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  3. Scientists have long sought the reasons for the relatively young age

Scientists have long sought the reasons for the relatively young age

游客2024-01-11  55
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. [br] Which of the following, if true, would cast most doubt on the conclusions drawn from Head’s higher-resolution models?
选项 A、The results of geographical survey prove that no crater larger than twelve kilometers exists on the surface of Mars.
B、Fragments from smaller impact events on Mars are highly unlikely to survive entry through the Earth’s atmosphere.
C、The velocity of rocks escaping from Mat’s gravity is greater when they have been loosened by a large impact.
D、Huge impacts on Mars are proven to be less rare than was previously thought.
E、A double-succession of large impacts is found to have occurred on Mars in a relatively short period of time.
答案 B
解析
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