50 Earth's Changing Face-Mid

Earth's Changing Face Written by Celeste Fraser

《地球的变化》作者:塞莱斯特·弗雷泽

Introduction "Mount Redoubt had recently erupted. When I arrived in Anchorage, Alaska, three days later, it was raining. I wiped the rain from my face and noticed that my fingers were black. What is that? I wondered. I looked around. A black film covered everything. I realized it was raining volcanic ash!" That story was told by a teacher. Mount Redoubt is a volcano. Volcanoes are places where gases, ash, and lava can spew out from beneath Earth's surface. Volcanoes are forces that create new features on Earth. Other forces, like water and wind, change existing features. Some changes happen quickly. Others take place very slowly. In this book you will read about Earth's changing "face."

“棱堡火山最近爆发了。 三天后，当我到达阿拉斯加的安克雷奇时，天正在下雨。 我擦去脸上的雨水，注意到我的手指是黑色的。 那是什么?我想知道。我环顾四周。 一片黑色胶片覆盖了一切。 我意识到正在下火山灰!”那个故事是一位老师讲的。 棱堡山是一座火山。 火山是气体、火山灰和熔岩从地表以下喷出的地方。 火山是在地球上创造新特征的力量。 其他力量，如水和风，改变了现有的特征。 有些变化发生得很快。 其他的则发生得非常缓慢。 在这本书中，你将读到地球变化的“面貌”。

Earth's Structure To understand Earth's surface, you have to look deep inside it. Imagine a hard-boiled egg. It has three layers: the eggshell, the white, and the yellow yolk inside. Earth has layers, too. Its layers differ in thickness, temperature, and weight. The Crust Earth's outer layer is called the crust. Unlike an eggshell, its thickness varies. It ranges from about 5 to 40 kilometers (3-30 mi.) The thickest crust is simply land that is higher in elevation. These are the landmasses where people live. We call the largest of these landmasses continents and the smaller ones islands. The thinnest part of the crust is land that is lower in elevation. It forms the floor of all the oceans.

要了解地球的表面，你必须深入观察它的内部。 想象一个煮熟的鸡蛋。 它有三层:蛋壳、蛋白和里面的黄色蛋黄。 地球也有层次。岩层的厚度、温度和重量各不相同。 地球的外层叫做地壳。 与蛋壳不同，它的厚度是不同的。 它的范围约为5至40公里(3-30英里)，最厚的地壳是海拔较高的陆地。 这些是人们居住的大陆。 我们把这些大陆中最大的称为大陆，较小的称为岛屿。 地壳最薄的部分是海拔较低的陆地。 它构成了所有海洋的底部。

The crust is not smooth like an eggshell but instead is uneven. The different shapes of land are called landforms. Look at the collection of pictures on pages 22 and 23 to see some of Earth's many landforms. We will learn about the forces that created and shaped these landforms in the next section.

它的外壳不像蛋壳那样光滑，而是不均匀的。 不同形状的土地被称为地貌。 请看第22页和第23页的图片集，看看地球上的许多地貌。 在下一节中，我们将了解创造和塑造这些地貌的力量。

The Mantle Deeper inside Earth, temperatures get hotter. This layer is called the mantle. The rock there is in a semi-liquid, rubbery state. The mantle is very thick, making up about 80 percent of the planet. The Core Deeper still, at the very center of Earth, is the core. It consists of two layers—the outer core and the inner core. Although both layers are made of iron and nickel, they are very different. The metals in the outer core are in liquid form, with a temperature of about 2200 degrees Celsius (4000°F). That's nearly as hot as the Sun's surface! The inner core is even hotter—about 5000 degrees Celsius (9000°F). With the rest of Earth's weight pressing down on it, the inner core is squeezed very tightly. It is a ball of solid metal. Wowser! Because lava can be so hot—up to 1250°C (2000°F)—there's nothing people can do to stop it!

在地球内部，温度越来越高。 这一层叫做地幔。 那里的岩石处于半液态，呈橡胶状。 地幔非常厚，约占地球面积的80%。 地核再深一点，在地球的正中心，是地核。 它由两层组成——外核和内核。 虽然这两层都是由铁和镍组成的，但它们非常不同。 外核的金属处于液态，温度约为2200摄氏度(4000华氏度)。 这几乎和太阳表面一样热!内核甚至更热——大约5000摄氏度(9000华氏度)。 由于地球的其余重量压在它身上，内核被挤压得非常紧。 它是一个实心金属球。 老古板!因为熔岩可以热到1250°C(2000°F)，人们无法阻止它!

Forces That Create Landforms Landforms such as mountains are constantly being created, inch by inch, over millions of years. To understand how and why, we need to understand more about Earth's interior. Moving Magma Moving Crust Like a cracked eggshell, Earth's crust is cracked. The pieces of crust are called plates. The plates move about as fast as your fingernails grow—two to three inches a year! To understand why, picture a pot of thick soup. The hottest soup is at the bottom of the pot, nearest the heat source. The coolest soup is at the surface, farthest from the heat source. If you have ever watched soup boil, you know that it moves. Hot substances rise. Cool substances sink. These temperature changes cause the soup to move in circular motions called convection currents.

形成地貌的力量像山脉这样的地貌在数百万年的时间里一寸一寸地不断被创造出来。 为了了解如何以及为什么，我们需要更多地了解地球内部。 移动的岩浆移动的地壳就像破裂的蛋壳一样，地壳也破裂了。 这些地壳碎片被称为板块。 指甲板的移动速度和你指甲的生长速度差不多——每年两到三英寸!要理解其中的原因，想象一锅浓汤。 最热的汤在锅底，离热源最近的地方。 最冷的汤在离热源最远的表面。 如果你曾经看过汤沸腾，你就知道它会流动。 热物质上升。冷的物质会下沉。 这些温度的变化导致汤以圆周运动移动，称为对流。