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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參考答案：
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4. ○2
5. ○1
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8. ○2
9. ○2
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11. ○1
12. ○4
13. ○4
14. An iridium-enriched sediment…
Large meteorite impacts…
Meteorite impacts can…
越來越多的證據(jù)表明隕石撞擊對地球造成的影響特別嚴重，尤其是生物進化領(lǐng)域。這種影響對地球上的生物來說，仍然是一種自然威脅。在20世紀，被人們所知悉的就有兩次大型隕石撞地球的事件發(fā)生。
當撞擊力度特別大時，隕石和地球的相撞將擾亂整個地球的環(huán)境，并引發(fā)一場生態(tài)災(zāi)難。記載最完整的這種災(zāi)難曾發(fā)生在6 500萬年前，在地質(zhì)歷史階段的白堊紀末期。地球歷史上的那次重大災(zāi)難造成了大量生物死亡，當時多達一半的物種滅絕。根據(jù)地質(zhì)史料記載，地球上有十幾次甚至更多大型的物種滅絕，古生物學家一直對白堊紀大滅絕非常感興趣，因為它標志著恐龍時代的結(jié)束。數(shù)千萬年以來，那些龐大的生物繁盛活躍著；然后突然間，它們消失了。
白堊紀末期，撞擊地球主體是一塊巨大隕石，它的質(zhì)量超過萬億噸，直徑至少在10公里。1980年科學家通過研究撞擊后形成的、覆蓋地球表面的塵霧沉積層，首次確認了這次撞擊。該沉積層富含稀有金屬銥和其他在隕石中含量較豐富但在地殼中卻很稀有的元素。即便這些物質(zhì)從隕石坑被挖掘出來后受到地球物質(zhì)的稀釋，其中的成分仍然很容易被鑒定出來。1990年，地質(zhì)學家已經(jīng)將那次撞擊的地點定位于墨西哥的尤卡地區(qū)�，F(xiàn)在被深埋于沉積物中的隕石坑，最初的直徑為200公里左右。
這次撞擊釋放出了巨大的能量，鑿出了一個約為月球第谷山口面積的兩倍大的隕石坑。那場爆炸將大量塵埃揚起至大氣層中，塵埃降至地面后逐漸形成沉積巖，通過測量沉積巖的厚度，我們可以判斷當時的大氣中的塵埃約有100萬億噸。如此大量的物質(zhì)存在于大氣層中，將會完全阻隔了陽光的照射，于是地球一瞬間進入了一個持續(xù)數(shù)月之久的寒冷黑暗時期。據(jù)估計，爆炸過程還產(chǎn)生了大量的硝酸和被溶解的巖漿并噴出地球外，造成了大面積火災(zāi)，大部分的森林和草原被燃盡。這些環(huán)境災(zāi)難很可能就是包括恐龍在內(nèi)的大規(guī)模物種滅絕的原因。
根據(jù)地質(zhì)學記載，一些其他大批生物的滅絕也被初步認定認為與類似的撞擊有關(guān)，但都沒有白堊紀的那次觸目驚心。不過即便是沒有具體史料依據(jù)，這種規(guī)模的撞擊顯然發(fā)生過，并且?guī)砹藶?zāi)難性的后果。然而對于一個生物種群而言算是大災(zāi)難，卻有可能給另一個種群創(chuàng)造了機會。每一次大滅絕過后，都會有新的物種爆炸式地進化去填補由滅絕造成的物種空缺。
隕石撞擊描繪了一個能夠制造全球性的災(zāi)難的途徑，這種災(zāi)難會對整個星球的生命體的進化帶來重大影響。據(jù)估計，已經(jīng)滅絕的所有物中，絕大部分都是由于這些撞擊造成的。這種觀點從根本上改變了我們對于生物進化的看法。一個物種生存的標準準則就是它成功地與其他物種對抗，并適應(yīng)緩慢變化的環(huán)境。然而還有一個同等重要的準則就是，可以從隨機的、由天體撞擊造成的全球生態(tài)災(zāi)難中幸存。
幾十年前，地球是宇宙射擊場的一個靶子，容易受到未知的隨機暴力事件的攻擊。1991年美國國會要求美國國家航空航天局調(diào)查大型撞擊對地球造成的危害。指揮這項研究的團隊通過詳細的分析得出這樣一個結(jié)論：隕石撞擊確實是危險的。盡管大型撞擊發(fā)生的風險依然存在，但是謹慎的研究這門也認為這種風險的出現(xiàn)幾率非常小。
