GRE写作素材之陨石撞击和恐龙的灭绝

GRE写作素材之陨石撞击和恐龙的灭绝

对于想要攻克GRE考试的考生来说，有一定的课外知识，可帮助考生更加迅速的理解考题。针对复杂多变的GRE写作题目，课外知识的积累，就变得尤为重要。今天，前程百利小编为大家带来的是GRE写作素材之陨石撞击和恐龙灭绝，希望对同学们的GRE考试有所帮助，下面就和小编一起来学习一下吧！

Meteorite Impact（陨石撞击）and Dinosaur Extinction（恐龙的灭绝）There is increasing evidence that the impacts of meteorites have had important effects on Earth, particularly in the field of biological evolution. Such impacts continue to pose a natural hazard（自然威胁）to life on Earth. Twice in the twentieth century, large meteorite objects are known to have collided with Earth.

越来越多的证据表明陨石撞击对地球造成的影响特别严重，尤其是生物进化领域。这种影响对地球上的生物来说，仍然是一种自然威胁。在20世纪，被人们所知悉的就有两次大型陨石撞地球的事件发生。

If an impact is large enough, it can disturb the environment of the entire Earth and cause an ecological catastrophe. The best-documented such impact took place 65 million years ago at the end of the Cretaceous period（白垩纪）of geological history. This break in Earth's history is marked by a mass extinction, when as many as half the species on the planet became extinct. While there are a dozen or more mass extinctions in the geological record, the Cretaceous mass

extinction has always intrigued （感兴趣）paleontologists （古生物学家）because it marks the end of the age of the dinosaurs. For tens of millions of years, those great creatures had flourished. Then, suddenly, they disappeared.

当撞击力度特别大时，陨石和地球的相撞将扰乱整个地球的环境，并引发一场生态灾难。记载最完整的这种灾难曾发生在6 500万年前，在地质历史阶段的白垩纪末期。地球历史上的那次重大灾难造成了大量生物死亡，当时多达一半的物种灭绝。根据地质史料记载，地球上有十几次甚至更多大型的物种灭绝，古生物学家一直对白垩纪大灭绝非常感兴趣，因为它标志着恐龙时代的结束。数千万年以来，那些庞大的生物繁盛活跃着；然后突然间，它们消失了。

The body that impacted Earth at the end of the Cretaceous period was a meteorite （陨石）with a mass of more than a trillion tons and a diameter（直径）of at least 10 kilometers. Scientists first identified this impact in 1980 from the worldwide layer of sediment（沉积）deposited from the dust cloud that enveloped the planet after the impact. This sediment layer is enriched in the rare metal iridium and other elements that are relatively abundant in a meteorite but very rare in the crust of Earth. Even diluted（削弱）by the terrestrial（陆地的）material excavated from the crater, this component of meteorites is easily identified. By 1990 geologists had located the impact site itself in the Yucat region of Mexico. The crater, now deeply buried in sediment, was originally about 200 kilometers in diameter.

将大量尘埃扬起至大气层中，尘埃降至地面后逐渐形成沉积岩，通过测量沉积岩的厚度，我们可以判断当时的大气中的尘埃约有100万亿吨。如此大量的物质存在于大气层中，将会完全阻隔了阳光的照射，于是地球一瞬间进入了一个持续数月之久的寒冷黑暗时期。据估计，爆炸过程还产生了大量的硝酸和被溶解的岩浆并喷出地球外，造成了大面积火灾，大部分的森林和草原被燃尽。这些环境灾难很可能就是包括恐龙在内的大规模物种灭绝的原因。

This impact released an enormous amount of energy, excavating a crater （火山口）about twice as large as the lunar crater Tycho. The explosion lifted about 100 trillion tons of dust into the atmosphere, as can be determined by measuring the thickness of the sediment layer formed when this dust settled to the surface. Such a quantity of material would have blocked the sunlight completely from reaching the surface, plunging （跳入）Earth into a period of cold and darkness that lasted at least several months. The explosion is also calculated to have produced vast quantities of nitric acid and melted rock that sprayed out over much of Earth, starting widespread fires that must have consumed most terrestrial forests and grassland. Presumably, those environmental disasters could have been responsible for the mass extinction, including the death of the dinosaurs.

白垩纪末期，撞击地球主体是一块巨大陨石，它的质量超过万亿吨，直径至少在10公里。1980年科学家通过研究撞击后形成的、覆盖地球表面