Official 37 Set 2

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
置顶

Soil Formation

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
What is the lecture mainly about?
  • A. The differences between mineralization and weathering

  • B. Processes that remove minerals from soil

  • C. Factors affecting the fertility of soil

  • D. Several processes involved in the creation of soil

显示答案 正确答案: D

我的笔记 编辑笔记

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    NARRATOR:Listen to part of a lecture in a geology class.

    MALE PROFESSOR:So we all know soil. It's important to plant growth, right?And we know that there're different types of soil in different places, and that some soils are more fertile than others.But what is soil and how is it formed?Well, we're going to go into this in some depth but for now let's just lay down the basics.Soil is composed of two kinds of material: inorganic material- basically, small pieces of rock-and organic material, which is animal and plant matter.OK, so what do you think?If I mix bits of rock with composted vegetables, will I get soil?The answer is no, because the formation of soil is a dynamic process.It involves not only the initial inputs the raw materials, but also the transformation of those materials and the movement of some of the materials and the loss of others.

    So the inputs are bits of rock and organic matter.Now, the bits of rock the inorganic input to soil, uh, they come from the breakdown of rocks on Earth's surface through a process called weathering.

    Weathering can be either physical or chemical.Physical weathering- uh, that's when exposure to the elements over time causes a rock to break up and eventually disintegrate.Um ...of course, some rocks are more resistant to physical weathering than others.If you think of the sand particles in soil- those are the result of physical weathering,and they have the same chemical composition as the original rock.Now, chemical weathering ... uh, that's the chemical breakup of rocks.It differs from physical weathering in that the chemical properties of the minerals are actually changed.The clay minerals you find in soil are the result of chemical weathering.Clay minerals are called secondary minerals because their composition has been altered.

    OK, so we have weathered rock, which needs to be combined with organic matter.So what does the organic input consist of?It's the remains of plants and animals-but mostly plants.Now, just as rocks are broken down by weathering, the animal and plant residues are broken down too.They're reduced to simple chemicals by microorganisms in a process called mineralization.

    And just as some rocks are more resistant than others to weathering, the compounds found in the soil's organic input resist mineralization at different rates.The compound cellulose is the major constituent of most plant tissue- it mineralizes relatively quickly.But there're woody substances in certain plants that strengthen the cell walls.They're found in smaller concentrations and their mineralization can take several years.

    Weathering and mineralization transform the inorganic and organic inputs in a number of ways.And it's partly from these transformations that soil gets its unique properties.How does it work? Uh, take the dark brown color of soil.After microorganisms have broken down the cellulose, we're left with two things: the microbes' waste and the more resistant plant material that microorganisms can't break down easily.These materials ultimately get transformed into a new material called humus.

    And when humus is combined with the clay minerals in soil, that's what gives soil its dark brown color.So now, if we've got clay and humus, these transformed materials, and we mix them together,we've got something very close to soil.But soil isn't static, and there're still other processes that go into the formation of soil-the movement and loss of materials.

    The soil in any location isn't a uniform mixture- its composition varies with depth.You see, mineral and organic materials move through soil vertically- some materials move more easily than others.Water carries the more mobile materials from the upper level of the soil to the lower levels.So the upper levels of the soil eventually get depleted of these materials, while the lower levels get enriched with them.And that creates distinct layers of soil, as far down as the rock underlying the soil.And the materials that dissolve easily in water can get lost completely if the water carries them horizontally out of the soil and into rivers.Now, of course, new mineral and organic material will be deposited at the surface and become incorporated into the soil,but you see how the processes of movement and loss contribute to the formation of soil.

  • 旁白:请听一段地质学讲座的节选片段。

    教授:所以呢,我们都认识土壤。土壤对于植物生长很重要,对吗?我们还知道,在不同地方有不同种类的土壤,一些土壤比另一些土壤更加肥沃。但是土壤到底是什么呢?土壤是怎么形成的呢?我们马上要来深度探讨这个问题,但是现在我们先要看一看一些基础的问题。土壤是由两种东西构成的:无机物质,基本上是小的岩石颗粒,还有有机物质,就是动物和植物的物质。好的。所以你们觉得呢?如果我把堆肥的植物和岩石混合起来,我能得到土壤吗?答案是不能,因为土壤的形成是一个动态的过程。它不仅包括原材料的初始投入,还包括这些材料的转化和一些材料的移动以及其他材料的损失。

    所以投入的是岩石和有机物。现在,岩石碎片是土壤的无机输入,它们来自地球表面岩石的分解,通过一个叫做风化的过程。

    风化作用既可以是物理的,也可以是化学的。物理风化作用,嗯……就是岩石长时间暴露在风雨之中,导致其分裂最终彻底分解。嗯……当然了,一些岩石比另一些岩石更能抗风化作用。如果你想到土壤里的沙粒,它们就是物理风化作用的结果,它们和原来的岩石的化学成分是一样的。现在说说化学风化作用,嗯……就是岩石的化学分解。这个过程和物理风化作用不一样,因为化学风化作用使得矿石的化学成分发生了改变。我们在土壤里发现的黏土矿物质就是化学风化作用的结果。黏土矿物质被称为次生矿物,因为它的成分发生了改变。

    好的。所以我们有风化的岩石,风化的岩石需要和有机物来结合(以形成土壤)。所以有机物的输入都是由什么构成的呢?那就是动植物的尸体,但是主要还是植物的尸体。就像岩石会在风化作用中分解一样,动植物的尸体也会分解。它们被微生物分解成简单的化学物质,这个过程叫做矿化。

    就像一些岩石比另一些岩石更加不容易被风化一样,土壤的有机物输入里的不同的有机物的矿化速率不同。纤维素化合物是大多数植物组织的主要成分。它矿化地非常快。但是在某些植物里有木质的物质,这种物质可以加强细胞壁。它们的浓度更低,矿化可以花费好几年。

    风化和矿化在多年间逐渐转化着土壤的无机物和有机物输入。部分由于这些转化过程,土壤获得了它独特的特性。所以它是怎么工作的呢?嗯……举棕黑色土壤作为例子。在微生物分解完纤维素之后,我们可以得到两种东西:细菌的垃圾和更加难以腐蚀的植物组织,这些组织更难被微生物分解。这些材料最终会被转化成一种新的叫做腐殖质的物质。

    当腐殖质和土壤中的黏土矿物质结合,这就使得土壤变成了棕黑色。所以,如果我们有了黏土和腐殖质,这些已经经过了转化的材料,我们把它们混合到一起,就可以得到一种类似于土壤的东西。但是土壤不是一成不变的,还有其他的过程会融入土壤的形成:物质的流动和流失。

    任何地点的土壤都不是一个统一的混合物,它的组成随着深度的不同而不同。你看,矿物质的和有机物的材料可以在土壤内部垂直地移动,一些物质比另一些物质移动更慢。水流将更多的移动物质从土壤的上层带入到了下层的土壤。所以高层的土壤最终流失掉了这些物质,低层的土壤则储存了更多的这些物质。这就创造了不同的土壤层,土壤一直分层到最底部的岩石。如果水流将它们水平地从土壤中冲到河里,容易溶解在水中的物质则会完全流失掉。当然了,在土壤表面会继续沉积新的矿物质和有机物,这些物质被吸收进土壤,这样我们就明白了土壤物质的移动和流失过程是如何影响土壤形成的。

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    题型分析:主旨题

    原文定位:

    So we all know soil. It’s important to plant growth, right? And we know that there’re different types of soil in different places, and that some soils are more fertile than others. But what is soil and how is it formed? Well, we’re going to go into this in some depth but for now let’s just lay down the basics.

    选项分析:

    原文开头教授引出今天讲座主旨,即分析土壤的成分和形成,且后文讲解了土壤的形成,与选项D一致,故选项D正确。

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