What is the earth made of? How did it come to be as it is? The science that answers these questions is geology. Rocks, minerals, fossils, earthquakes, volcanoes, caverns—these are some of the things geologists study. They study, too, the battle between land and sea that has been going on since the earth was young. They find out how mountains are formed and how they may be worn down.
The earth is made up of rocks of many kinds. In some places the rocks are arranged in layers. These rock layers are like pages in a great book. Geologists learn to read them just as most people read pages of printing. The rocks tell geologists about changes in climate, ancient lava flows, and changes in land and sea. Fossils embedded in the layers of rock make these rocks into a kind of picture book.
Geology is a big science. It is so big that it has to be divided into many smaller sciences. Each of these smaller sciences has its own name. If a person is especially interested in the living things of long ago, he studies paleontology. If he is interested in minerals, he studies mineralogy. If he wants to learn about rocks, he studies petrography. If he wants to know more about earthquakes, he studies seismology. There are still other branches.
People do not usually study geology just for the fun of finding out more about the earth. What geologists know can be put to use in many ways. Finding new deposits of oil is one of them. Planning ways of keeping rivers from stealing our soil is another. Helping choose good places for tunnels and dams is one more. The work of many geologists takes them to faraway places.