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1、L4 Unit 2-1Listening物种、环境The earth was born about 4.6 million years ago. The first life appeared about a billion years later. The first plant didnt appear until around 2 billion years ago. Until around 580 million years ago, life formedweresmall and microscopic (微笑的 ). Since that time, lives has evo
2、lved to many different types and species. However, scientists estimate that more than 99% of them are now extinct.They have been several extinction events in the history of the earth. In the extinction event, many life forms or species of life die out. The causes of the massive extinction events are
3、 unsoughtmystery. These events are not predictable and can happen at any time. Scientists think that some of that started by asteroid pass or volcano corruption. Events like this, can change the global conditions that life depends on.One major extinction event, happened about 66 million years ago. T
4、hat event may have been started by a large asteroid that hit the earth. As a result, the dinosaurs and about half of the all species on the planet, died out. When the asteroid hit the earth, it started a chain of events. A chain of event is a series of events linked together, like a chain.These part
5、icular chain of events happened over a period of months and years. When the asteroid hit the earth, it caused huge cloud of dust to enter the atmosphere. This cloud of dust blocked the sun and darken the earth for a period of months. Without enoughsunlight, plants and plant-eating animals, quickly d
6、ied. With the deaths of so many plants and animals, the food chain collapsed . This led to the deaths of many more species.Mass extinction events had played important part in the evolution of life. In fact, some extinction events had helped to accelerate evolution. For example, some mammals lived to
7、 the age of dinosaurs, but they couldnt compete. When the dinosaurs were removed, the mammals were able to compete more successfully. Once they could compete, mammal evolved to a higher state. Without the extinction event, perhaps we wouldnt be here today.Scientist estimate that there have been at l
8、east 5 massive extinctions in the pass 540 million years. They also believed that we had entered a new extinction event. Species are becoming extinct at a much faster rate than before. Instead of the asteroid and volcano corruptions, the current event is the result of human activities. Human activit
9、ies, for example, had led to global warming.Global warming is the result of an increase in carbon gases in our atmosphere. These gases trap heat from the sun, so the earth is getting warmer. As a result, sea levels are rising and weather patterns are changing. In addition, we humans are destroying h
10、abitats of many plants and animals. Cutting down forest and polluting rivers destroys the habitats of many forms of life.There is no longer any doubt that this is happening. Specials of lives are disappearing at an increasing rate. Global temperatures are rising and weather patterns are changing. Sc
11、ientists are warning us that fast action is necessary to save our future. If we dont act, we may go the way of the dinosaurs.L4 Unit 2-1 vocabulary身体系统、产业、技术The body circulatory system includes the heart and blood vessels. The heart pumps the bloods to all parts of body through a network of arteries
12、 and vein.The digestive system breaks down and absorbs food into the body. It supplies the energy that the body need s for growth and repair. After digestion, excess food is turned into waste and eliminated from the body.The nervous system includes the brain, spinal cordand nerves. This is your cont
13、rol system. It controls your muscles and organs included your circulatory system and digestive system.The respiratory system includes your nose and lungs. It brings air and oxygen into your body and remove the carbon dioxide from the body. The lungs are where oxygen enters the bloodstream and carbon
14、 dioxide is removed.Immune system protects body against the infections and diseases. Sneezing and fever are examples of how the immune systems works. If the infection invades the body and the immune system attacks it.The control use of fire allowed people to cook food and survive in the colder clima
15、tes. Fire provided the light so that people could work and socialize for longer hours.With the invention of agriculture, people can grow food and settle into communities. By growing food, people can spend less time hunting and more time on other things, such as art.The domestication of animals allow
16、s people to raise and use animals for food and work. By raise herds of animals, such as sheep, people have regular supply of meat and clothing. The strength of animals such as horses and oxen was used for work and transportation.The development of tools and machines has resulted in a more fashion manufacturing and construction. With better tools and machines, works can be done with fewer people and much lower cost.The development of science and eng
