文勇的新托福黄金&ccedil

isthebestanswerbecauseitistheonlydetailabouttheskelet

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在 1989 在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在 Basilosaurus 在在在在在在在在在在在在在在在在在在在在在在在 Basilosaurus 在在在在在 4000 在在在在在 Pakicifus 在在在在 1200 在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在 在在在在在在在在在在在在在在在在在在在在在在在在在在在在在 50 在在在在 Basilosaurus 在在在在在在在在在Basilosaurus 在在在在在在在在在在在在 在在在在在在在在在在在在在在在在在在在在 1994 在在在在在在在在在在在在在在在在在在在在在在在在在在在在在 Ambulocetus natans在在在在在在在在在4900 在在在在在在在在在在在在在在 Pakicetus 在在在 300 在在在在 Basilosaurus 在 900 在在在在在在在在在在在在在在 Ambulocetus natans 在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在 Ambulocetus natans 在在在在在在在在 在在在在在在在在在在在在在在在在在在在在在在——在在在在在在在 Ambulocetus 在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在 在 Ambulocetus 在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在在 19 Mail@liuwenyong.com 在在在在在在 www.liuwenyong.com 在在在在在在在在在在在在在在在,在在在在在在在在在在 DESERT FORMATION 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 exist is called desertification. It has been estimated that an additional one­fourth of the Earth's land surface is threatened by this process. Desertification is accomplished primarily through the loss of stabilizing natural vegetation and the subsequent accelerated erosion of the soil by wind and water. In some cases the loose soil is blown completely away, leaving a stony surface. In other cases, the finer particles may be removed, while the sand­sized particles are accumulated to form mobile hills or ridges of sand. 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 on the loose soil tends to transfer fine clay particles into the tiniest soil spaces, sealing them and producing a surface that allows very little water...
View Full Document

This note was uploaded on 09/17/2013 for the course LANGUAGE 13DL208 taught by Professor Wang during the Fall '13 term at East China Normal University.

Ask a homework question - tutors are online