Milankovitch proposed in the early twentieth century that : GMAT Reading Comprehension (RC)
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# Milankovitch proposed in the early twentieth century that

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Milankovitch proposed in the early twentieth century that [#permalink]

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17 Nov 2011, 12:57
Milankovitch proposed in the 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,
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
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.

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.

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.

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.

plz explain
If you have any questions
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Re: Milankovitch proposed in the early twentieth century [#permalink]

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17 Nov 2011, 18:34
1, E. This question, I guess :<
2, D "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"
3, C "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."

What's the OA?
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Re: Milankovitch proposed in the early twentieth century [#permalink]

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18 Nov 2011, 11:24
1. D
2. B
3. C
Could anyone explaine why 3 is not E? My way - They can be used to determine ice age =>ice age is atmospheric condition => They can be used to determine atmospheric conditions. What is wrong with that?
Source - OG page 386
Re: Milankovitch proposed in the early twentieth century   [#permalink] 18 Nov 2011, 11:24
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