Earths mantle lies below the crust and above the core. Scientists can

Question

Earth’s mantle lies below the crust and above the core. Scientists cannot examine the mantle directly but have inferred its structure by measuring how seismic waves from earthquakes are distorted as they traverse it. In laboratory experiments, researchers have also studied mineral formation at the high pressures and temperatures in the mantle. These measurements and experiments indicate that the mantle consists of several concentric layers, with different minerals predominating at different depths. As pressures and temperatures increase toward the core, they force the elements to rearrange into new crystal structures, forming different minerals.

Until 2004, scientists believed that the lower mantle was fairly uniformly composed of a dense form of magnesium silicate belonging to a family of crystals called perovskite that extended all the way down to the boundary between the mantle and the core. But seismic measurements revealed the lower mantle’s bottommost layer to be substantially denser than the rest. Since magnesium silicate perovskite has a tightly packed geometry that seemed to maximize the mass per unit volume,  the higher pressures in this bottommost layer were not expected to change the perovskite’s geometry.  Thus, scientists assumed that a greater abundance of heavy elements within the crystal must explain the higher density. However, this assumption was also problematic, because convection should stir the lower mantle, mixing the layers and producing a uniform distribution of elements.

In 2004, geophysicists managed to expose magnesium silicate to the extreme pressures and temperatures of this bottommost layer, producing an unexpected new, denser crystalline structure they called postperovskite. Because postperovskite would conduct heat away from Earth’s core more rapidly than perovskite would, scientists hypothesize that the early Earth’s core must have been hotter than previously thought. This suggests that the inner core cooled enough to solidify only about one billion years ago. The solid inner core strengthens Earth’s magnetic field. This field shields the surface from radiation from space, which can cause genetic mutations and would be especially dangerous for life on land. Thus, the growing intensity of the magnetic field about one billion years ago may have first allowed life to expand from the seas onto dry land. So postperovskite's discovery may help explain the timing of developments in life’s evolution.   1 
 1. The statement that "the higher pressures in this bottommost layer were not expect to change the perovskite's geometry" (see  highlighted text ) functions in the passage

A. support for a claim about magnesium silicate perovskite's tightly packed geometry
B. a premise supporting the claim that scientists made an incorrect assumption about the abundance of heavy elements within the perovskite
C. an explanation for the fact that a certain scientific assumption was found to be problematic
D. a description of a prediction for which the preceding statement about magnesium silicate perovskite provides the grounds
E. an experimental result on which a subsequent statement about postperovskite is intended to cast doubt

2 
 2. The passage most clearly states that Earth's inner core

A. contains a recently discovered crystalline mineral denser than magnesium silicate perovskite
B. first produced a magnetic field around the Earth about one billion years ago
C. after its solidification contributed to an increase in the incidence of genetic mutations
D. influences the amount of radiation reaching Earth's surface from space
E. was formerly believed to contain a greater abundance of heavy elements than the mantle contains

3 
 3. In the context of the passage, the main purpose of the first paragraph is to

A. state the main conclusion of the passage and explain the methodology by which that conclusion was inferred
B. describe the main experimental evidence supporting a conclusion stated in the second paragraph
C. provide background information to help readers understand the discussion in the second and third paragraphs
D. discuss a puzzling scientific observation for which the third paragraph provides a possible explanation
E. introduce the main topic of the passage and summarize the major findings discussed in the second and third paragraphs

4 
 4. The passage is mainly concerned with discussing

A. research into mineral formation in Earth's lower mantle, and interpretations of that research
B. the concentric layers of minerals that form Earth's core, mantle, and crust
C. competing hypotheses regarding the effects of postperovskite in Earth's mantle
D. the geometry and composition of two crystalline forms of magnesium silicate comprising distinct layers of Earth's lower mantle
E. a possible explanation of the observed effects Earth's core and mantle have on Earth's magnetic field, and of the consequences of those effects

CHECK HERE THE  SAME PASSAGE  WITH DIFFERENT SET OF QUESTIONS

https://gmatclub.com/forum/download/file.php?id=75446  https://gmatclub.com/forum/download/file.php?id=75445  https://gmatclub.com/forum/download/file.php?id=75444 
 https://gmatclub.com/forum/download/file.php?id=78181

Sajjad1994 · Answer

Explanation

1. The statement that "the higher pressures in this bottommost layer were not expect to change the perovskite's geometry" (see highlighted text) functions in the passage

Explanation

A.  suggests that the highlighted text serves as evidence or support for a claim regarding the tightly packed geometry of magnesium silicate perovskite. However, the highlighted statement itself does not directly assert or discuss the tightly packed geometry of perovskite. Instead, it mentions that scientists did not expect the geometry of perovskite to change under higher pressures.

B.  suggests that the highlighted text serves as a premise supporting the claim that scientists incorrectly assumed the abundance of heavy elements within perovskite. However, the highlighted text does not directly address the abundance of heavy elements within perovskite. Instead, it focuses on scientists' expectations regarding the behavior of perovskite under higher pressures.

C.  suggests that the highlighted text provides an explanation for why a certain scientific assumption (presumably about the behavior of perovskite) was found to be problematic. While the highlighted text does highlight scientists' unexpected findings regarding perovskite under higher pressures, it does not explicitly explain why the assumption was problematic.

D.   correctly identifies the function of the highlighted text in the passage. The preceding statement discusses scientists' expectations regarding the behavior of magnesium silicate perovskite under higher pressures, suggesting that its geometry would remain unchanged. The highlighted text then describes the prediction based on this expectation. Therefore, option D accurately reflects the role of the text in the passage.

E.  suggests that the serves as an experimental result that is subsequently challenged or cast into doubt by a subsequent statement about postperovskite. However, the text itself is not an experimental result but rather a prediction or expectation based on scientists' understanding of perovskite's properties.

Answer: D

Sajjad1994 · Answer

Explanation

2. passage most clearly states that Earth's inner core

Explanation

The passage mentions several key points about Earth's inner core:
 
  Solidification Timing : The solid inner core of the Earth cooled enough to solidify only about one billion years ago. 
  Strengthening the Magnetic Field : The solid inner core strengthens Earth’s magnetic field, which shields the surface from radiation from space. 
  Connection to Life's Evolution : The growing intensity of the magnetic field about one billion years ago may have allowed life to expand from the seas onto dry land.  
 A.  accurately reflects the discovery mentioned in the passage about the denser crystalline structure called postperovskite that was discovered in the bottommost layer of the lower mantle, not the inner core. Therefore, it is incorrect.

B.  incorrectly attributes the production of the magnetic field to the inner core. The passage states that the inner core strengthens the magnetic field, but it doesn't state that it first produced it. Therefore, it is incorrect.

C.  misinterprets the passage. The solidification of the inner core is associated with strengthening Earth's magnetic field, which shields the surface from radiation, thus decreasing the incidence of genetic mutations. Therefore, this option is incorrect.

D.   accurately reflects the information in the passage. The solid inner core strengthens Earth’s magnetic field, which shields the surface from radiation from space. Therefore, it is the correct answer.

E.  misinterprets the passage. The passage discusses the discovery of postperovskite in the lower mantle, not the inner core. Therefore, it is incorrect.

Answer: D

Sajjad1994 · Answer

Explanation

3. In the context of the passage, the main purpose of the first paragraph is to

Explanation

A  is incorrect because the  first paragraph  does not state the main conclusion of the passage. Instead, it introduces the topic and methodology used by scientists to study the mantle.

B  is incorrect because the first paragraph does not describe specific experimental evidence supporting a conclusion stated in the second paragraph. Instead, it provides background information about the structure of the mantle and the methods used to study it.

C.   This option is correct. The first paragraph provides essential background information about the mantle's structure and the methods used to study it, setting the stage for the subsequent discussion in the second and third paragraphs.

D  incorrect because the first paragraph does not discuss a specific scientific observation. It primarily introduces the topic and methodology of studying the mantle.

E  is incorrect because while the first paragraph introduces the main topic of the passage (Earth's mantle) and provides background information, it does not summarize the major findings discussed in the subsequent paragraphs.

Answer: C

av722 · Answer

Q1:

A. support for a claim about magnesium silicate perovskite's tightly packed geometry
What claim was made about mag. silicate's tightly packed geometry? A fact is given: 'since m.s. perovskite has a tightly packed geometry that seemed to maximize the mass per unit volume,' and a prediction (highlighted sentence) is given after the fact. But apart from that, no claim is made about it's tightly packed geometry.

B. a premise supporting the claim that scientists made an incorrect assumption about the abundance of heavy elements within the perovskite
Firstly, the highlighted sentence doesn't really support the scientist's assumption that the greater abundance of heavy elements within the crystal must explain the higher density. It's a prediction that was taken before the results were revealed. Secondly, the highlighted sentence doesn't support the claim that the scientists made an  incorrect  assumption.

C. an explanation for the fact that a certain scientific assumption was found to be problematic
The assumption that the 'greater abundance of heavy elements within the crystal must explain the higher density' was found to be problematic. But the highlighted sentence doesn't  explain  the above assumption. The latter was the assumption before the seismic measurement was taken, the former was the new assumption assigned given the surprising results.

D. a description of a prediction for which the preceding statement about magnesium silicate perovskite provides the grounds 
The "higher pressures in this bottommost layer  were not expected  to change the perovskite's geometry". That's a prediction right there. The previous sentence is a fact providing the ground for the prediction-- that it has a "tightly packed geometry".

E. an experimental result on which a subsequent statement about postperovskite is intended to cast doubt
Firstly, this sentence is not an experimental result. It says the higher pressures 'were not expected,' indicating that this is a prediction, rather than a result or observed effect. Additionally, the subsequent statement about the heavy elements is intended to provide an explanation for the higher density given what the scientist's expected, so this statement is certainly not intended to cast doubt.

Q2:
Best way to answer this question is to word match for 'Earth's inner core,' which shows up in the third paragraph.

A. contains a recently discovered crystalline mineral denser than magnesium silicate perovskite
From the previous paragraph, we know that the higher density is found in the  mantle , not the core. While there is a recently discovered crystalline mineral denser than m.s.p (postperovskite), there's no indication that its found in Earth's inner core.

B. first produced a magnetic field around the Earth about one billion years ago
From the third paragraph, we know that the 'inner core cooled enough to solidify only about one billion years ago' and the 'solid inner core strengthens Earth's magnetic field'. But the fact that the solid inner core  strengthens  Earth's magnetic field doesn't mean that it  first   produced  a magnetic field around one billion years ago. This choice distorts what's in the passage.

C. after its solidification contributed to an increase in the incidence of genetic mutations
The passage says the inner core cooled enough to solidify one billion years ago, and it being solid strengthens Earth's magnetic field. It  shields  radiation from space, which can cause genetic mutations. So, if anything, the solidification would reduce the incidence of genetic mutations.

D. influences the amount of radiation reaching Earth's surface from space 
Correct. As we've established: solid core -> strengthens magnetic field -> shields radiation from space. So the inner core absolutely does influence the amount of radiation reaching Earth's surface.

E. was formerly believed to contain a greater abundance of heavy elements than the mantle contains
This choice confuses the preceding paragraph's discussion about the contents of the mantle. There is no discussion about the comparison between the abundance of heavy metals within the core versus the mantle.

Q3:

A. state the main conclusion of the passage and explain the methodology by which that conclusion was inferred
The second sentence briefly touches on the methodology 'inferred ints structure by measuring how seismic waves from earthquakes are distorted as they traverse it,' but there is no conclusion in the first paragraph, so this is out.

B. describe the main experimental evidence supporting a conclusion stated in the second paragraph
Firstly, the experimental evidence introduced in the first paragraph is used to introduce the information in the second paragraph. There's not really a conclusion in the second paragraph. All evidence necessary for the assumptions discussed in the second paragraph is present in the second paragraph itself. Out.

C. provide background information to help readers understand the discussion in the second and third paragraphs 
Correct. This paragraph is providing background info abut the earth's mantle and its structure, and the second and third pargraphs elaborate on its structure and a hypothesis for what these findings may mean.

D. discuss a puzzling scientific observation for which the third paragraph provides a possible explanation
This pargraph never mentions a puzzling scientific observation. The second pargraph does that.

E. introduce the main topic of the passage and summarize the major findings discussed in the second and third paragraphs
While this paragraph does introduce, it doesn't summarize the major findings discussed in the second and third paragraphs. The second paragraph discusses explanations for a surprising observation about the lower mantle's bottommost layer and the third paragraph makes a hypothesis based on some of these findings. None of this information can be found in the first paragraph though.

Q4:

A. research into mineral formation in Earth's lower mantle, and interpretations of that research 
Correct. This is exactly what the passage does. The first paragraph introduces research into the mantle and its structure, the second paragraph details mineral formation in the lower mantle, and the second and third paragraphs discuss interpretations of results from the research.

B. the concentric layers of minerals that form Earth's core, mantle, and crust
While it does discuss the layers of minerals that form Earth's core and mantle, it never discusses the minerals in the crust. Out.

C. competing hypotheses regarding the effects of postperovskite in Earth's mantle
This is discussed in the second paragraph, but it's not the focus of the passage.

D. the geometry and composition of two crystalline forms of magnesium silicate comprising distinct layers of Earth's lower mantle
While the geometry and composition of m.s.p are discussed in the second paragraph, there's no mention of the geomtry and composition of postperovskite in the third paragraph. Additionally, the third paragraph veers off into hypotheses about this unexpected new structure. This choice doesn't accurately reflect what's discussed in the passage. Out.

E. a possible explanation of the observed effects Earth's core and mantle have on Earth's magnetic field, and of the consequences of those effects
While Earth's core and mantle are discussed, but there's no link between the mantle and Earth's magnetic field, only the core. The passage discusses how 'the field shields surface radiation from space,' which could be a consequence, but this is really set up to present a hypothesis. So not only is this inaccurate, but it distorts the role of parts of the passage and it only occurs in the third paragraph-- which isn't representative of the passage as a whole.

bharathhr · Answer

In question 1 , i choose C cus I also felt that the assumption that is mentioned in 2nd para that was held untill 2004 , that the whole lower mantle is made of Mg silicate , is problamatc since , if its that the case , the higher density of he lowermost layer cannot be explained by this, cus the geometry doesnt allow Mg silicate cant become more denser.

guddo · Answer

1. The statement that "the higher pressures in this bottommost layer were not expect to change the perovskite's geometry" (see  highlighted text ) functions in the passage

The highlighted statement is a  prediction based on the immediately preceding information . Because perovskite already appeared to have a tightly packed geometry that maximized mass per unit volume, scientists did not expect additional pressure to compress or rearrange that geometry further.

(A) support for a claim about magnesium silicate perovskite's tightly packed geometry

Incorrect. The direction is reversed. The tightly packed geometry is used to support the highlighted statement, not the other way around.

(B) a premise supporting the claim that scientists made an incorrect assumption about the abundance of heavy elements within the perovskite

Incorrect. The highlighted statement helped lead scientists to the heavy-element explanation, but the passage does not use it to show that this assumption was incorrect.

(C) an explanation for the fact that a certain scientific assumption was found to be problematic

Incorrect. The assumption about heavy elements was problematic because convection should mix the mantle and produce a uniform distribution of elements.

(D) a description of a prediction for which the preceding statement about magnesium silicate perovskite provides the grounds

Correct.   The preceding statement says that perovskite had a tightly packed geometry that seemed already to maximize density. On that basis, scientists predicted that the still higher pressures near the core would not change its geometry.

(E) an experimental result on which a subsequent statement about postperovskite is intended to cast doubt

Incorrect. The highlighted statement is a prediction or expectation, not an experimental result.

Answer: (D)

guddo · Answer

I see why (C) is tempting, but it refers to the  wrong assumption .

The highlighted sentence helps explain why scientists  turned to the heavy-element explanation : if pressure could not make perovskite denser by changing its geometry, the extra density had to come from something else.

But the passage says that this heavy-element assumption was problematic  because convection should mix the elements throughout the lower mantle , not because of perovskite’s geometry.

So the highlighted sentence is best described by (D): it is a  prediction based on the preceding statement  about perovskite already having a tightly packed geometry.

gullyboy09 · Answer

Hi  MartyMurray ,  KarishmaB , can you please help me with the question 2 here.

2. The passage most clearly states that Earth's inner core

D. influences the amount of radiation reaching Earth's surface from space

Passage states that "The solid inner core strengthens Earth’s magnetic field. This field shields the surface from radiation from space." It protects, but it doesn't influence the amount of radiation reaching the surface. For example, I use sunscreen which protects me from radiation but it doesn't influence the amount reaching. 
If we need to pick best of all then maybe D can be the answer, but then again I have two issues with it. First, generally when no option is correct, it tends to take more time as I had to go through all the options again. Second, question says "clearly states" which creates further doubt when one is choosing the answer D.

KarishmaB · Answer

Question 1

Think of it as a Boldface CR question. Every word in the correct option must make sense. 
  Given:   
 Since magnesium silicate perovskite has a tightly packed geometry that seemed to maximize the mass per unit volume, the  higher pressures in this bottommost layer were not expected to change the perovskite’s geometry . 
Thus, scientists assumed that a greater abundance of heavy elements within the crystal must explain the higher density. However, this assumption was also problematic, because convection should stir the lower mantle, mixing the layers and producing a uniform distribution of elements.

A. support for a claim about magnesium silicate perovskite's tightly packed geometry

The highlighted is actually an implication of the claim about magnesium silicate perovskite's tightly packed geometry. It doesn't provide support to the claim.

B. a premise supporting the claim that scientists made an incorrect assumption about the abundance of heavy elements within the perovskite
  
It does not support that scientists made an incorrect assumption (that there must be an abundance of heavy elements). In fact it supports the assumption that there must be an abundance of heavy elements. Since higher pressures were not expected to change the geometry so then  a greater abundance of heavy elements within the crystal makes sense. So it supports the assumption.

C. an explanation for the fact that a certain scientific assumption was found to be problematic
  
It does not explain why the assumption (that there must be an abundance of heavy elements) was found to be problematic. As we discussed above, it supports the assumption.

D. a description of a prediction for which the preceding statement about magnesium silicate perovskite provides the grounds
  
It describes a prediction (that perovskite's geometry does not change) and the preceding statement ( magnesium silicate perovskite has a tightly packed geometry that seemed to maximize the mass per unit volume) provides support to the prediction. This is correct.

E. an experimental result on which a subsequent statement about postperovskite is intended to cast doubt

It is not an experimental result. It was theorized (Note the words ... was not expected to change...)

Answer (D)

KarishmaB · Answer

Question 2

2. The passage most clearly states that Earth's inner core

A. contains a recently discovered crystalline mineral denser than magnesium silicate perovskite
B. first produced a magnetic field around the Earth about one billion years ago
C. after its solidification contributed to an increase in the incidence of genetic mutations
D. influences the amount of radiation reaching Earth's surface from space
E. was formerly believed to contain a greater abundance of heavy elements than the mantle contains

Note that we are talking about inner core here. Only the last paragraph talks about it.

Given:  
 Because postperovskite would conduct heat away from Earth’s core more rapidly than perovskite would, scientists hypothesize that the early Earth’s core must have been hotter than previously thought. This suggests that the inner core cooled enough to solidify only about one billion years ago. The solid inner core strengthens Earth’s magnetic field. This field shields the surface from radiation from space, which can cause genetic mutations and would be especially dangerous for life on land. Thus, the growing intensity of the magnetic field about one billion years ago may have first allowed life to expand from the seas onto dry land. So postperovskite's discovery may help explain the timing of developments in life’s evolution.

A. contains a recently discovered crystalline mineral denser than magnesium silicate perovskite

The bottom layer of the mantle contains this, not the core.

B. first produced a magnetic field around the Earth about one billion years ago

It strengthened the magnetic field 1 billion years ago. It did not first produce it.

C. after its solidification contributed to an increase in the incidence of genetic mutations

No. It helped shield life from mutations.

D. influences the amount of radiation reaching Earth's surface from space

Yes, it does. It strengthens the magnetic field which shields the Earth's surface from radiation from space.

E. was formerly believed to contain a greater abundance of heavy elements than the mantle contains

We don't know if this is true as per the passage. Heavy elements were discussed with respect to bottom layer of mantle only.

Answer (D)

KarishmaB · Answer

Question 3

3. In the context of the passage, the main purpose of the first paragraph is to

A. state the main conclusion of the passage and explain the methodology by which that conclusion was inferred
B. describe the main experimental evidence supporting a conclusion stated in the second paragraph
C. provide background information to help readers understand the discussion in the second and third paragraphs
D. discuss a puzzling scientific observation for which the third paragraph provides a possible explanation
E. introduce the main topic of the passage and summarize the major findings discussed in the second and third paragraphs

The first paragraph only gives us general background on the topic. The actual discussion on layers of mantle begins in the second paragraph and on the core, its impact on radiation and evolution of life is discussed in the third paragraph.

Hence option (C) is correct here.

gullyboy09 · Answer

Hi  KarishmaB , p assage states that "The solid inner core strengthens Earth’s magnetic field. This field shields the surface from radiation from space." It protects, but it doesn't influence the  amount  of radiation  reaching  the surface. For example, I use sunscreen which protects me from radiation but it doesn't influence the amount reaching.

KarishmaB · Answer

Question 4.

4. The passage is mainly concerned with discussing

A. research into mineral formation in Earth's lower mantle, and interpretations of that research
B. the concentric layers of minerals that form Earth's core, mantle, and crust
C. competing hypotheses regarding the effects of postperovskite in Earth's mantle
D. the geometry and composition of two crystalline forms of magnesium silicate comprising distinct layers of Earth's lower mantle
E. a possible explanation of the observed effects Earth's core and mantle have on Earth's magnetic field, and of the consequences of those effects

The discussion revolves around lower mantle layers of  magnesium silicate perovskite, postperovskite, how it impacted cooling of core and how that impacted magnetic field finally leading to life on land.

A. research into mineral formation in Earth's lower mantle, and interpretations of that research

This is correct. It does discuss research into mineral formation in Earth's lower mantle, and interpretations of that research (the whole core-magnetic field-life theory)

B. the concentric layers of minerals that form Earth's core, mantle, and crust

Certainly wrong because crust has no role to play in the discussion. Eliminate.

C. competing hypotheses regarding the effects of postperovskite in Earth's mantle.

Only one hypothesis is discussed regarding the effects of postperovskite in Earth's mantle (quick cooling of core and so on...)

D. the geometry and composition of two crystalline forms of magnesium silicate comprising distinct layers of Earth's lower mantle

The whole core-magnetic field interpretation is ignore in this option.

E. a possible explanation of the observed effects Earth's core and mantle have on Earth's magnetic field, and of the consequences of those effects

No discussion on mantle having impact of Earth's magnetic field so eliminate.

Answer (A)

KarishmaB · Answer

How does the sunscreen protect you from the radiation? It influences how much of the radiation reaches your skin. Without sunscreen, all the UV radiation would reach your skin, but with it, a negligible amount does. 
When the magnetic field shields the surface from radiation, it means it doesn't allow the radiation to reach the surface. So it impacts the amount of radiation that reaches the surface - 100% would have reached the surface without the field but now almost none does (0%). So the amount reaching the surface has changed.

gullyboy09 · Answer

But at the same time it is also possible that they are still reaching the surface but magnetic field (or sunscreen) fighting against them and saving us from not getting harmed.

guddo · Answer

2. The passage most clearly states that Earth's inner core

The passage explains that the inner core solidified about one billion years ago and that the  solid inner core strengthens Earth’s magnetic field . That magnetic field  shields Earth’s surface from radiation from space . Therefore, the inner core indirectly affects how much of that radiation actually reaches the surface.

(A) contains a recently discovered crystalline mineral denser than magnesium silicate perovskite

Incorrect. Postperovskite was discovered in the bottommost layer of the  mantle , not in the inner core.

(B) first produced a magnetic field around the Earth about one billion years ago

Incorrect. The passage says the solid inner core strengthens the magnetic field. It does not say that the magnetic field first appeared when the inner core solidified.

(C) after its solidification contributed to an increase in the incidence of genetic mutations

Incorrect. The passage suggests the opposite. A stronger magnetic field shields the surface from radiation that can cause genetic mutations.

(D) influences the amount of radiation reaching Earth's surface from space

Correct.   The solid inner core strengthens Earth’s magnetic field, and that field shields the surface from radiation from space. Therefore, the inner core indirectly  affects how much radiation reaches Earth’s surface .

(E) was formerly believed to contain a greater abundance of heavy elements than the mantle contains

Incorrect. The proposed greater abundance of heavy elements concerned the bottommost layer of the  lower mantle , not the inner core.

Answer: (D)

Earths mantle lies below the crust and above the core. Scientists can

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Earths mantle lies below the crust and above the core. Scientists can

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