Isn’t it surprising that scientists have a better understanding of how many stars there are in the galaxy (银河系) 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 l0 million and yet only 1.75 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(哺乳动物). 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 started in 1980 by the discovery of a huge diversity of insects in tropical forests. In one study of just 19 trees in Panama, 950 new species of beetles were discovered.
As scientists begin investigating other little-known ecosystem, 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(菌类) and other microbes (微生物). How many species these communities contain is still anyone’s guess.
What can you learn from the passage