The earth's atmosphere has a unique composition because of the cyclic flow of materials. Some of these cycles involve the movement of materials in and out of the earth's atmosphere. Carbon dioxide, for example, is a very minor part of the earth's atmosphere. It has been maintained as a minor component in a mostly balanced state for about the past 570 million years, cycling into and out of the atmosphere.

Water is also involved in a global cyclic flow between the atmosphere and the surface. Water on the surface is mostly in the ocean, with lesser amounts in lakes, streams, and underground. Not much water is found in the atmosphere at any one time on a worldwide basis, but billions of tons are constantly evaporating into the atmosphere each year and returning as precipitation in an ongoing cycle.

The cycling of carbon dioxide and water to and from the atmosphere takes place in a dynamic system that is energized by the sun. Radiant energy from the sun heats some parts of the earth more than others. Winds redistribute this energy with temperature changes, rain, snow, and other changes that are generally referred to as the weather.

Understanding and predicting the weather is the subject of meteorology. Meteorology is the science of the atmosphere and weather phenomena, from understanding everyday rain and snow to predicting not-so-common storms and tornadoes. Understanding weather phenomena depends on a knowledge of the atmosphere and the role of radiant energy on a spinning Earth that is revolving around the Sun. This chapter is concerned with understanding the atmosphere of the earth, its cycles, and the influence of radiant energy on the atmosphere.