第四部分 阅读理解（共六篇）
第五十篇
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 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 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 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 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. He 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 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.
词汇：
dioxide n. 二氧化物
lava n. 熔岩
Permian adj. 二叠纪
gigaton n. 十亿吨梯恩梯
genera n. 种类
dinosaurs n. 恐龙
asteroid n. 小行星
注释：
The Permian extinction 二叠纪物种灭绝
练习：
1. Why did older volcanic eruptions do more damage than more recent ones?
A) Because they killed off life more easily.
B) Because they were brighter.
C) Because they were larger.
D) Because they were hotter.
2. How did Wignall calculate the killing power of those older volcanic eruptions?
A) By estimating how long they lasted.
B) By counting the dinosaurs they killed.
C) By studying the chemical composition of lava.
D) By comparing the proportion of life wiped out with the volume of lava produced.
3. When did dinosaurs become extinct?
A) 300 million years ago.
B) 250 million years ago.
C) 60 million years ago.
D) 65 million years ago.
4. What can be inferred from paragraph 3 concerning dinosaurs?
A) They were killed off by an asteroid.
B) They died of drastic climate change.
C) They were wiped off by a volcanic eruption.
D) The cause of their extinction has remained a controversial issue.
5. What is the main thesis of the article?
A) Volcanic eruptions are not always deadly.
B) Older volcanic eruptions were more destructive.
C) Carbon dioxide emissions often give rise to global warming.
D) It is not easy to calculate the killing power of a volcanic eruption.
答案与题解：
1．A 问题问的是：为什么远古的火山爆发比近期的火山爆发破坏性更大？第一段是这么说的：古代的火山更具破坏力，不是因为它们更大，而是因为它们释放出的二氧化碳更能容易地毁灭生命。
2．D 问题问的是：Wignall是如何计算出远古火上爆发的杀伤力的？答案在第二段。第二段有这样一句话：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．他通过比较火山释放出的熔岩的体积与杀死生命的比例计算这些火山的杀伤效力。
3．C 问题问的是：恐龙是什么时候灭绝的?答案在第三段。其中有这么一句话：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．他没有提及6千5百万年前恐龙的灭绝是因为许多科学家相信恐龙的灭绝是受一颗小行星的影响。
4．D 问题问的是：第三段还可以推导出有关恐龙的什么样的信息?在讨论第三题的答案时，我们已经注意到了，Wignall没有提6千5百万年前恐龙的灭绝是否跟火山爆发有关是因为许多科学家相信恐龙的灭绝是受一颗小行星的影响。这就说明，关于恐龙灭绝的原因在科学家之间是有分歧的。
5．B 问题问的是：文章的主要论点是什么？答案在文章的第一句：Volcanoes were more destructive in ancient history, ．．．（古代火山更具破坏力）。
