Volcanoes were more destructive in ancient history, not because they were bigger, but becausethe carbon dioxide they released wiped out life with greater ease.
Paul Wignall from the University of Leeds was investigat,ing the link between volcaniceruptions and mass extinctions. Not all volcanic eruptions killed- off large numbers of animals, butall the mass extinctions over the past 300 million years coincided with huge formations of volcanicrock. To his surprise, the older the massive volcanic eruptions were, the more.damage they seemedto do. He calculated the "killing efficiency" for these volcanoes by comparing the proportion of lifethey killed off with the volume of lava that they produced. He found that size for size, oldereruptions 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 byfloods of volcanic rock in Siberia that cover an area roughly the size of western Europe. Thosevolcanoes are thought to have pumped out about 10 gigatonnes of carbon as carbon dioxide. Theglobal warming that followed wiped out 80 per cent of all manne genera at the time, and it took 5million years for the planet to recover. Yet 60 million years ago, there was another huge amount ofvolcanic activity and global warming but no mass extinction. Some animals did disappear but thingsreturned to normal within ten thousands of years. "The most recent ones hardly have an effect atall.”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 thatolder volcanoes had more killing power because more recent life forms were better adapted todealing with increased levels of C02.
Vincent Courtillot, director of the Paris Geophysical Institute in France, says that Wignall'sidea is provocative. But he says it is incredibly hard to do these sorts of calculations. He points outthat the killing power of volcanic eruptions depends on how long they lasted. And it is impossible totell whether the huge blasts lasted for thousands or millions of years. He also adds that it is difficultto estimate how much lava prehistoric volcanoes produced, and that lava volume may notnecessarily correspond to carbon dioxide emissions.
1.The revelation of his past led to his resignation.
A.imagination B.disclosure C.confirmation D.recall
2.Jensen is dangerous man, and can be very brutal.
A.careless B.cruel C.strong D.hard
3.You'll have to sprint if you want to catch the train.
A.jump B.escape C.run D.prepare
4.We are worried about this fluid situation full with uncertainty.
5.The new garment fits her perfectly.
6.The phobia may have its root in a childhood trauma.
7.They have built canals to irrigate the desert.
8.Her overall language proficiency remains that of a toddler.
9.The coastal area has very mild winter, but the central plains remain extremely cold.
10.The details of the costume were totally authentic.
11.We are aware of the potential problems.
12.The idea was quite brilliant.
13.Stock market price tumbled after rumor of a rise in interest rate.
14.The course gives you basic instruction in car maintenance.
15.All houses within 100 meters of the seas are at risk of flooding.
B.out of control