Use of English

Inside the Earth's Crust

Geology is the study of the Earth and the materials that make it (0) UP. One of the first things students learn is that rocks are usually divided into three main types. Sedimentary rocks are formed when layers of sand, mud or shells build (1) .......... over time and become hard. Igneous rocks, by contrast, are created when hot material from inside the Earth cools (2) .......... and turns solid. Metamorphic rocks are rocks that have changed because of intense heat or pressure, often deep (3) .......... the surface. These three groups are connected by what scientists call the rock cycle, in which one type can slowly turn (4) .......... another. The process is strongly affected by movement in the Earth's crust. Huge plates are constantly moving, although so slowly that we do not notice it in everyday life. When these plates push (5) .......... each other or pull apart, they can cause earthquakes, volcanoes and mountain building. Many people refer to this movement as tectonic activity. By carrying (6) .......... research in the field, geologists can work out how landscapes were formed. They also rely (7) .......... evidence from rock layers to understand the past. In this way, geology gives us a clearer picture of the forces that shape the planet we live (8) ...........