推 sa018858:謝謝林子育老師, 我當時閱讀就是她上的.... 12/21 01:02
19.
題目問的是Agassiz及其它同時代的地質學家
A：錯，因為文中有提到Agassiz等人已確定某些地理環境，如歐洲及北美的山區有被冰河覆
蓋。
B：對，因文中提到我們現在知道冰河的正確年代，以此類推。當年Agassiz及其它的地質學
家無法確認此事。
C：錯，因文中有提到Agassiz等人已知這些冰堆的成份，故不能選。
25.
第五段一開始作者就提到透過isotopic analysis of shells地質學家可以trace the
growth and shrinkage of continental glaciers，接著他又舉例”The oxygen isotope
ratio of the ocean changes as a great deal of water is withdrawn from it……”由
此可見透過isotopic analysis科學家可以計算出長久覆蓋於陸地的大冰原expand(growth)
以及contract(shrinkage)的頻率。
(以上內容由美加 林子育老師提供)
※ 引述《sa018858 (情定醫踢希..)》之銘言：
: 不好意思又來請教各位
: 因為TPO 19有些版友可能沒有, 所以附上全文..
: 如果美加助教可以幫我轉問老師, 我真的會非常的感激..
: 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.
: 19: It can be inffered from paragraph 2 that Agassiz and other geolosists of
: his time were not able to determin
: A. which geographic regions had been covered with ice sheets in the lat 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
: 答案是B.
: 想請教說文中不是已經說we now know the age of the glaciation accurately from...
: 答案怎麼會是B呢!? A與C反而還比較像答案不是嗎??
: 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.
: 25: In paragraph 5, why does the author include the information that the
: "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."??
: 答案:
: A. To explain how scientists were able to calculate how frequently the
: continental ice sheets expanded and contracted.
: 請問這答案在文中哪邊找的到呀? 完全不了解中...
: 麻煩各位解答了, 謝謝您花時間解答我的疑惑..
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