单选题

Older Volcanic Eruptions

Volcanoes were more destructive in ancient history, not because they were bigger, but because the carbon dioxide(二氧化碳) 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 Permian (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 percent 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 tens of thousands of years. "The most recent ones hardly have an effect at all," Wignall says. He ignored the extinction which wiped out the dinosaurs (恐龙) 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 ₂ .
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.

单选题 Older volcanic eruptions did more damage than more recent ones because ______.

【正确答案】 D

【答案解析】[解析] 事实细节题。根据第一段“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.”可知，在古代历史中，火山爆发之所以有很大的破坏性，并不是因为它们规模比较大，而是因为火山爆发释放出的二氧化碳能够很轻松地(with greater ease)消灭所有生物。“with greater ease”对应选项D中的“more easily”，故本题选D。

单选题 Wignall calculated the killing power of those older volcanic eruptions by ______.

单选题 When did dinosaurs become extinct?

单选题 It can be inferred from Paragraph 3 that the cause of dinosaur extinction is ______.

【正确答案】 D

【答案解析】[解析] 推理判断题。根据文章第三段倒数第二句“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.”可知，Wignall之所以选择忽略恐龙灭绝这个事实是因为许多科学家认为恐龙的灭绝是由小行星撞击造成的。根据第三段最后一句中的“He thinks that older volcanoes had more killing power”可知，Wignall认为远古火山杀伤力更大。综上所述，科学家们对恐龙灭绝的原因仍存有争议，故选D。