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冰河时代--essay代写范文

2016-12-24 来源: 51Due教员组 类别: Essay范文


essay代写范文 这篇短文讲的是 冰河时代的故事 冰河时代是指时间大约在1600000年前,地球表面覆盖着冰层,在冰原撤退和气候开始变得温暖。巨大的冰川融化,导致海平面上升。冰盖的消融导致不列颠岛被创造。当冰融化、丘陵被席卷成为通向大海的新鲜冲积土壤沉积在英国南部海岸。土壤的形成是一个漫长的活动,这可能需要长达数千年来完成。同样地,土壤的形成在英国南部是一个时新的活动,在冰河时代后的土地上有机质日渐积累。

The Ice Age refers to a time around 1.6 million years ago when the there was significant cooling of the earth’s atmosphere, land and waters. The Earth’s surface was extensively covered with sheets of ice. End of the ice ages was a rather recent event, some 10, 000 years ago, when the Holocene climate changes set in, only did the sheets of ice withdraw and the climate began to get warmer. Huge glaciers melted which lead to a rise in sea levels. The melting ice caps produced the English Channel and the island of Great Britain was created. As the ice on hills melted and swept forwards towards the sea fresh alluvial soil was deposited on the southern coast of England.

Soil formation is a very long activity and is a result of various different processes, which can take up to thousands of years to get completed. Likewise, soil formation in Southern England was a recent activity, in the post Ice Age era the land was exposed to things like weathering and organic matter accumulation.

Weathering is a process in which bare land is exposed to atmospheric and thus effects of natural elements like wind and rain lead to disintegration of the rocks, soils and minerals. In the recent Holocene era when ice sheets melted away the soils of England became exposed to the atmosphere and therefore a major part of the soil formation was owing to the weathering of the soil. Southern England soils were formed mostly courtesy of what is known as freeze-thaw weathering. Freeze-thaw weathering occurs when temperatures fall below freezing point as did in the Ice Ages, due to high temperature water that has crept into cracks in rocks freezes and as it freezes it increases in volume this expansion in ice exerts pressure on the rock which causes them to shatter in small pieces. Once the temperature raises again the water flows spreading the tiny fragments of rock across the soil. Rocks in Southern England have rich mineral content and once they were deposited across the land it resulted in fertile, mineral-enriched soil across the area. Another form of weathering that took place would be Carbonation. Carbonation occurs in areas that have rocks containing calcium carbonate, as was in the case of Southern England where the rocks are pre-dominantly limestone and chalk. Due to continuous rain in England the rainwater combined with carbon dioxide in the air to form a minor carbonic acid, which in a reaction with the calcium carbonate resulted in calcium bicarbonate in the soil

Another effect on soil formation is that of transportation and deposition. Transportation as the name suggests is when some matter is transported from one place to another. In this case the matter that travels is the soil and all sorts of weathered material on the land. Elements like wind, water and gravity take things from one place to another. As matter travels it usually gets deposited in other places, this is known as deposition. Transportation can be bad as it causes the soil to erode but as material is deposited in places too it is not entirely a bad thing. Similarly when the ice sheets melted and water rushed southwards into the sea, fragment of rocks and minerals got distributed to different parts of the Southern England. Before entering the sea the water slows down so, therefore, rich alluvium was deposited specifically around the south coast of England and its surrounding areas. As the Ice Ages melted away there was an increase in human activity as well as animal settlement on the land.

Animal settlement resulted in yet another form of transportation and deposition, which was through animal waste. Animals consume a lot of rich nutrients in their diet as the eat different plants, fruits and even living organisms which means that animal waste is very fertile, thus dung deposits all over the area made an important contribution to soil formation in the country.

Animals and plants not only contribute to soil formation through transportation and deposition but also through what are called Organic matter accumulations and decomposition. As living organisms die their bodies start to reduce this process is called decomposition. Decomposition is a fairly long process. When animals and plants start to decompose in large bunches the process is known as humification and the resultant substance is known as humus. Humus is a necessity for soil fertility. It has active sites that bind to ions of plant nutrients and it also helps soil retain its moisture. During the Holocene era organic matter accumulation was a source that effected soil formation eminently. Due to extraordinarily cold temperature and prevailing ice many living organisms dead and alive got buried in the ground. Between the beginning of Pleistocene era over a million years ago and the Holocene era some ten thousand year back large amounts of humus were formed under and between the endless layers of ice and snow. The humus then with the melting of the snow and ice too was deposited all over the area and specially in southern parts of the country as the waters drained out towards south and before reaching the sea it slowed down naturally which resulted in a lot of fertile humus being deposited in the areas surrounding the southern coast of England.

In the glaciations days of the Pleistocene eon the ground was too frozen to absorb water and the water above the ground was all ice and snow and too solid to immerse into the ground but once Holocene struck the ground thawed, ice melted and water flowed into the pores in the ground this lead to a rise in the water table of ground water which meant that the level of water under the ground rose to a very high level. This situation is called water logging. Water logging can be damaging for some plantations but waterlogged soils are usually good for the purpose of rice farmingWater logging especially did not become too much of a problem for the soil in Southern England due to the process of natural drainage and aeration. A drainage system refers to network of watercourses that is used to carry off excess water. A natural drainage system is one that consists of cracks and fissures in the ground, which were already in the ground before any human intervention. Even before man-made the fast flowing water had scarred the land and the ground already had cracks through which excess water flowed out and the soil retained just enough water to keep it moist and, therefore, the soil in Southern England is primarily clay. As there are frequent rainfalls in England the soil till today manages to retain enough water to stay in clay form.

In conclusion, the climatic changes in the past million years from the historic Ice Ages to the relatively recent Holocene era have brought about processes like weathering, transportation and deposition, organic matter accumulation, water logging and drainage and aeration, the aggregated effects of which has resulted in rich fertile soil being formed in Southern England starting from dark greyish brown, heavy clay loam on the top layer to a brown heavy clay into the earth and finally lighter greyish brown clay deeper into the surface of the earth.

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