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In choosing a method for determining climatic conditions

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In choosing a method for determining climatic conditions [#permalink]

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In choosing a method for determining climatic conditions that existed in the past, paleoclimatologists invoke four principal criteria. First, the material—rocks, lakes, vegetation, etc.—on which the method relies must be widespread enough to provide plenty of information, since analysis of material that is rarely encountered will not permit correlation with other regions or with other periods of geological history. Second, in the process of formation, the material must have received an environmental signal that reflects a change in climate and that can be deciphered by modern physical or chemical means. Third, at least some of the material must have retained the signal unaffected by subsequent changes in the environment. Fourth, it must be possible to determine the time at which the inferred climatic conditions held. This last criterion is more easily met in dating marine sediments, because dating of only a small number of layers in a marine sequence allows the age of other layers to be estimated fairly reliably by extrapolation and interpolation. By contrast, because sedimentation is much less continuous in continental regions, estimating the age of a continental bed from the known ages of beds above and below is more risky.

One very old method used in the investigation of past climatic conditions involves the measurement of water levels in ancient lakes. In temperate regions, there are enough lakes for correlations between them to give us a reliable picture. In arid and semiarid regions, on the other hand, the small number of lakes and the great distances between them reduce the possibilities for correlation. Moreover, since lake levels are controlled by rates of evaporation as well as by precipitation, the interpretation of such levels is ambiguous. For instance, the fact that lake levels in the semiarid southwestern United States appear to have been higher during the last ice age than they are now was at one time attributed to increased precipitation. On the basis of snow-line elevations, however, it has been concluded that the climate then was not necessarily wetter than it is now, but rather that both summers and winters were cooler, resulting in reduced evaporation.

Another problematic method is to reconstruct former climates on the basis of pollen profiles. The type of vegetation in a specific region is determined by identifying and counting the various pollen grains found there. Although the relationship between vegetation and climate is not as direct as the relationship between climate and lake levels, the method often works well in the temperate zones. In arid and semiarid regions in which there is not much vegetation, however, small changes in one or a few plant types can change the picture dramatically, making accurate correlations between neighboring areas difficult to obtain.

1. Which of the following statements about the difference between marine and continental sedimentation is supported by information in the passage?

(A) Data provided by dating marine sedimentation is more consistent with researchers’ findings in other disciplines than is data provided by dating continental sedimentation.

(B) It is easier to estimate the age of a layer in a sequence of continental sedimentation than it is to estimate the age of a layer in a sequence of marine sedimentation.

(C) Marine sedimentation is much less widespread than continental sedimentation.

(D) Researchers are more often forced to rely on extrapolation when dating a layer of marine sedimentation than when dating a layer of continental sedimentation.

(E) Marine sedimentation is much more continuous than is continental sedimentation.


2. Which of the following statements best describes the organization of the passage as a whole?

(A) The author describes a method for determining past climatic conditions and then offers specific examples of situations in which it has been used.

(B) The author discusses the method of dating marine and continental sequences and then explains how dating is more difficult with lake levels than with pollen profiles.

(C) The author describes the common requirements of methods for determining past climatic conditions and then discusses examples of such methods.

(D) The author describes various ways of choosing a material for determining past climatic conditions and then discusses how two such methods have yielded contradictory data.

(E) The author describes how methods for determining past climatic conditions were first developed and then describes two of the earliest known methods.


3. It can be inferred from the passage that paleoclimatologists have concluded which of the following on the basis of their study of snow-line elevations in the southwestern United States?

(A) There is usually more precipitation during an ice age because of increased amounts of evaporation.
(B) There was less precipitation during the last ice age than there is today.
(C) Lake levels in the semiarid southwestern United States were lower during the last ice age than they are today.
(D) During the last ice age, cooler weather led to lower lake levels than paleoclimatologists had previously assumed.
(E) The high lake levels during the last ice age may have been a result of less evaporation rather than more precipitation.


4. Which of the following would be the most likely topic for a paragraph that logically continues the passage?

(A) The kinds of plants normally found in arid regions
(B) The effect of variation in lake levels on pollen distribution
(C) The material best suited to preserving signals of climatic changes
(D) Other criteria invoked by paleoclimatologists when choosing a method to determine past climatic conditions
(E) A third method for investigating past climatic conditions


5. The author discusses lake levels in the southwestern United States in order to
(A) illustrate the mechanics of the relationship between lake level, evaporation, and precipitation
(B) provide an example of the uncertainty involved in interpreting lake levels
(C) prove that there are not enough ancient lakes with which to make accurate correlations
(D) explain the effects of increased rates of evaporation on levels of precipitation
(E) suggest that snow-line elevations are invariably more accurate than lake levels in determining rates of precipitation at various points in the past


6. It can be inferred from the passage that an environmental signal found in geological material would not be useful to paleoclimatologists if it

(A) had to be interpreted by modern chemical means
(B) reflected a change in climate rather than a long-term climatic condition
(C) was incorporated into a material as the material was forming
(D) also reflected subsequent environmental changes
(E) was contained in a continental rather than a marine sequence


7. According to the passage, the material used to determine past climatic conditions must be widespread for which of the following reasons?

I. Paleoclimatologists need to make comparisons between periods of geological history.
II. Paleoclimatologists need to compare materials that have supported a wide variety of vegetation.
III. Paleoclimatologists need to make comparisons with data collected in other regions.

(A) I only
(B) II only
(C) I and II only
(D) I and III only
(E) II and III only


8. Which of the following can be inferred from the passage about the study of past climates in arid and semiarid regions?

(A) It is sometimes more difficult to determine past climatic conditions in arid and semiarid regions than in temperate regions.

(B) Although in the past more research has been done on temperate regions, paleoclimatologists have recently turned their attention to arid and semiarid regions.

(C) Although more information about past climates can be gathered in arid and semiarid than in temperate regions, dating this information is more difficult.

(D) It is difficult to study the climatic history of arid and semiarid regions because their climates have tended to vary more than those of temperate regions.

(E) The study of past climates in arid and semiarid regions has been neglected because temperate regions support a greater variety of plant and animal life.

[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA
[Reveal] Spoiler: Question #4 OA
[Reveal] Spoiler: Question #5 OA
[Reveal] Spoiler: Question #6 OA
[Reveal] Spoiler: Question #7 OA
[Reveal] Spoiler: Question #8 OA

Last edited by broall on 25 Aug 2017, 08:53, edited 2 times in total.
Reformatted question, OA added

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Re: In choosing a method for determining climatic conditions [#permalink]

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New post 20 Feb 2010, 02:13
this RC has been lying around for two years without the answers being posted.

PLEASE GIVE THE ANSWERS.
PLEASE!

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Re: In choosing a method for determining climatic conditions [#permalink]

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New post 28 Feb 2010, 09:45
In my opinion:

1. a
2. b
3. e
4. e
5. b
6. d
7. c
8. a

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Re: In choosing a method for determining climatic conditions [#permalink]

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New post 28 Feb 2010, 19:24
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Hey All,

Very few instructors delve into RC at any length, so I thought I'd buck the trend and take this passage on. I don't have the official answers, but I'm generally confident on these. So take what I say as (almost) gospel truth. : )

I didn't just post the answers up top, because I think it's important you all look through the full explanations. To really improve at reading comp, you have to get this deep. Good luck!

The first thing is to outline intelligently. I'm a big fan of doing a very basic, structurally focused outline, as well as taking a stab at what I think the passage is ABOUT. I've repasted the passage below for my reference, and my outline and explanation continues below it.

PASSAGE:

In choosing a method for determining climatic conditions that existed in the past, paleoclimatologists invoke four principal criteria. First, the material—rocks, lakes, vegetation, etc.—on which the method relies must be widespread enough to provide plenty of information, since analysis of material that is rarely encountered will not permit correlation with other regions or with other periods of geological history. Second, in the process of formation, the material must have received an environmental signal that reflects a change in climate and that can be deciphered by modern physical or chemical means. Third, at least some of the material must have retained the signal unaffected by subsequent changes in the environment. Fourth, it must be possible to determine the time at which the inferred climatic conditions held. This last criterion is more easily met in dating marine sediments, because dating of only a small number of layers in a marine sequence allows the age of other layers to be estimated fairly reliably by extrapolation and interpolation. By contrast, because sedimentation is much less continuous in continental regions, estimating the age of a continental bed from the known ages of beds above and below is more risky.


One very old method used in the investigation of past climatic conditions involves the measurement of water levels in ancient lakes. In temperate regions, there are enough lakes for correlations between them to give us a reliable picture. In arid and semiarid regions, on the other hand, the small number of lakes and the great distances between them reduce the possibilities for correlation. Moreover, since lake levels are controlled by rates of evaporation as well as by precipitation, the interpretation of such levels is ambiguous. For instance, the fact that lake levels in the semiarid southwestern United States appear to have been higher during the last ice age than they are now was at one time attributed to increased precipitation. On the basis of snow-line elevations, however, it has been concluded that the climate then was not necessarily wetter than it is now, but rather that both summers and winters were cooler, resulting in reduced evaporation.

Another problematic method is to reconstruct former climates on the basis of pollen profiles. The type of vegetation in a specific region is determined by identifying and counting the various pollen grains found there. Although the relationship between vegetation and climate is not as direct as the relationship between climate and lake levels, the method often works well in the temperate zones. In arid and semiarid regions in which there is not much vegetation, however, small changes in one or a few plant types can change the picture dramatically, making accurate correlations between neighboring areas difficult to obtain.

Main Idea: Methods for determining past climates
Paragraph 1: Criteria for determining past climate
Paragraph 2: One old method: water levels in ancient lakes; not great
Paragraph 3: Another method: pollen profiles; also not great

This passage is generally about determining past climate conditions. While there are plenty more details I could've chosen to include in my outline, I imagine these will serve my purposes just fine. Now let's look at the questions.


1. Which of the following statements about the difference between marine and continental sedimentation is supported by information in the passage?

First, remember the location. This was from paragraph 1. Our outline helps us by pointing us in the right direction, because this was related to criteria, not the two methods. Let's look at what the passage told us:

Fourth, it must be possible to determine the time at which the inferred climatic conditions held. This last criterion is more easily met in dating marine sediments, because dating of only a small number of layers in a marine sequence allows the age of other layers to be estimated fairly reliably by extrapolation and interpolation. By contrast, because sedimentation is much less continuous in continental regions, estimating the age of a continental bed from the known ages of beds above and below is more risky.

(A) Data provided by dating marine sedimentation is more consistent with researchers’ findings in other disciplines than is data provided by dating continental sedimentation.
PROBLEM: There's no info on other disciplines here.

(B) It is easier to estimate the age of a layer in a sequence of continental sedimentation than it is to estimate the age of a layer in a sequence of marine sedimentation.
PROBLEM: This is backwards. Sedimentation is LESS CONTINUOUS in continental regions.

(C) Marine sedimentation is much less widespread than continental sedimentation.
PROBLEM: It doesn't say that.

(D) Researchers are more often forced to rely on extrapolation when dating a layer of marine sedimentation than when dating a layer of continental sedimentation.
ANSWER: Dangerous. We are told that extrapolation is useful for marine sedimentation, but not that researchers are "forced to rely on extrapolation".

(E) Marine sedimentation is much more continuous than is continental sedimentation.
ANSWER: It absolutely says this in the last sentence.

2. Which of the following statements best describes the organization of the passage as a whole?

This is a general question, so our outline should answer it.

(A) The author describes a method for determining past climatic conditions and then offers specific examples of situations in which it has been used.
PROBLEM: We don't get a method in the first paragraph, but we do get methods in the later ones. Backwards.

(B) The author discusses the method of dating marine and continental sequences and then explains how dating is more difficult with lake levels than with pollen profiles.
PROBLEM: Many. We don't compare lake levels and pollen profiles.

(C) The author describes the common requirements of methods for determining past climatic conditions and then discusses examples of such methods.
ANSWER: Looks just like our outline!

(D) The author describes various ways of choosing a material for determining past climatic conditions and then discusses how two such methods have yielded contradictory data.
PROBLEM: The two methods didn't yield contradictory data (as far as we know).

(E) The author describes how methods for determining past climatic conditions were first developed and then describes two of the earliest known methods.
PROBLEM: Tough one here. The explanation of the two later paragraphs is okay, but that's not the first paragraph (we don't talk about how they were "first developed").

3. It can be inferred from the passage that paleoclimatologists have concluded which of the following on the basis of their study of snow-line elevations in the southwestern United States?

A detail question. Where was that section on snow-line elevations again?

On the basis of snow-line elevations, however, it has been concluded that the climate then was not necessarily wetter than it is now, but rather that both summers and winters were cooler, resulting in reduced evaporation.

(A) There is usually more precipitation during an ice age because of increased amounts of evaporation.
PROBLEM: We aren't told anything about ice ages in general.

(B) There was less precipitation during the last ice age than there is today.
PROBLEM: We don't know anything about today.

(C) Lake levels in the semiarid southwestern United States were lower during the last ice age than they are today.
PROBLEM: See above.

(D) During the last ice age, cooler weather led to lower lake levels than paleoclimatologists had previously assumed.
PROBLEM: Be careful. The lake levels were actually HIGHER. (less evaporation)

(E) The high lake levels during the last ice age may have been a result of less evaporation rather than more precipitation.
ANSWER: There we go. That's what the passage says.

4. Which of the following would be the most likely topic for a paragraph that logically continues the passage?

General question. Tough, but our outline comes to the rescue. This passage is about methods of determining climate conditions, and we've already had two of them. So the most logical next paragraph would be a third method.

(A) The kinds of plants normally found in arid regions
PROBLEM: We don't discuss plants anywhere here.

(B) The effect of variation in lake levels on pollen distribution
PROBLEM: Pollen got its paragraph already.

(C) The material best suited to preserving signals of climatic changes
PROBLEM: That's one detail mentioned here and there in the passage, but not centrally.

(D) Other criteria invoked by paleoclimatologists when choosing a method to determine past climatic conditions
PROBLEM: That was paragraph one. We're done with that.

(E) A third method for investigating past climatic conditions
ANSWER: Yep. I dig it.

5. The author discusses lake levels in the southwestern United States in order to

We can do this one (specific) on our own. That was to show how that second method, lake levels, was kinda crappy.

(A) illustrate the mechanics of the relationship between lake level, evaporation, and precipitation
PROBLEM: Even though we do end up getting a bit of explanation this way, it's not WHY the author did it. Always be wary when the question asks you about intention, because it's not the same as content (i.e. "What's there?" is not the same as "What is the reason it's there.")

(B) provide an example of the uncertainty involved in interpreting lake levels
ANSWER: Looks pretty good.

(C) prove that there are not enough ancient lakes with which to make accurate correlations
PROBLEM: This gets mentioned as a problem, but it's not the point.

(D) explain the effects of increased rates of evaporation on levels of precipitation
PROBLEM: Again, we get this, but it's not the REASON the example is there.

(E) suggest that snow-line elevations are invariably more accurate than lake levels in determining rates of precipitation at various points in the past
PROBLEM: We get a BIT of this, but it's not the point. Also, it isn't the elevation that's accurate in determining the rate of precipitation, but the effect of snow-line elevations.


6. It can be inferred from the passage that an environmental signal found in geological material would not be useful to paleoclimatologists if it

This is a specific question related to a very small part of the first paragraph. Because this is an inference question, the correct answer will cleave VERY close to the passage, so let's look at it: Second, in the process of formation, the material must have received an environmental signal that reflects a change in climate and that can be deciphered by modern physical or chemical means.

(A) had to be interpreted by modern chemical means
PROBLEM: That's okay, as long as it's interpretable.

(B) reflected a change in climate rather than a long-term climatic condition
PROBLEM: No, that would be great. We just want to see any kind of change.

(C) was incorporated into a material as the material was forming
PROBLEM: The passage says that's what we want ("in the process of formation")

(D) also reflected subsequent environmental changes
ANSWER: This ends up referring to the next issue, so it's a bit dangerous. ("Third, at least some of the material must have retained the signal unaffected by subsequent changes in the environment.") This

(E) was contained in a continental rather than a marine sequence
PROBLEM: Either way is fine according to the passage.

7. According to the passage, the material used to determine past climatic conditions must be widespread for which of the following reasons?

This is another specific question, related to a small part of the passage. Let's look at it: "First, the material—rocks, lakes, vegetation, etc.—on which the method relies must be widespread enough to provide plenty of information, since analysis of material that is rarely encountered will not permit correlation with other regions or with other periods of geological history."

I. Paleoclimatologists need to make comparisons between periods of geological history.
ANSWER: Yep. It says at the end that they want to correlate with other periods of geologic history. That's the same as comparison. (Though they used a synonym shift, our term for replacing one word from the passage with some other word that means the same thing, to throw you off the trail).

II. Paleoclimatologists need to compare materials that have supported a wide variety of vegetation.
PROBLEM: Nope. The support of vegetation is unmentioned, even if the word "vegetation" is used.

III. Paleoclimatologists need to make comparisons with data collected in other regions.
ANSWER: Yep. Again, it's right there in the last line.

(A) I only
(B) II only
(C) I and II only
(D) I and III only
ANSWER: This is the answer.
(E) II and III only

8. Which of the following can be inferred from the passage about the study of past climates in arid and semiarid regions?

Definitely the toughest question here. It's inference, so we want to stay close to what's written, but we need to look at BOTH of the second too paragraph. In both examples, temperate regions get mentioned as easier to work with.

(A) It is sometimes more difficult to determine past climatic conditions in arid and semiarid regions than in temperate regions.
ANSWER: Looks good.

(B) Although in the past more research has been done on temperate regions, paleoclimatologists have recently turned their attention to arid and semiarid regions.
PROBLEM: We don't know what paleoclimatologists are focused on.

(C) Although more information about past climates can be gathered in arid and semiarid than in temperate regions, dating this information is more difficult.
PROBLEM: It simply doesn't say this.

(D) It is difficult to study the climatic history of arid and semiarid regions because their climates have tended to vary more than those of temperate regions.
PROBLEM: Dangerous, but this is NOT the reason cited that arid regions are tougher than temperate regions. For example, in the second example paragraph (pollen), the reason given is a lack of a variety of vegetation.

(E) The study of past climates in arid and semiarid regions has been neglected because temperate regions support a greater variety of plant and animal life.
PROBLEM: We don't know what the focus is on, or what has been neglected.

Word up.

Hope that helps!
_________________


Tommy Wallach | Manhattan GMAT Instructor | San Francisco


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Re: In choosing a method for determining climatic conditions [#permalink]

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New post 18 Mar 2010, 13:50
Thanks a LOT! Its really nice explanation!

Got them all right! :-D

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Re: In choosing a method for determining climatic conditions [#permalink]

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New post 04 May 2010, 09:34
Mine

1.E , 2.C, 3. E, 4.d, 5.B, 6.D, 7.D, 8.E

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Re: In choosing a method for determining climatic conditions [#permalink]

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New post 05 May 2010, 22:13
got the same answers. Thanks for the descriptions

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Re: In choosing a method for determining climatic conditions [#permalink]

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New post 25 Aug 2017, 08:54

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Re: In choosing a method for determining climatic conditions   [#permalink] 25 Aug 2017, 08:54
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