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

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New post 11 Jun 2015, 10:56
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.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.
OA:C


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.
OA:E


3.The author mentions the creation of blobs of different temperatures in the Earth’s outer core (lines 34-38) 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
OA:A


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.
OA:B


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.
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
OA:D

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New post 11 Jun 2015, 16:54
This passage comes from Barron's LSAT.

Not a good resource in my opinion. Actually for two reasons: becasue barron's per se as company (is not a business that might handle such company, the bast thing they did is for TOEFL not for exams such as GMAT) and because LSAT style, in my opinion, is not a good way to study for GMAT.

Hope this helps.
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New post 11 Jun 2015, 20:17
carcass wrote:
This passage comes from Barron's LSAT.

Not a good resource in my opinion. Actually for two reasons: becasue barron's per se as company (is not a business that might handle such company, the bast thing they did is for TOEFL not for exams such as GMAT) and because LSAT style, in my opinion, is not a good way to study for GMAT.

Hope this helps.



why are Lsat passages not a good source for Gmat preparation?.. I have no material left other than this to prepare any way....

This passage is from Old Lsat Papers btw...
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New post 12 Jun 2015, 01:50
I dont think this is a 700-level passage.
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New post 16 Jun 2015, 10:54
Even I felt the questions are bit easy. I was re reading whether I understood correctly.

RaviChandra wrote:
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.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.
OA:C


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.
OA:E


3.The author mentions the creation of blobs of different temperatures in the Earth’s outer core (lines 34-38) 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
OA:A


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.
OA:B


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.
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
OA:D


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New post 21 Dec 2018, 22:59
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.
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New post 21 Dec 2018, 23:00
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.
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Re: It is a fundamental tenet of geophysics that the Earth’s magnetic   [#permalink] 21 Dec 2018, 23:00
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