2017年武漢大學(xué)考博英語真題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.

【參考翻譯】

科學(xué)家說，在地球早期，不斷撞擊地球的小行星和彗星在其表面覆蓋著熔巖，但仍有可能留下了支持生命進(jìn)化的綠洲?？茖W(xué)家補(bǔ)充說，這項(xiàng)新的研究表明，在行星的嬰兒期，地球表面是一個(gè)地獄般的環(huán)境，但可能不像人們通常認(rèn)為的那么地獄般的環(huán)境。

地球大約在45億年前形成。它生命的前5億年被稱為冥古宙。盡管這段時(shí)間占地球歷史的10%以上，但我們對(duì)它知之甚少，因?yàn)槲覀兯赖哪甏^38億年的巖石很少。

對(duì)于大多數(shù)冥人來說，地球及其太陽系內(nèi)部的姐妹世界受到了巨大的宇宙沖擊?！叭藗冋J(rèn)為，由于這些圍繞地球飛行的小行星和彗星與地球相撞，早期地球的環(huán)境可能是地獄般的，”該研究的主要作者、科羅拉多州博爾德西南研究所的行星科學(xué)家西蒙娜·馬爾基(Simone Marchi)說。希臘神話中，冥王冥王是冥府世界的主宰。

然而，在過去十幾年左右的時(shí)間里，一幅截然不同的冥王圖景開始浮現(xiàn)。馬爾基說，對(duì)從這段經(jīng)濟(jì)時(shí)期以來被困在顯微鏡下鋯石晶體中的礦物質(zhì)的分析“表明當(dāng)時(shí)地球表面有液態(tài)水，這與之前認(rèn)為冥古宙是地獄的說法相沖突”。這就可以解釋為什么地球上最早的生命出現(xiàn)在哈代——也許在那個(gè)年代，地球并不像之前想象的那樣荒涼。

撞擊地球的確切時(shí)間和強(qiáng)度尚不清楚。為了了解這種轟擊的影響，Machi和他的同事觀察了月球，月球表面有大量的坑坑洼洼，模擬了當(dāng)時(shí)它的近鄰地球所經(jīng)歷的撞擊。

Marchi說:“我們還研究了由于這些早期碰撞而傳遞到地球的高親鐵元素(與鐵緊密結(jié)合的元素)，比如黃金，這些元素的數(shù)量告訴我們這些碰撞的結(jié)果是地球吸收的總質(zhì)量?！毕惹暗难芯勘砻鳎@些影響可能只占目前地球質(zhì)量的0.5%。研究人員發(fā)現(xiàn)，“在冥河期間，地球表面受到非常大的碰撞，受到撞擊物的嚴(yán)重影響”。超過100公里(60英里)或者非常非常大的撞擊物?！爱?dāng)?shù)厍蚺c這么大的物體發(fā)生碰撞時(shí)，會(huì)融化大量的地殼和地幔，覆蓋表面的很大一部分，”Marchi補(bǔ)充說。這些發(fā)現(xiàn)表明，地球表面被大量的熔融巖石一次又一次地掩埋，足以覆蓋地球表面好幾次。研究人員說，這有助于解釋為什么在冥河中幸存下來的巖石如此之少。

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2017年武漢大學(xué)考博英語真題匯總