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   托福閱讀真題 Desert formation (5)

  Paragraph 1: The deserts, which already occupy approximately a fourth of the Earth’s land surface, have in recent decades been increasing at an alarming pace. The expansion of desertlike conditions into areas where they did not previously exists is called desertification. It has been estimated that an additional one-Fourth of the Earth’s land surface is threatened by this process.

  Paragraph 3: Even in the areas that retain a soil cover, the reduction of vegetation typically results in the loss of the soil’s ability to absorb substantial quantities of water. The impact of raindrops in the loose soil tends to transfer fine clay particles into the tiniest soil spaces, sealing them and producing a surface that allow very little water rates. The gradual drying of the soil caused by its diminished ability to absorb water results in the further loss of vegetation, so that cycle of progressive surface deterioration is established.