51 Earth's Changing Face-High

Earth's Changing Face Written by Celeste Fraser

《地球的变化》作者:塞莱斯特·弗雷泽

Introduction "I had to delay my trip to Anchorage, Alaska. Mount Redoubt had just erupted, sending ash high up into the air. Planes were grounded. When I finally arrived, it was raining. I wiped the rain from my face and noticed my fingers were black. What is that? I wondered. I looked at the street, sidewalk, and parked cars and saw that a black film covered them, too. It was raining volcanic ash!" That story was told by a teacher who went to Alaska in 1989. Volcanoes erupt all over the world. A volcano is a place where gases, ash, and lava can spew out from deep beneath Earth's surface. Volcanoes are examples of forces that create new features on Earth. Other forces, like moving water and wind, create new features and alter existing features. Some of these changes happen quickly and violently. Others take place very slowly, over millions of years. In this book, you will read about Earth's changing "face."

“我不得不推迟去阿拉斯加安克雷奇的行程。 棱堡火山刚刚爆发，火山灰直冲云霄。 飞机停飞。当我终于到达时，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。我看了看街道、人行道和停着的汽车，发现它们也被一层黑色的薄膜覆盖着。 当时正在下火山灰!”这个故事是一位1989年去阿拉斯加的老师讲的。 世界各地都有火山爆发。 火山是从地球表面深处喷出气体、火山灰和熔岩的地方。 火山是在地球上创造新特征的力量的例子。 其他的力量，如流动的水和风，创造了新的特征，改变了现有的特征。 其中一些变化发生得又快又剧烈。 其他的则发生得非常缓慢，持续了数百万年。 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 with a cracked shell. It has three layers: the eggshell that surrounds it, the white, and the yellow yolk inside. Earth has layers, too. Scientists think that Earth formed about 4.6 billion years ago. As more and more matter gathered to create our planet, the force of gravity pulled on it, and the outer layers pressed down on the lower layers with greater and greater force. This squeezing of matter produced several layers and intense heat beneath the surface. The conditions that formed Earth also cause its outer surface to constantly change.

要了解地球的表面，你必须深入观察它的内部。 想象一个有裂纹壳的煮熟的鸡蛋。 它有三层:包裹它的蛋壳、里面的蛋黄和蛋黄。 地球也有层次。科学家认为地球形成于46亿年前。 随着越来越多的物质聚集在一起，形成了我们的星球，引力作用于它，外层物质以越来越大的力压住下层物质。 这种物质的挤压在地表下产生了几层和强烈的热量。 形成地球的条件也导致它的外表面不断变化。

The Crust Earth's outer layer is called the crust. It completely surrounds the planet, but unlike an eggshell, it differs greatly in thickness. The crust's thickness ranges from about 5 to 40 kilometers (3-30 mi.). The thickest crust is simply higher in elevation. This thicker crust forms the landmasses where people live. We call the largest of these landmasses continents and the smaller landmasses islands. The thinner part of the crust is lower in elevation. It forms the floor of all the oceans.

地球的外层叫做地壳。 它完全包围着地球，但与蛋壳不同的是，它的厚度有很大的不同。 地壳的厚度约为5至40公里(3-30英里)。 最厚的地壳只是海拔较高。 这些较厚的地壳形成了人们居住的大陆。 我们称这些大陆中最大的为大陆，较小的为岛屿。 地壳较薄的部分海拔较低。 它构成了所有海洋的底部。

The crust is not smooth like an eggshell but instead is uneven, made of various features called landforms. The most common landforms are those that rise above the surface, such as mountains and hills. But there are hundreds of different landforms, including plains, valleys, and canyons. Look at the collection of photographs 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. The Mantle Deeper inside Earth, temperatures get hotter, and pressure increases. The layer just below the crust 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. Though both layers are made of the metals iron and nickel, they are very different. The metals in the outer core are liquid and about 2200 degrees Celsius (4000°F)— nearly as hot as the Sun's surface! The inner core is even hotter— about 5000 degrees Celsius (9000°F). It is under such great pressure that despite the extreme heat, it cannot melt. Instead, it is squeezed so intensely that it is a hot ball of solid metal.

地壳不像蛋壳那样光滑，而是不均匀的，由各种各样的地貌组成。 最常见的地貌是那些高于地表的地貌，如山脉和丘陵。 但是有数百种不同的地貌，包括平原、山谷和峡谷。 请看第22页和第23页的照片集，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。 在地球内部，温度越来越高，压力也越来越大。 地壳下面的一层叫做地幔。 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构成的，但它们非常不同。 外核的金属是液态的，温度约为2200摄氏度(4000华氏度)——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)。 在如此巨大的压力下，尽管温度极高，它仍无法融化。 相反，它被如此强烈地挤压，以至于它是一个固体金属的热球。

Forces That Create Landforms Earth's 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 has lots of cracks. The large sections of crust are called plates. The plates move about as fast as your fingernails grow— two to three inches a year! To better understand how plates move, let's think about a pot of thick soup. The hottest part of the soup is at the bottom, 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. Hotter soup rises. Cooler soup sinks. The mixing of the hot and cooler soup causes it to move in a circular motion called a convection current.

地球上的地貌，比如山脉，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，地壳有许多裂缝。 地壳的大块被称为板块。 指甲板的移动速度和你指甲的生长速度一样快——每年两到三英寸!为了更好地理解盘子是如何移动的，让我们想象一锅浓汤。 汤里最热的部分在底部，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。 更热的汤上升。更凉爽的汤槽。 热汤和冷汤的混合使它以一种称为对流的圆周运动运动。