49 Earth's Changing Face-Low

Earth's Changing Face Written by Celeste Fraser

Introduction "Mount Redoubt had recently erupted. When I arrived in Anchorage, Alaska, three days later, it was raining. The streets and sidewalks looked black. 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 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."

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. They differ in thickness, temperature, and weight. The Crust The 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 higher land. 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 forms the floor of all the oceans.

The crust is not smooth like an eggshell. Instead, it is made up of uneven shapes. These different shapes are called landforms. Look at the collage 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.

The Mantle Deeper inside Earth, temperatures get hotter. The layer underneath the crust is called the mantle. The rock there is in a semi-liquid state. The mantle which is very thick, makes up most 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. These layers are very different from one another. The outer core is liquid. It has 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). 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!

Forces That Create Landforms Some landforms like mountains, are constantly being created. To understand how and why, we need to learn more about the inside of Earth. Moving Magma Moving Crust Like a cracked eggshell, Earth's crust is cracked. The pieces of crust are called plates. The plates move 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.