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  3. Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered on

Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered on

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问题            Scientists have long sought the reasons for the relatively young age of the
       majority of Martian meteorites discovered on Earth 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
(5)     driving meteorites to Earth 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
(10)    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 on Earth. 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 reach Earth are
(15)    predictably biased toward younger ages.
According to the passage, astronomers studying Martian meteors discovered on Earth were perplexed by them for which of the following reasons?
选项 A、The meteors found on Earth were too young to have originated from the impacts in question.
B、The meteors found on Earth 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 the Earth.
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 on Earth was inexplicably based toward youth.
答案E
解析
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