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  3. HOW SOIL IS FORMED (1) Soil formation is a dynamic process that takes place in different environments. It is strongly influe

HOW SOIL IS FORMED (1) Soil formation is a dynamic process that takes place in different environments. It is strongly influe

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问题                                                 HOW SOIL IS FORMED
    (1) Soil formation is a dynamic process that takes place in different environments. It is strongly influenced by the parent material, climate (largely vegetation and temperature and water exchanges), topography (the elevations, depressions, directions and angles of slopes, and other surface features of the landscape), and time.
    (2) The parent material is the unconsolidated mass on which soil formation takes place. This material may or may not be derived from the on-site geological substrate or bedrock on which it rests. Parent materials can be transported by wind, water, glaciers, and gravity and deposited on top of bedrock. Because of the diversity of materials involved, soils derived from transported parent materials are commonly more fertile than soils from parent materials derived in place. Whatever the parent material, whether derived in place from bedrock or from transported materials, it ultimately comes from geological materials, such as igneous, sedimentary, and metamorphic rocks, and the composition of the rocks largely determines the chemical composition of the soil.
    (3) Climate is most influential in determining the nature and intensity of weathering and the type of vegetation that further affects soil formation. The soil material experiences daily and seasonal variations in heating and cooling. Open surfaces exposed to thermal radiation undergo the greatest daily fluctuations in heating and cooling, soils covered with vegetation the least. Hill slopes facing the sun absorb more heat than those facing away from the sun. Radiant energy has a pronounced effect on the moisture regime, especially the evaporative process and dryness. Temperature can stimulate or inhibit biogeochemical reactions in soil material.
    (4) Water is involved in all biogeochemical reactions in the soil because it is the carrier of the acids that influence the weathering process. Water enters the soil material as a liquid and leaves it as a liquid by percolation (the slow movement of water through the soil’s pores) and as a gas through evaporation. The water regime—the water flow over a given time—in soil material is sporadic, and in many parts of the Earth is highly seasonal. Water that enters the soil during heavy rainfall and snow melt moves down through the soil. As it moves, it leaves behind suspended material and may carry away mineral matter in solution, a process called leaching. On sloping land, water distributes materials laterally (sideways) through the soil.
    (5) Topography is a major factor in soil development. [A] More water runs off and less enters the soil on steep slopes than on relatively level land. [B] Water draining from slopes enters the soil on low and flat land. [C] Thus soils and soil material tend to be dry on slopes and moist and wet on the low land. [D] Steep slopes are subject to surface erosion and soil creep—the down slope movement of soil material, which accumulates on lower slopes and lowlands.
    (6) Vegetation, animals, bacteria, and fungi all contribute to the formation of soil. Vegetation, in particular, is responsible for organic material in the soil and influences its nutrient content. For example, forests store most of their organic matter on the surface, whereas in grasslands most of the organic matter added to the soil comes from the deep fibrous root systems. Organic acids produced by vegetation accelerate the weathering process.
    (7) The weathering of rock material and the accumulation, decomposition, and mineralization of organic material require considerable time. Well-developed soils in equilibrium with weathering, erosion, and biotic influences may require 2,000 to 20,000 years for their formation, but soil differentiation from parent material may take place in as short a time as 30 years. Certain acid soils in humid regions develop in 2,000 years because the leaching process is speeded by acidic materials. Parent materials heavy in texture require a much longer time to develop into soils because of an impeded downward flow of water. Soils develop more slowly in dry regions than in humid ones. Soils on steep slopes often remain poorly developed regardless of geological age because rapid erosion removes soil nearly as fast as it is formed. Floodplain soils age little through time because of the continuous accumulation of new materials. Such soils are not deeply weathered and are more fertile than geologically old soils because they have not been exposed to the leaching process as long. The latter soils tend to be infertile because of long-time leaching of nutrients without replacement from fresh material.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
选项 A、Transported parent materials, parent materials derived in place from bedrock, and various kinds of rocks all contribute to the composition of a soil.
B、The chemical composition of a soil is ultimately determined by the geological materials from which it forms, regardless of where or how the parent material originates.
C、The parent material from which a soil is formed ultimately conies from igneous, sedimentary, and metamorphic rocks.
D、The composition of the geological materials from which the parent material was originally derived can be determined by studying the chemical composition of the soil.
答案B
解析 本题考查对文中高亮句子的理解和同义转述，属于句子简化题。解题关键在于找出本句主干，即it ultimately comes from geological materials, such as igneous, sedimentary, and metamorphic rocks, and the composition of the rocks largely determines the chemical composition of the soil，意为“它(母质)最终还是来源于地质材料，而岩石(地质材料)的成分在很大程度上决定土壤的化学成分”。与此意思最为相符的是B项“无论母质来源于何处或者如何起源，土壤的化学成分最终取决于形成土壤的地质材料”。A项“被搬运的母质，以及从基岩衍生的母质和各式岩石材料都有助于土壤形成”的主干结构是“母质和岩石材料利于土壤形成”，与原文句子想要表达的意思不符。C项“形成土壤的母质最终来自火成岩、沉积岩和变质岩”，原文说的是母质最终来源于地质材料，比如这三种岩石，而未限定为这三种岩石，C项不能完全转述高亮句子含义。D项“母质来源的地质材料成分可以通过研究土壤的化学成分来确定”，该句可理解为对高亮句中“岩石的成分在很大程度上决定了土壤的化学成分”这一信息的推理，但未能表达高亮句的意思。
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