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1、精选优质文档-倾情为你奉上HOW LIFE BEGAN ON THE EARTHNo one knows exactly how the earth began, as it happened so long ago. However, according to a widely accepted theory, the universe began with a Big Bang that threw matter in all directions. After that, atoms began to form and combine to create stars and other
2、bodies. For several billion years after the Big Bang, the earth was still just a cloud of dust. What it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust settled into a solid globe. The earth became so violent that it was not clear whether the shape would last or
3、not. It exploded loudly with fire and rock. They were in time to produce carbon, nitrogen, water vapour and other gases, which were to make the earths atmosphere. What is even more important is that as the earth cooled down, water began to appear on its surface. Water had also appeared on other plan
4、ets like Mars but, unlike the earth, it had disappeared later. It was not immediately obvious that water was to be fundamental to the development of life. What many scientists believe is that the continued presence of water allowed the earth to dissolve harmful gases and acids into the oceans and se
5、as. This produced a chain reaction, which made it possible for life to develop. Many millions of years later, the first extremely small plants began to appear on the surface of the water. They multiplied and filled the oceans and seas with oxygen, which encouraged the later development of early shel
6、lfish and all sorts of fish. Next, green plants began to grow on land. They were followed in time by land animals. Some were insects. Others, called amphibians, were able to live on land as well as in the water. Later when the plants grew into forests, reptiles appeared for the first time. They prod
7、uced young generally by laying eggs. After that, some huge animals, called dinosaurs, developed. They laid eggs too and existed on the earth for more than 140 million years. However, 65 million years ago the age of the dinosaurs ended. Why they suddenly disappeared still remains a mystery. This disa
8、ppearance made possible the rise of mammals on the earth. These animals were different from all life forms in the past, because they gave birth to young baby animals and produced milk to feed them. Finally about 2.6 million years ago some small clever animals, now with hands and feet, appeared and s
9、pread all over the earth. Thus they have, in their turn, become the most important animals on the planet. But they are not looking after the earth very well. They are putting too much carbon dioxide into the atmosphere, which prevents heat from escaping from the earth into space. As a result of this
10、, many scientists believe the earth may become too hot to live on. So whether life will continue on the earth for millions of years to come will depend on whether this problem can be solved. A VISIT TO THE MOONLast month I was lucky enough to have a chance to make a trip into space with my friend Li
11、 Yanping, an astronomer. We visited the moon in our spaceship!Before we left, Li Yanping explained to me that the force of gravity would change three times on our journey and that the first change would be the most powerful. Then we were off. As the rocket rose into the air, we were pushed back into
12、 our seats because we were trying to escape the pull of the earths gravity. It was so hard that we could not say anything to each other. Gradually the weight lessened and I was able to talk to him. Why is the spaceship not falling back to the earth? On the earth if I fall from a tree I will fall to
13、the ground. I asked. We are too far from the earth now to feel its pull, he explained, so we feel as if there is no gravity at all. When we get closer to the moon, we shall feel its gravity pulling us, but it will not be as strong a pull as the earths. I cheered up immediately and floated weightless
14、ly around in our spaceship cabin watching the earth become smaller and the moon larger.When we got there, I wanted to explore immediately. Come on, I said. If you are right, my mass will be less than on the earth because the moon is smaller and I will be able to move more freely. I might even grow t
15、aller if I stay here long enough. I shall certainly weigh less! I laughed and climbed down the steps from the spaceship. But when I tried to step forward, I found I was carried twice as far as on the earth and fell over. Oh dear, I cried, walking does need a bit of practice now that gravity has chan
16、ged. After a while I got the hang of it and we began to enjoy ourselves.Leaving the moons gravity was not as painful as leaving the earths. But returning to the earth was very frightening. We watched, amazed as fire broke out on the outside of the spaceship as the earths gravity increased. Again we
17、were pushed hard into our seats as we came back to land. That was very exhausting but very exciting too, I said. Now I know much more about gravity! Do you think we could visit some stars next time? Of course, he smiled, which star would you like to go to?CAUGHT BY A BLACK HOLEThe spaceship warned L
18、i Yanping and me to be ready as we were approaching the black hole. We could see some faint lights around what looked like an empty space. Li Yanping said, That empty hole is like a mouth always needing to be fed. Those lights are things that are being pulled into it by the gravity of the hole. We w
19、atched with interest and amazement at the lights which seemed to be going fainter and fainter round the edge of the black hole. Just then the lights on our spaceship went out and the computer stopped working. What was happening? I tried to turn the spaceship away from the hole but it would not move.
20、 Would it eat us too? Suddenly the spaceship jumped and began to move round the edge of the hole too. The gravity of the black hole was pulling us into its mouth. As the spaceship moved round the black hole, I felt rather sick. My mouth went dry and I closed my eyes. All the stories about what happe
21、ned when you were caught by the gravity of a black hole seemed to be true.But then the spaceship jumped again. This time it moved sideways and away from the edge of the black hole. Someone watching me would have seen the spaceship flying like a bird away from the black hole. But we felt nothing. At
22、last we were able to look around us. Luckily the computer had started working again. We realized that we had discovered something new about black holes. If you go inside the edge of a black hole, it will eat you and there is no escape; but if you do not, you may have an opportunity to escape. How ex
23、citing!Unit5A TRIP ON THE TRUE NORTHLi Daiyu and her cousin Liu Qian were on a trip to Canada to visit their cousins in Montreal on the Atlantic coast. Rather than take the aeroplane all the way, they decided to fly to Vancouver and then take the train west to east across Canada. The thought that th
24、ey could cross the whole continent was exciting. Their friend, Danny Lin, was waiting at the airport. He was going to take them and their baggage to catch The True North, the cross-Canada train. On the way to the station, he chatted about their trip. Youre going to see some great scenery. Going east
25、ward, youll pass mountains and thousands of lakes and forests, as well as wide rivers and large cities. Some people have the idea that you can cross Canada in less than five days, but they forget the fact that Canada is 5,500 kilometres from coast to coast. Here in Vancouver, youre in Canadas warmes
26、t part. People say it is Canadas most beautiful city surrounded by mountains and the Pacific Ocean. Skiing in the Rocky Mountains and sailing in the harbour make Vancouver one of Canadas most popular cities to live in. Its population is increasing rapidly. The coast north of Vancouver has some of th
27、e oldest and most beautiful forests in the world. It is so wet there that the trees are extremely tall, some measuring over 90 metres.That afternoon aboard the train, the cousins settled down in their seats. Earlier that day, when they crossed the Rocky Mountains, they managed to catch sight of some
28、 mountain goats and even a grizzly bear and an eagle. Their next stop was Calgary, which is famous for the Calgary Stampede. Cowboys from all over the world come to compete in the Stampede. Many of them have a gift for riding wild horses and can win thousands of dollars in prizes. After two days tra
29、vel, the girls began to realize that Canada is quite empty. At school, they had learned that most Canadians live within a few hundred kilometres of the USA border, and Canadas population is only slightly over thirty million, but now they were amazed to see such an empty country. They went through a
30、wheat-growing province and saw farms that covered thousands of acres. After dinner, they were back in an urban area, the busy port city of Thunder Bay at the top of the Great Lakes. The girls were surprised at the fact that ocean ships can sail up the Great Lakes. Because of the Great Lakes, they le
31、arned, Canada has more fresh water than any other country in the world. In fact, it has one-third of the worlds total fresh water, and much of it is in the Great Lakes.That night as they slept, the train rushed across the top of Lake Superior, through the great forests and southward towards Toronto.
32、 “THE TURE NORTH” FROM TORONTO TO MONTREALThe next morning the bushes and maple trees outside their windows were red, gold and orange, and there was frost on the ground, confirming that fall had arrived in Canada. Around noon they arrived in Toronto, the biggest and most wealthy city in Canada. They
33、 were not leaving for Montreal until later, so they went on a tour of the city. They went up the tall CN Tower and looked across the lake. In the distance, they could see the misty cloud that rose from the great Niagara Falls, which is on the south side of the lake. The water flows into the Niagara
34、River and over the falls on its way to the sea.They saw the covered stadium, home of several famous basketball teams. As they walked north from the harbour area, Li Daiyu said, Lin Fei, one of my mothers old schoolmates, lives here. I should phone her from a telephone booth.They met Lin Fei around d
35、usk in downtown Chinatown, one of the three in Toronto. Over dinner at a restaurant called The Pink Pearl, the cousins chatted with Lin Fei, who had moved to Canada many years earlier. We can get good Cantonese food here, Lin Fei told them, because most of the Chinese people here come from South Chi
36、na, especially Hong Kong. Its too bad you cant go as far as Ottawa, Canadas capital. Its approximately four hundred kilometres northeast of Toronto, so it would take too long.The train left late that night and arrived in Montreal at dawn the next morning. At the station, people everywhere were speak
37、ing French. There were signs and ads in French, but some of them had English words in smaller letters. We dont leave until this evening, said Liu Qian. Lets go downtown. Old Montreal is close to the water. They spent the afternoon in lovely shops and visiting artists in their workplaces beside the w
38、ater. As they sat in a buffet restaurant looking over the broad St Lawrence River, a young man sat down with them.Hello, my name is Henri. Im a student at the university nearby, he said, and I was wondering where you are from. The girls told him they were on a train trip across Canada and that they
39、had only one day in Montreal. Thats too bad, he said. Montreal is a city with wonderful restaurants and clubs. Most of us speak both English and French, but the city has French culture and traditions. We love good coffee, good bread and good music.That night as the train was speeding along the St La
40、wrence River toward the Gulf of St Lawrence and down to the distant east coast, the cousins dreamed of French restaurants and red maple leaves.IQALUIT- THE FROZEN TOWNThe reporter, Beth Allen, arrived in a northern community called Iqaluit in Nunavut .Nunavut was created in 1999 as a special area fo
41、r Inuit people. Its name means Our Land in their language. It is in the farthest northeastern area of Canada, north of the Arctic Circle, and is very cold - the average winter temperature in Nunavut is 35 degrees below zero. Beth said, I knew it would be cold in January, but not this cold! Maybe the
42、re is a dog sled that can take me into town. The quiet man who had been on the plane with her said, Ill take you into town, but I dont have a dog sled. Most people only use the dogs for competitions. Why are you visiting Iqaluit? Beth answered, Im writing a story for my newspaper about Iqaluit - wed
43、 like to advertise it as a holiday place, but I think its too cold. The man laughed. My name is Simon and I am Inuit, he said. I think its too far north here for holidays but more and more tourists are coming. They like ice fishing and photographing polar bears. I stay as far away from polar bears a
44、s possible. I like my warm office and my warm house. Beth asked, What do you do in an office? Dont you hunt animals for a living? I thought you lived in ice houses. Im a business man. My grandfather would live in ice houses when he hunted in winter, but not so many people do that now. The old men us
45、ed to make one in a few hours. They used to live in skin tents in summer - the tents were easy to move so the people could follow the animals. A few minutes later they arrived in Iqaluit, a town with a population of 6,000, on Simons snowmobile. It was two oclock in the afternoon, but it was already
46、dark, and all the houses shone with bright lights. Beth said, Why is it so dark? Its the middle of the day! Simon replied, Its dark in the day because we are so far north. You should come in June. The sun shines all night in the north then. Thats why its called The Land of the Midnight Sun. There were people on the streets and snowmobiles everywhere. There were even a few dog teams.专心-专注-专业