Milankovitch proposed in the early twentieth century that the ice ages

Question

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.  
 1 
 D 
 1. In the passage, the author is primarily interested in 
(A) suggesting an alternative to an outdated research method.
(B) introducing a new research method that calls an accepted theory into question.
(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.
(E) initiating a debate about a widely accepted theory.

2 
 D 
 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.

3 
 B 
 3. It can be inferred from the passage that the isotope record taken from ocean sediments would be less useful to researchers if which of the following were true? 
(A) It indicated that lighter isotopes of oxygen predominated at certain times.
(B) It had far more gaps in its sequence than the record taken from rocks on land.
(C) It indicated that climate shifts did not occur every100,000 years.
(D) It indicated that the ratios of oxygen 16 and oxygen18 in ocean water were not consistent with those found in fresh water.
(E) It stretched back for only a million years.

4 
 C 
 4. According to the passage, which of the following is true of the ratios of oxygen isotopes in ocean sediments? 
(A) They indicate that sediments found during an ice age contain more calcium carbonate than sediments formed at other times.
(B) They are less reliable than the evidence from rocks on land in determining the volume of land ice.
(C) They can be used to deduce the relative volume of land ice that was present when the sediment was laid down.
(D) They are more unpredictable during an ice age than in other climatic conditions.
(E) They can be used to determine atmospheric conditions at various times in the past.

5 
 B 
 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

6 
 C 
 6. According to the passage, which of the following is (are) true of the ice ages?  
Ⅰ. The last ice age occurred about 25,000 years ago. 
Ⅱ. Ice ages have lasted about 10,000 years for at least the last several hundred thousand years. 
Ⅲ. Ice ages have occurred about every 100,000 years for at least the last several hundred thousand years.
(A) Ⅰ only
(B) Ⅱ only
(C) Ⅲ only
(D) Ⅰand II only
(E) Ⅰ,Ⅱ and Ⅲ

7 
 E 
 7. It can be inferred from the passage that calcium carbonate shells 
(A) are not as susceptible to deterioration as rocks.
(B) are less common in sediments formed during an ice age.
(C) are found only in areas that were once covered by land ice.
(D) contain radioactive material that can be used to determine a sediment's isotopic composition.
(E) reflect the isotopic composition of the water at the time the shells were formed.

8 
 B 
 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.

9 
 A 
 9. The purpose of the last paragraph of the passage is to  
(a) offer a note of caution 
(b) introduce new evidence 
(c) present two recent discoveries 
(d) summarize material in the preceding paragraphs 
(e) offer two explanations for a phenomenon

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raiprem123 · Accepted Answer

Really... a tough one.. I was completely blown ......

here are my answers with explanations:

1. In the passage, the author is primarily interested in

Ans : (D) presenting a theory and describing a new method to test that theory
The author mentions the theory presented by Milankovitch and states that for some time this theory was untestable. It is also mentioned in next para that a recent discovery helps in testing the validity of the theory mentioned by Milankovitch.

2. The author of the passage would be most likely to agree with which of the following statements about the Milankovitch theory?

Ans : Answering this question consumed most of my time while solving this passage. I was confused between options A and D. My pick for this is
(D) It is one plausible explanation, though not the only one, for the ice ages.

As it has already been mentioned in the passage that Milankovitch's theory can be tested if chronology of ice ages is known. Now measuring the relative amount of land ice that existed during various times in the earth's past is helpful in determining the chronology of ice ages and the amount of land ice can be predicted using the findings of the recent discovery. So the answer B, C and E are out. Now between A and D we need to confirm if the theory is the only way to find the volume of land ice. The author mentions in last passage that there are some other factors as well such as volcanic particulates or variations in the amount of sunlight received by the earth which could potentially have affected the climate. The only reason for which the author chose the Milankovitch's theory is that it is testable. There are other factors but they are not considered just because of the lack of information about them.

3. Itcan be inferred from the passage that the isotope record taken from ocean sediments would be less usefulto researchers if which of the following were true?
Ans : (B) It had far more gaps in its sequence than the record taken from rocks on land.
It is clearly mentioned in lines 37-39 that records taken from ocean sediments are advantageous because they are more continuous in nature that those taken from rocks on land.

4. According to the passage, which of the following is true of the ratios of oxygen isotopes in ocean sediments?
Ans : (c) They can be used to deduce the relative volume of land ice that was present when the sediment was laid down.
It is clearly mentioned in lines 12 to 14 that 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.

5. It can be inferred from the passage that precipitation formed from evaporated ocean water has
Ans : (B) less oxygen 18 than does ocean water
It is mentioned in lines 20 to 24 that when water evaporates the heavier isotope remains in ocean water. This clearly causes the concentration of oxygen 18 to decrease in evaporated water. So precipitation formed from evaporated water will have less oxygen 18 than that in oceanic precipitations.

6. Itcan be inferred from the passage that calcium carbonate shells
Ans : (E) reflect the isotopic composition of the water at the time the shells were formed
From lines 24 to 29 it can be inferred that calcium carbonate shells were constructed using the oceanic water at the time of their composition. So the oxygen isotope's concentration found in their analysis will show the concentration of isotopes in oceanic water.

Carcass, It has taken a lot of time in formatting the question in my post but if some errors are still persisting, I am worried about them. Request you to review the answers and explanations. Its 3:40 am here...So i m gonna sleep with hope to get reply from you when i wake up .... It was really tough question.

:done

Pressing +1 Kudos is the best way to say Thanks!

:done Pressing +1 Kudos is the best way to say Thanks!

DmitryFarber · Answer

It's important to compare the content in the final paragraph to the rest of the passage. It introduces new considerations (volcanic ash, variations in sunlight) that might also explain ice ages. True, it reiterates that Milankovitch's theory is testable, but in no way does it summarize the passage. The paragraph is saying "Here are some other possible explanations. Milankovitch's explanation (orbital variations) is being tested, but that doesn't mean these other factors may not turn out to be important." Therefore, the author is sounding a note of caution. Despite the promising results so far, we can't be sure that this theory is the answer.

TheMechanic · Answer

I guess I can help. The choice B has several issues: Re-Stating the question and dissecting choices bit by bit.

18. 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. No where it is claimed in the passage that theory presented is the only claim. In context of the last para it is clearly implied that it is one of the plausible theory explaining the ice-ages. (B) It is too limited to provide a plausible explanation for the ice ages, despite recent research findings. phrase "too limited" makes this option incorrect. Referring back to passage, in particular last line, " Yet the lack of information about other possible factors affecting global climate does not make them unimportant." - implies that author is kinda CONCERN about neglecting these factors even while author is identifying advantages of Milankovitch theory. This choice is too negative and changes the author stand point altogether. (C) It cannot be tested and confirmed until further research on volcanic activity is done. Directly contradicting author's view in the last para. (D) It is one plausible explanation, though not the only one, for the ice ages. Bingo!!! This basically implies that the presented theory by Milankovitch is one of the possible explanation but not the only one since there are other factors or theories(implied) which might have contributed to the ice age. (E) It is not a plausible explanation for the ice ages, although it has opened up promising possibilities for future research. Author concludes the passage indicating skepticism of ignoring factors like volcanic eruptions and duration of sunlight. He never recommends,explicitly, that an extended research is needed to prove something. Hence out! Hope it helps

DmitryFarber · Answer

19 and 21? I'm on it!

19. It can be inferred from the passage that the isotope record taken from ocean sediments would be less useful to researchers if which of the following were true?
(A) It indicated that lighter isotopes of oxygen predominated at certain times.
(B) It had far more gaps in its sequence than the record taken from rocks on land.
(C) It indicated that climate shifts did not occur every 100,000 years.
(D) It indicated that the ratios of oxygen 16 and oxygen18 in ocean water were not consistent with those found in fresh water.
(E) It stretched back for only a million years.

We're looking for something that would make this method less useful to researchers. B is a problem because we're taking away one of the stated advantages of the method. (Specifically, this knocks out the second advantage described in paragraph 3.)

A) The lighter isotope (16)  always  predominates, so this can't be a problem! (The passage states that only a few molecules out of every thousand have the heavier 18.)
C) This might be a problem for Milankovitch's theory, but not for researchers. The  method  is still useful, whether it supports the theory or casts doubt on it.
D) If fresh water samples gave us totally different indications of when the ice ages occurred, that would be a problem. However, just seeing variation between fresh and salt water doesn't tell us anything. Maybe the ratios in fresh water are  supposed  to be different, so we can't really interpret this without more information. 
E) A million years is a long time! How do we know it's long enough for what we want? Ice ages appear to occur about once every hundred thousand years, and the author feel comfortable announcing this pattern after looking back a few hundred thousand years, or a few ice ages. By this standard, going back a million years would seem to be more than enough.

DmitryFarber · Answer

21. 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

The support for B is right here: "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."

Translation? When water evaporates, the heavier 18 gets left behind. When that evaporated water gets trapped in ice and doesn't return, the ocean gets steadily higher in oxygen 18. This can only happen if the missing water has less 16 than normal ocean water. (For a real-world connection, compare this to what happens with salt. When ocean water evaporates, the salt is left behind.)

bpdulog · Answer

Why is C incorrect here? Doesn't the oxygen 18 enriched water eventually turn into ice?

DmitryFarber · Answer

bpdulog  There's no indication that the 18-enriched water turns to ice. It's in the ocean, and the passage doesn't say that the ocean freezes.

However, that doesn't matter anyway. The question is asking us to compare rain from evaporated ocean water with continental ice sheets. That rain is exactly what forms the ice sheets, so they should have roughly the same concentration of oxygen 18 (a very low one, if any at all!).

Akshit03 · Answer

9. The purpose of the last paragraph of the passage is to 
(a) offer a note of caution 
(b) introduce new evidence 
(c) present two recent discoveries 
(d) summarize material in the preceding paragraphs 
(e) offer two explanations for a phenomenon

Why is B or C wrong?
B: it does introduce 2 evidence of new possibilities?
C: It does present 2 discoveries?

DmitryFarber · Answer

Akshit03  If you look carefully at the last paragraph, you'll see that no actual discoveries are cited. In fact, no evidence is presented at all. The author simply mentions some possible complicating factors (or even competing explanations) that we may need to consider. This is a common form of "disclaimer" in a science passage, since evidence in favor of one theory doesn't automatically rule out other possibilities.

However, there's another important point here. Even if the paragraph  did  cite discoveries or evidence, that wouldn't make B or C the right answer. The question is asking us for the purpose of the paragraph, not just a detail. The overall purpose of this passage is to warn us that while there is some support for the Milankovitch theory, we can't rule out other factors yet. This is a more important and larger overall point than simply looking at one or two pieces of evidence.

nikitamaheshwari · Answer

"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."

Can someone please provide translation for this one? karishma GMATNinja

Can someone please provide translation for this one?  karishma   GMATNinja

kornn · Answer

Dear  AjiteshArun   IanStewart   VeritasKarishma   DmitryFarber   GMATGuruNY   VeritasPrepHailey   MartyTargetTestPrep   GMATNinja

Why is Q7 choice D. wrong?
 
According to the passage:
 
We know that oxygen in the shell is radioactive because it is used in RADIOMETRIC methods.

I also note that the "isotopic composition" part in choice D. also appears in the correct choice E. as well.

IanStewart · Answer

Nowhere does the passage tell you that it is possible to "determine a sediment's isotopic composition", using radioactivity or otherwise. All you learn from the passage is that radiometric methods can be used to date sediment "with sufficient accuracy".

KarishmaB · Answer

Earth has a water cycle. Water evaporates from the ocean and falls as rain on land. It collects in the rivers and comes back to the ocean eventually. 
When an ice age begins, continental ice sheets start expanding. From where does this ice come? It is formed by the water that evaporates from he ocean but does not return back to the ocean. After all, water is not created to make ice sheets. It is the same circulated water.

When an ice age begins, the continental ice sheets grow,  - ice sheets grow
 steadily reducing the amount of water evaporated from the ocean that will eventually return to it.  - returning water is reduced
 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  - Heavier water does not evaporate. O16 water does evaporate. Since water is not returning, O16 water concentration keeps dropping.

varotkorn  - Hope this is clear now.

KarishmaB · Answer

Note what the passage says:

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.

(B) It is too limited to provide a plausible explanation for the ice ages, despite recent research findings.

Does the author think that the M theory does not provide a plausible explanation? No. He says there is strong connection. All he says is that other factors could have an impact too.

(D) It is one plausible explanation, though not the only one, for the ice ages.

So yes, he think it is one plausible explanation. But other factors could have an impact too so there could be other explanations too.

Answer must be (D)

homersimpsons · Answer

OE 
Q1. In the passage, the author is primarily interested in
A. suggesting an alternative to an outdated research method
B. introducing a new research method that calls an accepted theory into question
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
E. initiating a debate about a widely accepted theory
 Main idea 
This question concerns the main point of the passage. A careful examination of the overall structure of the passage will reveal the main point. In the first paragraph, the author briefly presents Milankovitch’s theory and explains why it could not be tested early on. In the second and third paragraphs, the author describes how a new method allows testing of the theory and shows how evidence from the testing supports the theory. While the final paragraph acknowledges that other factors should be considered, the author’s primary interest in this passage is in presenting Milankovitch’s theory and the recently discovered method for testing it.
A. A new research method is described, but no previous method is discussed.
B. As described in the passage, the new method tests and confirms the theory; there is no mention that the theory is accepted or that the method casts doubt on it.
C. Nothing in the passage suggests that “instability of data” is an issue.
D.  Correct . The author presents Milankovitch’s theory and describes the oxygen isotope method of testing it.
E. The theory is nowhere said to be “widely accepted” and the author does not debate the theory.
 The correct answer is D.

Q2. 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.
 Application  
The author’s reaction to the statements about the Milankovitch theory must be based on how the author treats the theory in the passage. The first, second, and third paragraphs describe the theory and the use of a new research method to test the theory. The passage states that data from these tests have established a strong connection between variations in the Earth’s orbit and the periodicity of the ice ages, suggesting that the author of the passage believes the theory is plausible. In the final paragraph, the author points to other factors that might be involved, suggesting that the theory might not provide a complete explanation.
A. In the last paragraph, the author suggests that because there are still other untested factors that may have effects on climate, other explanations are possible.
B. Though in the last paragraph the author points to other factors that may be involved, these are not presented by the author as indicating limitations that diminish the plausibility of the theory—they are acknowledged merely as possibilities that are not now understood—and nothing else in the passage suggests that the theory is “too limited.”
C. The author shows how the theory has been tested; volcanic activity is not part of this theory.
D.  Correct . The author’s presentation of the theory and the tests of the theory show that the author finds the theory plausible; the mention of other factors shows the author does not think that all other explanations have been ruled out, even if they are as yet untested.
E. The theory was a plausible explanation from its beginning, but it was not testable until recently; scientists would be unlikely to try to devise means to test a theory that did not strike them as antecedently plausible.
 The correct answer is D.

Q3. It can be inferred from the passage that the isotope record taken from ocean sediments would be less useful to researchers if which of the following were true?
A. It indicated that lighter isotopes of oxygen predominated at certain times.
B. It had far more gaps in its sequence than the record taken from rocks on land.
C. It indicated that climate shifts did not occur every 100,000 years.
D. It indicated that the ratios of oxygen 16 and oxygen 18 in ocean water were not consistent with those found in fresh water.
E. It stretched back for only a million years.
 Inference 
To make an inference about the isotope record from ocean sediments, examine what the passage says about that record. The third paragraph discusses that record and lists its two advantages. First, it is a global record with remarkably little variation in samples from varied locations. Second, it is more continuous than the record from rocks. If either of these advantages were not true, then it is logical to infer that the record would be less useful.
A. According to lines 14–16, the lighter isotope does predominate; this is part of the record and does not affect its usefulness.
B.  Correct . In lines 37–42, the author states that an advantage of the ocean record is that it is a more continuous record than that taken from rocks on land. If this were not true, the ocean record wouldbe less useful.
C. If the record were to show that the shifts did not occur every 100,000 years, Milankovitch’s theory would be weakened. This impact on the theory does not make the isotope record less useful to researchers. The record is useful precisely because it can offer evidence to confirm or refute such theories.
D. This inconsistency would not affect the usefulness of the ocean-water record. Researchers would simply need to accommodate the fresh-water inconsistency.
E. The record would still be useful. Lines 42–46 attest to the establishment of a pattern based on data from the past several hundred thousand years.
 The correct answer is B.

Q4. According to the passage, which of the following is true of the ratios of oxygen isotopes in ocean sediments?
A. They indicate that sediments found during an ice age contain more calcium carbonate than sediments formed at other times.
B. They are less reliable than the evidence from rocks on land in determining the volume of land ice.
C. They can be used to deduce the relative volume of land ice that was present when the sediment was laid down.
D. They are more unpredictable during an ice age than in other climatic conditions.
E. They can be used to determine atmospheric conditions at various times in the past.
 Supporting ideas 
The phrase according to the passage suggests that the answer to the question is most likely stated in the passage. Lines 12–14 state that the relative volume of land ice can be deduced from the ratio of oxygen 18 to oxygen 16 in ocean sediments.
A. There is no evidence in the passage about this point.
B. The ocean record is described in lines 38–39 as more continuous, so it is unlikely to be less reliable. In any case, reliability is not discussed.
C.  Correct . Lines 12–14 explain that the land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes.
D. There is no evidence in the passage to support this statement.
E. The passage does not discuss the use of this record in determining past atmospheric conditions.
 The correct answer is C.

Q5. 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
 Inference 
Any inference about precipitation from evaporated ocean water needs to be based on what the passage says. Lines 20–22 show that heavier isotopes tend to be left behind when water evaporates from the ocean surfaces. Therefore, the evaporated water would contain less oxygen 18 and the remaining ocean water would contain more. It is logical to infer that precipitation formed from this evaporated water would also contain less oxygen 18.A. Lines 20–24 explain that the water remaining in the ocean after evaporation has more oxygen 18.
B.  Correct . Since the heavier isotopes tend to be left behind, there will be less oxygen 18 in the evaporated water and in the precipitation that forms from it.
C. The passage suggests that the ocean water evaporates and through subsequent precipitation helps form the ice sheets, so the amount of oxygen 18 in the ice sheets should be similar to the amount in the precipitation formed from the evaporated water.
D. The passage does not discuss precipitation formed from water on land.
E. The passage does not discuss precipitation formed from fresh water.
 The correct answer is B.

Q7. It can be inferred from the passage that calcium carbonate shells
A. are not as susceptible to deterioration as rocks
B. are less common in sediments formed during an ice age
C. are found only in areas that were once covered by land ice
D. contain radioactive material that can be used to determine a sediment’s isotopic composition
E. reflect the isotopic composition of the water at the time the shells were formed
 Inference 
Any inference about calcium carbonate shells needs to be based on what the passage says about these shells. Lines 24–32 explain the role of these shells in forming sediments and establishing a chronology for ice ages. The shells were constructed with oxygen atoms drawn from the surrounding ocean. Lines 29–32 make it clear that if the sediments reveal a higher ratio of oxygen 18, it is because more oxygen 18 had been left behind when the ocean water evaporated and contributed to the growth of continental ice sheets. It can thus be inferred that the shells that make up those sediments must reflect the proportion of oxygen 18 found in the ocean water at the time they were formed.
A. The only mention of rocks in the passage is a comparison of “gappiness” of the rock and sedimentary specimen records in lines 38–39; this information does not allow any firm inference to be made with respect to relative susceptibility to deterioration, though a more continuous record might be the
result of less susceptibility to deterioration.
B. The passage does not make any reference to the relative abundance of these shells during ice ages; no such inference can be drawn.
C. The only information in the passage that might support this statement is found in lines 29–32, but that information, about the correlation between oxygen ratios in sediment specimens and land ice, describes a relation that implies nothing about distributions of such specimens.
D. Though the passage does indirectly indicate that the shells contained radioactive material, nothing in the passage suggests that radioactive material is used to determine isotopic composition.
E.  Correct.  The passage explains that oxygen atoms in the surrounding water are one of the building blocks of calcium carbonate shells. The isotopic composition of the surrounding water changes during the ice age cycles, so it is logical that the isotopic composition of the shells will change depending on when they were formed.
 The correct answer is E.

Sujeet07 · Answer

Reading Strategy.........

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 . T he 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  .

Red  - Main Idea and need to understand
 Yellow  - Skim it
 Green  - Skip or Skim (generally i do not prefer skipping any part , because we have know what is mentioned in that part of paragraph so that while solving question we know the exact place in the passage where we need to come back and read.)

1st Paragraph  - Milankovitch proposed a theory-the ice ages were caused by variations in the Earth’s orbit around the Sun and sometime it is untestable.
 2nd Paragraph  - A recent discovery and its explanation
 3rd Paragraph  - Advantages
 4th Paragraph  - Others factor is also important to consider , but this theory is still important.

Himanshuv0 · Answer

In the Q5, option C was eliminated by stating that the subsequent precipitation helps in forming the ice sheet. 
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I am not the infer this above statement from the passage. Can you help me with it?

ReedArnoldMPREP · Answer

The passage states:

This tells us that water evaporates from the ocean, but during an ice age, the growth of the continental ice sheet FOR SOME REASON means less of that water returns to the ocean. The most likely reason is because much of that water stays in the continental ice sheet.

It is, I suppose, a little bit 'outside the passage' to assume that this is because that water *becomes* the ice sheet (that is, the passage neither directly nor implicitly discusses how a continental ice sheet is formed).

However, here's the good news. Even if you're not certain that much of the evaporated ocean ice freezes up and becomes part of the ice sheets, there's no justification for choosing answer C. Regardless of how the ice sheets are made, nothing in the passage implies that there is less O18 in ocean evaporated than there is the continental ice sheets.

So no matter what, we can eliminate C.

B, however, is logically inferred.

This tells the water that does not get evaporated is 'enriched' (has more of) Oxygen 18. This means what is evaporated has relatively LESS O18.

ag153 · Answer

KarishmaB  can you please breakdown Question 9? Why not E and B, C?

Milankovitch proposed in the early twentieth century that the ice ages

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GMAT Reading Comprehension (RC) Questions

Milankovitch proposed in the early twentieth century that the ice ages

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