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万物简史(MP3+中英字幕) 第306期:地下的烈火(14)

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Because we can't see into the Earth, we have to use other techniques, which mostly involve reading waves as they travel through the interior. We also know a little bit about the mantle from what are known as kimberlite pipes, where diamonds are formed. What happens is that deep in the Earth there is an explosion that fires, in effect, a cannonball of magma to the surface at supersonic speeds. It is a totally random event. A kimberlite pipe could explode in your backyard as you read this.
我们无法看到地球的深处,因此不得不使用别的方法,主要包括观察波在地球内部的传播形式,从而推断那里的情况。我们从所谓的金伯利岩筒(即形成钻石的地方)得知一点地幔的情况。那里的情况是,地球深处存在一种爆炸,能把岩浆炮弹以超声速发射到地面。这完全是一种没有规律的现象。你在阅读本书的时候,一个金伯利岩筒有可能在你家的后花园爆炸。
big holeBecause they come up from such depths—up to 120 miles down—kimberlite pipes bring up all kinds of things not normally found on or near the surface: a rock called peridotite, crystals of olivine, and—just occasionally, in about one pipe in a hundred—diamonds. Lots of carbon comes up with kimberlite ejecta, but most is vaporized or turns to graphite. Only occasionally does a hunk of it shoot up at just the right speed and cool down with the necessary swiftness to become a diamond. It was such a pipe that made Johannesburg the most productive diamond mining city in the world, but there may be others even bigger that we don't know about. Geologists know that somewhere in the vicinity of northeastern Indiana there is evidence of a pipe or group of pipes that may be truly colossal. Diamonds up to twenty carats or more have been found at scattered sites throughout the region. But no one has ever found the source. As John McPhee notes, it may be buried under glacially deposited soil, like the Manson crater in Iowa, or under the Great Lakes.
由于它通到下面很深的地方——深达200公里——金伯利岩筒带上来各种地面上或地面附近通常找不到的东西:如橄榄岩、橄榄石晶体以及钻石。带上来钻石是很偶然的,100个岩筒中大约只有1个会办这等好事。金伯利岩筒的喷出物带上来大量的碳,但大部分都化成蒸气,或变成石墨。只是在偶尔的情况下,一团碳以恰到好处的速度喷上来,并以必要的速度快速冷却,终于变成了钻石。正是由于这类岩筒,南非成了世界上出产钻石最多的国家,但很可能别的国家蕴藏量还要丰富,我们现在还不知道。地质学家们知道,印第安纳州东北部附近有个地方,有迹象表明存在着巨大的岩筒或岩筒群。20克拉或更大克拉数的钻石在整个地区的不同地点已有发现。但是,没有人找到源头。约翰·麦克菲指出,它也许埋在冰河沉积土底下,就像艾奥瓦州的曼森大坑,或者在五大湖下面。
重点单词   查看全部解释    
swiftness ['swiftnis]
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n. 迅速,敏捷
 
explode [iks'pləud]
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vt. 爆炸,驳倒
vi. 爆炸,爆发(感情)
 
involve [in'vɔlv]
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vt. 包含,使陷入,使忙于,使卷入,牵涉
联想记忆
source [sɔ:s]
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n. 发源地,来源,原始资料
 
explosion [iks'pləuʒən]
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n. 爆炸,爆发,激增
 
evidence ['evidəns]
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n. 根据,证据
v. 证实,证明
联想记忆
diamond ['daiəmənd]
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n. 钻石,像钻石的物质,菱形,纸牌的方块,棒球内场
 
occasionally [ə'keiʒənəli]
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adv. 偶尔地
 
random ['rændəm]
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adj. 随机的,随意的,任意的
adv. 随
 
productive [prə'dʌktiv]
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adj. 能生产的,有生产价值的,多产的
联想记忆
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