There is increasing evidence that the impacts of meteorites have had important effects on Earth, particularly in the field of biological evolution. Such impacts continue to pose a natural hazard to life on Earth. Twice in the twentieth century, large meteorite objects are known to have collided with Earth.
If an impact is large enough, it can disturb the environment of the entire Earth and cause an ecological catastrophe. The best-documented such impact took place 65 million years ago at the end of the Cretaceous period of geological history. This break in Earth's history is marked by a mass extinction, when as many as half the species on the planet became extinct. While there are a dozen or more mass extinctions in the geological record, the Cretaceous mass extinction has always intrigued paleontologists because it marks the end of the age of the dinosaurs. For tens of millions of years, those great creatures had flourished. Then, suddenly, they disappeared.
The body that impacted Earth at the end of the Cretaceous period was a meteorite with a mass of more than a trillion tons and a diameter of at least 10 kilometers. Scientists first identified this impact in 1980 from the worldwide layer of sediment deposited from the dust cloud that enveloped the planet after the impact. This sediment layer is enriched in the rare metal iridium and other elements that are relatively abundant in a meteorite but very rare in the crust of Earth. Even diluted by the terrestrial material excavated from the crater, this component of meteorites is easily identified. By 1990 geologists had located the impact site itself in the Yucat region of Mexico. The crater, now deeply buried in sediment, was originally about 200 kilometers in diameter.
This impact released an enormous amount of energy, excavating a crater about twice as large as the lunar crater Tycho. The explosion lifted about 100 trillion tons of dust into the atmosphere, as can be determined by measuring the thickness of the sediment layer formed when this dust settled to the surface. Such a quantity of material would have blocked the sunlight completely from reaching the surface, plunging Earth into a period of cold and darkness that lasted at least several months. The explosion is also calculated to have produced vast quantities of nitric acid and melted rock that sprayed out over much of Earth, starting widespread fires that must have consumed most terrestrial forests and grassland. Presumably, those environmental disasters could have been responsible for the mass extinction, including the death of the dinosaurs.
Several other mass extinctions in the geological record have been tentatively identified with large impacts, but none is so dramatic as the Cretaceous event. But even without such specific documentation, it is clear that impacts of this size do occur and that their results can be catastrophic. What is a catastrophe for one group of living things, however, may create opportunities for another group. Following each mass extinction, there is a sudden evolutionary burst as new species develop to fill the ecological niches opened by the event.
Impacts by meteorites represent one mechanism that could cause global catastrophes and seriously influence the evolution of life all over the planet. According to some estimates, the majority of all extinctions of species may be due to such impacts. Such a perspective fundamentally changes our view of biological evolution. The standard criterion for the survival of a species is its success in competing with other species and adapting to slowly changing environments. Yet an equally important criterion is the ability of a species to survive random global ecological catastrophes due to impacts.
Earth is a target in a cosmic shooting gallery, subject to random violent events that were unsuspected a few decades ago. In 1991 the United States Congress asked NASA to investigate the hazard posed today by large impacts on Earth. The group conducting the study concluded from a detailed analysis that impacts from meteorites can indeed be hazardous. Although there is always some risk that a large impact could occur, careful study shows that this risk is quite small.
Paragraph 1: There is increasing evidence that the impacts of meteorites have had important effects on Earth, particularly in the field of biological evolution. Such impacts continue to pose a natural hazard to life on Earth. Twice in the twentieth century, large meteorite objects are known to have collided with Earth.
1. The word “pose” in the passage is closest in the meaning to
○claim
○model
○assume
○present
Paragraph 2: If an impact is large enough, it can disturb the environment of the entire Earth and cause an ecological catastrophe. The best-documented such impact took place 65 million years ago at the end of the Cretaceous period of geological history. This break in Earth's history is marked by a mass extinction, when as many as half the species on the planet became extinct. While there are a dozen or more mass extinctions in the geological record, the Cretaceous mass extinction has always intrigued paleontologists because it marks the end of the age of the dinosaurs. For tens of millions of years, those great creatures had flourished. Then, suddenly, they disappeared.
2. In paragraph 2, why does the author include the information that dinosaurs had flourished for tens of millions of years and then suddenly disappeared?
○ To support the claim that the mass extinction at the end of the Cretaceous is the best-documented of the dozen or so mass extinctions in the geological record
○ To explain why as many as half of the species on Earth at the time are believed to have become extinct at the end of the Cretaceous
○ To explain why paleontologists have always been intrigued by the mass extinction at the end of the Cretaceous
○ To provide evidence that an impact can be large enough to disturb the environment of the entire planet and cause an ecological disaster
Paragraph 3: The body that impacted Earth at the end of the Cretaceous period was a meteorite with a mass of more than a trillion tons and a diameter of at least 10 kilometers. Scientists first identified this impact in 1980 from the worldwide layer of sediment deposited from the dust cloud that enveloped the planet after the impact. This sediment layer is enriched in the rare metal iridium and other elements that are relatively abundant in a meteorite but very rare in the crust of Earth. Even diluted by the terrestrial material excavated from the crater, this component of meteorites is easily identified. By 1990 geologists had located the impact site itself in the Yucat region of Mexico. The crater, now deeply buried in sediment, was originally about 200 kilometers in diameter.
3. Which of the following can be inferred from paragraph 3 about the location of the meteorite impact in Mexico?
○ The location of the impact site in Mexico was kept secret by geologists from 1980 to 1990.
○ It was a well-known fact that the impact had occurred in the Yucat region.
○ Geologists knew that there had been an impact before they knew where it had occurred.
○ The Yucat region was chosen by geologists as the most probable impact site because of its climate.
4. According to paragraph 3, how did scientists determine that a large meteorite had impacted Earth?
○ They discovered a large crater in the Yucat region of Mexico.
○ They found a unique layer of sediment worldwide.
○ They were alerted by archaeologists who had been excavating in the Yucat region.
○ They located a meteorite with a mass of over a trillion tons.
Paragraph 4: This impact released an enormous amount of energy, excavating a crater about twice as large as the lunar crater Tycho. The explosion lifted about 100 trillion tons of dust into the atmosphere, as can be determined by measuring the thickness of the sediment layer formed when this dust settled to the surface. Such a quantity of material would have blocked the sunlight completely from reaching the surface, plunging Earth into a period of cold and darkness that lasted at least several months. The explosion is also calculated to have produced vast quantities of nitric acid and melted rock that sprayed out over much of Earth, starting widespread fires that must have consumed most terrestrial forests and grassland. Presumably, those environmental disasters could have been responsible for the mass extinction, including the death of the dinosaurs.
5. The word “excavating” in the passage is closest in the meaning to
○ digging out
○ extending
○ destroying
○ covering up
6. The word “consumed” in the passage is closest in the meaning to
○ changed
○ exposed
○ destroyed
○ covered
7. According to paragraph 4, all of the following statements are true of the impact at the end of the Cretaceous period EXCEPT:
○ A large amount of dust blocked sunlight from Earth.
○ Earth became cold and dark for several months.
○ New elements were formed in Earth's crust.
○ Large quantities of nitric acid were produced.
Paragraph 5: Several other mass extinctions in the geological record have been tentatively identified with large impacts, but none is so dramatic as the Cretaceous event. But even without such specific documentation, it is clear that impacts of this size do occur and that their results can be catastrophic. What is a catastrophe for one group of living things, however, may create opportunities for another group. Following each mass extinction, there is a sudden evolutionary burst as new species develop to fill the ecological niches opened by the event.
8. The phrase “tentatively identified” in the passage is closest in the meaning to
○ identified after careful study
○ identified without certainty
○ occasionally identified
○ easily identified
Paragraph 6: Impacts by meteorites represent one mechanism that could cause global catastrophes and seriously influence the evolution of life all over the planet. According to some estimates, the majority of all extinctions of species may be due to such impacts. Such a perspective fundamentally changes our view of biological evolution. The standard criterion for the survival of a species is its success in competing with other species and adapting to slowly changing environments. Yet an equally important criterion is the ability of a species to survive random global ecological catastrophes due to impacts.
9. The word “perspective” in the passage is closest in the meaning to
○ sense of values
○ point of view
○ calculation
○ complication
10. Paragraph 6 supports which of the following statements about the factors that are essential for the survival of a species?
○ The most important factor for the survival of a species is its ability to compete and adapt to gradual changes in its environment.
○ The ability of a species to compete and adapt to a gradually changing environment is not the only ability that is essential for survival.
○ Since most extinctions of species are due to major meteorite impacts, the ability to survive such impacts is the most important factor for the survival of a species.
○ The factors that are most important for the survival of a species vary significantly from one species to another.
Paragraph 7: Earth is a target in a cosmic shooting gallery, subject to random violent events that were unsuspected a few decades ago. In 1991 the United States Congress asked NASA to investigate the hazard posed today by large impacts on Earth. The group conducting the study concluded from a detailed analysis that impacts from meteorites can indeed be hazardous. Although there is always some risk that a large impact could occur, careful study shows that this risk is quite small.
11. 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.
○ Until recently, nobody realized that Earth is exposed to unpredictable violent impacts from space.
○ In the last few decades, the risk of a random violent impact from space has increased.
○ Since most violent events on Earth occur randomly, nobody can predict when or where they will happen.
○ A few decades ago, Earth became the target of random violent events originating in outer space.
12. According to the passage, who conducted investigations about the current dangers posed by large meteorite impacts on Earth?
○Paleontologists
○Geologists
○The United States Congress
○NASA
Paragraph 6: Impacts by meteorites represent one mechanism that could cause global catastrophes and seriously influence the evolution of life all over the planet. █According to some estimates, the majority of all extinctions of species may be due to such impacts. █Such a perspective fundamentally changes our view of biological evolution. █The standard criterion for the survival of a species is its success in competing with other species and adapting to slowly changing environments. █Yet an equally important criterion is the ability of a species to survive random global ecological catastrophes due to impacts.
13. Look at the four squares [█] that indicate where the following sentence can be added to the passage.
This is the criterion emphasized by Darwin's theory of evolution by natural selection.
Where would the sentence best fit?
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Scientists have linked the mass extinction at the end of the Cretaceous with a meteorite impact on Earth.
●
●
●
Answer choices
○Scientists had believed for centuries that meteorite activity influenced evolution on Earth.
○An iridium-enriched sediment layer and a large impact crater in the Yucat provide evidence that a large meteorite struck Earth about 65 million years ago.
○The site of the large meteorite impact at the end of the Cretaceous period was identified in 1990.
○Large meteorite impacts, such as one at the end of the Cretaceous period, can seriously affect climate, ecological niches, plants, and animals.
○There have also been large meteorite impacts on the surface of the Moon, leaving craters like Tycho.
○Meteorite impacts can be advantageous for some species, which thrive, and disastrous for other species, which become extinct.
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参考答案：
1. ○4
2. ○3
3. ○3
4. ○2
5. ○1
6. ○3
7. ○3
8. ○2
9. ○2
10. ○2
11. ○1
12. ○4
13. ○4
14. An iridium-enriched sediment…
Large meteorite impacts…
Meteorite impacts can…
越来越多的证据表明陨石撞击对地球造成的影响特别严重，尤其是生物进化领域。这种影响对地球上的生物来说，仍然是一种自然威胁。在20世纪，被人们所知悉的就有两次大型陨石撞地球的事件发生。
当撞击力度特别大时，陨石和地球的相撞将扰乱整个地球的环境，并引发一场生态灾难。记载最完整的这种灾难曾发生在6 500万年前，在地质历史阶段的白垩纪末期。地球历史上的那次重大灾难造成了大量生物死亡，当时多达一半的物种灭绝。根据地质史料记载，地球上有十几次甚至更多大型的物种灭绝，古生物学家一直对白垩纪大灭绝非常感兴趣，因为它标志着恐龙时代的结束。数千万年以来，那些庞大的生物繁盛活跃着；然后突然间，它们消失了。
白垩纪末期，撞击地球主体是一块巨大陨石，它的质量超过万亿吨，直径至少在10公里。1980年科学家通过研究撞击后形成的、覆盖地球表面的尘雾沉积层，首次确认了这次撞击。该沉积层富含稀有金属铱和其他在陨石中含量较丰富但在地壳中却很稀有的元素。即便这些物质从陨石坑被挖掘出来后受到地球物质的稀释，其中的成分仍然很容易被鉴定出来。1990年，地质学家已经将那次撞击的地点定位于墨西哥的尤卡地区。现在被深埋于沉积物中的陨石坑，最初的直径为200公里左右。
这次撞击释放出了巨大的能量，凿出了一个约为月球第谷山口面积的两倍大的陨石坑。那场爆炸将大量尘埃扬起至大气层中，尘埃降至地面后逐渐形成沉积岩，通过测量沉积岩的厚度，我们可以判断当时的大气中的尘埃约有100万亿吨。如此大量的物质存在于大气层中，将会完全阻隔了阳光的照射，于是地球一瞬间进入了一个持续数月之久的寒冷黑暗时期。据估计，爆炸过程还产生了大量的硝酸和被溶解的岩浆并喷出地球外，造成了大面积火灾，大部分的森林和草原被燃尽。这些环境灾难很可能就是包括恐龙在内的大规模物种灭绝的原因。
根据地质学记载，一些其他大批生物的灭绝也被初步认定认为与类似的撞击有关，但都没有白垩纪的那次触目惊心。不过即便是没有具体史料依据，这种规模的撞击显然发生过，并且带来了灾难性的后果。然而对于一个生物种群而言算是大灾难，却有可能给另一个种群创造了机会。每一次大灭绝过后，都会有新的物种爆炸式地进化去填补由灭绝造成的物种空缺。
陨石撞击描绘了一个能够制造全球性的灾难的途径，这种灾难会对整个星球的生命体的进化带来重大影响。据估计，已经灭绝的所有物中，绝大部分都是由于这些撞击造成的。这种观点从根本上改变了我们对于生物进化的看法。一个物种生存的标准准则就是它成功地与其他物种对抗，并适应缓慢变化的环境。然而还有一个同等重要的准则就是，可以从随机的、由天体撞击造成的全球生态灾难中幸存。
几十年前，地球是宇宙射击场的一个靶子，容易受到未知的随机暴力事件的攻击。1991年美国国会要求美国国家航空航天局调查大型撞击对地球造成的危害。指挥这项研究的团队通过详细的分析得出这样一个结论：陨石撞击确实是危险的。尽管大型撞击发生的风险依然存在，但是谨慎的研究这门也认为这种风险的出现几率非常小。
