Faint Young Sun Paradox托福听力原文翻译及问题答案

Faint Young Sun Paradox托福听力原文翻译及问题答案

一、Faint Young Sun Paradox托福听力原文：

NARRATOR:Listen to part of a lecture in an astronomy class.

MALE PROFESSOR:Today I want to talk about a paradox that ties in with the topic we discussed last time. We were discussing the geological evidence of water—liquid water—on Earth and Mars three to four billion years ago.So what evidence of a liquid water environment did we find in rock samples taken from the oldest rocks on Earth?

MALE STUDENT:Uh,like pebbles?fossilized algae?MALE PROFESSOR:Right.And on Mars?FEMALE STUDENT:Dry channels?MALE PROFESSOR:Good...all evidence of water in liquid form—large quantities of it.Now remember when we talked about star formation,we said that as a star ages,it becomes brighter.Right? Hydrogen turns into helium,which releases energy.So our standard model of star formation suggests that the Sun wasn't nearly as bright three to four billion years ago as it is today,which means that temperatures on Earth and Mars would have been lower...which,in turn,suggests??

MALE STUDENT:There would have been ice on Earth or Mars...?

MALE PROFESSOR:Correct...if the young Sun was much fainter and cooler than the Sun today,liquid water couldn't have existed on either planet.Now,this apparent contradiction between geologic evidence and the stellar evolution model became known as"the faint young Sun paradox."Now,there have been several attempts to solve this paradox.

First there was the greenhouse-gas solution. Well,you're probably familiar with the greenhouse gas effect,so I won't go into details now. The idea was that trapped greenhouse gases in the atmospheres of Earth and Mars might have caused temperatures to rise enough to compensate for the low heat the young Sun provided.And so it would have been warm enough on these planets for liquid water to exist.So what gas do you think was the first suspect in causing the greenhouse effect?

FEMALE STUDENT:Um,carbon dioxide,I guess...like today?MALE PROFESSOR:In fact,studies indicate that four billion years ago,carbon dioxide levels in the atmosphere were much higher than today's levels.But the studies also indicate that they weren't high enough to do the job—take up for a faint Sun.Well,

then,some astronomers came up with the idea that atmospheric ammonia may have acted as a greenhouse gas, but ammonia would have been destroyed by the ultraviolet light coming from the Sun,and it had to be ruled out,too.

Another solution,mm,which was proposed much later,was that perhaps the young Sun wasn't faint at all.Perhaps it was bright. So it's called the"bright young Sun"solution,according to which the Sun would have provided enough heat for the water on Earth and Mars to be liquid..But how could the early Sun be brighter and hotter than predicted by the standard model? Well,he answer is"mass."

MALE STUDENT:You mean the Sun had more mass when it was young?MALE PROFESSOR:Well,if the young Sun was more massive than today's,it would have been hotter and brighter than the model predicts. But this would mean that it has lost mass over the course of four billion years.

FEMALE STUDENT:Is that possible?MALE PROFESSOR:Actually,the Sun is constantly losing mass through the solar wind?a stream of charged particles constantly blowing off the Sun.We know the Sun's current rate of mass loss?but if we assume that this rate has been steady over the last four billion years,the young Sun wouldn't have been massive enough to have warmed Earth,let alone Mars—not enough to have caused liquid water.MALE STUDENT:Maybe the solar wind was stronger then?MALE PROFESSOR:There is evidence that the solar wind was more intense in the past, but we don't know for sure how much mass our Sun's lost over the last four billion years.Astronomers tried to estimate what solar mass could produce the required luminosity to explain liquid water on these planets.They also took into account that with a more massive young Sun,the planets would be closer to the Sun than they are today.And they found that about seven percent more mass would be required.

FEMALE STUDENT:So the young Sun had seven percent more mass than our Sun?MALE PROFESSOR:Well,we don't know. According to observations of young Sun-like stars,our Sun may have lost as much as six percent of its initial mass,which doesn't quite make it. On the other hand,this estimate is based on a small sample,and the"bright young Sun"solution is appealing.We simply need more data to determine the mass-loss rate of stars.So there's reason to believe that we'll get an answer to that piece of the puzzle one day.

二、Faint Young Sun Paradox托福听力中文翻译：

旁白：在天文学课上听一节课的一部分。

男教授：今天我想谈谈一个与我们上次讨论的话题相关的悖论；我们讨论了三四十亿年前地球和火星上存在水-液态水的地质证据。那么，我们从地球上最古老的岩石样本中发现了什么液态水环境的证据呢？

男学生：呃，像鹅卵石？藻类化石？男教授：对。在火星上呢？女生：干渠？男教授：好。。。所有液态水的迹象都会形成大量的液态水。现在请记住，当我们谈到恒星形成时，我们说过，随着恒星年龄的增长，它会变得更亮。对吧；氢变成氦，释放能量。因此，我们的恒星形成的标准模型表明，太阳在三十亿到四十亿年前还没有今天那么明亮，这意味着地球和火星的温度会更低。。。这反过来又表明？？

男学生：地球或火星上会有冰。。。？

男教授：对。。。如果年轻的太阳比今天的太阳暗得多、冷得多，那么这两颗行星上都不可能存在液态水。现在，地质证据和恒星演化模型之间的这种明显矛盾被称为“微弱的年轻太阳悖论”现在，有人试图解决这一矛盾。

首先是温室气体解决方案&nbsp；嗯，你可能对温室气体效应很熟悉，所以我现在就不详细介绍了；当时的想法是，地球和火星大气层中的温室气体可能导致温度上升，足以补偿年轻太阳提供的低热。因此，这些行星上的温度足以让液态水存在。那么你认为引起温室效应的第一个嫌疑是什么气体呢？

女生：嗯，二氧化碳，我想。。。比如今天？男教授：事实上，研究表明，40亿年前，大气中的二氧化碳含量远远高于今天的水平。但研究还表明，它们的高度不足以在昏暗的太阳下完成这项工作。好

然后，一些天文学家提出了大气氨可能是温室气体的想法；但是氨会被太阳发出的紫外线所破坏，因此也必须排除这种可能性。

另一个解决方案，mm，是在很久以后提出的，可能是年轻的太阳一点也不暗淡。也许它是明亮的&nbsp；因此，它被称为“明亮的年轻太阳”解决方案，根据该解决方案，太阳将为地球和火星上的水提供足够的热量，使其成为液体。。但是，早期的太阳怎么可能比标准模型预测的更明亮、更热呢；嗯，他的答案是“质量”

男学生：你是说太阳年轻时质量更大？男教授：嗯，如果年轻的太阳比今天的质量更大，它会比模型预测的更热、更亮；但这意味着它在40亿年的时间里失去了质量。

女生：可能吗？男教授：事实上，太阳通过太阳风不断失去质量？一股带电粒子流不断地从太阳上吹走。我们知道太阳目前的质量损失率吗？但是，如果我们假设这一速度在过去40亿年中保持稳定，那么年轻的太阳就不会有足够的质量来加热地球，更不用说火星了，也不足以产生液态水。男学生：也许当时太阳风更强？男教授：有证据表明，过去太阳风更强烈；但我们不确定太阳在过去40亿年中损失了多少质量。天文学家试图估计太阳质量能产生所需的光度来解释这些行星上的液态水。他们还考虑到，如果年轻的太阳质量更大，那么这些行星将比现在离太阳更近。他们发现需要增加大约7%的质量。

女学生：那么年轻的太阳的质量比我们的太阳多7%？男教授：嗯，我们不知道；根据对年轻的类太阳恒星的观察，我们的太阳可能已经失去了其初始质量的6%，但这并不能使其完全恢复；另一方面，这一估计是基于一个小样本，而“年轻明亮的太阳”解决方案很有吸引力。我们只需要更多的数据来确定恒星的质量损失率。所以我们有理由相信，总有一天我们会找到这个谜题的答案。

三、Faint Young Sun Paradox托福听力问题：

Q1:1.What is the main propose of the lecture?

A.To compare solutions to the greenhouse-gas problem

B.To examine methods used to study star formation in other solar systems

C.To discuss evidence for liquid water on young Earth and Mars

D.To discuss attempts to solve a puzzle related to the Sun

Q2:2.Why is geological evidence of liquid water on Earth and Mars three to four billion years ago problematic?

A.It suggests that the solar system is younger than it could possibly be.

B.It suggests that the young Sun was less bright than it is today.

C.It challenges the prevailing model of star formation.

D.It contradicts theories about the beginning of the universe.

Q3:3.Why did the greenhouse-gas solution fail to explain the early presence of liquid water on Earth and Mars?[Click on 2 answers.]

A.The types of gases that were present in their atmospheres could not have caused temperatures to rise.

B.There was insufficient carbon dioxide in their atmospheres to produce a greenhouse effect.

C.Solar radiation would have destroyed the ammonia in their atmospheres.

D.Clouds of ammonia would have lowered temperatures by blocking out sunlight.

Q4:4.Why does the professor mention the solar wind?

A.To explain a way the Sun is losing mass

B.To point out that it was less intense billions of years ago

C.To suggest a reason for early climate differences between Earth and Mars

D.To explain the importance of solving the faint-young-Sun paradox

Q5:5.What factor did astronomers consider when calculating the required solar mass for liquid water to exist on Earth and Mars?

A.The young Sun lost mass at a slower rate than it currently does.

B.The young Sun was closer to the planets than it currently is.

C.The young Sun had less solar wind activity than it currently does.

D.The young Sun comprised greater amounts of helium than it currently does.

Q6:6.What is the professor's attitude about the bright-young-Sun solution?

A.He is surprised that it is not more widely accepted.

B.He feels that it raises too many unanswerable questions.

C.He is confident that future research will determine whether it is true.

D.He expects that other possible solutions to the paradox will be proposed.

四、Faint Young Sun Paradox托福听力答案：

A1:正确答案：D

A2:正确答案：C

A3:正确答案：BC

A4:正确答案：A

A5:正确答案：B

A6:正确答案：C