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  3. The human species came into being at the time of the greatest biological diversity in the history of the Earth. Today, as human

The human species came into being at the time of the greatest biological diversity in the history of the Earth. Today, as human

admin2012-06-10  40
问题     The human species came into being at the time of the greatest biological diversity in the history of the Earth. Today, as human populations expand and alter the natural environment, they are reducing biological diversity to its lowest level. The ultimate consequences of this biological reduction are beyond calculation, but they are certain to be harmful. That, in essence, is the biodiversity crisis.
    The history of global diversity can be summarized as follows: after the initial flowering of multicellular animals, there was a swift rise in the number of species in early Paleozoic times (between 600 and 430 million years ago), then plate-alike stagnation for the remaining 200 million years of the Paleozoic era, and finally a slow but steady climb through the Mesozoic and Cenozoic eras to diversity’s all-time high. This history suggests that biological diversity was hard won and a long time in coming. Furthermore, this pattern of increase was set back by five massive extinction episodes. The most recent of these, during the Cretaceous period, is by far the most famous, because it ended the age of the dinosaurs, giving hegemony to the mammals, thus ultimately making possible the dominance of the human species over the Earth. But the Cretaceous crisis was minor compared with the Permian extinctions 240 million years ago, during which between 77 and 96 percent of marine animal species perished. It took five million years, well into Mesozoic times, for species diversity to begin a significant recovery.
    Within the past 10,000 years biological diversity has entered a wholly new era. Human activity has had a devastating effect on species diversity, and the rate of human-induced extinctions is accelerating. Half of the bird species of Polynesia have been eliminated through hunting and the destruction of native forests. The list of such biogeographic disasters is extensive.
    Because every species is unique and irreplaceable, the loss of biodiversity is the most profound process of environmental change. Its consequences are also the least predictable because the value of the Earth’s species remains largely unstudied and unappreciated; unlike material and cultural wealth, which we understand because they are the substance of our everyday lives, biological wealth is usually taken for granted. This is a serious strategic error, one that will be increasingly regretted as time passes.
What is true about the Cretaceous crisis according to the author?
选项 A、It was the most famous devastating extinction episode in history.
B、It is the most devastating extinction episode up until now.
C、It was less devastating to species diversity than is the current biodiversity crisis.
D、The dinosaurs comprised the great majority of species that perished during the crisis.
答案A
解析 由题干关键词，将信息定位于第二段倒数第二句“但是白垩纪的危机不足以与2．4亿年前二叠纪的大灭绝相比，那时有77％至96％的动物物种灭绝”，从而排除[B]；再根据倒数第三句“发生在白垩纪的大灭绝是五次大灭绝中最有名的一次，它结束了恐龙时代，将霸权地位让给了哺乳动物，因此最终使人类主宰地球成为可能”，由此可排除[D]，确定答案为[A]。而[C]文中并未提到。
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