Ore deposits supply much of the raw material on which modern industrial society is based. "If you can't grow it, it has to be mined," say mining geologists about the materials consumers use. In addition, much of what is grown would not be possible without metals. Platinum, for example, is used as a catalyst in the chemical reaction that produces nitrogen for fertilizer, and metals are used in the production of pesticides, petroleum, and plows. But the winning of metal has not come without a cost. Mining has historically been a dangerous business and one prone to environmental problems. Mining, beneficiation, and smelting have led to the introduction of unacceptable levels of metals into lakes, streams, and ground water. It has injected dust into the atmosphere and spread metals and acid rain across the land. Subsurface mining has caused surface subsidence problems now plaguing some old mining towns. Mines are an economic necessity and actually occupy only slightly more United States land area than airports. A clean environment is also a necessity for health and quality of life. Although problems from mining's early days remain, modern mining methods are considerably safer and have a much less negative environmental impact. Pollution control during the mining and processing of ore, and land reclamation after mine closure are now being considered as one of the economic factors in determining if mineralized rock is indeed ore.