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【托福在线听写】第八营——yuminjieningyu 4月29日——地球interior

2011-04-29 15:40 三立在线 admin

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摘要:我很高兴你们提出了关于地球内部是由神马物质组成的问题!事实上,由于这个是你们下一次阅读的作业,那就让我用这节课剩下的这几分钟谈一下这个问题。在这个世纪初几个重要的

我很高兴你们提出了关于“地球内部是由神马物质组成”的问题!事实上,由于这个是你们下一次阅读的作业,那就让我用这节课剩下的这几分钟谈一下这个问题。在这个世纪初几个重要的发现帮助地理学家呈现了一些更准确的地球内部构造的图像。第一个核心的发现跟地震波有关,记住:它们是由地震引起的震动。科学家们发现它们在地球内部可以传播数千英里。这个发现使得地理学家们可以探究地球内部的组成。你瞧,这个探究揭示了这些震动有两种。激波(术语)或者说是P波和垂直波或者说是S波。研究发现P波能在液体和固体中传播,然而S波只能在固体介质中传播。在1906年,一位英国科学家发现P波在一些特定的深度传播速度放慢但是继续向更深的地方传播。相反S波会消失或者反射回来。所以他得出结论这个深度划分了固态地幔和液态地核之间的界限。三年以后另外一个界限也被发现了。就是在地幔和地壳之间的界限。对于地球我们仍然有很多需要探究的。例如,地理学家们知道地核具有很高的温度,从火山流出的熔浆就是这个发现的证据。但是我们还是不确定这种高温的能量来源于哪里。

 

I’m glad you brought up the question of our investigations into the makeup of the Earth interior. In fact, since this is the topic of your reading assignment for next time, let me spend these last few minutes of class talking about it. There were several important discoveries in the early part of this century that helped geologists develop more accurate picture of the Earth interior. The first key discovery had to do with seism waves. Remember they are the vibrations caused by earthquakes. Well, scientists found that they traveled thousands of miles through the Earth interior. This finding enabled geologists to study the inner parts of the Earth. You see, these studies revealed that these vibrations were of two types: compression or P waves and sheer or S waves. And researches found that P waves traveled through both liquids and solids while S waves traveled only through solid matter. In 1906, a British geologist discovered that P waves slowed down at a certain depth but kept traveling deeper. On the other hand, S waves either disappeared or were reflected back. So he concluded that the depth marked the boundary between a solid mantle and a liquid core. Three years later, another boundary was discovered that between the mantle and the earth crust. There’s still a lot to be learned about the Earth. For instance, geologists know that the core is hot. Evidence of this is the molten lava that flows out of volcanoes. But we’re still not sure what the source of the heat is.


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