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Question 1ReadingAround 1130 A.D., a group of highly intelligent and creative humans called the Anasazi from New Mexicos Chaco Canyon vanished without a trace. Judging from available evidence, historians have suggested that the Anasazis disappearance was more likely to be caused by a severe summer drought. First of all, the time when the Anasazi abandoned their village coincided with the beginning of a sixty-year summer drought caused by global warming. During this time, uncommonly long heat waves swept across the world, making colder regions warmer and causing severe droughts in the Americas. Scientists believe that the summer drought at Chaco Canyon was so severe that the Anasazi could not cope with it. In the end, they were forced to choose between starvation or migration. Second, at Chaco Canyon, archeologists have discovered irrigation systems including diversion dams and canals directing water to the fields. The presence of these systems indicates that the Anasazi suffered shortages of water, and as a countermeasure for the crisis, they built irrigation systems to store water for drinking and growing crops. However, the drought caused by the global warming eventually may have been so overwhelming that it compelled the Anasazi to leave. Finally, before the big summer drought, Chaco Canyons natural springs and fertile soil contributed to the tribes population growth. Perhaps, the tribes population had overgrown, and then the people were approaching the limit of local resources during the sixty-year summer drought. The subsequent food shortages forced this ancient people to migrate to a more habitable area. The fact that the Anasazi abruptly fled from their dwelling and left behind numerous artifacts suggests that they were displaced by a major natural disaster. 276Listening I think the evidence supporting the claim that the Anasazi disappeared because of a severe drought is shaky. First of all, there may have been a global warming in the past, and the subsequent droughts throughout the world affected different places, but the global warming did not affect areas where the Anasazi lived. The evidence suggests that some trees have existed at Chaco Canyon for thousands of years. If there had been a drought at Chaco Canyon, these trees would probably have died. Second, the fact that irrigation systems such as dams, canals were found in places where the Anasazi lived does not necessarily mean that this prehistoric tribe suffered severe droughts and abandoned their homeland as a result. On the contrary, the irrigation systems that existed for 150 years would indicate that the Anasazi were fully aware of their problems of water shortages and they somehow developed the technology to store water and divert it to grow corn, squash, and beans in a desert-like land. Scientists have found evidence that the Anasazi providently stored their crops against drought years, suggesting that this prehistoric people did not vanish because of a drought. Finally, drought is only a hypothesis for the Anasazis disappearance. Recent findings by climatologists suggest that the great drought at Chaco Canyon was not severe enough to drive a nation of people to abandon their homes. The fact that the Anasazi abruptly left their homes might suggest they were attacked by another warring tribe rather than threatened by a drought. We should also consider other causes such as disease or overuse of farmland. In sum, the evidence so far is not enough to support the claim that the Anasazi vanished simply because of a severe drought. 288阅读文章认为Anasazi人大举逃离住所的原因如下：第一， 有证据显示当时发生全球暖化，引发的干旱促使Anasazi人逃离。第二， 考古发现的灌溉系统，可推论出当年Anasazi人遭受严重旱灾。第三， 有证据显示Anasazi人口过多，干旱期间无法养活众多人口。教授怀疑前述论点，理由如下：第一， 当地有树木存活了数千年，若当年干旱严重，树木必定死亡，证明当年干旱没有影响。第二， 灌溉系统反而证明Anasazi人有对抗干旱的能力，所以不会因为干旱而出走。第三， 新的证据发现当年干旱不太严重，此外，Anasazi人仓促逃离，更合理的推论是遭到他族攻击或疾病侵袭。The professor casts doubt on the view that the Anasazi, a prehistoric tribe from Chaco Canyon, vanished mainly because of a severe drought. First of all, although there was a rise in temperatures and ensuing droughts throughout the world, the global warming did not affect the homeland of the Anasazi. Trees have existed at Chaco canyon for many years. If there had been droughts at the Chaco Canyon, these trees would probably have died. Besides, these trees show no trace of a life-threatening drought. Second, the existence of irrigation systems does not necessarily mean that this place was plagued by severe droughts. On the contrary, the irrigation systems may suggest this prehistoric people developed the skill to survive in a desert-like land. Finally, drought is only a conjecture for the Anasazis disappearance. There is no direct evidence that the great drought was severe enough to drive a nation of people from their homes. Alternative explanations include war, disease, and overuse of farmland. In a word, it is questionable that the Anasazi vanished simply because of a severe drought. 178Question 2Reading Marco Polo (1254-13242), a Venetian trader and explorer, gained fame for his worldwide travels recorded in the book The Travels of Marco Polo. However, recently some scholars have raised doubts that Marco Polo even traveled to China. First of all, for one who was supposed to have lived in China for 17 years, Marco Polo never picked up any Chinese or Mongolian place-names. In fact, the names of the directions and locations used by Marco Polo in his book about China correspond to those used by the Persian historian Rashid al-Din (1247-1317), who was Polos contemporary and one of the most important chroniclers of the Mongol period. Such a glaring omission put a large dent in Marco Polos credibility as a traveler to China?Second, for someone who is supposed to have traveled all the way to the interior of China, there is the curious omission of any reference to the popular pastimes and cultural practices of the Chinese? For instance, Marco Polo did not mention the Chinese love of tea and the ubiquitous teahouses, which no traveler to China would be likely to miss. This is another major cause for suspicion?Finally, when we look into the original records of the Chinese and Mongols, there is no evidence that Marco Polo served at the court of the Mongol ruler, or was appointed to the post of governor of Yang Zhou. This is an honor, which Marco Polo claims the great Mongol ruler bestowed on him for three years? So it is unlikely that Marco Polo actually traveled to China and reached the court of the great Mongol ruler Kublai khan? 271ListeningDid Marco Polo ever travel to China during the Mongol period and stay there for 17 years? Some scholars claim to have found inconsistencies proving Marco Polo did not travel to China, but I do not find their arguments convincing. First of all, it is true that Marco Polo never used any Chinese or Mongolian place-names in his book, and the place-names in his travel book are largely of a Persian origin. Yet it is worth remembering that Persian was the major language used in trade between the two continents of Asia and Europe in the 13th and 14th centuries. Therefore it would be perfectly normal for Marco Polo to borrow Chinese place-names from the Persian source. Second, the fact that Marco Polo failed to include references to tea and teahouses in China does not necessarily disprove that this Venetian ever went to China. The fact is, the culture of tea drinking at teahouses was popular mainly in the southern part of China. In those days, people in northern China had not yet developed an interest in tea drinking. While in China, Marco Polo stayed for the most part in northern China. Thus, if he failed to mention tea, it would be understandable. Finally, just because the name Marco Polo was not found in pre-modern Chinese documents does not mean that he did not serve at the court of the Mongol ruler, or that he was not appointed to the post of governor of Yang Zhou. It is possible that Marco Polo was referred to by a different name that is unrecognizable to modern historians. The official records of the ancient Chinese court sometimes did not use peoples real names. Or, perhaps, the records referring to Marco Polo may simply have been lost. 295阅读文章认为马可波罗根本没有到过中国，怀疑的理由如下：第一， 马可波罗在中国住了17年，他的书中没有用任何中文或蒙文的地名，用的中国地名反而是波斯历史学家所用的波斯文。第二， 马可波罗的书中没有提到中国人喝茶，以及普遍存在的茶楼。第三， 中文与蒙文的史籍没有记载马可波罗这个人。教授不赞成前述观点，理由如下：第一， 当年波斯文是亚欧贸易主要语言，马可波罗书中用到波斯文翻译的中国地名是正常的，不足以证明他没有到过中国。第二， 当年喝茶的文化主要流行于中国南方，马可波罗主要逗留于中国北方，所以没有提到喝茶，是可以理解的。第三， 中文与蒙文的史籍没有记载马可波罗不足以证明他没有到过中国，因为中蒙文史籍可能以现代人不法辨识的名字来记载马可波罗，或者记载马可波罗的史籍遗失。The professor challenges the view that Marco Polo never traveled to China by offering different explanations of Marco Polos omissions of certain things in his travel book. First of all, although the place-names in Marco Polos travel book are borrowed from Persian, it does not mean that he did not go to China. The reason is that in those times Persian was the major trade language between Europeans and Asians. Therefore it would be normal for Marco Polo to borrow Chinese place-names from the Persian source. Second, it is correct that Marco Polo did not mention tea and teahouses in China, but it does not necessarily prove that Polo did not go to China. Tea was popular mainly in southern China and people in northern China had not yet developed an interest in tea drinking. Since Marco Polo stayed for the most part in northern China, it would be understandable that he failed to mention tea. Finally, the fact that Marco Polo was not found in pre-modern Chinese documents does not mean that he never went to China. It is possible that Marco Polo was mentioned by a different name that is not recognizable to modern historians, or, that the records that mentioned Marco Polo were simply lost. 209Question 3ReadingHow did the moon form? Scientists hypothesized that a piece of space debris the size of Mars struck the Earth just after the formation of the solar system, ejecting large volumes of heated material from the outer layers of both objects. A disk of orbiting material was formed, and this matter eventually coalesced to form the Moon. Nevertheless this giant-impact theory is questionable for the following reasons. First, if the Earth had been smacked hard enough to lose such a big piece of its mantle, the impact would have left a huge mark on the surface of the Earth. Yet so far, no trace of a giant impact has been found on the surface of the Earth. Without evidence proving that a huge collision took place, the validity of the giant-impact theory is in doubt. Second, if the Moon came from material that once made up the Earth, then the rocks on the Earth and the Moon should be much more similar in composition. However, the make-up of the rocks on the Moon is quite different from that on the Earth. For example, the rocks on the Moon contain few volatile substances such as water. This fact makes it unlikely that the Moon formed directly from the Earth. Finally, the density of the Moon is much lower than that of the Earth. The Moon has a low density compared to the terrestrial planets. Recent findings even suggest that the moons core constitutes only 2-4 percent of its total mass, compared to a terrestrial core with about 30 percent of the Earths mass. Therefore, the differences between the Moon and the Earth greatly weaken the giant-impact theory. 276ListeningWhile the giant-impact theory of how the Moon formed has been heavily criticized, I do not find these criticisms convincing. Here is why. First of all, it is true that so far no trace of a giant impact has been found on the surface of the Earth. Yet we should remember that the giant crash took place more than four billion years ago. Any trace of the collision might have been erased by the forces of nature. The Earths surface is made up of a number of enormous rock plates and they have collided with each other over millions of years, resulting in tremendous change in the map of the planet. Therefore, if there had been any impact between the Earth and a space rock, the impact mark might have disappeared long ago. Second, it is a fact that rocks on the Moon do not contain water, while those on Earth do. However, as the Moon formed out of the collision of space rocks, the heat from the collision made the entire Moon molten. The temperatures on this newly formed Moon were extremely high. With such high temperatures, any water there might have evaporated and gone off into space. So, the absence of water on the Moon is not surprising. Finally, we know that the density of the Earths surface is lower than that of the Earths center. Since the Moon was originally part of the Earths surface, not the Earths core, its density should be consistent with the density of the Earths surface. This is exactly what we find. The density of the Moon is consistent with that of the Earths surface, which further supports the giant-impact theory of the Moons formation. 283有理论认为，月球是太空岩石与地球相撞形成的，阅读文章怀疑此理论，理由如下：第一， 太空岩石若真的曾经撞击过地球，必定会留下痕迹，但找不到此种撞击痕迹。第二， 若月球真的是太空岩石与地球相撞形成的，月球与地球岩石必定有相似的成分，但研究发现，月球岩石没有水，组成份子与地球岩石差异甚大。第三， 月球的密度低于地球密度很多，两者差异太大，故撞击理论难以成立。教授不赞成前述观点，理由如下：第一， 太空岩石撞击过地球后，留下的痕迹找不到是正常的，因为撞击发生于四十亿年前，地壳运动早就使痕迹消失了。第二， 月球形成之初，温度极高，若有水分，也会蒸发掉，所以月球上没有水是可以理解的。第三， 没错，月球的密度低于地球密度很多，但月球部分来自地球表面，而非地心，地球表面的密度小于地心，月球接受的物质来自地表，所以月球密度比地球密度低是正常的。范文：In the lecture, the professor challenges the criticism of the view that Moon was formed from a giant collision between the Earth and a giant space rock. He believes in the giant-impact theory. First of all, although no trace of a giant impact has been found on the surface of the Earth, we should be aware that the giant impact took place more than four billion years ago. With the tremendous changes on the Earths surface over billions of years as a result of violent tectonic movements, the mark left by the impact would have long disappeared. Second, as the Moon formed out of the collision of space rocks, the heat from the collision did not allow any water to remain on the Moon. Therefore, it is not surprising that scientists did not find water components on the Moon. Finally, while the density of the Moons is lower than that of the Earth, it does not mean that the Moon did not form out of the debris from the Earth. Since the Moon was originally part of the Earths surface, rather than the Earths core, its density should be consistent with the density of the Earths surface. This is exactly what we find. To sum up, the giant-impact theory on the Moons formation is valid. 215Question 4 ReadingIn late June of 1908, a fireball exploded above the remote Russian forests of Tunguska, Siberia, destroying more than 800 square miles of trees. While scientists think the Tunguska explosion was caused by an asteroid, recent studies have shown that the event was most likely the result of a “swamp gas” explosion, rather than an object from outer space. Here is why.First of all, if an asteroid exploded above Tunguska, it would have left some traces at the impact site. But so far neither its fragments nor any impact craters have been discovered in Tunguska after repeated expeditions. In January 2001, a meteoric explosion took place over Canada. The meteoric explosion left abundant fragments. Therefore, if the same event happened in Tunguska, something would be found. Second, if it was a large asteroid that slammed into Earth, the impact on land would have caused a huge crater. Researchers first proposed that Lake Cheko, a 164-foot-deep lake located just 5 miles northwest of the epicenter of destruction, might have been the impact crater. Nevertheless researchers concluded that it was not an impact crater. Without a smoking gun, the asteroid impact theory simply could not hold. Finally, judging from the butterfly pattern of trees knocked sideways in Tunguska, the explosion must have occurred close to the ground. Note that Tunguska is a swampland extending to thousands of kilometers. In the beginning of summer, all swamps in the region would be defrosting, releasing in a very short time a large quantity of “swamp gas”, or methane gas. Scientists point out that the most likely culprit was a huge cloud of well mixed methane and air, which was common in Siberia. The truth is, comets and meteors do not explode when encountering Earths atmosphere. 291ListeningThe Tunguska explosion is the largest impact event in recent history. This explosion has sparked heated debate in the science community. The latest explanation for the Tunguska event is a methane gas explosion, but I dont find it convincing. First of all, those for a methane gas explosion claim that the lack of asteroid or comet particles at the Tunguska explosion site proves that the impact was unlikely to be caused by an asteroid. But the absence of asteroid fragments doesnt mean the asteroid did not hit Tunguska. It was 19 years after the Tunguska explosion that scientists went to the scene to find evidence. Any traces left at the impact site would have been destroyed by the forces of nature. In contrast, just two weeks after the meteoric explosion occurred in Canada, scientists rushed to the site to search for meteoric remains. Second, those against the asteroid theory argue that if an asteroid slammed into the Earth, the impact would have caused a huge crater on Earth. However, the asteroid did not have to crash into the Earth as an intact rock. When an asteroid or comet enters the Earth, it could explode in the lower atmosphere before hitting the ground. Under rapid heat and pressure, the space rock slamming into the Earth