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老托福听力30篇下载之地球内部构成（原文+翻译）
老托福听力30篇下载之地球内部构成（原文+翻译）。

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I'm glad you brought up the question of our investigations into the makeup of the Earth's 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 a more accurate picture of the Earth's interior. The first key discovery had to do with seismic waves. Remember they are the vibrations caused by earthquakes. Well, scientists found that they traveled thousands of miles through the Earth's 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 shear or S waves. And researchers found that P waves travel through both liquids and solids, while S waves travel 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's 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.
我很高兴你对我们关于地球内部构成的研究提出问题。

事实上，这个话题将是你们的下一个阅读作业，现在让我用占用课堂上的几分钟说说这个话题。

在这个世纪有几个重要的发现，它们帮助地质学家显影出一张更精准的地球内部构成图。

第一个关键的发现与震波有关。

记住震波是地震引起的震动。

于是科学家发现这些震波是穿过数千英里从地球内部传来的。

这个发现使科学家能够研究地球里面的部分。

你看，这些研究显示震动有两种类型：压缩波或者叫P型波，和切变波或者叫S型波。

研究人员还发现P型波可以穿过液体和固体，而S型波只能穿过固体物品。

在1906年，一位英国地质学家发现P型波在一定的深度传播很慢，但是会继续向更深的地方传播。

另一方面，S型波不是消失就是被反射回来，所以他推断出深度标志着固体地幔与液体地心的边界。

三年后，另一个边界被发现，是地幔与地壳的边界。

还有很多关于地球的奥秘等着我们去了解。

例如，地质学家根据从火山流出的熔岩知道地心是炎热的，但是我们还是不能确定地心热量的来源是什么。