The dry mountain ranges of the western United States contain rocks dating back 440 to 510 million years, to the Ordovician period, and teeming with evidence of tropical marine life. This rock record provides clues about one of the most significant radiations (periods when existing life-forms gave rise to variations that would eventually evolve into entirely new species) in the history of marine invertebrates. During this radiation the number of marine biological families increased greatly, and these families included species that would dominate the marine ecosystems of the area for the next 215 million years. Although the radiation spanned tens of millions of years, major changes in many species occurred during a geologically short time span within the radiation and, furthermore, appear to have occurred worldwide, suggesting that external events were major factors in the radiation. And , in fact, there is evidence of major ecological and geological changes during this period: the sea level dropped drastically and mountain ranges were formed, in this instance, rather than leading to large-scale extinctions, these kinds of environmental changes may have resulted in an enriched pattem of habitats and nutrients, which in turn gave rise to the Ordovician radiation. However, the actual relationship between these environmental factors and the diversification of life forms is not yet fully understood
Q4: The passage is primarily concerned with
A.evaluating the evidence of a major geologic period and determining its duration
B.describing an evolutionary phenomenon and speculating about its cause
C.explaining the mechanisms through which marine life-forms evolved during a particular period
D.analyzing the impact on later life-forms of an important evolutionary development
E.contrasting a period of evolutionary change with other such periods
嗯,谢谢
但是 证据出现的地方
"in fact, there is evidence of major ecological and geological changes during this period: the sea level dropped drastically and mountain ranges were formed, in this instance, rather than leading to large-scale extinctions, these kinds of environmental changes may have resulted in an enriched pattem of habitats and nutrients, which in turn gave rise to the Ordovician radiation."
不是和B选项"They may have created conditions favorable to the evolution of many new life-forms"相符吗?
答案E"They hastened the formation of the extensive dry regions found in the western united states"在文中也没有找到依据
糊涂了~~作者: AnttiZhang 时间: 2012-2-16 06:50
我觉得rather than leading to large-scale extinctions只是个插入语,these kinds of environment changes巴拉巴拉的其实是在修饰the sea level dropped drastically and mountain ranges were formed。
欢迎光临 国际顶尖MBA申请交流平台--TOPWAY MBA (http://forum.topway.org/)