問題詳情

IV. Reading Section: 26%Meteorite Impact and Dinosaur Extinction1.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 tolife on Earth. Twice in the twentieth century, large meteorite objects are known to have collidedwith Earth.2. If an impact is large enough, it can disturb the environment of the entire Earth and cause anecological catastroph
(E) The best-documented such impact took place 65 million years ago at theend of the Cretaceous period of geological history. This break in Earth’s history is marked by amass extinction, when as many as half the species on the planet became extinct. While there area dozen or more mass extinctions in the geological record, the Cretaceous mass extinction hasalways intrigued paleontologists because it marks the end of the age of the dinosaurs. For tens ofmillions of years, those great creatures had flourishe
(D) Then, suddenly, they disappeare
(D)3. The body that impacted Earth at the end of the Cretaceous period was a meteorite with a mass ofmore than a trillion tons and a diameter of at least 10 kilometers. Scientists first identified thisimpact in 1980 from the worldwide layer of sediment deposited from the dust cloud thatenveloped the planet after the impact. This sediment layer is enriched in the rare metal iridiumand 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 iseasily identifie
(D) By 1990 geologists had located the impact site itself in the Yucatán region ofMexico. The crater, now deeply buried in sediment, was originally about 200 kilometers indiameter.4. This impact released an enormous amount of energy, excavating a crater about twice as large asthe 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 dustsettled to the surfac
(E) Such a quantity of material would have blocked the sunlight completelyfrom reaching the surface, plunging Earth into a period of cold and darkness that lasted at leastseveral months. The explosion is also calculated to have produced vast quantities of nitric acidand melted rock that sprayed out over much of Earth, starting widespread fires that must haveconsumed most terrestrial forests and grasslan
(D) Presumably, those environmental disasterscould have been responsible for the mass extinction, including the death of the dinosaurs.5. Several other mass extinctions in the geological record have been tentatively identified with largeimpacts, but none is so dramatic as the Cretaceous event. But even without such specificdocumentation, it is clear that impacts of this size do occur and that their results can becatastrophi
(C) What is a catastrophe for one group of living things, however, may createopportunities for another group. Following each mass extinction, there is a sudden evolutionaryburst as new species develop to fill the ecological niches opened by the event.6. Impacts by meteorites represent one mechanism that could cause global catastrophes andseriously influence the evolution of life all over the planet. According to some estimates, themajority of all extinctions of species may be due to such impacts. Such a perspectivefundamentally changes our view of biological evolution. The standard criterion for the survivalof a species is its success in competing with other species and adapting to slowly changingenvironments. Yet an equally important criterion is the ability of a species to survive randomglobal ecological catastrophes due to impacts.7. Earth is a target in a cosmic shooting gallery, subject to random violent events that wereunsuspected a few decades ago. In 1991 the United States Congress asked NASA to investigatethe hazard posed today by large impacts on Earth. The group conducting the 55 study concludedfrom a detailed analysis that impacts from meteorites can indeed be hazardous. Although there isalways some risk that a large impact could occur, careful study shows that this risk is quite small.
1. The word “pose” on line 2 is closest in meaning to
(A) claim
(B) model
(C) assume
(D) present

參考答案

答案：D
難度：非常困難0
統計：A(0),B(0),C(1),D(0),E(0)

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