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# The last ice age has left its tell-tales written quite clearly across

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Tuck School Moderator
Joined: 31 Aug 2016
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The last ice age has left its tell-tales written quite clearly across  [#permalink]

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04 Sep 2018, 18:25
Question 1
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based on 32 sessions

50% (03:13) correct 50% (03:20) wrong

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Question 2
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based on 41 sessions

53% (01:29) correct 48% (01:20) wrong

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Question 3
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based on 35 sessions

41% (01:25) correct 59% (01:04) wrong

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The last ice age has left its tell-tales written quite clearly across the landscape. When Louis Agassiz first promulgated his theory that ice had once covered the Swiss countryside, he looked to the valleys there that retain glaciers to this day. Like other observers, he noted the presence of strange boulders, called "erratics," tossed down in valleys like flotsam after a flood had drained away. He saw the strange polish along the bedrock—a sheen imparted as if by some massive swipe of sandpaper; he saw the debris of rocks and boulders fringing the margin of existing glaciers. He saw what can be seen still, markings in stone that indicated that ice once flowed over vast stretches of land now clear and verdant.

The Australian climate historian L.A. Frakes has prospected through various theories proposed to account for those early ice ages. He isn‘t terribly enthusiastic about any of the possible culprits, but his choice for the least unlikely of them all emerges out of the recent revival of what was once a radically unorthodox idea: that continents drift over the face of the planet. Frakes argues that the glaciers originated at sites near the poles and that the ice ages began because the continents of the early earth had drifted to positions that took more and more of their land nearer to the polar regions.

More land near the poles meant that more precipitation fell as snow and could be compacted on land to form glaciers. With enough glaciers, the increase in the amount of sunlight reflected back into space off the glistening white sheen of the ice effectively reduced the amount by which the sun warmed the earth, creating the feedback loop by which the growth of glaciers encouraged the growth of more glaciers. Rocks have been found in North America, Africa and Australia whose ages appear to hover around the 2.3 billion-year-old mark. That date and their spread are vague enough, however, to make it almost impossible to determine just how much of the earth was icebound during the possible range of time in which each of the glacial deposits was formed.

Uncertainties about both the timing and the extent of these glaciers also muddy the search for the cause of the ancient ice ages. The record is so spotty that geologists are not sure whether areas near the equator or nearer the poles were the coolest places on earth. It‘s also possible that volcanic eruptions had tossed enough dust into the atmosphere to screen out sunlight and cool the earth.

Such traces are the currency of science—data—and like money, a richness of data both buys you some credibility and ties you down, eliminating at least some theoretically plausible explanations. For this early period, theorists have come up with a variety of ideas to explain the ancient ice ages, all elegant and mostly immune to both proof and criticism. For example, a change in the earth‘s orbit could have reduced the amount of sunlight reaching the planet. However, the only physical signature of such an event that would show in the rocks would be the marks of the glaciers themselves.

1. There is an implicit assumption in the statement that geologists don‘t know whether the coolest places on earth were near the poles or near the equator. The assumption is that:

A. both polar and equatorial glacial deposits have been found.

B. certain geological information can be considered lost forever.

C. it is more important to determine the date of the ice ages than the extent of the glaciers.

D. the glaciers were extremely mobile in spite of their mass.

E. areas around the equator are usually hotter than those around the poles

2. Suppose that an advocate of the "change in orbit" theory of the ancient ice ages criticizes a defender of the "volcanic eruption" theory on the grounds that only some of the glacial records contain evidence of prior volcanic activity. The defender might justifiably counter this attack by pointing out that:

A. a change in the earth‘s orbit would have increased rather than reduced the sunlight reaching the planet.

B. volcanoes could not possibly release enough dust to block the atmosphere.

C. a theory that has some supporting evidence is better than a theory that cannot be proved.

D. a theory should be so constructed as to be immune from proof.

3. Suppose paleobotanists discover that during geological periods of reduced sunlight, ancient forests died away, leaving fossilized remains. What is the relevance of this information to the passage?

A. It supports the claim that dust from volcanic eruptions caused the ice ages.

B. It weakens the claim that dust from volcanic eruptions caused the ice ages.

C. It supports the claim that ice ages were accompanied by widespread loss of vegetation.

D. It weakens the claim that the only evidence of a change in orbit would be glacier marks.

E. It has no relevance to the passage

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The last ice age has left its tell-tales written quite clearly across  [#permalink]

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12 Sep 2018, 05:52
9 mins all correct.

OEs..

1) Try to get a basic prediction for assumption questions if possible. If scientists don‘t know whether the poles or the equator were the coolest, they must have some sort of evidence that both were awfully cold. (A) fits this. If unsure, try the denial test: If glacial deposits haven‘t been found at both, then one should be demonstrably colder than the other.

(B): Distortion. The argument that scientists are unsure doesn‘t depend on the idea that some geological information is forever gone. While this may be true, it‘s not why scientists are unsure.

(C): Out of Scope. This has nothing to do with the statement.

(D): Out of Scope. Even if this were true, it still wouldn‘t explain why geologists were unsure which part of the earth had been the coolest.

(E): Out of Scope. This has nothing to do with the statement.

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Re: The last ice age has left its tell-tales written quite clearly across  [#permalink]

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12 Sep 2018, 05:54

2) The author mentions both of these theories; paraphrase what is said about them: the volcanic theory has some evidence in glacial records; the orbital change theory has no evidence at all. The volcano-scientist would be quick to point this out in his defense; (C) says the same thing.

(A): Out of Scope. We have no way of knowing from the passage the consequences of a change of orbit.

(B): Opposite. The advocate of the volcano theory wouldn‘t help his cause with this.

(D): Distortion. While the author mentions that these theories are immune from proof, that‘s not necessarily something in their favour, nor would it distinguish the vulcanologist‘s argument from that of the orbital theorists.

(E): Out of scope.

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Re: The last ice age has left its tell-tales written quite clearly across  [#permalink]

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12 Sep 2018, 05:55

3) What would cause reduced sunlight? Only an orbital change. Think back on what the author says about the orbital change theory: its only evidence is the glaciation itself. This new evidence would therefore weaken the author‘s argument about the orbital theory: (D).

(A): Out of Scope. Though volcanic eruptions can lead to a reduction in the amount of sunlight that reaches earth, it isn't necessarily the case here.

(B): Out of Scope. As above. This evidence is outside the scope of the volcanic theory.

(C): Opposite. The author never makes this claim.

(E):It does have relevance to the passage as described above

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Re: The last ice age has left its tell-tales written quite clearly across  [#permalink]

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13 Sep 2018, 11:29
7:12.All correct.Found this to be straightforward. Excuse me for the timing though.

If any explaining is needed pls ask...I'll do my best.
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Re: The last ice age has left its tell-tales written quite clearly across  [#permalink]

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26 Oct 2018, 23:17
Can anybody explain how Option C - It supports the claim that ice ages were accompanied by widespread loss of vegetation.
of Question 3 is opposite.
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Re: The last ice age has left its tell-tales written quite clearly across  [#permalink]

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27 Oct 2018, 01:52
NonPlus wrote:
Can anybody explain how Option C - It supports the claim that ice ages were accompanied by widespread loss of vegetation.
of Question 3 is opposite.

I would have said C for question 3 too

Sent from my iPhone using GMAT Club Forum mobile app
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Joined: 09 Mar 2016
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The last ice age has left its tell-tales written quite clearly across  [#permalink]

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27 Oct 2018, 03:35
malbash01 wrote:
NonPlus wrote:
Can anybody explain how Option C - It supports the claim that ice ages were accompanied by widespread loss of vegetation.
of Question 3 is opposite.

I would have said C for question 3 too

Sent from my iPhone using GMAT Club Forum mobile app

malbash01
NonPlus

hey guys hope you are ejoying your gmat weekend

Question: Suppose paleobotanists discover that during geological periods of reduced sunlight, ancient forests died away, leaving fossilized remains. What is the relevance of this information to the passage?

Now C is wrong because there is no claim that ice ages were accompanied by widespread loss of vegetation.

I guess you guys chose C based on the extract below, which is wrong.

“It‘s also possible that volcanic eruptions had tossed enough dust into the atmosphere to screen out sunlight and cool the earth”

However the key information to correct answer is in the extract below:

For example, a change in the earth‘s orbit could have reduced the amount of sunlight reaching the planet. However, the only physical signature of such an event that would show in the rocks would be the marks of the glaciers themselves.

The first sentence in red is a claim without evidence, and the second sentence in blue emphasizes that only event based on physical signature i.e. evidence in this case -marks in the rocks- is the only prove of a change in orbit

Hence D would weaken claim that the only evidence of a change in orbit is glacier marks, if paleobotanists had discovered that during geological periods of reduced sunlight, ancient forests died away, leaving fossilized remains.

cheers
D
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Re: The last ice age has left its tell-tales written quite clearly across  [#permalink]

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27 Oct 2018, 03:55
Got all three questions correct, however, it took me more than four minutes to read and briefly summarize the passage...

I feel like that lack of speed might kick my behind during the actual test. Did anyone else encounter this timing problem due to the length of the passage?
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https://gmatclub.com/forum/verbal-strategies-268700.html#p2082192

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The last ice age has left its tell-tales written quite clearly across  [#permalink]

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27 Oct 2018, 04:10
Arro44 wrote:
Got all three questions correct, however, it took me more than four minutes to read and briefly summarize the passage...

I feel like that lack of speed might kick my behind during the actual test. Did anyone else encounter this timing problem due to the length of the passage?

hey Arro44

speed comes with practice, I actually lack speed too, but I mostly concentrate on accuracy of questions answered correctly speed comes with consistent practice

have a good weekend
The last ice age has left its tell-tales written quite clearly across   [#permalink] 27 Oct 2018, 04:10
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