P1：M提出一個(gè)理論, 指出其缺陷
To establish such a chronology it is necessary
to determine the relative amounts of land ice that
(10)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
(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 (calcium carbonate: n.[化]碳酸鈣) 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.
P2: 一個(gè)新發(fā)現(xiàn)可彌補(bǔ)M理論的缺陷
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.
P3：新發(fā)現(xiàn)的優(yōu)點(diǎn)
However, it is important to note that other
(50)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
(55)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.
P4：其他的理論也不容忽視
70. In the passage, the author is primarily interested in
主題題(D)
suggesting an alternative to an outdated research method
introducing a new research method that calls an accepted theory into question
emphasizing the instability of data gathered from the application of a new scientific method
presenting a theory and describing a new method to test that theory(D)
initiating a debate about a widely accepted theory
To establish such a chronology it is necessary
to determine the relative amounts of land ice that
(10)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
(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 (calcium carbonate: n.[化]碳酸鈣) 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.
P2: 一個(gè)新發(fā)現(xiàn)可彌補(bǔ)M理論的缺陷
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.
P3：新發(fā)現(xiàn)的優(yōu)點(diǎn)
However, it is important to note that other
(50)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
(55)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.
P4：其他的理論也不容忽視
70. In the passage, the author is primarily interested in
主題題(D)
suggesting an alternative to an outdated research method
introducing a new research method that calls an accepted theory into question
emphasizing the instability of data gathered from the application of a new scientific method
presenting a theory and describing a new method to test that theory(D)
initiating a debate about a widely accepted theory