《2020年3月15日GRE阅读机经》由会员分享，可在线阅读，更多相关《2020年3月15日GRE阅读机经（6页珍藏版）》请在金锄头文库上搜索。
1、2020 年 3 月 15 日 GRE 阅读机经Reading ComprehensionAlthough passenger pigeons, now extinct, were abundant in eighteenth-and nineteenth-century America, archaeological studies at twelfth-century Cahokian sites in the present-day United States examined household food trash and found that traces of passenger
2、 pigeon were quite rare. Given that the sites were close to a huge passenger pigeon roost documented by John James Audubon in the nineteenth century and that Cahokians consumed almost every other animal protein source available, the archaeologist conducting the studies concluded the passenger pigeon
3、 population had once been very limited before increasing dramatically in post-Columbian America. Other archaeologists have criticized those conclusions on the grounds that passenger pigeon bones would not be likely to be preserved. But all the archaeological projects found plenty of bird bones-and e
4、ven some tiny bones from fish.7. The author of the passage mentions tiny bones from fish primarily in order toA. Explain why traces of passenger pigeon are rare at Cahokian sitesB. Support a claim about the wide variety of animal proteins in the Cahokian dietC. Provide evidence that confirms a theor
5、y about the extinction of the passenger pigeonD. Cast doubt on the conclusion reached by the archaeologists who conducted the studies discussed in the passageE. Counter an objection to an interpretation of the data obtained from Cahokian sites8. Which of the following, if true, would most call into
6、question the reasoning of the archaeologists conducting the studies?A. Audubon was unable to correctly identify twelfthcentury Cahokian sites.B. Audubon made his observations before passenger pigeon populations began to decline.C. Passenger pigeons would have been attracted to household food trash.D
7、. Archaeologists have found passenger pigeon remains among food waste at eighteenth-century human settlements.E. Passenger pigeons tended not to roost at the same sites for very many generations.In 1995 the Galileo spacecraft captured data about Jupiter s atmosphere -namely, the absence of most of t
8、he predicted atmospheric water-that challenged prevailing theories about Jupiters structure. The unexpectedness ofthis finding fits a larger pattern in which theories about planetary composition and dynamics have failed to predict the realities discovered through space exploration. Instead of normal
9、 planets whose composition could be predicted by theory, the planets populating our solar system are uniqueindividuals whose chemical and tectonic identities were created through numerous contingent events. One implication of this is that although the universe undoubtedly holds other planetary syste
10、ms, the duplication of the sequence that produced our solar system and the development of life on Earth is highly unlikely.Recently planetary scientists have suggested that the external preconditions for the development of Earthsbiosphere probably included four paramount contingencies. First, a clim
11、ate conducive to life on Earth depends upon the extraordinarily narrow orbital parameters that define a continuously habitable zone where water can exist in a liquid state. If Earth s orbit were only 5 percent smaller than it is, temperatures during the early stages of Earths historywould have been
12、high enough to vaporize the oceans. If the Earth-Sun distance were as little as 1 percent larger, runaway glaciation on Earth about 2 billion years ago would have caused the oceans to freeze and remain frozen to this day.Second, Jupiter s enormous mass prevents most Sun 一 bound comets from penetrati
13、ng the inner solar system. It has been estimated that without this shield, Earth would have experienced bombardment by comet-sized impactors a thousandtimes more frequently than has actually been recorded during geologica l time. Even if Earths surface were notactually sterilized by this bombardment
14、, it is unlikely that any but the most primitive life-forms could have survived. This suggests that only planetary systems containing bothterrestrial planets like Earth and gas giants like Jupiter might be capable of sustaining complex life-forms.Third, the gravitational shield of the giant outer pl
15、anets, while highly efficient, must occasionally fail to protect Earth. Paradoxically, while the temperatures required for liquid water exist only in the inner solar system, the key building blocks of life, including water itself, occur primarily beyond the asteroid belt. Thus the evolution of life
16、has depended on a frequency of cometary impacts sufficient to convey water, as well as carbon and nitrogen, from these distant regions of the solar system to Earth while stopping short of an impact magnitude that would destroy the atmosphere and oceans.Finally, Earth s unique and massive satellite, the Moon, plays a crucial role in stabilizing the obliquity of Earth srotational axis, This obliquity creates the terrest
