职称英语综合阅读文章及译文(终审稿)1635.pdf
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1、 职称英语综合阅读文章及译文 文稿归稿存档编号:KKUY-KKIO69-OTM243-OLUI129-G00I-FDQS58-MG129 【经典资料,文档,可编辑修改】【经典考试资料,答案附后,看后必过,文档,可修改】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 Wig
2、nall 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
3、 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 that they produced.He found that size for size,older eruptions were at least 10 times as e
4、ffective at wiping out life as their more recent rivals.The Permian 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 of
5、carbon as carbon dioxide.The global warming that followed wiped out 80 per cent of all marine genera 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 di
6、d 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.He
7、thinks that older volcanoes had more killing power because more recent life forms were better adapted to dealing with increased levels of CO2.Vincent Courtillot,director of the Paris Geophysical Institute in France,says that Wignalls idea is provocative.But he says it is incredibly hard to do these
8、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,a
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