托福阅读常考话题及练习题推荐三：冰川（2）

► Paragraph 1： 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.

1.The word “accumulations” in the passage is closest in meaning to

A. signs

B. pieces

C. types

D. deposits

2.The word “heterogeneous” in the passage is closest in meaning to

A. remaining

B. varied

C. familiar

D. layered

3. 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

► Paragraph 2：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.

4.The word “enjoy” in the passage is closest in meaning to

A. experience

B. resemble

C. expect

D. dominate

5.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

► Paragraph 3： 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.

6. 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.

► Paragraph 3：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.

► Paragraph 4：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.

7. According to paragraph 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

8.The word “reveal” in the passage is closest in meaning to

A. result from

B. vary with

C. show

D. preserve

9. 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

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