56 What's Inside Planet Earth?-High

What's Inside Planet Earth? FOCUS Question What is below Earth's surface, and how do we know?

地球内部是什么? 焦点问题地球表面以下是什么，我们怎么知道?

What's Down There? What might you experience if you could journey to Earth's center. You may have watched a science fiction movie or read a fiction book about taking such a voyage. Nobody has actually gone there, however, and it's likely impossible. That's why, until recently, Earth's interior remained a mystery. Scientists could only speculate about what lies deep below Earth's surface. Earth is composed of three main layers. The crust is the outermost and thinnest layer. The middle layer, which lies beneath the crust, is the mantle. The core is the innermost layer. This layer is divided into a liquid outer core and a solid inner core. But how do we know this? Let's find out how scientists solved the mystery.

下面有什么?如果你能去地心旅行，你会经历什么? 你可能看过一部科幻电影或读过一本关于这样一次航行的小说。 然而，没有人真正去过那里，而且这很可能是不可能的。 这就是为什么直到最近，地球内部仍然是一个谜。 科学家们只能推测地球表面深处的东西。 地球主要由三层组成。 地壳是最外层也是最薄的一层。 位于地壳下面的中间层是地幔。 核心是最内层。 这一层分为液态的外核和固态的内核。 但是我们是怎么知道的呢?让我们来看看科学家们是如何解开这个谜团的。

Interior Sleuths Solving the mystery of Earth's interior wasn't easy for geologists— scientists who study Earth. People can't see through solid rock or dig to Earth's center. The deepest hole ever drilled only reaches about 12 kilometers (7.5 mi.). Instead, geologists use two kinds of information to study Earth's interior. They use direct evidence and indirect evidence. Observations you can make yourself are direct evidence. Scientists observe rocks and lava on Earth's surface. They study rocks from mines and holes drilled below the surface. Indirect evidence is information you use to infer an answer when you can't make observations yourself. It includes recordings of earthquake waves called seismic (SIZE-mik) waves. By studying these waves, geologists can infer what lies thousands of kilometers below the surface.

对于研究地球的地质学家来说，解开地球内部之谜并不容易。 人们无法看穿坚硬的岩石，也无法挖到地球的中心。 迄今为止钻得最深的洞只有12公里(7.5英里)。 相反，地质学家使用两种信息来研究地球内部。 他们使用直接证据和间接证据。 你自己的观察就是直接的证据。 科学家观察地球表面的岩石和熔岩。 他们研究来自矿山和地表下钻孔的岩石。 间接证据是当你无法自己观察时用来推断答案的信息。 它包括被称为地震(SIZE-mik)波的地震波记录。 通过研究这些波，地质学家可以推断出地表以下数千公里处的情况。

Seismic Waves During an earthquake, seismic waves move outward throughout Earth. Instruments around the world record these seismic waves. The waves include P waves, which can travel through solids and liquids, and S waves, which can travel through solids but not liquids. When seismic waves move from one material into a different material, their speed and direction change. Either their path bends or the new material blocks them. If Earth were made up of a single layer of the same material, the seismic waves would pass straight through the planet. Instead, however, seismic waves bend or stop. Using this indirect evidence, scientists inferred that Earth consists of different layers. These layers must be made up of different materials.

地震时，地震波在地球上向外传播。 世界各地的仪器记录了这些地震波。 这些波包括P波，它可以穿过固体和液体，S波可以穿过固体，但不能穿过液体。 当地震波从一种物质移动到另一种物质时，它们的速度和方向会发生变化。 要么是他们的路径弯曲，要么是新材料挡住了他们。 如果地球是由一层相同的物质组成的，那么地震波就会直接穿过地球。 相反，地震波会弯曲或停止。 利用这些间接证据，科学家推断地球由不同的层组成。 这些层必须由不同的材料组成。

The Crust Earth's crust is the layer we call home. It's thousands of degrees cooler than the other layers. Geologists know more about it than the mantle or core because they can collect direct evidence. The crust is broken into pieces, called tectonic plates, which slowly move on Earth's surface. The movement and interaction of these plates create and change landforms. Plate movements create mountains, volcanoes, trenches, and mid-ocean ridges. The crust varies in thickness and is made up of different rock types. The continental crust makes up the continents and consists mostly of a type of rock called granite. The oceanic crust is under the oceans and consists mostly of basalt.

地壳地壳是我们称之为家的层。 它比其他层的温度低几千度。 地质学家比地幔或地核更了解地幔，因为他们可以收集直接证据。 地壳被分解成碎片，称为构造板块，它们在地球表面缓慢移动。 这些板块的运动和相互作用创造并改变了地貌。 板块运动创造了山脉、火山、海沟和洋中脊。 地壳的厚度各不相同，由不同的岩石类型组成。 大陆地壳组成大陆，主要由一种叫做花岗岩的岩石组成。 海洋地壳位于海洋下面，主要由玄武岩组成。

The Mantle Both P and S waves pass through the crust and mantle. Scientists infer that this likely means both layers are solid. Seismic waves also travel faster in the mantle, meaning that the mantle is denser than the crust. To learn more about the mantle (see page 5), scientists study volcanoes. During an eruption, mantle rock is forced up to the surface. This rock reveals that the mantle is made mostly of rock called peridotite (puh-RI-duh-tite). Although the mantle is mostly solid, it moves slowly over time. The tectonic plates in the crust sit on top of the mantle. Heat within the mantle moves by way of convection currents. These currents help move the plates and therefore can change landforms on Earth's surface.

P波和S波都能穿过地壳和地幔。 科学家推断，这可能意味着两层都是固体。 地震波在地幔中的传播速度也更快，这意味着地幔的密度比地壳大。 为了更多地了解地幔(见第5页)，科学家们研究火山。 火山喷发时，地幔岩石被推上地表。 这块岩石揭示了地幔主要由橄榄岩(puh-RI-duh-tite)组成。 虽然地幔大部分是固体，但随着时间的推移，它移动缓慢。 地壳中的构造板块位于地幔的顶部。 地幔内的热量以对流的方式移动。 这些洋流帮助板块移动，因此可以改变地球表面的地貌。