A wealth of information is buried in the liquids, gases, and mineral deposits of rock. Geochemists must understand this information and use it to make decisions about a range of industrial and scientific research applications. Understanding the chemical composition of rocks tells oil companies where to drill for oil, enables scientists to put together broad-based theories about the way the earth is changing, helps environmental management companies decide how to dispose of toxic or hazardous substances, and steers mining companies toward using natural resources with a minimum environmental impact.