer core might disturb the heat-circulation pattern within the outer core
 Since disturbing the heat circulation pattern equals inducing a change in the polarity, correct

(B) provide proof for the proposal that ventilation of heat from the outer core into the mantle triggers polarity reversal
 Provide proof might be too extreme here.

(C) give an example of the way in which heat circulates between the Earth’s outer core and the Earth’s exterior
  Not in line with pre-thinking

(D) describe how the outer core maintains its temperature by venting its excess heat into the Earth’s mantle
 Not in line with pre-thinking

(E) argue in favor of the theory that heat circulation in the Earth’s interior  produces the magnetic field 
 Not in line with pre-thinking

SajjadAhmad  would you please explain why B is wrong?
   ------------------------------------------------------------------------------------------

4.Which one of the following statements regarding the polarity of the Earth’s magnetic field is best supported by information in the passage?

Pre-thinking

Inference question

Let's evaluate the statements
 
(A) Most, but not all, geophysicists agree that the Earth’s magnetic field may exist in two distinct polarity states.
 Cannot be inferred

(B)   Changes in the polarity of the Earth’s magnetic field have occurred more often in the recent past that in the distant past.
 Can be inferred: "and that these reversals have been taking place at an increasing rate."

(C) Heat transfer would cause reversals of the polarity of the Earth’s magnetic field to occur more quickly than would asteroid impact.
 Cannot be inferred

(D) Geophysicists’ understanding of the reversal of the Earth’s magnetic field has increased significantly since the introduction of the heat-transfer hypothesis.
 Cannot be inferred

(E) Friction near the boundary of the inner and outer cores brings on reversal of the polarity of the geomagnetic field.
 Cannot be inferred

------------------------------------------------------------------------------------------

5.Which one of the following can be inferred regarding the two proposals discussed in the passage?

Pre-thinking

Inference question

I would say that the first one is more credible than the second one
 
(A) Since their introduction they have sharply divided the scientific community.
 Cannot be inferred

(B) Both were formulated in order to explain changes  in the frequency  of polarity reversal.
 Cannot be inferred

(C) Although no firm conclusions regarding them have yet been reached,  both have been extensively investigated. 
 Cannot be inferred

(D)   They are not the only proposals scientists have put forward to explain the phenomenon of polarity reversal.
 "Several explanations for this phenomenon have been proposed."

(E)  Both were introduced some time ago and have since fallen into disfavor among geophysicists. 
 Cannot be inferred

------------------------------------------------------------------------------------------

6.The author mentions each of the following as possible contributing causes to reversals of the Earth’s magnetic field EXCEPT

Pre-thinking

Detail question

Let's evaluate the statements
 
(A) changes in the way heat circulates within the outer core fluid
"The reversal phenomenon may be triggered when something disturbs the heat circulation pattern of the outer core fluid, and with it the magnetic field."

(B) extended periods of colder temperatures on the Earth’s surface
"In this scenario an extended period of cold and darkness results from the impact of an asteroid large enough to send a great cloud of dust into the atmosphere."

(C) the creation of circulation blobs of outer core material of different temperatures
"For example, such heat transfer could create hotter (rising) or cooler (descending) blobs of material from the inner and outer boundaries of the fluid core, thereby perturbing the main heat-circulation pattern."

(D)   changes in circulation patterns in the Earth’s oceans
 Not mentioned

(E) clouding of the Earth’s atmosphere by a large amount of dust
 "In this scenario an extended period of cold and darkness results from the impact of an asteroid large enough to send a great cloud of dust into the atmosphere. "

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It is a good day to be alive!

Sajjad1994 · Answer

(B)  distorts information in the text, which makes it clear that magnetic field reversal is thought to be caused by a disturbance in heat circulation patterns in the outer core read the lines in the passage:

The reversal phenomenon may be triggered when something disturbs the heat circulation pattern of the outer core fluid, and with it the magnetic field.

Hope it helps

Hoozan · Answer

Hi  SajjadAhmad 
Please help me understand option (C) and (D) of Q.6

The last few lines of the para 4 mention 
(1) drop in ocean temperature
(2) redistribution of Earth's seawater

How is the redistribution of Earth's sea water different from "changes in circulation patterns of Earth's oceans"
----------------------------

(C)  the creation of  circulation  blobs of outer core material of different temperatures
 
How is "circulation" blobs correct.

From the first few lines of para 2 we can see that Blobs are creating. How can we infer that they are circulating?

Sajjad1994 · Answer

Don't forget this is an  EXCEPT  question, In “all/EXCEPT” questions, your task is to find the choice that isn’t true.

Why  C  is wrong?

Changes in oceanic circulation patterns aren’t mentioned anywhere in the text as possible contributors to magnetic field reversals. The  “asteroid-impact hypothesis”  does speak of temperature drops in and redistribution of seawater, but these events are different from changes in oceanic circulation patterns.

(C)  is part of the  “heat-transfer hypothesis.”  so C could be a possible cause of to reversals of the Earth’s magnetic field but not  D

Sajjad1994 · Answer

Sorry i am late in the party but i found this tag today so answering.

The author mentions hotter and cooler blobs in the context of describing the  “heat-transfer hypothesis.”  This hypothesis suggests that heat circulation patterns in the outer core are affected by the way in which heat is vented from the outer core.

(B)  distorts information in the text, which makes it clear that magnetic field reversal is thought to be caused by a disturbance in heat circulation patterns in the outer core, see these lines in the passage (Last few lines of para 2)

The reversal phenomenon may be triggered when something disturbs the heat circulation pattern of the outer core fluid, and with it the magnetic field.

Hope this helps

dadele · Answer

The passage talks about distribution of Earth's sea water. We are not told that if that has any relation to circulation patterns of oceans.

KeepMovingForward · Answer

16-17 min 1/6 correct.

Seemed easy passage. But the results say otherwise.

Skywalker18

Any suggestion on how to improve on RC? Will appreciate your input here.

I have already completed OG and GmatPrep material. Gave GMAT once too but could only manage 690 Q49V35. Need at least 750.

Thanks!

tkorzhan1995 · Answer

Sajjad1994 , can you please explain based on what we can infer D for Q5? What other proposals have been put forward?

Sajjad1994 · Answer

Explanation

5. Which one of the following can be inferred regarding the two proposals discussed in the passage?

Difficulty Level:   700

Explanation

Although this passage discusses just two hypotheses about magnetic field reversal, we’re told that others exist. The last sentence of the text explicitly refers to  “theories that depend on extraterrestrial intervention”  and  “theories like the first”  (i.e., “earthly” theories).

(A)  is beyond the scope of the text. We’re not told what geophysicists, in general, think about these hypotheses, let alone whether  “they have sharply divided the scientific community.”  All we can infer from the text is that there is some support for both hypotheses.

(B)  These two hypotheses were formulated to address the  “underlying causes”  of magnetic field reversal. That they might also address the issue of reversal frequency is simply a byproduct of their primary function.

(C)  is a  “half-right, half-wrong”  choice. True, no firm conclusions about either hypothesis have yet been reached; but there’s no information about the extent to which the two have been explored.

(E)  is beyond the scope of the text. We aren’t told precisely when either hypothesis was formulated. Moreover, both hypotheses have at least some support among geophysicists.

Answer: D

desertEagle · Answer

6.The author mentions each of the following as possible contributing causes to reversals of the Earth’s magnetic field EXCEPT

(A) changes in the way heat circulates within the outer core fluid
"The reversal phenomenon may be triggered when something disturbs the heat circulation pattern of the outer core fluid, and with it the magnetic field."

(B) extended periods of colder temperatures on the Earth’s surface
"In this scenario an extended period of cold and darkness results from the impact of an asteroid large enough to send a great cloud of dust into the atmosphere."

(C) the creation of circulation blobs of outer core material of different temperatures
"For example, such heat transfer could create hotter (rising) or cooler (descending) blobs of material from the inner and outer boundaries of the fluid core, thereby perturbing the main heat-circulation pattern."

(D) changes in circulation patterns in the Earth’s oceans
Not mentioned

(E) clouding of the Earth’s atmosphere by a large amount of dust
"In this scenario an extended period of cold and darkness results from the impact of an asteroid large enough to send a great cloud of dust into the atmosphere. "

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It is a fundamental tenet of geophysics that the Earth’s magnetic fiel

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