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共用题干 Older Volcanic EruptionsVolcanoes

书海库2019-12-17  6
问题 共用题干Older Volcanic Eruptions
Volcanoes were more destructive in ancient history,not because they were bigger,but because the carbon dioxide they released wiped out life with greater ease.
Paul Wignall from the University of Leeds was investigating the link between volcanic eruptions and mass extinctions.Not all volcanic eruptions killed off large numbers of animals,but all the mass extinctions over the past 300 million years coincided with huge formations of volcanic rock.To his surprise,the older the massive volcanic eruptions were,the more damage they seemed to do.He calculated the"killing efficiency"for these volcanoes by comparing the proportion of life they killed off with the volume of lava（熔 岩）that they produced.He found that size for size,older eruptions were at least 10 times as effective at wiping out life as their more recent rivals.
The Peimian（二叠纪）extinction,for example,which happened 250 million years ago,is marked by floods of volcanic rock in Siberia that cover an area roughly the size of western Europe.Those volcanoes are thought to have pumped out about 10 gigatonnes（十亿吨）of carbon as carbon dioxide.The global warming that followed wiped out 80 prcent of all marine genera（种类）at the time , and it took 5 million years for the planet to recover.Yet 60 million years ago,there was another huge amount of volcanic activity and global warming but no mass extinction.Some animals did disappear but things returned to normal within ten thousands of years."The most recent ones hardly have an effect at all."Wignall says.He ignored the extinction which wiped out the dinosaurs 65 million years ago,because many scientists believe it was primarily caused by the impact of an asteroid（小行星）.He thinks that older volcanoes had more killing power because more recent life forms were better adapted to dealing with increased levels of CO<sub>2</sub>.
Vincent Courtillot,director of the Paris Geophysical Institute in France,says that Wignall's idea is provocative.But he says it is incredibly hard to do these sorts of calculations.He points out that the killing power of volcanic eruptions depends on how long they lasted.And it is impossible to tell whether the huge blasts lasted for thousands or millions of years.He also adds that it is difficult to estimate how much lava prehistoric volcanoes produced,and that lava volume may not necessarily correspond to carbon dioxide emissions.
选项 Why were older volcanic eruptions more destructive than more recent ones according to Wignall?A:Because they were brighter.B:Because they were larger.C:Because more recent life forms were better adapted to CO<sub>2</sub>.D:Because older volcanic eruptions released more lava.
答案C
解析由第三段最后一句可知，Wi gnall认为远古的火山之所以有更大的杀伤力，是因为近期的生物能更好地适应二氧化碳的增多。 根据第二段第四句可知，杀伤效率是通过比较火山释放出的熔岩的体积与杀死生命的比例来计算出来的。 根据第三段第一句可知，二叠纪物种灭绝发生在两亿五千万年以前。 根据第三段的前三句，二叠纪后的全球变暖毁灭了80%的海洋生物，因此只有20%的海洋生物度过了这场劫难。A项不正确，其他选项说法正确。 最后一段表明了Vincent Courtillot的观点。由本段第一句“…Wignall ' s idea is provocative”可知，他认为Wignall的观点很具争议性，而且Wignall计算火山杀伤效力的想法难以付诸实践，因此他对Wignall的观点是持否定态度的。
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