In 1912, the GermangeologistAlfred Wegener proposed that Earth’s continents aremobilerafts of lightercrustthat have shifted over time byplowingtheir way through the densercrustof the oceans. The theory, calledcontinentaldrift, waspartlymotivated by theapparentfit, like puzzle pieces, of the coastlines of South America and Africa. Wegener first presented his theory ofcontinentaldriftat a meeting and in a paper, and then as a book, The Origin of Continents and Oceans, published in 1915. He continued to write updated versions of this work until his death in an ill-fatedexpeditionto Greenland in 1930. Wegener maintained that Earth is composed ofconcentricshells of increasingdensityfromcrusttocore. Theoutermostshell is notcontinuousbut made ofcontinentalblocks of lighter rock called sial (anacronymfor silica- and aluminum-rich rock) floating in the denser sima (silica- and magnesia-rich rock)underlyingthe oceans. All the continents had been joined in thesupercontinentofPangaea. As thecontinentbroke up, the pieces moving apart left bits behind, explaining the presence of nonvolcanic islands and island chains, according to Wegener. Where the moving pieces collided, mountains formed. They were thrust up either by theplowingof the continents through the sima, as in the case of the Andes, or by the colliding of two blocks of sial, as in the case of the Himalayas. As for the force drivingcontinentaldrift, Wegenerinitiallyinvoked Polfluchtkraft—a force causing flight from the poles as a result of Earth’srotation—and later thetidalforce resulting from thegravitationalattraction between Earth and the Moon and Sun.

One of the mostinfluentialgeologists to join the mobilist camp, as the drifters school became known, was Arthur Holmes. Holmes recognized the importance ofradioactiveheat—which had recently been discovered—and realized that there must be amechanismto remove it from Earth’sinterior. Thatmechanism, he argued, isconvection—the rising of lessdensematerial and the sinking of moredensematerial. He went on toproposethat themantle(the part of Earth’sinteriorbelow the outercrustand above thecore) convects in large, circulating patterns, and that thismotioncarries the continents across Earth’s surface. He also relatedcrustalmovement andmantleconvectionto the evolution of mountain belts. Wegener adopted Holmes’smechanismin the lastrenditionof his theory. Holmes, for his part, presented his grand concept of adynamicEarth in hisinfluentialand popular text Principles of PhysicalGeology, published in 1944.

Although it was eventually supplanted by the theory ofplatetectonics, Wegener’s theory ofcontinentaldriftinfluenced science because it explaineddisparateobservations, because it was placed in thecontextof existing theories, and because it offered acoherentview of Earth’s evolution. For example, Wegener showed not only that the coastlines on opposite sides of the Atlantic fit together, but that geologic features on the different continents fit as well. He asserted that the Appalachians, which can be traced northward through the CanadianMaritimeProvinces, match the Caledonian Mountains in Scotland and Norway. He marshaled evidence from the distributions offossiland living species toarguethat land bridges joining continents were less likely than a singlecontinent. The example commonly cited is that ofMesosaurus, a shorelinescavengerreptilethat lived in the Permian period and is found as fossils in rocks on both sides of the South Atlantic Ocean. Mesosauruswas thought not to be a great swimmer, certainly not able to cross an ocean.

Wegener also found supporting evidence in ancient climates. Mountingobservations indicated that the past climate of many regions was much different from the present climate. In the tropics, geologists had found sand andgravelleft by ancient glaciers, and in rainy regions they had locatedprehistoricdeserts. Then there was the discovery, by a Britishexpedition, of plant fossils only 600 kilometers (370 miles) from the SouthPole. Particularly puzzling was evidence suggesting that widely different climates in different regions had occurred at the same time, so one could notaccountfor different climates by claimingsimplythat the whole of Earth was once hotter or once cooler than now. Wegener solved thisdilemmaby showing that observations of paleoclimate could be explained if the positions of the continents had shiftedrelativeto those of the poles.

Questions:
question_stem: According to paragraph 1, the presence of nonvolcanic islands was an indication to Wegener that
choices: tag: A
text: the sial was lighter than was once believed

tag: B
text: a supercontinent that existed at one time broke apart

tag: C
text: nonvolcanic islands were formed from the sima rather than the sial

tag: D
text: island chains existed prior to the formation of the supercontinent Pangaea
answer_key: B
explanation: 根据题干中关键词”nonvolcanic islands” 定位到“As the continent broke up, the pieces moving apart left bits behind, explaining the presence of nonvolcanic islands and island chains, according to Wegener.”可知非火山岛的出现是为了表明大陆曾经是一个整体，后来 broke up 了，对应 B 选项。A，C 不在定位范围，D 未提及。

question_stem: Why are the Andes and Himalaya mountains mentioned in the discussion in paragraph 1?
choices: tag: A
text: To contrast the ways in which islands and mountains formed

tag: B
text: To describe two ways in which movements of land formed mountains

tag: C
text: To provide examples of mountain ranges that are no longer in their original locations

tag: D
text: To explain the differences between sial and sima with well-known geographic areas
answer_key: B
explanation: 该题型重点找题干细节所要论证的观点句，the Himalayas 和 the Andes 两个例子都是论证前一句话 mountains 形成的，对应 B 选项。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: Wegener’s term “Polfluchtkraft” was first used to mean Earth’s rotation and later the gravitational attraction between Earth and the Moon and Sun.

tag: B
text: Continental drift required a powerful driving force that was created by the combination of Earth’s rotation and tidal movements, which Wegener called “Polfluchtkraft.”

tag: C
text: At first Wegener believed that the movement of the continents was caused by Earth’s rotation but later came to believe that the drift was caused by powerful tides.

tag: D
text: According to Wegener, the great force of continental drift first affected Earth’s rotation at the poles and later also affected the gravitational force of Earth’s tides.
answer_key: C
explanation: 原句子主要意思是：关于驱动大陆漂移的力，Wegener 一开始认为是地球自转导致的力，后来认为是在地球与月球太阳间的重力引力。重点突出了导致大陆漂移先后２个不同的原因，存在因果关系。A 选项重点说“Polfluchtkraft”先后被用于解释什么现象，意思不对；B 选项认为地球自转和潮汐合并是 Polfluchtkraft，跟原文冲突；C 选项，讲到了因果关系，且分了不同时段，正确；D 选项因果反了。

question_stem: What does paragraph 2 suggest about how Holmes influenced Wegener’s thinking?
choices: tag: A
text: He encouraged Wegener to consult the geologists who formed the drifters school.

tag: B
text: He convinced Wegener that the mantle contained a great deal of radioactive heat.

tag: C
text: He demonstrated to Wegener that the density of geographic material was less important than its pattern of movement.

tag: D
text: He provided Wegener with a more accurate explanation of the mechanism by which continents moved and mountains evolved.
answer_key: D
explanation: 题干问 Holmes 如何影响 Wegner 的想法，段落倒数第2句话提到“Wegener adopted Holmes’s mechanism in the last rendition of his theory.”到文章前文把 Homes 的 mechanism 具体内容找到就可以了,具体内容是“That mechanism…the evolution of mountain belts.”A 选项鼓励 Wegner 去咨询地质学家没有提到，B 选项的内容属于 mechanism 涵盖的内容，C 的比较级没有，排除。D 选项对应 mechanism 的内容，正确。

question_stem: What is the importance of Wegener’s observation that “the Appalachians, which can be traced northward through the Canadian Maritime Provinces, match the Caledonian Mountains in Scotland and Norway”?
choices: tag: A
text: It provides additional evidence for Wegener’s claim that separate continents were once connected to each other.

tag: B
text: It indicates that the mechanism by which all mountainous areas on Earth formed was the same.

tag: C
text: It suggests that continental drift occurred in a northward direction.

tag: D
text: It challenges the role of the Atlantic Ocean in shaping continental coastlines.
answer_key: A
explanation: 题干问关于阿巴拉契亚山脉观察有什么重要性，这个部分，跟前一句的例子方向是一致的，都是为了说明 Wegner 关于大陆漂移理论的观点，所以对应选项 A，B, C, D 都跟答案角度无关，排除。

question_stem: The word “asserted” in the passage is closest in meaning to
choices: tag: A
text: claimed

tag: B
text: worried

tag: C
text: repeated

tag: D
text: doubted
answer_key: A
explanation: assert=claim 认为，声称。

question_stem: Mesosaurus is mentioned in paragraph 3 to make which of the following points?
choices: tag: A
text: The presence of its fossils suggests that a land bridge once existed across the South Atlantic Ocean.

tag: B
text: the fact that a reptilian species scavenged along the shoreline indicates that various species must have been there when reptiles arrived.

tag: C
text: The dating of its fossils to the Permian period led Wegener to believe that this was the time when major movements of rocks and continents ended.

tag: D
text: The lack of this species’ swimming ability supports the idea that the shores where its fossils were found must have been joined at one time.
answer_key: D
explanation: 题目问 Mesosaurus 是想论证什么观点，对应倒数第3句话“He marshaled evidence from the distributions of fossil and living species to argue that land bridges joining continents were less likely than a single continent.”重点是为了说明地球上的大陆曾是一整块的超级大陆“single continent”，对应 D 选项，其他3个选项跟这个方向没有关系，都排除。

question_stem: What was the dilemma that Wegener solved?
choices: tag: A
text: Why prehistoric fossils occurred in deserts but not rainy regions

tag: B
text: Whether sand and gravel were once part of ancient glaciers

tag: C
text: How to explain great climatic variations occurring at the same time among various regions

tag: D
text: Whether the overall temperature of Earth was once hotter or colder
answer_key: C
explanation: 通过题干关键词 dilemma，对应到原文最后一句话 Wegener solved this dilemma… 把 this dilemma 的具体内容还原即可，找到前一句话：让人很费解的证据表明不同区域在同一时间出现了不同的气候，而这一现象无法简单地用整个地球曾经比现在更冷或者更热来表达。说明难题是无法解释同一时间为什么不同区域气候不一样，对应 C 选项。