GRE考试

【单选题】Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered onEarth in comparison with the age of Mars, an enigma exarcebated by the fact that the Martian rocks were ejected Line by only six or seven separate impact events. Previous tests had predicted that driving meteorites toEarth would require a collision with an asteroid immense enough to make a crater 12-kilometers across, but because such huge impacts are extremely infrequent, it was unlikely that enough of them could have occurred to explain our planet’’s Martian meteorite collection. Now astronomer James Head’’s higher-resolution models demonstrate that collisions making craters only three kilometers across can jettison 10 million fragments, each about 10 centimeters across, into space, a distribution sufficient to cause some of them to be found onEarth. Sections of the planet covered by debris (thus likely to be made up of older terrain) would require larger and hence rarer impacts, and thus meteorites which reachEarth are predictably biased toward younger ages.Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered onEarth in comparison with the age of Mars, an enigma exarcebated by the fact that the Martian rocks were ejected Line by only six or seven separate impact events. Previous tests had predicted that driving meteorites toEarth would require a collision with an asteroid immense enough to make a crater 12-kilometers across, but because such huge impacts are extremely infrequent, it was unlikely that enough of them could have occurred to explain our planet’’s Martian meteorite collection. Now astronomer James Head’’s higher-resolution models demonstrate that collisions making craters only three kilometers across can jettison 10 million fragments, each about 10 centimeters across, into space, a distribution sufficient to cause some of them to be found onEarth. Sections of the planet covered by debris (thus likely to be made up of older terrain) would require larger and hence rarer impacts, and thus meteorites which reachEarth are predictably biased toward younger ages. According to the passage, astronomers studying Martian meteors discovered onEarth were perplexed by them for which of the following reasons
A、The meteors found onEarth were too young to have originated from the impacts in question.
B．The meteors found onEarth were too old to be easily dateD、
C．Not enough impact events have been recorded in recent history to explain how any young meteors would have reached theEarth.
D．Impacts on Mars have been so small that scientists question how any meteors have reached the earth.
E．The age distribution of meteors found onEarth was inexplicably based toward youth.

网考网参考答案：E
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