Milankovitch proposed in the early twentieth century that the ice ages

Hey there!
Can anyone of you help me with them?
RC11332-08
RC11332-09
Regards
sherlockholmes21

Hi sherlockholmes21,

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.

Explanation: Option B is clearly stated in the passage as: "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."
Other options can also be directly eliminated based on the above lines.


For Question 9 please refer the answer: https://gmatclub.com/forum/milankovitch ... l#p2233367

Let me know if you still have doubts.
Thanks.

Can any one explain me how this is E

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

Hi Divyanagireddi,

Not sure what's your doubt, the answer to the 6th Question is C.


Thanks.

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A. suggesting an alternative to an outdated research method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.

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. 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.

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.

All correct in 9 mins 10 seconds! wish I can get this speed and accuracy with 700 level questions and passages!

This should not have a sub 600 tag.

So, if water sample is picked from the ocean, it already has a higher concentration of Oxygen 18. And, once this sample is evaporated, more O 16 is lost than O 18. Thus, logically, precipitate must carry more O 18 than ocean. Can anyone help me understand where I am going wrong?

you are right but the question asked is about evaporated water not the remaining water
5. It can be inferred from the passage that precipitation formed from evaporated ocean water has

What is the ppt in the water that is evaporated?

So the answer for Q2 should be B? is n't it?




DmitryFarber could you please share your opinion?

CrackVerbal IanStewart EducationAisle GMATNinja : Kindly suggest for Q2: why not B?
The author of passage didn't mention there could be other explanation, he just said that in the exisitng explanation , there could be additional parameters.
So B looks exactly what is said in the last para but D is something which is not mentioned ( D says there can be other explanations but didn't say there can be other parameters to consider the explanation)

What am I missing here?

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?

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.

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

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)

Thanks- in E, why can't we say that saying other factors play a role be an explanation for a phenomenon? KarishmaB

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:



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!!!