Official19 托福阅读Passage3 Discovering the Ice Ages文本+题目原文+答案解析【雷哥托福】2019-02-11 11:06:11 发布 来源：雷哥托福 阅读量:3203
TPO19 托福阅读Passage3 Discovering the Ice Ages 文本+题目原文+答案解析
Discovering the Ice Ages
In the middle of the nineteenth century, Louis Agassiz, one of the first scientists to study glaciers, immigrated to the United States from Switzerland and became a professor at Harvard University, where he continued his studies in geology and other sciences. For his research, Agassiz visited many places in the northern parts of Europe and North America, from the mountains of Scandinavia and New England to the rolling hills of the American Midwest. ■ In all these diverse regions, Agassiz saw signs of glacial erosion and sedimentation.■ In flat plains country, he saw moraines (accumulations of earth and loose rock that form at the edges of glaciers) that reminded him of the terminal moraines found at the end of valley glaciers in the Alps. ■ The heterogeneous material of the drift (sand, clay, and rocks deposited there) convinced him of its glacial origin. ■
The areas covered by this material were so vast that the ice that deposited it must have been a continental glacier larger than Greenland or Antarctica. Eventually, Agassiz and others convinced geologists and the general public that a great continental glaciation had extended the polar ice caps far into regions that now enjoy temperate climates. For the first time, people began to talk about ice ages. It was also apparent that the glaciation occurred in the relatively recent past because the drift was soft, like freshly deposited sediment. We now know the age of the glaciation accurately from radiometric dating of the carbon-14 in logs buried in the drift. The drift of the last glaciation was deposited during one of the most recent epochs of geologic time, the Pleistocene, which lasted from 1.8 million to 10,000 years ago. Along the east coast of the United States, the southernmost advance of this ice is recorded by the enormous sand and drift deposits of the terminal moraines that form Long Island and Cape Cod.
It soon became clear that there were multiple glacial ages during the Pleistocene, with warmer interglacial intervals between them. As geologists mapped glacial deposits in the late nineteenth century, they became aware that there were several layers of drift, the lower ones corresponding to earlier ice ages. Between the older layers of glacial material were well- developed soils containing fossils of warm-climate plants. These soils were evidence that the glaciers retreated as the climate warmed. By the early part of the twentieth century, scientists believed that four distinct glaciations had affected North America and Europe during the Pleistocene epoch.
This idea was modified in the late twentieth century, when geologists and oceanographers examining oceanic sediment found fossil evidence of warming and cooling of the oceans. Ocean sediments presented a much more complete geologic record of the Pleistocene than continental glacial deposits did. The fossils buried in Pleistocene and earlier ocean sediments were of foraminifera—small, single-celled marine organisms that secrete shells of calcium carbonate, or calcite. These shells differ in their proportion of ordinary oxygen (oxygen-16) and the heavy oxygen isotope (oxygen-18). The ratio of oxygen-16 to oxygen-18 found in the calcite of a foraminifer's shell depends on the temperature of the water in which the organism lived. Different ratios in the shells preserved in various layers of sediment reveal the temperature changes in the oceans during the Pleistocene epoch.
Isotopic analysis of shells allowed geologists to measure another glacial effect. They could trace the growth and shrinkage of continental glaciers, even in parts of the ocean where there may have been no great change in temperature— around the equator, for example. The oxygen isotope ratio of the ocean changes as a great deal of water is withdrawn from it by evaporation and is precipitated as snow to form glacial ice. During glaciations, the lighter oxygen-16 has a greater tendency to evaporate from the ocean surface than the heavier oxygen-18 does. Thus, more of the heavy isotope is left behind in the ocean and absorbed by marine organisms. From this analysis of marine sediments, geologists have learned that there were many shorter, more regular cycles of glaciation and deglaciation than geologists had recognized from the glacial drift of the continents alone.
TPO19托福阅读 Passage1 Discovering the Ice Ages 题目
Question 1 of 14: The word "accumulations" in the passage is closest in meaning to
Question 2 of 14: The word “heterogeneous” in the passage is closest in meaning to
Question 3 of 14: According to paragraph 1, what persuaded Louis Agassiz that glaciation in the past had been widespread?
A. Geologic differences between mountain valleys and flat plains
B. The presence of similar glacial material in many different regions
C. Geologic research on mountain glaciers in the Alps
D. Evidence of regional differences in the drift caused by glacial erosion
Question 4 of 14: The word “enjoy” in the passage is closest in meaning to
Question 5 of 14: It can be inferred from paragraph 2 that Agassiz and other geologists of his time were not able to determine
A. which geographic regions had been covered with ice sheets in the last ice age
B. the exact dates at which drifts had been deposited during the last ice age
C. the exact composition of the drifts laid during the last ice age
D. how far south along the east coast of the United States the ice had advanced during the last ice age
Question 6 of 14: According to paragraph 3, what did geologists conclude as a result of finding well-developed soils containing warm- climate plant fossils between layers of glacial drift?
A. There had been only one warm period before the Pleistocene epoch
B. There had been multiple periods of mild weather between ice ages
C. Several glacial periods occurred after the Pleistocene epoch
D. Some earlier epochs were warmer than the Pleistocene
Question 7 of 14: According to paragraphs 3 and 4, scientists modified their theory about the exact number of glaciations because of evidence obtained from
A. ocean sediments
B. interglacial soils
C. glacial deposits
D. air samples
Question 8 of 14: The word “reveal" in the passage is closest in meaning to
A. result from
B. vary with
Question 9 of 14: According to paragraph 4, scientists use foraminifera shells to learn about Pleistocene ocean conditions by
A. measuring the amount of calcium carbonate present in the shells
B. determining the proportion of shell in each layer of sediment
C. comparing shells deposited during the Pleistocene with those buried earlier
D. calculating the relative quantity of two oxygen isotopes in the calcite
Question10 of 14: It can be inferred from paragraph 5 that forammifera fossil shells containing calcite with high percentages of oxygen-16 were deposited at times when
A. polar ice extended as far as equatorial regions of land and sea
B. extensive glaciation was not occurring
C. there were no great increases in ocean temperature
D. there was heavy snowfall on continental glaciers
Question11 of 14: In paragraph 5, why does the author include the information that the “oxygen isotope ratio of the ocean changes as a great deal of water is withdrawn from it by evaporation and is precipitated as snow to form glacial ice”?
A. To explain how scientists were able to calculate how frequently the continental ice sheets expanded and contracted
B. To explain how scientists have determined that there was no great change in ocean temperatures at the equator during past glaciations
C. To provide evidence that oxygen-16 has a greater tendency to evaporate than does oxygen-18
D. To suggest that equatorial marine organisms absorb more heavy isotopes than do marine organisms elsewhere
Question 12 of 14: According to the passage, when did scientists begin to realize that more than one ice age had occurred?
A. In the mid nineteenth century
B. In the late nineteenth century
C. In the early twentieth century
D. In the late twentieth century
Question13 of 14: Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?
In his view, there could be no other explanation for the composition of such drift.
A. In all these diverse regions, Agassiz saw signs of glacial erosion and sedimentation.
B. In flat plains country, he saw moraines (accumulations of earth and loose rock that form at the edges of glaciers) that reminded him of the terminal moraines found at the end of valley glaciers in the Alps.
C. The heterogeneous material of the drift (sand, clay, and rocks deposited there) convinced him of its glacial origin.
Question14 of 14: Louis Agassiz was the first to note signs of glacial erosion and sedimentation in diverse regions of Europe and North America.
A. Evidence of a pattern of glacier-like deposits eventually convinced most geologists that an enormous continental glacier had extended into the temperate zone
B. Glacial research showed that many layers of ice were deposited, with each new period of glaciation extending farther south than the one before
C. Isotopic analysis of marine sediments showed that periods of glaciation and deglaciation were more frequent, shorter, and more cyclic than previously thought
D. Nineteenth-century geologists came to accept the idea that the areas covered by polar ice had reached as far as the equator, a far larger area than Agassiz had thought
E. Nineteenth-century geologists studying the layers of drift concluded that during the Pleistocene epoch, several glaciations had occurred with warm periods between them
F. Research involving foraminifera fossil shells shows that ocean temperatures in the Northern Hemisphere varied greatly during the most extensive periods of glaciation
TPO54托福阅读Passage3 Discovering the Ice Ages 真题解析
Question 1 of 14
Question 2 of 14
Question 3 of 14
解析：对应到第一段第二、三句。提到Agassiz去了很多地方，在不同的地方都发现了冰蚀和沉积痕迹，所以答案是B。D的regional difference与原文相反；A的geologic difference原文未提及，C答非所问。
Question 4 of 14
Question 5 of 14
Question 6 of 14
解析：以warm-climate plant fossils做关键词定位至第三段第三句，但这句没提到结论是什么。而开头的主旨句说了在Pleistocene时期共有好几次冰川时期，而且期间有几次温暖时期。可见后面证据的展开都是为了支持这一主旨句的，所以正确答案是B。
Question 7 of 14
解析：以modified their theory做关键词定位至第四段第一句，提到改变了idea的原因是他们看了oceanic sediment里面的化石，所以证据是来自ocean sediment的，答案是A。
Question 8 of 14
Question 9 of 14
Question 10 of 14
Question 11 of 14
Question 12 of 14
Question 13 of 14
解析：插入句中的in his view, no other explanation说明插入句前一句肯定提到了某人的一个观点，所以选D，D前一句的convince him of…说明了他的结论性的观点。
Question 14 of 14