Revolution energy sources have expanded to include gas, coal, oil, steam, and fissionable materials.

Mineral resources produce the tools that enable society to supply water, food, fuel, and manufactured goods to growing populations. Exploration and extraction respond quickly to market values of minerals, and market values vary according to technological innovation. Certain minerals will always be needed, but there is a point at which the price of supplying a product to market is more than the price of developing techniques that may render that product obsolete. Because technological developments cannot be predicted in the long run, the need for some minerals cannot be predicted.

Curiously enough, research into the formation of all these resources involves an understanding of fluid movement within solid materials. Separate investigations of the solid, fluid, and gaseous envelopes of the Earth are no longer possible. Researchers now are reorienting their goals to address an earth system that integrates geology, hydrology, and atmospheric sciences with biochemical elements. The breadth of the earth system allows for full appreciation of the consequences of concentration and redistribution of material by natural causes and human intervention.

Often the search for resources is frustrated, and even when it is successful their extraction can be difficult and dangerous. To warrant the effort there must be a degree of profit. As market values change, managers must decide whether a particular resource is economic. If it is economic, it is worth the effort to discover and extract deposits. There are unlimited amounts of all the compounds and elements that humankind needs, but they are not usually concentrated into deposits that are economically worthwhile. If a deposit is worth the effort, or if it can be reasonably assumed that it will become worthwhile, it is classified as a reserve. New discoveries and new extraction techniques contribute to the increasing quantity of what can be considered reserves.

But the rising population continually puts more demand on available resources. As accumulations of waste material grow and concentrations become more hazardous, a new factor affects assessments of a resource's economic value: the cost of landscape reclamation and by-product neutralization. Communities have come to understand that they can no longer dump sewage into streams and let solid wastes accumulate indefinitely. Mining enterprises have come to understand that they can no longer leave mountainsides gouged and stripped, with piles of tailings leaching toxic compounds into the watershed.

As understanding of the earth system grows, resource scientists can moderate the effects of society on nature. One exciting research area is the ability of wetlands to clean contaminated fluids. Wetlands and marshes were once considered useless wasted tracts. If not left to hunters and trappers, these regions were often drained. Researchers have now concluded that the chemical and biological processes that prevail in marshy environments can remove toxic compounds from contaminated water. Constructed wetlands are now being introduced as systems that cleanse wastewater and return acid levels to natural levels. Specific bacteria can clean up specific compounds through bioleaching, biosorption, and bioreduction.

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