Official 47 Passage 3

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Coral Reefs

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Which of the following can be inferred from paragraph 3 about the Pacific atolls?

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  • A
    They were once fringing reefs around the coasts of islands.
  • B
    They were first observed by Darwin during his voyage on the Beagle.
  • C
    They will eventually become fringing reefs.
  • D
    They are located where the ocean floor does not sink.
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正确答案: A

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  • 译文
  • An important environment that is more or less totally restricted to the intertropical zone is the coral reef. Coral reefs are found where the ocean water temperature is not less than 21 °C, where there is a firm substratum, and where the seawater is not rendered too dark by excessive amounts of river-borne sediment. They will not grow in very deep water, so a platform within 30 to 40 meters of the surface is a necessary prerequisite for their development. Their physical structure is dominated by the skeletons of corals, which are carnivorous animals living off zooplankton. However, in addition to corals there are enormous quantities of algae, some calcareous, which help to build the reefs. The size of reefs is variable. Some atolls are very large-Kwajelein in the Marshall Islands of the South Pacific is 120 kilometers long and as much as 24 kilometers across-but most are very much smaller, and rise only a few meters above the water. The 2,000 kilometer complex of reefs known as the Great Barrier Reef, which forms a gigantic natural breakwater off the northeast coast of Australia, is by far the greatest coral structure on Earth.



    Coral reefs have fascinated scientists for almost 200 years, and some of the most pertinent observations of them were made in the 1830s by Charles Darwin on the voyage of the Beagle. He recognized that there were three major kinds: fringing reefs, barrier reefs, and atolls; and he saw that they were related to each other in a logical and gradational sequence. A fringing reef is one that lies close to the shore of some continent or island. Its surface forms an uneven and rather rough platform around the coast, about the level of low water, and its outer edge slopes downwards into the sea. Between the fringing reef and the land there is sometimes a small channel or lagoon. When the lagoon is wide and deep and the reef lies at some distance from the shore and rises from deep water it is called a barrier reef. An atoll is a reef in the form of a ring or horseshoe with a lagoon in the center.



    Darwin's theory was that the succession from one coral reef type to another could be achieved by the upward growth of coral from a sinking platform, and that there would be a progression from a fringing reef, through the barrier reef stage until, with the disappearance through subsidence (sinking) of the central island, only a reef-enclosed lagoon or atoll would survive. A long time after Darwin put forward this theory, some deep boreholes were drilled in the Pacific atolls in the 1950s. The drill holes passed through more than a thousand meters of coral before reaching the rock substratum of the ocean floor, and indicated that the coral had been growing upward for tens of millions of years as Earth's crust subsided at a rate of between 15 and 51 meters per million years. Darwin s theory was therefore proved basically correct. There are some submarine islands called guyots and seamounts, in which subsidence associated with sea-floor spreading has been too speedy for coral growth to keep up.



    Like mangrove swamps, coral reefs are extremely important habitats. Their diversity of coral genera is greatest in the warm waters of the Indian Ocean and the western Pacific. Indeed, they have been called the marine version of the tropical rain forest, rivaling their terrestrial counterparts in both richness of species and biological productivity. They also have significance because they provide coastal protection, opportunities for recreation, and are potential sources of substances like medicinal drugs. At present they are coming under a variety of threats, of which two of the most important are dredging and the effects of increased siltation brought about by accelerated erosion from neighboring land areas.


  • 或多或少完全局限于热带的重要环境是珊瑚礁。珊瑚礁在水温不低于21°C的海洋中被发现,那里有坚实的底层,并且海水中不不因为过量的河流沉积物而显得太暗。它们不会在深海里生长,所以一个有30到40米表面的地台是其发展的必要前提。它们的物理结构主要取决于珊瑚的骨骼,它们是以浮游动物为食的食肉动物。然而,除了珊瑚,还有大量的藻类帮助建立珊瑚礁(一些富含钙质的)。珊瑚礁的大小是多种多样的。一些环礁是非常巨大的一南太平洋的马绍尔群岛的Kwajelein有120公里长,24公里宽一^但大多数都是非常小的,而伸出水面才几米。被称为大堡礁2000千米的珊瑚礁群,是迄今为止最大的珊瑚结构之一,它在澳大利亚东北海岸形成一个巨大的天然堤。

    珊瑚礁吸引了科学家将近200年,其中最相关的一些观察是由查尔斯达尔文在1830年Beagle航行中完成的。他认为,主要有三种(珊瑚礁):岸礁、堡礁和环礁;他发现它们在一个逻辑等级序列上彼此相关。岸礁是一种靠近一些大陆或岛屿海岸的珊瑚礁。在海岸周围吗,它的表面形成了一个不平且粗糙的平台,差不多是低水位的高度,它的外边成坡向下进入大海。岸礁和土地之间有时有沟道道或环礁湖。当环礁湖又宽又深,并且暗礁离岸边有一些距离,并从从深水中升上来时,它被称为一个障碍礁。环礁是一个环形或马蹄形的礁,中间有一个环礁湖。

    达尔文的理论是:从一个珊瑚礁类型到另一个类型的演替,可通过沉台珊瑚向上增长实现,从岸礁开始有一个的进展过程,经过堡礁阶段,在中央岛下沉消失后,只有被暗礁包围的泻湖或珊瑚礁会生存下来。在达尔文提出这一理论很长时间以后,在上世纪50年代,太平洋环礁上进行了一些深钻孔。在到达海底的岩石层之前,钻孔穿过超过一千米的珊瑚,这证明了当地沉淀率在15~51米百万年时,珊瑚已经向上增长了数千万年。达尔文的理论基本上是正确的。有一些海底岛屿被称为海山,其中沉降与海底扩张的速度有关,那里的(沉降速度)太快了,已经不能让珊瑚保持增长。

    像红树林沼泽,珊瑚礁是非常重要的栖息地。们在印度洋和西太平洋的温暖水域中,珊瑚属的多样性是最大的。事实上,他们被称为热带雨林的海洋版,与它们陆地相对物在物种丰富度和生物生产力上相匹敌。它们同样有重要性,因为他们提供沿海保护、娱乐机会和潜在的物质来源(如药物)。目前它们正在各种各样的威胁下,其中最重要的两种是挖掘和由于附近海域加速侵蚀引起的增加的淤积。
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    解析

    题型分类:推理题

    题干分析:关键词:the Pacific atolls

    原文定位:定位:第三段第二句

    选项分析:

    根据定位句A long time after Darwinin the 1950s.”,但提供的信息有限,我们需要继续向下阅读,直至看到“Darwin s theory basically correct”,最终确定这之间的内容全部服务于对段落首句的支持,即达尔文关于珊瑚礁演化的理论。

    A选项说atoll曾经是fringing reef,符合理论内容

    B选项说这个理论最初发现于加尔号的航行,与原文表述不符(航行时发现的是珊瑚礁的三大分类);

    C选项说atoll最终形成fringing reef,与达尔文的理论内容相矛盾;

    D选项说atoll生长于不会下沉的海底,根据理论内容的说法,珊瑚礁的整个演替过程就是基于平台的不断下沉,因此不正确。


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