托福阅读tpo56R-3原文+译文+题目+答案+背景知识

TPO56 阅读-3 Conditions on Early Earth and the Beginnings of Life

原文 .................................................................................................................................................. 1

译文 .................................................................................................................................................. 2

题目 .................................................................................................................................................. 3

答案 .................................................................................................................................................. 8

背景知识........................................................................................................................................... 8

原文

Conditions on Early Earth and the Beginnings of Life

①A little more than 3.8 billion years ago is a good estimate of when life began on

Earth. How it began remains speculative. There is no standard theory; there is

instead a confusion of conflicting theories that attack the problem from different

angles. This is a change from 1953 when a classic experiment on the origin of life

was published. Then, Stanley Miller and Harold Urey had just completed their

famous laboratory simulation of the conditions of an early Earth at the University

of Chicago. When Miller and Urey let electric sparks course like lightning through

an “atmosphere” of methane, ammonia, and hydrogen, which circulated above

an “ocean” of boiling water, they found that a reddish substance, rich in amino

acids, accumulated in their glass apparatus. Amino acids, when strung together in

long folded chains, form proteins, and proteins are the building blocks of the living

cell. From the spontaneous synthesis of amino acids to the spontaneous origin of

life on the primitive Earth did not seem such a long way to go.

②That early optimism has proven profoundly mistaken, for at least two reasons.

The first is simply that it is, in fact, a long way from amino acids to life. The hardest

part about creating life is not making the amino acids that go into proteins; or the

sugars, phosphates, and bases that go into DNA, which carries the cell’s genetic

blueprint; or the lipids that form its protective membrane. The hardest part about

creating life is not making the “bricks”: it is assembling them into a finished

structure. That is what all the theories that have emerged since the Miller-Urey

experiment are primarily about, and the conflict among them shows no signs of

being resolved soon.

③Furthermore, in recent years even the fundamental premise of that landmark

experiment has been called into question. Today most researchers who study early

Earth do not believe that its atmosphere was primarily methane and ammonia,

which would have been a strongly reducing atmosphere, where reducing means

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hydrogen-rich. Methane and ammonia are both comparatively fragile molecules

that might easily have been broken apart by the ultraviolet sunlight that bathed

the young Earth, which had not yet evolved an ozone shield. More important, the

idea that Earth was hot to begin with as a result of its violent birth, when large

asteroids collided to form it, implies that its early atmosphere was rich in carbon

dioxide rather than methane. That is the form in which carbon would be released

by exploding asteroids.

④The bottom line is that the early atmosphere is not likely to have been a giant

Miller-Urey experiment; it would have been mostly nitrogen and carbon dioxide. In

such an atmosphere it is indeed hard to make the molecular bricks of life, let alone

a living organism. It is hard even to make the chemical compounds necessary for

life. The most important compounds are formaldehyde and hydrogen cyanide,

which, brought together in the presence of water, react to produce amino acids,

from which the bricks are made. Formaldehyde and hydrogen cyanide, then, seem

to be essential stages on the chemical road to life, and hydrogen cyanide especially

cannot be made in great quantities in a carbon-dioxide atmosphere. Both

compounds, however, are abundant in comets like Halley, Hyakutake, and

Hale-Bopp. Presumably they are in other comets as well.

⑤Here, then, is an elegant solution to the dilemma. The dilemma is that the old

view of how life began conflicts with the new view of how Earth began and how it

acquired an ocean. The solution, perhaps, is to deliver the organic precursors of life

with the same vehicles that almost certainly helped create the ocean: icy comets.

Researchers have calculated that over the course of Earth’s history, comets have

delivered an amount of organic matter to the planet that is nearly a million times

its present biomass—the total mass of all living things. Most of the organic matter

would have arrived during the heavy bombardment that ended 3.8 billion years

ago.

译文

早期地球的条件以及生命的开始

①38 亿多年前是地球上生命开始的一个很好的估计。它是如何开始的仍然是推测性的。没有标准的理论；相反，存在相互矛盾的理论的混淆，这些理论从不同的角度解决这个问题。这是来自于1953年的一个改变，当时一个经典的对于生命起源的实验被发表了。当时，斯坦利米勒和哈罗德尤里刚刚在芝加哥大学完成了他们著名的早期地球条件实验室模拟。当 Miller 和 Urey 让电火花像闪电一样穿过由甲烷、氨和氢组成的“大气层”，“大气层”在由沸水组成的“海洋”上方循环，他们发现一种富含氨基酸的微红物质积聚在他们的玻璃杯中仪器。氨基酸以长折叠链串在一起时形成蛋白质，而蛋白质是活细胞的组成

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部分。从氨基酸的自发合成到原始地球上生命的自发起源似乎并没有多远的路要走。

②至少出于两个原因，这种早期的乐观情绪已被证明是大错特错的。事实上，第一个理由很简单，从氨基酸到生命还有很长的路要走。创造生命最困难的部分不是制造用以形成蛋白质的氨基酸，或者用以形成DNA（DNA携带着细胞的遗传蓝图）的糖、磷酸盐和碱基，或形成其保护膜的脂质。创造生命最困难的部分不是制造“砖块”： 而是将它们组装成一个完整的结构。这就是自Miller-Urey实验以来出现的所有理论的主要内容，而且它们之间的冲突没有迹象表明会很快得到解决。

③此外，近年来，甚至这个具有里程碑意义的实验的基本前提也受到质疑。今天，大多数研究早期地球的研究人员都认为它的大气层主要不是甲烷和氨气，甲烷和氨气可能是一种强还原性大气层，还原性意味着富含氢气。甲烷和氨都是相对脆弱的分子，很容易被照射尚未形成臭氧层的年轻地球的紫外线分解掉。更重要的是，有种说法说，地球诞生时情况非常剧烈，当时大型小行星碰撞形成地球，因此地球一开始的时候是非常热的。这意味着它早期的大气层富含二氧化碳而不是甲烷。这种情况中，碳会因爆炸的小行星而被释放出来。

④最重要的是，早期的大气不太可能是一个巨大的Miller-Urey实验；它可能主要是氮气和二氧化碳。在这样的大气中，确实很难制造出构成生命的分子“砖块”，更不用说一个活的有机体了。甚至制造生命所必需的化合物也很困难。最重要的化合物是甲醛和氰化氢，它们在有水的情况下聚集在一起，反应生成氨基酸，而生命的“砖块”是由氨基酸制成的。因此，甲醛和氰化氢似乎是通往生命的化学道路上必不可少的阶段，在二氧化碳大气中，尤其无法大量制造氰化氢。然而，这两种化合物在哈雷、百武和海尔波普等彗星中都很丰富。据推测，它们也存在于其他彗星中。

⑤那么，这里有一个解决困境的优雅的方法。困境在于，关于生命如何开始的旧观点与关于地球如何开始以及它如何获得海洋的新观点相冲突。或许，解决方案是，形成生物有机的前身的东西是跟几乎肯定帮助创建了海洋的载体是一个东西：冰彗星。研究人员计算出，在地球的历史进程中，彗星向地球输送的有机物数量几乎是其目前生物量（所有生物的总质量）的一百万倍。大部分有机物是在 38 亿年前结束的猛烈轰炸期间到达的。

题目

1. Paragraph 1 suggests that Miller and Urey’s experiment resulted in which of the

following reactions in the scientific community when the results were published in

1953 ?

was considered impossible that amino acids had been created in a laboratory

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experiment.

were doubts about the existence of an atmosphere on early Earth.

conflicting theories about the origin of life quickly developed because of

confusion about the results of the experiment.

e amino acids were synthesized in the experimental conditions, it seemed

possible that life on Earth might also have evolved in these conditions.

2. The word “resolved” in the passage is closest in meaning to

tood

ten

d

ed

3. Which of the sentences below best expresses the essential information in the

highlighted sentence in the passage? Incorrect choices change the meaning in

important ways or leave out essential information.

e Earth’s early atmosphere was composed primarily of methane and

ammonia with little hydrogen, most researchers today do not believe that it was

strongly reducing.

most researchers do not believe that the early Earth had a strongly

reducing atmosphere made primarily of methane and ammonia.

view of early Earth that most scientists hold today is that its atmosphere was

hydrogen-rich rather than containing primarily methane and ammonia.

researchers do not believe that the early Earth had a methane and

ammonia atmosphere that reduced into hydrogen.

③Furthermore, in recent years even the fundamental premise of that landmark

experiment has been called into question. Today most researchers who study early

Earth do not believe that its atmosphere was primarily methane and ammonia,

which would have been a strongly reducing atmosphere, where reducing means

hydrogen-rich. Methane and ammonia are both comparatively fragile molecules

that might easily have been broken apart by the ultraviolet sunlight that bathed

the young Earth, which had not yet evolved an ozone shield. More important, the

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idea that Earth was hot to begin with as a result of its violent birth, when large

asteroids collided to form it, implies that its early atmosphere was rich in carbon

dioxide rather than methane. That is the form in which carbon would be released

by exploding asteroids.

4. According to paragraph 3, why do scientists believe that Earth’s early

atmosphere did not primarily consist of methane and ammonia?

ids entering the atmosphere would have introduced other molecules that

caused the breakdown of methane and ammonia.

lack of an ozone shield would have allowed ultraviolet sunlight to break

down methane and ammonia.

hydrogen in the atmosphere at that time would have reduced methane and

ammonia into simpler substances.

carbon dioxide in the atmosphere at that time would have reduced methane

and ammonia into simpler substances.

5. According to paragraphs 2 and 3, after the early optimism about explaining how

life on Earth emerged, scientists believed all of the following EXCEPT:

ning the origin of basic organic molecules was not the most difficult

problem.

could more easily learn how life formed because they knew the structure of

DNA.

and Urey’s experiment did not adequately explain how the structure of

life formed.

and Urey were wrong about the composition of the early atmosphere.

6. According to paragraph 4, why would hydrogen cyanide have been rare on the

early Earth?

enough amino acids had formed yet to support the production of hydrogen

cyanide.

en cyanide cannot form in the atmosphere that scientists now believe the

early Earth had.

early Earth did not have the amino acids and formaldehyde that are

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necessary to form hydrogen cyanide.

en-cyanide compounds would have been unstable without a lot of water

present.

7. The word “Presumably” in the passage is closest in meaning to

is reasonable to suppose

s

t a doubt

is widely believed

8. In paragraph 5, why does the author remark that most of the organic material

brought to Earth by comets would have arrived by 3.8 billion years ago, the

estimated time for when life on Earth began?

suggest that it was the end of the comet bombardment that allowed life to

emerge on Earth

imply that at the time when life emerged on Earth, there was nearly a million

times as much organic matter on Earth as there is now

support the claim that organic material from comets could explain how life

was able to emerge on Earth

help explain the gap in time between when organic matter arrived on Earth

and when the atmosphere was able to support life

9. Look at the four squares [ ] that indicate where the following sentence could

be added to the passage.

Existing theories about the early atmosphere were used to help design the study.

Where would the sentence best fit? Click on a square [ ] to add the sentence to

the passage.

①A little more than 3.8 billion years ago is a good estimate of when life began on

Earth. How it began remains speculative. There is no standard theory; there is

instead a confusion of conflicting theories that attack the problem from different

angles. [■]This is a change from 1953 when a classic experiment on the origin of

life was published. Then, Stanley Miller and Harold Urey had just completed their

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famous laboratory simulation of the conditions of an early Earth at the University

of Chicago. [■]When Miller and Urey let electric sparks course like lightning

through an “atmosphere” of methane, ammonia, and hydrogen, which circulated

above an “ocean” of boiling water, they found that a reddish substance, rich in

amino acids, accumulated in their glass apparatus. [■]Amino acids, when strung

together in long folded chains, form proteins, and proteins are the building blocks

of the living cell. [■]From the spontaneous synthesis of amino acids to the

spontaneous origin of life on the primitive Earth did not seem such a long way to

go.

10. Directions: An introductory sentence for a brief summary of the passage is

provided below. Complete the summary by selecting the THREE answer choices

that express the most important ideas in the passage. Some sentences do not

belong in the summary because they express ideas that are not presented in the

passage or are minor ideas in the passage. This question is worth 2 points.

In 1953, the Miller-Urey experiment showed that amino acids form spontaneously

under conditions then thought to be similar to those of early Earth.

Answer Choices:

Miller-Urey experiment was significant at the time because it seemed to

account for the steps between the creation of amino acids and the synthesis of

DNA.

ists now agree on how amino acids and DNA formed but not about how

formaldehyde and hydrogen cyanide were produced in an early atmosphere of

mainly carbon dioxide and nitrogen.

ists now believe that Earth’s early atmosphere was very different from the

Miller and Urey experiment and that in the actual early atmosphere amino acids

would not spontaneously form.

many scientists believe that life on Earth must be explained by the

development of life forms elsewhere in the solar system that were then brought to

Earth by comets.

most important chemical compounds necessary for life could not have been

abundant in the actual early atmosphere, so some scientists believe they were

probably delivered by comets.

scientists realize that the most difficult problem is to explain how life

emerged from the basic organic molecules, rather than to explain how those

building blocks were formed.

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答案

1-5. D C B B B

6-9.B A C B

10. CEF

小结题解析

C选项对应文章第三四段的内容。

E选项对应第四五段的内容。

F选项对应第二段的内容。

A选项对应第一段的内容，但是文章并没有说实验解释了“the steps between

the creation of amino acids and the synthesis of DNA”。文章说的是氨基酸的合成到生命的形成之间似乎距离已经很近了，没有提及DNA的合成。

B选项，文章中并没有提及科学家们“agree on”这些事情，反而文章说在早期的大气状况下，这些物质很难形成。

D选项，文章说的是comets把有机物带到了地球上来。而不是说comets把太阳系其他地方的生命带到地球上来。

背景知识

地球的形成：追溯到46亿年前，共分为四个阶段

地球的形成可以追溯到约46亿年前，也就是太阳系形成的时期。当时的太阳系是由大量的气体和尘埃云团组成，这些物质在引力的作用下，逐渐凝聚成为太阳系的各个行星和卫星。

地球的形成过程可概括为以下四个阶段：原始太阳系盘阶段、固态行星体阶段、巨型碰撞阶段和行星演化阶段。

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第一阶段：原始太阳系盘阶段

在太阳系形成早期，太阳的周围有一个叫做原始太阳系盘的巨大环境。该环境中包括大量的氢气和其他元素晶体颗粒。这些质量非常小的晶体颗粒被太阳引力牵引起来，在空间中逐渐聚合形成了大约1厘米大小的颗粒，这个过程被称为微观聚集。随着时光的推移，这些小颗粒不断聚集形成更大的颗粒，最终形成了尘埃云团。这些尘埃云团不断吸引周围的气体，最终形成行星形成时的原始气体云。

第二阶段：固态行星体阶段

随着原始太阳系盘中的气体演变为原始气体云，它逐渐变得致密并开始缩小。位于太阳系中心的太阳吸引着周围的气体，将其捆绑成一个巨大的亚恒星物体。随着亚恒星物体的不断生长和收缩，它内部的温度不断升高。当内部温度达到千度级别时，它开始混合为熔块，并通过流动的运动物理过程分离并凝固成为半固态的固态行星体。

这个阶段的重点是固态行星体的生长和早期演化，包括固态行星体之间的碰撞、聚结，演变为更大的行星类物体，形成了原始行星的模式。最终一个小行星在引力的作用下逐渐聚集成为一个大块头，这个大块头就是我们熟悉的地球的前身。

第三阶段：巨型碰撞阶段

在地球形成后的几千万年内，它经历了一个叫做“巨型碰撞阶段”的过程，这个过程可能是地球发展史上最重要的时期之一。据天文学家猜测，这个巨型碰撞发生在地球与另一个大小类似的天体——有可能是一颗行星，也可能是一个大型的火星或一个冰川天体之间相撞而形成。这样的一次碰撞不仅给地球带来了许多物质，而且还改变了地球的轨道倾角，使得太阳系中的其他行星轨道的倾角也发生了不同程度的改变。

碰撞造成了大量物质的喷射，其中部分物质被聚集成月球。这场碰撞还使地球的旋转轴从它原来的水平位置倾斜了23.5度。这种倾斜带来了四季的变化和气候变化，影响了地球的生物多样性和演化。

第四阶段：行星演化阶段

自地球形成后，它不断经历着各种变化和演化。在行星演化的过程中，地震、火山喷发、地质碰撞等自然现象形成了地球的形态地貌，分化出不同的岩石结构，例如岩浆熔岩层、地球表层等等。透过这些地质现象，人们可以理解地球的性质和变化，了解地球更多的历史故事和未来发展趋势。

地球是经历了一个漫长的过程而形成的，这个漫长的过程涉及太阳系的大气物质凝集、各种物质在引力作用下的缓慢聚集以及各种物理化学过程的交织，并

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最终发展成为一个充满生命，资源丰富，充满生气的星球。

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