Day 1

Passage 1

Mammoth Extinction

① Mammoth, the common name for several extinct species of the elephant family, hadlong,curved tusks which grew to approximately 3m(about10.1ft.)in length,and aprominent hump on the back.The first mammoths appeared in Africa during the early Pliocene Epoch, almost 5 million years ago. The first North American mammoths migrated across the Bering Strait from Asiain to Alaska during aperiod of low sea levels nearly 2million years ago.By the beginning of the Pleistocene Epoch,about 1.6million years ago,mammoths inhabited North America,Europe,and Asia.Scientists believe that most mammoths had died out toward the end of the Pleistocene Epoch, about 11,000 years ago. Yet the cause of their extinction remains unsolved.

② Some scientists hold the proposal that the mammoths'extinction were triggered by climatic change.During the Late Pleistocene,the environment of the northern territories of Eurasia, (ranging from Western Europe toAlaska,) was generally open, tending towardsteppe-like.It is known as the Mammoth Steppe,an ecosystem remarkable for its unusual combination of mammal species.The Mammoth Steppe was very productive and characterized by very diverse flora and fauna,with alargevariety in species.It would have sustained mammalian herds all year round.Yet as the planet warmed during the Pleistocene-Holocene transition, a drastic rearrangement of its floral and faunal components occurred which led to a marked change in the distribution of species.The steppes there gave way to silt,dust,and ice-based tundral landscapes,dominated in some places by forests and in others by mosses.As the ecosystem of the Mammoth Steppe collapsed and was replaced by the modern tundra and steppe belts of Eurasia, mammoth became extinct after having survived many climatic changes during several hundreds of thousands of years.

③ However,other researchers tend to form a different theory.They believe the Clovis people, who were big-game hunters, could help explain an unsolved puzzle of the Americas in the late Pleistocene:the catastrophic extinction of dozens of species of large animals.Across the Americas, millions of large animals disappeared, including the mammoth. These extinctions were thought to coincide with the arrival of Clovis groups, a chronological coincidence that led University of Arizona ecologist Paul Martin to propose the hypothesis of Pleistocene overkill, as the Pleistocene-Holocene transition is also the period during which humans spread into Northern Siberia and crossed Beringia on their journey to America. This hypothesis, first put forward in 1167, contends that the Clovis big-game hunters caused the extinctions. Martin suggested that overkill was especially likely—even inevitable—if Clovis groups were the first Americans. These giant animals, if they had never faced human hunters before, would have been especially vulnerable prey to this new, dangerous, two-legged predator.【1】

④ Over time, however, it became clear that the Pleistocene overkill hypothesis was not strongly supported by the archaeological record.Archaeologists have yet to document a single Clovis sloth kill, horse kill, camel kill, or a kill of any of the other several dozen mega faunal species. Whatever caused the extinction of these animals, it was not human hunting. Currently, the extinction remains a puzzle.

——2012年 5月 26日北美机经

1. All of the following are mentioned in Paragraph 2 as contributing to the extinction of mammoth EXCEPT ______ .

A. the atmosphere generally warmed up

B. the disappearance of their natural habitat

C. the human invasion into Northern Siberia

D. the violent rearrangement of Mammoth Steppes floral and faunal composition

2. According to Paragraph 4, why was the overkill hypothesis weakly supported?

A. Scientists are more inclined to adopt the climatic change hypothesis.

B. Apart from mammoth, other several dozen megafaunal species also died out.

C. The archaeologists cannot find any evidence on the Clovis killing of other animals to support the mammoth overkill hypothesis.

D. The time of mammoth extinction doesn't agree with that of the Clovis settlement.

词汇练习：

阅读下列句子，用所给单词（或词组）的正确形式填空：

extinct

collapse

archaeological

drastic

territory

sustain

document

hypothesis

catastrophic

trigger

vulnerable

migrate

inevitable

1. The fossil consists of a complete skull of an archaeocyte, an ______ group of ancestors of modern cetaceans.（OG：The Origins of Cetaceans）

2. In addition, there were other immigrants who ______ west in search of new homes, material success, and better lives.（TPO-20：Westward Migration）

3. Nomadism has further consequences. It means that pastoralist societies occupy and can influence very large ______ .（TPO-14：Pastoralism in Ancient Inner Eurasia）

4. Moreover, our humanness must be ______ through social interaction—and fairly constantly so.（TPO-11：Types of Social Groups）

5. The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more ______ in a whole series of such recurrent extinction episodes.（TPO-11：Mass Extinctions）

6. The labor movement gathered some momentum in the decade before the Panic of 1837, but in the depression that followed, labor's strength ______ .（OG：Artisans and Industrialization）

7. Experiments have also cast serious doubt on the belief that yawning is ______ by a drop in blood oxygen or a rise in blood carbon dioxide.（TPO-18：The Mystery of Yawning）

8. But even without such specific documentation, it is clear that impacts of this size do occur and that their results can be ______ .（Official Model Exam：Meteorite Impact and Dinosaur Extinction）

9. The time had come to formulate a ______ .（TPO-7：The Geologic History of the Mediterranean）

10. Sigmund Freud, for example, believed that aggressive impulses are ______ reactions to the frustrations of daily life.（OG：Aggression）

11. These higher-frequency sounds do not travel as far, and so may better conceal the individuals producing them, who are especially ______ to predators in their ground nests.（TPO-11：Begging by Nestlings）

12. The ______ evidence clearly indicates, though, that Teotihuacán was the center that did arise as the predominant force in the area by the first century A.D.（TPO-8：The Rise of Teotihuacán）

13. Why does the fossil record not ______ the series of evolutionary changes during the evolution of animals?（TPO-1：The Cambrian Explosion）

参考答案：

1. extinct

2. migrated

3. territories

4. sustained

5. drastic

6. collapsed

7. triggered

8. catastrophic

9. hypothesis

10. inevitable

11. vulnerable

12. archaeological

13. document

【1】与今日百句译（Sentence 1）相同的句型。