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Sub 505 Level|   Long Passage|   Science|                           
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Milankovitch proposed in the early twentieth century that the ice ages 05 Apr 2022, 02:42
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KarishmaB can you please breakdown Question 9? Why not E and B, C?
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Para 1:
Milankovitch proposed in the early twentieth century that the ice ages were caused by variations in the Earth’s orbit around the Sun. For sometime this theory was considered untestable...

Para 2:
Recent discovery makes determination possible

Para 3:
These data have established a strong connection between variations in the Earth’s orbit and the periodicity of the ice ages. (So Milankovitch's theory has been tested and found meritorious)

Para 4:
However, it is important to note that other factors, such as volcanic particulates or variations in the amount of sunlight received by the Earth, could potentially have affected the climate.

Para 4 says - hold on! We know that Milankovitch's theory seems to work but other factors also could have a role to play. These other factors have not been tested because of lack of info but it doesn't mean that they did not have a role to play.

9. The purpose of the last paragraph of the passage is to
(a) offer a note of caution
Correct. It tells us to realise that though Milankovitch's theory is promising, other factors could be important too.

(b) introduce new evidence
No evidence is presented. We have just been told that no info is available on other factors but they could be important.

(c) present two recent discoveries
The last para doesn't present any recent discoveries.

(d) summarize material in the preceding paragraphs
It does not summarise previous material. Previous material explains how the theory has been tested. The last para was written to caution us about not ignoring other factors.

(e) offer two explanations for a phenomenon
The last para does not offer any explanations for ice ages. It only says that other factors could have played a role too.

Answer (A)
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Milankovitch proposed in the early twentieth century that the ice ages 25 Apr 2022, 10:29
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Milankovitch proposed in the early twentieth century that the ice ages were caused by variations in the Earth’s orbit around the Sun. For sometime this theory was considered untestable, largely because there was no sufficiently precise chronology of the ice ages with which the orbital variations could be matched.

To establish such a chronology it is necessary to determine the relative amounts of land ice that existed at various times in the Earth’s past. A recent discovery makes such a determination possible: relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments. Almost all the oxygen in water is oxygen 16, but a few molecules out of every thousand incorporate the heavier isotope 18. When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it. Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18. The degree of enrichment can be determined by analyzing ocean sediments of the period, because these sediments are composed of calcium carbonate shells of marine organisms, shells that were constructed with oxygen atoms drawn from the surrounding ocean. The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down.

As an indicator of shifts in the Earth’s climate, the isotope record has two advantages. First, it is a global record: there is remarkably little variation in isotope ratios in sedimentary specimens taken from different continental locations. Second, it is a more continuous record than that taken from rocks on land. Because of these advantages, sedimentary evidence can be dated with sufficient accuracy by radiometric methods to establish a precise chronology of the ice ages. The dated isotope record shows that the fluctuations in global ice volume over the past several hundred thousand years have a pattern: an ice age occurs roughly once every 100,000 years. These data have established a strong connection between variations in the Earth’s orbit and the periodicity of the ice ages.

However, it is important to note that other factors, such as volcanic particulates or variations in the amount of sunlight received by the Earth, could potentially have affected the climate. The advantage of the Milankovitch theory is that it is testable: changes in the Earth’s orbit can be calculated and dated by applying Newton’s laws of gravity to progressively earlier configurations of the bodies in the solar system. Yet the lack of information about other possible factors affecting global climate does not make them unimportant.
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Hi avigutman

First, thank you so much for tagging this RC passage in your another post. This is an interesting RC passage, but I had some troubles with the fifth question. After reading all the previous posts contributed by members and experts, I think I am more clear now, and wonder whether you could check my line of thinking and few questions when you have time. :)

The following is the fifth question and an excerpt that includes the information we need to solve the question:

Quote:

5. It can be inferred from the passage that precipitation formed from evaporated ocean water has
(A) the same isotopic ratio as ocean water
(B) less oxygen 18 than does ocean water
(C) less oxygen 18 than has the ice contained in continental ice sheets
(D) a different isotopic composition than has precipitation formed from water on land
(E) more oxygen 16 than has precipitation formed from fresh water
Show more

When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it. Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18. The degree of enrichment can be determined by analyzing ocean sediments of the period, because these sediments are composed of calcium carbonate shells of marine organisms, shells that were constructed with oxygen atoms drawn from the surrounding ocean. The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down.

When I read the passage for the first time, I overlooked the word "continental" completely, and thus thought that the passage is talking about "the ice sheets on ocean". As I misunderstood that the author says that the ice sheets "on ocean" grows when the ocean water freezes, I incorrectly thought that these ice sheets should, like ocean water, have more oxygen 18 than the precipitation from evaporated ocean water.

Later, I found out that the passage talks about the ice sheets on the lands (on the continents) and this make all the difference. Now I see that the author is saying: when the ice sheets on land grows, the amount of evaporated ocean water that returns to the ocean reduces (even though technically, the author never clearly says that the ice sheets on land comes from the precipitation of evaporated ocean water.) Since much oxygen 16 has left the ocean water and gets trapped in the ice sheets on land, the higher the ratio of oxygen 18 to oxygen 16 in the ocean sediments, the heavier ice sheets on the lands.

I think I learn a lesson from my mistake--overlooking even an adjective can cause great harm sometimes....

Meanwhile, I have a question for one sentence:

When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it.

The complex part for me is that the word "water" has two modifiers--"evaporated from the ocean" and "that will eventually return to it (the ocean)". Without the second modifier, the sentence would carry a totally different meaning that "the amount of evaporated water will reduce," which would imply that more oxygen 16 would stay in the ocean. Unfortunately, I neglected the second modifier at my first read and thus misunderstood the meaning completely.

My question is: when we meet this kind of long-and-two-layer modifiers structure, do we always need to pay attention to the two modifiers at the same time? I am sorry if this question is not good enough, but I hope to know how you experts address this kind of structure efficiently.

Separately, I've watched some of your videos on the RC section. They are highly helpful and I am curious if we are to read this passage efficiently, which parts should we highlight more? Personally I think that reading the introduction of the oxygen 18 and oxygen 16 in the second paragraph is really time consuming and takes much energy. I wonder whether you would read this introduction for the first read (if you have not met a question that asks details of the part.)

Thank you so much!!! :)
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Milankovitch proposed in the early twentieth century that the ice ages 25 Apr 2022, 12:00
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GraceSCKao
I am curious if we are to read this passage efficiently, which parts should we highlight more? Personally I think that reading the introduction of the oxygen 18 and oxygen 16 in the second paragraph is really time consuming and takes much energy. I wonder whether you would read this introduction for the first read (if you have not met a question that asks details of the part.)
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In this passage, I only read the first and last sentence of each paragraph in my initial read. From that I gathered the following:
    *Milankovitch proposed early last century that orbital variations (of earth around the sun) caused the ice ages
    *This theory WAS considered untestable because our data on the chronology of ice ages wasn't precise enough... Until?
    *Data on the relative amounts of land ice are needed in order to achieve the required precision (see previous bullet)
    *The ratio O18:O16 is correlated with land ice (YAY) so we can use that to get the required precision in order to test the theory from the first bullet
    *The isotope record (the O18:O16 ratio) has two advantages: (1) and (2).
    *These data (from the isotope record) have established a strong connection between orbital variations and ice ages [reminder to myself: correlation doesn't prove causation]
    *Other factors could have potentially affected the climate [so even if orbital variations were a cause of the ice ages, they may have been just one of many causes]
    *[Obviously] just because we don't know about other factors doesn't mean they're not important

GraceSCKao
When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it.

The complex part for me is that the word "water" has two modifiers--"evaporated from the ocean" and "that will eventually return to it (the ocean)". Without the second modifier, the sentence would carry a totally different meaning that "the amount of evaporated water will reduce," which would imply that more oxygen 16 would stay in the ocean. Unfortunately, I neglected the second modifier at my first read and thus misunderstood the meaning completely.

My question is: when we meet this kind of long-and-two-layer modifiers structure, do we always need to pay attention to the two modifiers at the same time?
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Yes, we always need to pay attention to the two modifiers at the same time. I think the only way to achieve this difficult task is to think deeply about the meaning - which you must have done in order to discover the antecedent of the pronoun "it" in that sentence. In general, as you would have seen me saying in my videos: on RC we must either read very slowly, thoughtfully, and carefully - or not at all. In this case, I wouldn't have read that sentence at all. I would have used only the following sentence to answer question 5:
Quote:
Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18.
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But, if you do read the complicated sentence with the adjective (continental) and the two essential modifiers, GraceSCKao, then yes, you must read it slowly, carefully, and thoughtfully.
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Milankovitch proposed in the early twentieth century that the ice ages 26 Apr 2022, 05:32
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avigutman

In this passage, I only read the first and last sentence of each paragraph in my initial read. From that I gathered the following:
    *Milankovitch proposed early last century that orbital variations (of earth around the sun) caused the ice ages
    *This theory WAS considered untestable because our data on the chronology of ice ages wasn't precise enough... Until?
    *Data on the relative amounts of land ice are needed in order to achieve the required precision (see previous bullet)
    *The ratio O18:O16 is correlated with land ice (YAY) so we can use that to get the required precision in order to test the theory from the first bullet
    *The isotope record (the O18:O16 ratio) has two advantages: (1) and (2).
    *These data (from the isotope record) have established a strong connection between orbital variations and ice ages [reminder to myself: correlation doesn't prove causation]
    *Other factors could have potentially affected the climate [so even if orbital variations were a cause of the ice ages, they may have been just one of many causes]
    *[Obviously] just because we don't know about other factors doesn't mean they're not important

*
Yes, we always need to pay attention to the two modifiers at the same time. I think the only way to achieve this difficult task is to think deeply about the meaning - which you must have done in order to discover the antecedent of the pronoun "it" in that sentence. In general, as you would have seen me saying in my videos: on RC we must either read very slowly, thoughtfully, and carefully - or not at all. In this case, I wouldn't have read that sentence at all. I would have used only the following sentence to answer question 5:

Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18.

But, if you do read the complicated sentence with the adjective (continental) and the two essential modifiers, GraceSCKao, then yes, you must read it slowly, carefully, and thoughtfully.
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Thank you avigutman so much for your explanations on the approach and the question! :)
I think that your approach is really helpful for people who want to boost efficiency and get the main idea of the passage, but I need more practice to fully adopt the approach--I read much more parts at my first read even though I reminded myself to use this approach.

Meanwhile, could I have a follow-up question on the eighth question? It is not as problematic to me as the fifth question was, and I have no problem with the correct option (B), but I am curious about the incorrect option (E).

Quote:

8. According to the passage, one advantage of studying the isotope record of ocean sediments is that it
(A) corresponds with the record of ice volume taken from rocks on land.
(B) shows little variation in isotope ratios when samples are taken from different continental locations.
(C) corresponds with predictions already made by climatologists and experts in other fields.
(D) confirms the record of ice volume initially established by analyzing variations in volcanic emissions.
(E) provides data that can be used to substantiate records concerning variations in the amount of sunlight received by the Earth.
Show more


The passage mentions in the third paragraph that the isotope record can act as an indicator of shifts in the Earth’s climate, and mentions in the fourth paragraph that other factors, such as variations in the amount of sunlight received by the Earth, could potentially have affected the climate.

I feel that even though the option (E), unlike the option(B), is not directly mentioned by the author as one of the advantages, the option (E) is not absolutely wrong either, as we can infer from the passage that since the isotope records indicate the change in global climate and the variation in the amount of sunlight received could have affected the climate, the records might have some relation with the variation in the amount of sunlight.

I wonder what makes the option (E) incorrect, besides the fact the the option (B) is a better option. Is it because the use of word "substantiate" too strong in the option (E)? As we do not know how the change in the amount of sunlight would impact the relative amount of ice (at least it is not addressed in this passage), we cannot say that the records can be used to prove the data concerning the amount of sunlight to be true, can we? (The records might act as supplement to the data, but cannot substantiate it.)


Thank you so much for your time and thoughts! :)
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Milankovitch proposed in the early twentieth century that the ice ages 26 Apr 2022, 05:47
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GraceSCKao
I think that your approach is really helpful for people who want to boost efficiency and get the main idea of the passage, but I need more practice to fully adopt the approach--I read much more parts at my first read even though I reminded myself to use this approach.
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Skipping the details is great for efficiency and for the main idea question, but it's even more useful (surprisingly) for the detail questions. Each incorrect answer to a detail question has something in the passage that could cause people to select it (otherwise no-one would ever select it, and the question wouldn't make it past the experimental phase - the test writers would have to replace an incorrect answer that never gets selected with an incorrect answer that does get selected). So, by skipping all the details we inoculate ourselves against the trap answers. Once we get a detail question, we should go hunt for *just* the answer to that question, avoiding all other details in the passage.
GraceSCKao
The passage mentions in the third paragraph that the isotope record can act as an indicator of shifts in the Earth’s climate, and mentions in the fourth paragraph that other factors, such as variations in the amount of sunlight received by the Earth, could potentially have affected the climate.
we can infer from the passage that since the isotope records indicate the change in global climate and the variation in the amount of sunlight received could have affected the climate, the records might have some relation with the variation in the amount of sunlight.
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Your inference is valid, GraceSCKao, but only thanks to your use of the word "might" (boldfaced in your quote). The leap from "might have some relation with" to "can be used to substantiate records" is extreme. (even with no leap, the answer would be wrong because the question stem said "according to.")
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Milankovitch proposed in the early twentieth century that the ice ages 27 Apr 2022, 12:23
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Why isnt D the answer for 5 when it clearly written that O-18 gets left behind - implying evaporated water doesnt contain O-18 at all. But option B suggests that by saying 'less' O-18 than ocean water.
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Milankovitch proposed in the early twentieth century that the ice ages 29 Apr 2022, 22:10
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Careful--neither the passage nor the answer choices are dealing in absolutes or extremes. The passage says that heavier isotopes tend to be left behind when water evaporates. That doesn't mean that the evaporated water has none of the O-18. In any case, whether it had none or just a reduced degree, B would still have to be true. If the concentration of O18 in ocean water were, say, .01%, we'd know that the concentration in ocean water was somewhere less than .01%, and perhaps as low as 0. Either way, that's less.

As for D, it is talking about the molecules that evaporate from water on land. We don't know much about that water, or what its concentration is. Is this just glaciers? Does some O-18 find its way into those from other sources? Could this include lakes, etc.? We just don't know. We don't have the relevant info to prove this choice.
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Milankovitch proposed in the early twentieth century that the ice ages 21 Aug 2022, 01:49
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2. The author of the passage would be most likely to agree with which of the following statements about the Milankovitch theory?
Why B is incorrect?
(B) It is too limited to provide a plausible explanation for the ice ages, despite recent research findings.

If we look at the last para, the author has shown limitation in theory as we have not considered other factors. So if we look at the purpose of last para, it shows limitation to Milankovitch theory despite recent findings about the new method.
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Milankovitch proposed in the early twentieth century that the ice ages 21 Aug 2022, 22:57
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KarishmaB

2. The author of the passage would be most likely to agree with which of the following statements about the Milankovitch theory?
Why B is incorrect?
(B) It is too limited to provide a plausible explanation for the ice ages, despite recent research findings.

If we look at the last para, the author has shown limitation in theory as we have not considered other factors. So if we look at the purpose of last para, it shows limitation to Milankovitch theory despite recent findings about the new method.
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2. The author of the passage would be most likely to agree with which of the following statements about the Milankovitch theory?
(A) It is the only possible explanation for the ice ages.
(B) It is too limited to provide a plausible explanation for the ice ages, despite recent research findings.
(C) It cannot be tested and confirmed until further research on volcanic activity is done.
(D) It is one plausible explanation, though not the only one, for the ice ages.
(E) It is not a plausible explanation for the ice ages, although it has opened up promising possibilities for future research.

Notice that the first three paragraphs as used to show that Milankovitch's theory explains the ice ages. The third paragraph ends with:
These data have established a strong connection between variations in the Earth’s orbit and the periodicity of the ice ages.
So the author shows that his theory is a plausible explanation.

The last paragraph is cautionary - that other factors could have influenced as well. So there could be other theories that could work too. This doesn't mean that Milankovitch's theory is limited and does not explain ice ages. It does but other factors could have played a role too.
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Milankovitch proposed in the early twentieth century that the ice ages 19 May 2025, 23:00
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Hi KarishmaB GMATNinja DmitryFarber GMATNinjaTwo

In question-1, not entirely clear why option C is wrong and D is correct?

(C) emphasizing the instability of data gathered from the application of a new scientific method.

(D) presenting a theory and describing a new method to test that theory.

If we read the passage, the author presented Milankovitch's theory which was untestable for quite some time but it can be tested due to a recent discovery (isotope method), then the author described the method and its advantages, and finally, says that there can be other important variables apart from earth's rotation. In a nutshell, the author wanted to describe the method and point out the limitations at the end, that's why he wrote the passage.

Keeping above in mind, doesn't option C describes the primary purpose? Is it wrong because "instability of data" is a bit vague here?

I know that OA is option D but doesn't it miss the last paragraph of the passage?

Can we say that D is not perfect but it is the best among all?


Please let me know what exactly did I miss here as I usually find primary purpose questions a bit tricky.
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Milankovitch proposed in the early twentieth century that the ice ages 22 May 2025, 21:59
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Q1 - Answer: (D)
Explanation: The passage starts by introducing Milankovitch's theory that orbital variations cause ice ages. It then explains that this theory was previously untestable. The core of the passage then describes a "recent discovery" – the oxygen isotope method – which makes testing the theory possible. The rest of the passage details how this method works and how it provides data that supports the Milankovitch theory. Therefore, the author's primary purpose is to present the theory and then explain the new method that allows it to be tested.
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Milankovitch proposed in the early twentieth century that the ice ages 24 May 2025, 21:32
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I don't see the appeal of C. First, it's very narrow. Even if I didn't know what "emphasizing the instability" meant, I'd determine that the passage is doing more than just telling us about the data that was collected. In fact, the actual data was barely mentioned. Additionally, that first part makes it completely wrong. "Instability of data" isn't vague; it's a very specific thing to assert--that the data collected from the isotope method is unstable. There's no mention of this! (And of course, if D leaves off a few things, C leaves off all that and more.)

As for D, it's true that it doesn't get to the cautionary part at the end, but keep in mind that this is not a structure question. We're just asked for the primary purpose. The main point here is that there is a theory that we couldn't test for a long time, but that we can now test (and support) the theory with this new method. D covers that perfectly. So it's not just the best--the right answer should be more than that! It's the only answer that accurately answers the question.
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Hi KarishmaB GMATNinja DmitryFarber GMATNinjaTwo

In question-1, not entirely clear why option C is wrong and D is correct?

(C) emphasizing the instability of data gathered from the application of a new scientific method.

(D) presenting a theory and describing a new method to test that theory.

If we read the passage, the author presented Milankovitch's theory which was untestable for quite some time but it can be tested due to a recent discovery (isotope method), then the author described the method and its advantages, and finally, says that there can be other important variables apart from earth's rotation. In a nutshell, the author wanted to describe the method and point out the limitations at the end, that's why he wrote the passage.

Keeping above in mind, doesn't option C describes the primary purpose? Is it wrong because "instability of data" is a bit vague here?

I know that OA is option D but doesn't it miss the last paragraph of the passage?

Can we say that D is not perfect but it is the best among all?


Please let me know what exactly did I miss here as I usually find primary purpose questions a bit tricky.
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Milankovitch proposed in the early twentieth century that the ice ages 29 Jun 2025, 05:20
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Why not D in Q7 ("It can be inferred from the passage that calcium carbonate shells")?
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Milankovitch proposed in the early twentieth century that the ice ages 04 Jul 2025, 00:22
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There's no indication that any of the isotopes in question are radioactive. There's a mention of radiometric dating, but the passage doesn't explain how this is done or what part of the sediment is used for this purpose. We can't be expected to know anything about what radioactive elements may be involved, but for what it's worth, oxygen 16 and oxygen 18 are both stable.
YotamG1
Why not D in Q7 ("It can be inferred from the passage that calcium carbonate shells")?
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