托福 托福 27 - The Formation of Volcanic Islands
题目
1 2 3 4 5 6 7 8 9 10 11 12 13 14
4.The word “instructive” in the passage is closest in meaning to
  • A.clear
  • B.detailed
  • C.informative
  • D.familiar
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    阅读原文 中文译文

    Earth’s surface is not made up of a single sheet of rock that forms a crust but rather a number of “tectonic plates” that fit closely, like the pieces of a giant jigsaw puzzle. Some plates carry islands or continents others form the seafloor. All are slowly moving because the plates float on a denser semi-liquid mantle, the layer between the crust and Earth’s core. The plates have edges that are spreading ridges (where two plates are moving apart and new seafloor is being created), subduction zones (where two plates collide and one plunges beneath the other), or transform faults (where two plates neither converge nor diverge but merely move past one another). It is at the boundaries between plates that most of Earth’s volcanism and earthquake activity occur.

    Generally speaking, the interiors of plates are geologically uneventful. However, there are exceptions. A glance at a map of the Pacific Ocean reveals that there are many islands far out at sea that are actually volcanoes----many no longer active, some overgrown with coral----that originated from activity at points in the interior of the Pacific Plate that forms the Pacific seafloor.

    How can volcanic activity occur so far from a plate boundary? The Hawaiian Islands provide a very instructive answer.Like many other island groups, they form a chain. The Hawaiian Islands Chain extends northwest from the island of Hawaii. In the 1840s American geologist James Daly observed that the different Hawaii islands seem to share a similar geologic evolution but are progressively more eroded, and therefore probable older, toward the northwest. Then in 1963, in the early days of the development of the theory of plate tectonics. Canadian geophysicist Tuzo Wilson realized that this age progression could result if the islands were formed on a surface plate moving over a fixed volcanic source in the interior. Wilson suggested that the long chain of volcanoes stretching northwest from Hawaii is simply the surface expression of a long-lived volcanic source located beneath the tectonic plate in the mantle. Today’s most northwest island would have been the first to form. They as the plate moved slowly northwest, new volcanic islands would have forms as the plate moved over the volcanic source. The most recent island, Hawaii, would be at the end of the chain and is now over the volcanic source.

    Although this idea was not immediately accepted, the dating of lavas in the Hawaii (and other) chains showed that their ages increase away from the presently active volcano, just as Daly had suggested. Wilson’s analysis of these data is now a central part of plate tectonics. Most volcanoes that occur in the interiors of plates are believed to be produced by mantle plumes, columns of molten rock that rise from deep within the mantle. A volcano remains an active “hot spot” as long as it is over the plume. The plumes apparently originate at great depths, perhaps as deep as the boundary between the core and the mantle, and many have been active for a very long time. The oldest volcanoes in the Hawaii hot-spot trail have ages close to 80 million years. Other islands, including Tahiti and Easter Islands in the pacific, Reunion and Mauritius in the India Ocean, and indeed most of the large islands in the world’s oceans, owe their existence to mantle plumes.

    The oceanic volcanic islands and their hot-spot trails are thus especially useful for geologist because they record the past locations of the plate over a fixed source. They therefore permit the reconstruction of the process of seafloor spreading, and consequently of the geography of continents and of ocean basins in the past. For example, given the current position of the Pacific Plate, Hawaii is above the Pacific Ocean hot spot. So the position of The Pacific Plate 50 million years ago can be determined by moving it such that a 50-million-year-old volcano in the hot-spot trail sits at the location of Hawaii today. However because the ocean basins really are short-lived features on geologic times scale, reconstruction the world’s geography by backtracking along the hot-spot trail works only for the last 5 percent or so of geologic time.

    地球的外壳并不是由单块岩石形成的,而是许多的“构造板块”严密的组合在一起的,就像是一个巨大的拼图。一些板块承载着岛屿或是大陆,其它的则形成海底。所有板块都在缓慢移动,因为它们都漂浮在密度更大的半液态的介于地壳和地核之间的地幔上。板块的边缘是扩张脊(两个板块分离,新的海底形成的地方),俯冲带(两板块碰撞,一个倾入到另一个下面),或者是形成断层(两板块既不聚集也不分散,但只是互相错位)。板块边界是地球上的火山和地震的高发地。 一般地,板块内部在地质上是平静的,但也有例外。扫一眼太平洋的地图就知道那里有许多在大海深处的岛屿,它们其实都是火山,其中有许多已经不活动了,一些长满了珊瑚。这些火山都起源于当时太平洋板块内部一些部位在形成太平洋海底时的地质活动。 为什么火山活动发生在离板块边缘这么远的地方呢?夏威夷群岛提供了一个非常有启发性的答案。就像其它的群岛一样,它们形成了一个岛链。夏威夷群岛链从夏威夷岛向西北扩张。在十八世纪40年代,地质学家James Daly观察到不同的夏威夷岛屿看起来经历了相似的演变过程,但它们所受腐蚀一个比一个严重,所以越往西北方向的岛屿形成时间可能越早。1963年,在大陆板块理论的早期,加拿大的地质学家Tuzo Wilson意识到岛屿年龄的增加可能是因为这些岛屿是板块表面从一个板块内部的固定火山源上方移动的结果。Wilson解释说,夏威夷向西北延伸的火山长链只是一个长期存于板块下、地幔中的火山源在板块表面的表现。现今最靠西北的岛屿可能是最先形成的。它们随着板块向西北移动。新的火山会随着板块的移动在火山源处形成。最年轻的岛屿,夏威夷岛,应该是在岛链的末端,现在应该在火山源上。 虽然这个理论并没有被很快接受,夏威夷和其它群岛岩浆的年龄测试表明了它们的年龄都从活跃的火山开始依次增加,正如Daly所说。Wilson对数据的分析已经成为了板块构造论的核心部分。大多的发生在板块内部的火山爆发都是由地幔柱造成的;地幔柱是从地幔深处涌出的熔岩柱体。只要火山在一个地幔柱上面,它就是一个活动的“热点”。地幔柱很显然是起源于很深的地方,很可能位于地核和地幔的交界处,并且已经活跃了很久。由夏威夷热点形成的最老的火山已经有近8千万年的时间了。其它的岛屿,包括太平洋的塔希提岛和东部群岛,印度洋留尼汪岛和毛里求斯群岛,实际上,多数世界上大洋中大岛都是由地幔柱的扩展形成的。 海洋火山岛和它们的热点轨迹对于地质学家尤其有用,因为它们记录了过去的板块在固定火山源上方的位置。他们因此可以重现海底扩张的过程,以及大陆和大洋盆地过去的地理位置发展过程。比如,根据太平洋板块现在的位置,夏威夷岛在太平洋热点上面。所以太平洋板块5千万年前的位置可以通过移动太平洋板块使得一座有5五千万年历史的岛屿位于夏威夷岛现在所在的热点上以获得。但是,由于海洋盆地在地质年代上是相对短命的,用热点追踪的方法重建世界的地形只适用于最近的百分之五左右的地质时间。

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    最新提问
    • wx_6697
      觉得B C 意思一样,不知道选哪个
    • wx_5576
      这道题C为什么对,E为什么不对?
    • wx_5576
      B为什么不能选啊?
    • wx_6697
      TPO30 passage 2 Q5我选的 D,不明白为啥不对?
    • wx_6697
      鑫哥,TPO6passage3Q5 答案是给错了吗?好多人都选A
    • wx_6697
      这题也很容易选错选成了D
    • wx_6697
      这道题A为什么错了
    • 芊儿
      为什么这道题不选c??a中的variety不是应该对应文中的differentiating 吗??求解!
    • wx_1000
      这道题不选E是因为太细节了吗
    • 王金阁
      这个题为什么不选C啊。。。
    • 芊儿
      这道题的D选项不是和文中的better able to reproduce in open settings相对应么??
    • 风荨火
      有大佬解释一下这个为啥选D嘛?
    • 以沫
      请问这个D 在哪里提现?为什么D错?
    • 芊儿
      第六题 的C选择为什么不对,感觉A是明显驳斥啊...
    • wx_6697
      鑫哥,这道题D是从哪里看出来的
    • wx_6697
      这题选的A,根据是Joly’s calculations clearly supported those geologists who insisted on an age for Earth far in excess of a few million years.想问鑫哥为啥不选A
    • wx_6697
      这题我选的是C依据是into a new habitat outside of its natural range, it may adapt to the new environment and leave its enemies behind.C为啥错了呢?鑫哥
    • wx_8861
      F选项的weather-related destruction在哪里体现了呢?原文最后一段的开头Among the costs里的costs是不是打错了?应该是coast?
    • wx_6697
      求问这道题B为啥不选,原文依据:viable seeds of pioneer species can be found in large numbers on some forest floors.
    • 与托福的斗争史
      与托福的斗争史 去解答 去解答
      这题为什么选C?
    • 小雨淅沥哗啦的下
      小雨淅沥哗啦的下 去解答 去解答
      B哪里错了
    • 小雨淅沥哗啦的下
      小雨淅沥哗啦的下 去解答 去解答
      B为啥不对
    • 李浩然
      B选项错误,是因为残缺么?
    • wx_100
      请问在做题的时候如何排除c呢。看了答案,感觉是该选a的,但是当时做题脑子一热,就特别钟爱c,也没看其他选项。。求敲醒。。
    • wx xxxxx
      请问鑫哥,这段开头有写As one pesticide replaces another为什么不是对应a new pesticide is developed?
    • wx_7695
      鑫哥,从哪里看出来这个masks 不是use呀,原文说了wear呀
    • haiyuqiao
      @鑫哥,这题the damage will continue 不应该对应前面的 the target species evolves resistance to it,然后As one pesticide replaces another,不应该是结束了time cycle 吗
    • wx_2065
      鑫哥,想知道E错在哪里?
    • wx_7695
      鑫哥,B选项 cannot extended to earlier geological periods. 原文说的意思是后来的进化无法估计吧
    • wx_2163
      B为什么不选
    • wx_7780
      鑫哥,这个哪里看不use了。BD是修饰错,C是无中生有,怎么能直接选出A?
    • 100
      看到第一句话,以为是中心句就选了A... 为什么不能选A呢
    • 100
      为什么选b?
    • gu33
      请问下 这里选D的原因是 因为 evolutionary approach 对应着 原文的 Rates of evolution 嘛? 这里我选了C。。不是很懂 插入句和 D的关系 求解答
    • 我是啦啦啦
      我是啦啦啦 去解答 去解答
      这个题A哪里错了?是因为主语不对吗?这个C比A多一步推理啊
    • haiyuqiao
      鑫哥,D选项里的19世纪出现了很多假设,原文中并没有提到啊
    • wx_7060
      为什么选a 呢。我觉得a是细节。F哪错了?
    • wx_1105
      我想问一下,这道题为什么不能选A呢?
    • wx_8122
      D为什么不选
    • wx_1655
      f选项哪里说了
    • chaulaw
      鑫哥,原文是below经济损害水平,D是一触发经济损害就用,这也对吗?
    • chaulaw
      interclan婚姻是对的吗?不是只在自己的family结婚扩大家族吗?
    • wx_6697
      鑫哥,这道题答案是不是错了,好多人选D 我也选的D求解答
    • wx_6697
      这道题应该是一道易错题,每个选项的都有,然而我选的A错了,求解
    • wx_6697
      鑫哥,这题的C是怎么得到的?B也没有找到啊?难道不是应该选B
    • wx_6697
      鑫哥,还有这个,好多人选A答案是不是错了
    • wx_6697
      求问D是从哪里得出来的,我选的B呀哎呀
    • wx_4185
      it is difficult to say how far they were intended to be portraits rather than generalized images 这句话怎么理解呢
    • 此楠楠
      请问下这个插入题怎么选的呢?
    • 此楠楠
      求鑫哥讲解下A选项。。。 Even though in error, Joly’s calculations clearly supported those geologists who insisted on an age for Earth far in excess of a few million years.