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The deserts, which already occupy approximately a fourth of the Earth's land surface, have in recent decades been increasing at an alarming pace.--沙漠已经占据了地球表面积约四分之一,而且最近几十年正以惊人的速度扩张。
The expansion of desertlike conditions into areas where they did not previously exist is called desertification. It has been estimated that an additional one-fourth of the Earth's land surface is threatened by this process.--沙漠化是指类似沙漠的环境漫延到原本并非沙漠的区域。据估计,地球表面另外四分之一的地方正面临沙漠化威胁。
Desertification is accomplished primarily through the loss of stabilizing natural vegetation and the subsequent accelerated erosion of the soil by wind and water.--沙漠化主要通过以下过程实现:首先自然植被不断减少,随后风力和雨水加速了土壤的腐蚀。
In some cases the loose soil is blown completely away, leaving a stony surface.--有的时候松散的土壤全部被风刮走,留下石质化的表层;
In other cases, the finer particles may be removed, while the sand-sized particles are accumulated to form mobile hills or ridges of sand.--其它情况下细小的沙粒可能会被吹走,而正常沙粒大小的砂子不断堆积,从而形成移动的沙丘或者沙脊。