2016职称英语考试真题理工A级阅读理解第一篇(网友版)

Older Volcanic Eruptions

Volcanoes were more destructive in ancient history, not because they werebigger, but because the carbon dioxide they released wiped out life with greaterease.

Paul Wignall from the University of Leeds was investigating the link betweenvolcanic eruptions and mass extinctions. Not all volcanic eruptions killed offlarge numbers of animals, but all the mass extinctions over the past 300 millionyears coincided with huge formations of volcanic rock. To his surprise, theolder the massive volcanic eruptions were, the more damage they seemed to do. Hecalculated the "killing efficiency" for these volcanoes by comparing theproportion 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 effectiveat wiping out life as their more recent rivals.

The Permian extinction, for example, which happened 250 million years ago, ismarked by floods of volcanic rock in Siberia that cover an area roughly the sizeof western Europe. Those volcanoes are thought to have pumped out about 10gigatonnes of carbon as carbon dioxide. The global warming that followed wipedout 80 per cent of all marine genera at the time, and it took 5 million yearsfor the planet to recover. Yet 60 million years ago, there was another hugeamount of volcanic activity and global warming but no mass extinction. Someanimals did disappear but things returned to normal within ten thousands ofyears. "The most recent ones hardly have an effect at all," Wignall says. Heignored the extinction which wiped out the dinosaurs 65 million years ago,because many scientists believe it was primarily caused by the impact of anasteroid. He thinks that older volcanoes had more killing power because morerecent life forms were better adapted to dealing with increased levels ofCO2.

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 dothese sorts of calculations. He points out that the killing power of volcaniceruptions depends on how long they lasted. And it is impossible to tell whetherthe huge blasts lasted for thousands or millions of years. He also adds that itis difficult to estimate how much lava prehistoric volcanoes produced, and thatlava volume may not necessarily correspond to carbon dioxide emissions.

Black Holes Trigger

Scientists have long understood that supermassive black holes weighingmillions or billions of suns can tear apart stars that come too close.The blackhotels gravity pulls harder on the nearest part of the star，an imbalance thatpulls the star apart over a period of minutes or hours，once it gets closeenough.

Scientists say this Uneven pulling is not the only hazard facing the star.Thestrain of these unbalanced forces can also trigger a nuclear explosion powerfulenough to destroy the star from within.Matthieu Brassart and Jean-Pierre Luminetof the Observatoire de Paris in Meudon，France1，carried out computer simulationsof the final moments of such an unfortunate star‘s life，as it veered towards asupermassive black hole.

When the star gets close enough，the uneven forces flatten it into a pancakeshape.Some previous studies had suggested this flattening would increase thedensity and temperature inside the star enough to trigger intense nuclearreactions that would tear it apart.But other studies had suggested that thepicture would be complicated by shock waves generated during the flatteningprocess and that no nuclear explosion should occur.

The new simulations investigated the effects of shock waves in detail，andfound that even when their effects are included，the conditions favor a nuclearexplosion.“There will be an explosion of the star — it will be completelydestroyed，” Brassart says. Although the explosion obliterates the star，it savessome of the star‘s matter from being devoured by the black hole.The explosion ispowerful enough to hurl much of the star’s matter out of the black hole‘sreach，he says.

The devouring of stars by black holes may already have been observed，althoughat a much later stage.It is thought that several months after the event thatrips the star apart，its matter starts swirling into the hole itself.It heats upas it does so，releasing ultraviolet light and X-rays.

If stars disrupted near black holes really do explode，then they could inprinciple allow these events to be detected at a much earlier stage，says JulesHatpern of Columbia University in New York，US2.“It may make it possible to seethe disruption of that star immediately if it gets hot enough，” he says.

Brassart agrees.“Perhaps it can be observed in the X-rays and gamma rays，butit‘s something that needs to be more studied，” he says.Supernova researcherChris Fryer of the Los Alamos National Laboratory in Los Alamos，NewMexico，US3，says the deaths of these stars are difficult to simulate，and he isnot sure whether the researchers have proven their case that they explode in theprocess.

词汇：

supermassive adj.特大质量的

imbalance/im5bAlEns/n.不平衡，不平衡

veer/ viE/v.转向，改变方向

flatten/5flAtn/v.使成扁平，夷平

pancake/5pAnkeik/n.薄煎饼

obliterate/E5blitEreit/v.抹去，除去，消除

devour/di5vauE(r)/v.吞没;毁灭

swirl/swE：l/打旋，旋动

gamma rays γ 射线

supernova/7sju：pE5nEuvE/n.超新星