1. What is the lecture mainly about?
A. An example of rapid climate change
B. A comparison of two mechanisms of climate change
C. The weather conditions in the present-day Sahara
D. Recent geological findings made in the Sahara
2.Not long ago, the Sahara had a different climate. What evidence does the professor mention to support this? [Click on 3 answers.]
A. Ancient pollen
B. Bones from large animals
C. Rock paintings
D. Agriculture in ancient Egypt
E. Underground water
3.In the lecture, what do the Ice Age and the creation of the Sahara Desert both illustrate about past climate changes? [Click on 2 answers.]
A. That some climate changes benefitted the development of civilization
B. That some climate changes were not caused by human activity
C. That some climate changes were caused by a decrease of moisture in the atmosphere
D. That some climate changes were caused by changes in Earth’s motion and position
4.What started the runaway effect that led to the Sahara area of north Africa becoming a desert?
A. The prevailing winds became stronger.
B. The seasonal rains moved to a different area.
C. The vegetation started to die off in large areas.
D. The soil lost its ability to retain rainwater.
5.The professor mentions a theory that people migrating from the Sahara were important to the development of the Egyptian civilization. Which sentence best describes the professor’s attitude toward this theory?
A. It is exciting because it perfectly explains recent archaeological discoveries.
B. It is problematic because it goes too far beyond the generally available data.
C. It raises an interesting possibility and he hopes to see more evidence for it.
D. It cannot be taken seriously until it explains how the migrants got to Egypt.
6.Why does the professor say this:
A. To correct a misstatement he made about the Sahara’s climate
B. To suggest that the current dryness of the Sahara is exaggerated
C. To indicate that scientists are not in agreement about the Sahara’s past climate
D. To emphasize the difference between the current and past climates of the Sahara
答案：1A 2ACE 3BD 4B 5C 6D
Listen to part of a lecture in an Earth Science class.
MALE PROFESSOR
We’re really just now beginning to understand how quickly drastic climate change can take place. We can see past occurrences of climate change that took place over just a few hundred years. Take hm the Sahara desert in Northern Africa.(题目1. What is the lecture mainly about? A. An example of rapid climate change 答案出处)
The Sahara was really different 6,000 years ago. I mean, you wouldn’t call it a tropical paradise or anything--ah or maybe you would if you think about how today in some parts of the Sahara it only rains about once a century.(题目6.Why does the professor say this: ah or maybe you would if you think about how today in some parts of the Sahara it only rains about once a century. D. To emphasize the difference between the current and past climates of the Sahara 答案出处) Hm but basically, you had greenery and you had water. And what I find particularly interesting, amazing, really what really indicates how un-desert-like the Sahara was thousands of years ago, was something painted on a rock prehistoric art –hippopotamuses. As you know, hippos need a lot of water, and hence... (题目2.Not long ago, the Sahara had a different climate. What evidence does the professor mention to support this? [Click on 3 answers.] C. Rock paintings 答案出处；此处出现了生词hippopotamuses,如果词汇量够大，知道是河马的意思能够使听力非常顺畅；大多人遇到的问题就是，听到河马这个词时反应不过来同时又因为想记下这个词或者回忆这个词的词义而错过之后的听力内容导致漏听，从而掌握不了文章的逻辑；应对办法：听力文本中的生词有一部分是以专有名词形式出现的，对于这些词做笔记时可以做特殊标注，如HIPPOP,起到提示定位的作用，如果这个生词很重要，在题干或选项中出现时，可以根据标注找到定位)Hence what?
FEMALE STUDENT
They need to live near a large source of water year-round.
MALE PROFESSOR
That’s right.
MALE STUDENT
But how’s that proof that the Sahara used to be a lot wetter? I mean, the people who painted those hippos…well, couldn’t they have seen them on their travels?
MALE PROFESSOR
OK, in principle they could, Carl. But the rock paintings aren’t the only evidence. Beneath the Sahara are huge aquifers, basically a sea of fresh water that’s perhaps a million years old, filtered through rock layers. And, ah an-an then there’s fossilized pollen from low shrubs and grasses that once grew in the Sahara. In fact these plants still grow ah but hundreds of miles away in more vegetated areas. Anyway, it’s this
fossilized pollen, along with the aquifers, and the rock paintings—these three things are all evidence that the Sahara was once much greener than it is today, that there were hippos and probably elephants, and giraffes, and so on.(题目2.Not long ago, the Sahara had a different climate. What evidence does the professor mention to support this? [Click on 3 answers.] A. Ancient pollen C. Rock paintings E. Underground water 答案出处 注意托福听力常见的就是对一个问题的答案反复阐述并作总结，记录笔记时留意重复出现的内容和总结部分的内容)MALE STUDENT
So, what happened?
MALE PROFESSOR
How did it happen? Well now we’re so used to hearing about how human activities are affecting the climate, right; but that takes the focus away from the natural variations in the Earth’s climate. Like the Ice Age, right? The planet was practically covered in ice just a few thousand years ago.(题目3.In the lecture, what do the Ice Age and the creation of the Sahara Desert both illustrate about past climate changes? [Click on 2 answers.] B. That some climate changes were not caused by human activity答案出处)
Now, as far as the Sahara goes, there’s some recent literature that points to the migration of the monsoon in that area.
FEMALE STUDENT & MALE STUDENT
“huh?”
MALE PROFESSOR
What do I mean? OK. A monsoon is a seasonal wind that can bring in a large amount of rainfall. Now, if the monsoon migrates, well that means the rains move to another area, right?(题目4.What started the runaway effect that led to the Sahara area of north Africa becoming a desert? B. The seasonal rains moved to a different area.答案出处)
So what caused the monsoon to migrate? Well, the answer is the dynamics of Earth’s motions--the same thing that caused the Ice Age, by the way.The Earth’s not always the same distance from the Sun. And it’s not always tilting toward the Sun at the same angle. There’re slight variations in these two parameters. They’re gradual variations, but their effects can be pretty abrupt, and can cause the climate to change in just a few hundred years.(题目3.In the lecture, what do the Ice Age and the creation of the Sahara Desert both illustrate about past climate changes? [Click on 2 answers.] D. That some climate changes were caused by changes in Earth’s motion and position答案出处)
FEMALE STUDENT
That’s abrupt?
MALE PROFESSOR
Well, yeah, considering that other climate shifts take thousands of years, this one’s pretty abrupt. So these changes in the planet’s motions, they caused the climate to change; but it was also compounded.What the Sahara experienced was a sort of runaway drying effect.
As I said, the monsoon migrated south—so there was less rain in the Sahara. The land started to get drier—which in turn caused a huge decrease in the amount of vegetation, because vegetation doesn’t grow as well in dry soil, right? And then, less vegetation means the soil can’t hold water as well—the soil loses its ability to retain water when it does rain. So then you have less moisture to help clouds form…nothing to evaporate for cloud formation. And then the cycle continues—less rain, drier soil, less vegetation, fewer clouds, less rain, etcetera, etcetera.(题目5.The professor mentions a theory that people migrating from the Sahara were important to the development of the Egyptian civilization. Which sentence best describes the professor’s attitude toward this theory? C. It raises an interesting possibility and he hopes to see more evidence for it.答案出处)
MALE STUDENT
But what about the people who made the rock paintings?
MALE PROFESSOR
Good question. No one really knows. But there might be some connection to ancient Egypt. At about the same time that the Sahara was becoming a desert, mm…5,000 years ago, Egypt really began to flourish out in the Nile River Valley. And that’s not that far away. So it’s only logical to hypothesize that a lot of these people migrated to the Nile Valley when they realized that this was more than a temporary drought. And some people take this a step further--and that’s ok, that’s science--and they hypothesize that this migration actually provided an important impetus in the development of ancient Egypt.
Well, we’ll stay tuned on that.
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