We live in a society which depends on natural resources. Our high standard of living requires use of the land, water, and mineral endowment of the Earth. In using these resources, we may affect our environment and alter our options for land and resource use in the future. How can we ensure an adequate supply of this natural wealth in the future? In what ways are we irreversibly altering our natural environment? How can we avoid undesirable or unacceptable side effects of man's use of the land and prevent or mitigate earth-related hazards? To respond to these and other similar questions, knowledge about the Earth, its structure, its resources, and its dynamics is essential.