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Milankovitch proposed inthe early twentieth century that the

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Milankovitch proposed inthe early twentieth century that the [#permalink] New post 22 Aug 2013, 10:21
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Milankovitch proposed inthe early twentieth
century that the ice ages were caused by variations
in the Earth's orbit around the Sun. For some
time this theory was considered untestable,
(5) largelybecause 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
(10) existed at various times inthe Earth's past. Arecent
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
(15) 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
(20) 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
(25) 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
(30) 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
(35) 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,
(40) 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
(45) 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.
(50) 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
(55) 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. Yetthe lack of
information about other possible factors affecting
(60) global climate does not make them unimportant.
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

[Reveal] Spoiler:
D


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.

[Reveal] Spoiler:
D


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?
(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.

[Reveal] Spoiler:
B


According to the passage, which of the following is
true of the ratios of oxygen isotopes in ocean
sediments?
(A) They indicatethat sediments found during an ice
age contain more calcium carbonate than
sediments formed at other times.
(B) They are less reliablethan the evidence from
rocks on land in determining the volume of
land ice.
(0 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 inthe past.

[Reveal] Spoiler:
C


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

[Reveal] Spoiler:
B


Itcan 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

[Reveal] Spoiler:
E



Try this difficult passage in its entirely...........OA later because I want discussion about this one.

Please provide answers with explanations. Thanks for your collaboration
_________________

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Re: Milankovitch proposed inthe early twentieth century that the [#permalink] New post 22 Aug 2013, 14:00
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carcass wrote:
Milankovitch proposed inthe early twentieth
century that the ice ages were caused by variations
in the Earth's orbit around the Sun. For some
time this theory was considered untestable,
(5) largelybecause 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
(10) existed at various times inthe Earth's past. Arecent
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
(15) 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
(20) 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
(25) 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
(30) 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
(35) 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,
(40) 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
(45) 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.
(50) 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
(55) 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. Yetthe lack of
information about other possible factors affecting
(60) global climate does not make them unimportant.
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

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.

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?
(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.

According to the passage, which of the following is
true of the ratios of oxygen isotopes in ocean
sediments?
(A) They indicatethat sediments found during an ice
age contain more calcium carbonate than
sediments formed at other times.
(B) They are less reliablethan the evidence from
rocks on land in determining the volume of
land ice.
(0 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 inthe past.

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

Itcan 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



Try this difficult passage in its entirely...........OA later because I want discussion about this one.

Please provide answers with explanations. Thanks for your collaboration


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. :wave: :done

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Re: Milankovitch proposed inthe early twentieth century that the [#permalink] New post 22 Aug 2013, 18:20
Bingo !..

i also got the same answers ! .. you are right
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Re: Milankovitch proposed inthe early twentieth century that the [#permalink] New post 23 Aug 2013, 10:13
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