2017年武汉大学考博英语真题3

Reading Comprehension 3

Asteroids and comets that repeatedly smashed into the early Earth covered the planet's surface with molten rock during its earliest days,but still may have left oases of water that could have supported the evolution of life,scientists say.The new study reveals that during the planet's infancy,the surface of the Earth was a hellish environment,but perhaps not as hellish as often thought,scientists added.

Earth formed about 4.5 billion years ago.The first 500 million years of its life are known as the Hadean Eon.Although this time amounts to more than 10 percent of Earth's history,little is known about it,since few rocks are known that are older than 3.8 billion years old.

For much of the Hadean,Earth and its sister worlds in the inner solar system were pummeled with an extraordinary number of cosmic impacts."It was thought that because of these asteroids and comets flying around colliding with Earth,conditions on early Earth may have been hellish,"said lead study author Simone Marchi,a planetary scientist at the Southwest Research Institute in Boulder,Colorado.This imagined hellishness gave the eon its name—Hadean comes from Hades,the lord of the underworld in Greek mythology.

However,in the past dozen years or so,a radically different picture of the Hadean began to emerge.Analysis of minerals trapped within microscopiczircon crystals dating from this econ"suggested that there was liquid water on the surface of the Earth back then,clashing with the previous picture that the Hadean was hellish,"Marchi said.This could explain why the evidence of the earliest life on Earth appears during the Hadean—maybe the planet was less inhospitable during that eon than previously thought.

The exact timing and magnitude of the impacts that smashed Earth during the Hadean are unknown.To get an idea of the effects of this bombardment,Machi and his colleagues looked at the moon,whose heavily cratered surface helped model the battering that its close neighbor Earth must have experienced back then.

"We also looked at highly siderophile elements(elements that bind tightly to iron),such as gold,delivered to Earth as a result of these early collisions,and the amounts of these elements tells us the total mass accreted by Earth as the results of these collisions,"Marchi said.Prior research suggests these impacts probably contributed less than 0.5 percent of the Earth's present-day mass.The researchers discovered that"the surface of the Earth during the Hadean was heavily affected by very large collisions,by impactors[?m'p?kt?]larger than 100 kilometers(60 miles)or so—really,really big impactors,'Marci said."When Earth has a collision with an object that big,that melts a large volume of the Earth's crust and mantle,covering a large fraction of the surface,"Marchi added.These findings suggest that Earth's surface was buried over and over again by large volumes of molten rock—enough to cover the surface of the Earth several times.This helps explain why so few rock survive from the Hadean,the researchers said.

9．Why is little known about the Earth's first 500 million years?

A．Because it is an imagined period of time.

B．Because this period is of little significance.

C．Because it is impossible to know about this period.

D．Because no rocks are available as research evidence.

10．Why is the early Earth imagined to be hellish?

A．Because it was often smashed by asteroids and comets.

B．Because back then Hades,the lord of Hell,resigned.

C．Because it was so according to Greek mythology.

D．Because back then there was no life.

11．Why was the early Earth in fact less inhospitable than often thought?

A．Because minerals of the Hadean have been found suggesting the existence of life.

B．Because the clashing brought by asteroids and comets was not completely damaging.

C．Because during the Hadean there already existed the evidence of life.

D．Because there had already been liquid water on the Earth back then.

12．How can the moon help with the understanding of the impacts that smashed the Earth?

A．The moon once smashed into the Earth too.

B．The moon was battered earlier than the Earth.

C．The moon,as a close neighbor,is easier to observe.

D．The moon's surface is heavily cratered as the Earth's.

【参考翻译】

科学家说，在地球早期，不断撞击地球的小行星和彗星在其表面覆盖着熔岩，但仍有可能留下了支持生命进化的绿洲。科学家补充说，这项新的研究表明，在行星的婴儿期，地球表面是一个地狱般的环境，但可能不像人们通常认为的那么地狱般的环境。

地球大约在45亿年前形成。它生命的前5亿年被称为冥古宙。尽管这段时间占地球历史的10%以上，但我们对它知之甚少，因为我们所知道的年代超过38亿年的岩石很少。

对于大多数冥人来说，地球及其太阳系内部的姐妹世界受到了巨大的宇宙冲击。“人们认为，由于这些围绕地球飞行的小行星和彗星与地球相撞，早期地球的环境可能是地狱般的，”该研究的主要作者、科罗拉多州博尔德西南研究所的行星科学家西蒙娜·马尔基(Simone Marchi)说。希腊神话中，冥王冥王是冥府世界的主宰。

然而，在过去十几年左右的时间里，一幅截然不同的冥王图景开始浮现。马尔基说，对从这段经济时期以来被困在显微镜下锆石晶体中的矿物质的分析“表明当时地球表面有液态水，这与之前认为冥古宙是地狱的说法相冲突”。这就可以解释为什么地球上最早的生命出现在哈代——也许在那个年代，地球并不像之前想象的那样荒凉。

撞击地球的确切时间和强度尚不清楚。为了了解这种轰击的影响，Machi和他的同事观察了月球，月球表面有大量的坑坑洼洼，模拟了当时它的近邻地球所经历的撞击。

Marchi说:“我们还研究了由于这些早期碰撞而传递到地球的高亲铁元素(与铁紧密结合的元素)，比如黄金，这些元素的数量告诉我们这些碰撞的结果是地球吸收的总质量。”先前的研究表明，这些影响可能只占目前地球质量的0.5%。研究人员发现，“在冥河期间，地球表面受到非常大的碰撞，受到撞击物的严重影响”。超过100公里(60英里)或者非常非常大的撞击物。“当地球与这么大的物体发生碰撞时，会融化大量的地壳和地幔，覆盖表面的很大一部分，”Marchi补充说。这些发现表明，地球表面被大量的熔融岩石一次又一次地掩埋，足以覆盖地球表面好几次。研究人员说，这有助于解释为什么在冥河中幸存下来的岩石如此之少。

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2017年武汉大学考博英语真题汇总