全新版大学英语听说教程3答案

　　Word Bank

　　galaxy n. one of the large groups of stars in the universe 星系

　　database n. a very large collection of related data arranged for convenient access, generally in a computer 数据库

　　mammal n. a type of animal in which the female gives birth to babies, not eggs, and feeds them on milk from her body 哺乳动物

　　microbe n. a living thing that is so small that it can’t be seen without a microscope 微生物;细菌

　　Panama a country in Central America 巴拿马(中美洲国家)

　　Script

　　Isn’t it surprising that scientists have a better understanding of how many stars there are in the galaxy than how many species there are on Earth? Their estimates of global species diversity vary from 2 to 100 million species. Most people agree on an estimate of somewhere near 10 million and yet only 1.5 million have actually been named. Current knowledge of species diversity is limited. This problem becomes more serious because there is a lack of a central database or list of the world’s species.

　　New species are still being discovered — even new birds and mammals. On average, about three new species of birds are found each year, and since 1990, 10 new species of monkeys have been discovered. Other groups are still far from being completely described; an estimated 40 percent of freshwater fishes in South America have not yet been classified.

　　Scientists were startled in 1980 by the discovery of a huge diversity of insects in tropical forests. In one study of just 19 trees in Panama, 960 new species of beetles were discovered.

　　As scientists begin investigating other little-known ecosystems, like the soil and the deep sea, “surprising” discoveries of species become commonplace. There is nothing strange about this, though, since as many as a million undescribed species are believed to live in the deep sea. And one gram of a small-sized piece of land might hold 90 million bacteria and other microbes. How many species these communities contain is still anyone’s guess.