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草莓小菇凉:说的非常好,十分有道理,棒棒棒!

06-08 15:44:55

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OG真题练习-Geology and Landscape

Geology and Landscape

Most people consider the landscape to be unchanging, but Earth is a dynamic body, and its surface is continually altering-slowly on the human time scale, but relatively rapidly when compared to the great age of Earth (about 4,500 billion years). There are two principal influences that shape the terrain: constructive processes such as uplift, which create new landscape features, and destructive forces such as erosion, which gradually wear away exposed landforms.

Hills and mountains are often regarded as the epitome of permanence, successfully resisting the destructive forces of nature, but in fact they tend to be relatively short-lived in geological terms. As a general rule, the higher a mountain is, the more recently it was formed; for example, the high mountains of the Himalayas are only about 50 million years old. Lower mountains tend to be older, and are often the eroded relics of much higher mountain chains. About 400 million years ago, when the present-day continents of North America and Europe were joined, the Caledonian mountain chain was the same size as the modern Himalayas. Today, however, the relics of the Caledonian orogeny (mountain-building period) exist as the comparatively low mountains of Greenland, the northern Appalachians in the United States, the Scottish Highlands, and the Norwegian coastal plateau.

The Earth's crust is thought to be divided into huge, movable segments, called plates, which float on a soft plastic layer of rock. Some mountains were formed as a result of these plates crashing into each other and forcing up the rock at the plate margins. In this process, sedimentary rocks that originally formed on the seabed may be folded upwards to altitudes of more than 26,000 feet. Other mountains may be raised by earthquakes, which fracture the Earth's crust and can displace enough rock to produce block mountains. A third type of mountain may be formed as a result of volcanic activity which occurs in regions of active fold mountain belts, such as in the Cascade Range of western North America. The Cascades are made up of lavas and volcanic materials. Many of the peaks are extinct volcanoes.

Whatever the reason for mountain formation, as soon as land rises above sea level it is subjected to destructive forces. The exposed rocks are attacked by the various weather processes and gradually broken down into fragments, which are then carried away and later deposited as sediments. Thus, any landscape represents only a temporary stage in the continuous battle between the forces of uplift and those of erosion.

The weather, in its many forms, is the main agent of erosion. Rain washes away loose soil and penetrates cracks in the rocks. Carbon dioxide in the air reacts with the rainwater, forming a weak acid (carbonic acid) that may chemically attack the rocks. The rain seeps underground and the water may reappear later as springs. These springs are the sources of streams and rivers, which cut through the rocks and carry away debris from the mountains to the lowlands.

Under very cold conditions, rocks can be shattered by ice and frost. Glaciers may form in permanently cold areas, and these slowly moving masses of ice cut out valleys, carrying with them huge quantities of eroded rock debris. In dry areas the wind is the principal agent of erosion. It carries fine particles of sand, which bombard exposed rock surfaces, thereby wearing them into yet more sand. Even living things contribute to the formation of landscapes. Tree roots force their way into cracks in rocks and, in so doing, speed their splitting. In contrast, the roots of grasses and other small plants may help to hold loose soil fragments together, thereby helping to prevent erosion by the wind.

大部分人认为自然风景是一成不变的,事实上地球是一个动态的机体,他的外貌在人类文明进程中一直保持着持续缓慢的变化。当然,与大约4万5千亿年前的冰河时代的地貌变化相比,这个进程的确快了很多。主要有两种影响会改变地形:建设性的过程,如产生新的地表特征的地壳隆起;和破坏性的力量,如缓慢清除突出地貌的地表侵蚀。

山峰和山脉因为能够经受得住自然的洗礼,通常被认作是永恒的代名词,但地质学的角度上来说,他们的存在实际上从是相对比较短暂的。一般来说,山峰越高,形成得越晚。例如喜马拉雅山,她只有5000万年的历史。低矮山峦的历史往往更加久远,它们通常是高耸的山脉崩塌后的遗留物。在大约4亿年前,当今天的北美和欧洲大陆相结合的时候,加勒多尼亚山脉与现今的喜马拉雅山脉同样雄伟,但是,加勒多尼亚山脉的形成(造山运动)在今天遗留下来的却只是相对非常低矮的格林兰山脉:美国的北阿巴拉契亚山区,苏格兰高地和挪威海岸高原。

地壳分裂成为巨大可移动的板块,板块在柔软的岩石可塑层中漂移。有的时候,这些板块互相冲击并迫使板块边缘的岩石突起,从而形成山脉。在这个过程中,原本形成在海床上的沉积岩可能被拱起高达26,000多英尺。在另一种情况下,地震将地壳震裂。产生的岩石堆积形成断块山,从而形成山脉。还有一种情况,活火山带的火山运动也会促使山脉的形成,例如北美洲西部的喀斯喀特山脉,他的产生就是由火山岩和火山灰形成的,上面的许多山峰都是死火山。

不论山脉形成的具体原因是什么,一旦陆地高出海平面,都难逃脱被外力摧毁的厄运。裸露的岩石遭受着不断变化天气的攻击,逐渐被碾成碎石块带走,然后形成沉积岩。因此,任何地貌都只是一个短暂的阶段,它所代表的是造山与侵蚀两种力量持续斗争。

多种多样的天气加速了大自然对地貌的侵蚀。雨水冲刷了疏松的土壤并渗入到岩石的缝隙。二氧化碳在空气中与雨水相互作用形成了可以对岩石进行化学腐蚀的弱酸(碳酸)。雨水渗透到地下并能在不久后以泉水的形式流出,那些从岩石间穿过并将碎石从高山带到平原的溪水就是来源于这些泉水。

在严寒的环境下,岩石能被冰霜粉碎。冰川在长期寒冷的区域形成,这些缓慢移动的大量冰块带着大量的腐蚀岩屑阻断了山谷。在干旱地带,风是大自然侵蚀的主要手段。它带着沙子中的微粒冲击着裸露的岩石表面,把岩石吹散成更多的沙粒。动植物们对自然风景的形成也是功不可没,大树植根于岩缝之中,加速了岩石的碎裂。相比之下,草根和其他矮小植物则利于固定土壤,弱化了风蚀作用的影响。

中文翻译

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.

  • A.When they are relatively young, hills and mountains successfully resist the destructive forces of nature. B.Although they seem permanent, hills and mountains exist for a relatively short period of geological time. C.Hills and mountains successfully resist the destructive forces of nature, but only for a short time. D.Hills and mountains resist the destructive forces of nature better than other types of landforms. Hills and mountains are often regarded as the epitome of permanence, successfully resisting the destructive forces of nature, but in fact they tend to be relatively short-lived in geological terms.
正确答案: B

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