Geologists examine rocks and minerals in order to formulate and test theories on natural processes affecting the earth and to explore for mineral resources. They may also study fossil remains of animals and plant life and observe the flow of fluids and gases through rocks to determine the ages and rates of change of various parts of the earth's crust, as well as the possibility of oil and gas deposits. They contribute to environmental impact studies by examining the effects of wind, water, earthquakes, landslides, or volcanic action on landforms.
Geologists also determine sources of groundwater and possible contamination effects.
A number of experienced geologists go into business for themselves, offering their services as consulting geologists to the public. Economic geologists locate earth materials such as minerals and solid fuels. Petroleum geologist attempt to locate oil and natural gas deposits below the earth's surface. Engineering geologists evaluate sites for construction of buildings, highways airports, tunnels, dams and other structures. The latter also study the flow of groundwater and pollution effects.