关于地球的资料用英语介绍六十词左右

The area of desert in the world is growing every year. Many parts of the world which once had large populations and produced plenty of crops, have become deserts. Dunhuang in China, deep in the heart of the Gebi Desert, was once a great city.

Cattle are one cause of the problem. In good years, famers increase the numbers of their cattle. Then one year, the rains fail to come. The farmers do not want to kill any of their cattle, so the cattle eat ail the grass and anything that grows on poorer land. If this continues for several years, the grass never grows again and the land becomes a desert. One suggested answer is for farmers to limit the numbers of their cattle.

Another problem is that good soil is gradually lost. When trees are cut down, there is nothing to hold the soil in place on the hillside. So when if rains, the soil is washed down the hills and into the rivers. Strong winds can also blow away the valuable soil that lies on the top of the fields.