Earth resources

Earth’s resources of metals, nonmetals, and energy undergird every modern, technological society.

Renewable versus Nonrenewable Resources

All earth resources can be subdivided into two broad categories. The first category contains the renewable resources. The word “renewable” means that these resources are replenished by nature as rapidly as humans use them up, provided good judgment is used. Renewable resources include the energy of the wind, the timber cut in a forest, and the animals used for food. Each of these earth resources is constantly being renewed by the energy that reaches the earth’s surface from the sun. As long as the sun’s rays reach Earth, this pattern of replenishment can continue.

The resources in the second category are known as nonrenewable resources. These are resources that will not be renewed in a human lifetime. Only limited quantities of these resources are present in the earth’s crust, and they are not replenished by natural processes operating within short periods. Examples of nonrenewable resources include coal, oil, iron, diamonds, and aluminum. While it is true that certain of these resources, such as coal and oil, are being formed within the earth’s crust continuously, the processes are exceedingly slow, being measured in thousands or millions of years; the rate of use far exceeds the rate of replacement. The difference between renewable and nonrenewable resources is sometimes summed up as, “If you don’t grow it, you have to mine it.”

Metals

Earth resources of primary interest to the economic geologist can be divided into three categories: metals, nonmetals, and energy sources. Metals are a group of chemical elements that typically share a high metallic luster, or shine. Additionally, they can all be melted, conduct heat and electricity, and be pounded into thin sheets or drawn into thin wires.

Metals can be divided into two classes based on their abundance in the earth. The first class, which has been called the abundant metals, consists of those metals that individually constitute 0.1 percent or more of the earth’s crust by weight. The metals in this category are iron, aluminum, manganese, magnesium, and titanium. The second class of metals, which are called the scarce metals, consists of those metals that individually constitute less than 0.1 percent of the crust. This class includes such metals as copper, lead, zinc, nickel, mercury, silver, gold, and platinum.

Certain common metals, such as steel, brass, bronze, and solder, are not pure metals but alloys—chemical mixtures of two or more metals that have characteristics of strength, durability, or corrosion resistance superior to those of the component metals. Steel, for example, is an alloy in which iron is the main constituent.

Metals are rarely found in a pure state within the earth’s crust. Only the metals gold, silver, copper, platinum, and iron are ever found uncombined. All other metals are found chemically bonded with additional elements to form minerals. Geologists use the term “ore deposit” to describe a rock containing metals or metal-bearing minerals from which the pure metal can be profitably extracted. Whether a rock is an ore deposit depends on a variety of factors, including how difficult it is to extract the metal from the metal-bearing mineral, how large and accessible the ore deposit is, whether valuable by-products can be obtained, and what the current price of the metal is on world markets.

Nonmetals

The second major category of Earth resources is nonmetals. The term “nonmetal” is widely employed by geologists to describe substances extracted from the earth that are neither sources of metals nor sources of energy. Nonmetals are mined and processed either because of the nonmetallic elements they contain or because they have some highly desirable physical or chemical characteristic. Some of Earth’s major nonmetallic resources are fertilizers, chemicals, abrasives, gems, and building materials.

Fertilizers contain the elements nitrogen, potassium, and phosphorus. Most of the nitrogen required for fertilizer production is chemically extracted from the air, so the supply is renewable. The potassium and the phosphorus, however, come from rocks dug from the ground—potash salt layers and phosphate rocks—the supply of which is nonrenewable.

Several earth resources provide important raw materials for the chemical industry. They include salt, which is obtained from seawater and underground beds of rock salt; sulfur, a by-product of oil production; and substances such as borax and soda ash, which are obtained from the beds of dry desert lakes. Abrasives are very hard substances used for grinding, polishing, and cleaning. They are obtained from rock and mineral substances dug out of the earth and pulverized. Gems are earth materials that are attractive to the eye. They can be categorized as precious and semiprecious.

Building materials include the stones obtained from quarries, such as granite, sandstone, limestone, marble, and slate. There also is a high demand for crushed rock, which is used as highway roadbed and for concrete aggregate. Sand and gravel are also used in making concrete. A number of other useful products are prepared from earth materials: cement; plaster, from the mineral gypsum; brick and ceramics, from clay; glass, from very pure sand or sandstone rock; and asbestos, from flame-resistant mineral fibers that can be woven into fireproof cloth or mixed with other substances to make fireproof roofing shingles and floor tiles.

Energy Sources

The third major category of earth resources is energy sources. Energy sources are frequently divided into mineral fuels, which are nonrenewable, and a second, renewable group. The first group contains coal, uranium, and oil and gas.

Crude oil and petroleum provided 0.9 percent of the United States’ electricity and 4.1 percent of world electricity produced in 2014, based on World Bank data. Natural gas accounted for 26.9 percent of US electricity and 21.6 percent of world electricity that year. According to the US Energy Information Administration (EIA), Americans consumed over 7.2 billion barrels of petroleum products—including transportation and heating fuels—and 27.5 trillion cubic feet of natural gas in 2016. Crude oil is a naturally occurring liquid composed of the elements hydrogen and carbon, combined into compounds known as hydrocarbons; natural gas is a gaseous form of these hydrocarbons. The oil and gas accumulate underground over long periods in source rocks and migrate into reservoir rocks, where they are trapped. Extraction is accomplished by means of drilling. Two related earth resources are oil shale, a source rock that contains oil, and tar sands, reservoir rocks exposed at the surface.

Coal is another important energy source. According to the World Bank, in 2014, it generated 39.7 percent of the nation’s electricity and 40.7 percent globally. Coal originates when partly decayed plant material accumulates on the floor of bogs and swamps, and is buried by overlying sediments that compact the plant material into carbon-rich rocks. The various grades of coal are lignite (brown coal), bituminous coal (soft coal), and anthracite (hard coal). Peat is partly decayed plant material that was never buried at all. Coal is mined at the surface in strip mines or mined underground. Coal, oil, and gas are referred to collectively as “fossil fuels.”

Uranium is a silver-gray metal used in nuclear reactors to produce electricity. According to the World Bank, in 2014, nuclear reactors met 19.2 percent of American electricity needs and 10.6 percent of global electricity needs. Within a reactor, uranium undergoes neutron-induced disintegration, producing heat. This heat is used to drive an electrical generator, just as in conventional power plants. Uranium occurs as veins or grains within a variety of rock types and is mined with standard mining methods.

Many potential energy sources are renewable and mostly underutilized. Foremost among these is hydroelectric power, or water power. This power is generated by means of water falling from a dammed reservoir; the force of the falling water turns the turbine of an electric generator. Barring unforeseen climate changes or silting of the reservoir behind the dam, hydroelectric power can be considered a renewable resource. Sunlight, the wind, the tides, the steam from geysers, and the earth's own heat are also renewable energy sources, as are living things, in the form of firewood and human and animal power. Newer applications are gasohol- and methane-fired boilers that use gases fermented from vegetation or cow manure. The EIA reported in 2017 that renewable resources provided 14.9 percent of the electricity generated in the United States in 2016: 6.5 percent from hydroelectric plants, 5.6 percent from wind farms, 1.5 percent from burning biomass, 0.9 percent from solar installations, and 0.4 percent from geothermal plants. Globally, renewable sources generated a combined 6 percent of electricity in 2014, based on World Bank data. The controlled burning of garbage has been adopted in Europe and has tremendous potential for the future.

Study of Earth Sources

Mineral deposits are quite rare in the earth’s crust; either they consist of substances that are uncommon to begin with (gold, for example) or else they are composed of common substances—such as the pure sand used to make glass—that have been concentrated into workable accumulations. Much study has gone into why such concentrations exist. One valuable tool has been the plate tectonics theory, which proposes that the earth’s surface is divided into a few large plates that are slowly moving with respect to one another. Intense geologic activity occurs at plate boundaries, and many mineral deposits are believed to have been formed this way.

It becomes more and more difficult to find mineral deposits, as all the easily discoverable ones have already been found. Aerial prospecting was made possible by the airplane, and it has now been replaced by satellite imaging. Most prospecting, however, is based on the search for buried deposits and utilizes indirect methods for detecting favorable underground geologic conditions. A preferred technique is seismic prospecting, in which sound waves are created underground by means of small explosive charges and are then bounced off underground rock layers in order to determine their structure. Gravitational and magnetic mapping are also powerful techniques.

Further ways in which Earth resources are studied include calculating estimated available reserves in view of anticipated future demands; comparing the fuel values of various energy sources; analyzing the environmental problems and types of pollution caused by the extraction, refining, and utilization of various mineral resources; and investigating ways to conserve, recycle, or develop substitutes for mineral resources that are in short supply.

Economic Extraction of Mineral Resources

Various techniques have been developed for the economical extraction of mineral resources from the earth. Frequently, extraction costs are the controlling factor in whether a mineral deposit can be profitably worked. In general, extraction techniques can be divided into two groups: surface mining and underground methods. Surface methods are preferred whenever possible, because they are lower in cost. The traditional surface methods are quarrying, open-pit mining, and strip mining. Strip mining involves the removal of large amounts of overburden so that the mineral deposit can be reached. Underground mining methods include the excavation of shafts, tunnels, and rooms. Flat-lying coal beds are excavated by longwall mining, in which one long stretch of coal is stripped off at a time. The rock above the machine is supported by movable supports, and as the machine advances the roof in the mined-out area is allowed to subside. Fluids such as petroleum can be removed by means of drilled wells.

Mineral resources extracted from the earth rarely are ready to be sent directly to market. Generally, they require processing to separate undesirable substances from desirable ones. This processing may involve physical separation, as in the case of separating diamonds from rock pebbles of the same size, or chemical separation, which is required to remove metals from the sulfur they are combined with in certain ores. Even after the pure mineral substance is obtained, further treatment may be required, as in the smelting of iron to obtain steel or the refining of petroleum to obtain gasoline.

Support for Modern Technology

Earth’s resources of metals, nonmetals, and energy supplies support all modern technology. Houses and automobiles, televisions and refrigerators, airplanes and roads, jewelry and sandpaper, the electricity that lights a playing field and the gasoline that powers a car—a nearly endless list of goods depends on the ability to utilize or harness the resources of the earth.

A technological society relies on metals. Iron is needed for steel manufacture, aluminum for lightweight aircraft construction, manganese for toughening steel for armor plate, and titanium for making heat-resistant parts in jet engines. Among the scarcer metals, copper is needed for electrical wiring, lead for car batteries and nuclear reactor shielding, zinc for galvanized roofing nails, nickel for stainless steel, and mercury for silent electric switches. Silver is used for making photographic film, utensils, jewelry, and coins; gold for coins, jewelry, and dental work; and platinum for jewelry and industrial applications where corrosion resistance is essential. Tin, tungsten, and tantalum are needed for batteries and capacitors used in electronic devices.

Among nonmetallic earth resources, fertilizers are used for agriculture; salt, sulfur, and soda for the chemical industry; and abrasives for sandpaper and grinding wheels. The construction industry uses cut stone, crushed rock, cement, plaster, brick, glass, and asbestos.

The energy sources obtained from the earth enable humans to perform many tasks faster than they could manually and others that they could not perform at all. Because most machines run on electricity, the output of the energy source often must first be converted into an electric current, while The internal combustion engine converts gasoline or diesel directly into power in conventional automobiles, trucks, and forklifts. Probably the best example of the direct use of an energy source is a wind-powered sailboat—a way of using energy that has not changed in more than five thousand years.

Principal Terms

alloy: a substance composed of two or more metals or of a metal and certain nonmetals

by-product: a secondary or incidental product of the refining process

fossil fuel: an energy source, such as coal, oil, or natural gas, which is formed from the remains of partly decayed organic matter

mineral: a naturally occurring, inorganic crystalline substance with a unique chemical composition

nonrenewable resource: an Earth resource that is fixed in quantity and will not be renewed within a human lifetime

ore deposit: a natural accumulation of mineral matter from which the owner expects to extract a metal at a profit

reservoir rock: the geologic rock layer in which oil and gas often accumulate; often sandstone or limestone

source rock: the geologic rock layer in which oil and gas originate; often the rock type known as shale

Bibliography

Boyle, Godfrey, ed. Renewable Energy. 2d ed. New York: Oxford University Press, 2004. Provides a complete overview of renewable energy resources. Discusses solar energy, bioenergy, geothermal energy, hydroelectric energy, tidal power, wind energy, and wave energy. Covers the basic physics principles, technology, and environmental impacts. Features references and a further reading list with each chapter.

Carlson, Diane H., et al. Physical Geology: Earth Revealed. 9th ed. New York: McGraw-Hill Science/Engineering/Math, 2010. A thorough introduction to physical geology. Includes a computer disc that corresponds to chapters and topics explored. Bibliography and index.

Chiras, Daniel D., and John P. Reganold. Natural Resource Conservation: Management for a Sustainable Future. 10th ed. Boston: Addison Wesley, 2009. Discusses resource use and solutions regarding sustainability and conservation. Covers case studies, laws, regulations and international treaties. Discusses natural resources, geographic information systems, and remote sensing.

Craig, James R., et al. Earth Resources and the Environment. 4th ed. Upper Saddle River, N.J.: Prentice Hall, 2010. Covers all Earth resources. Includes helpful line drawings, maps, tables, and charts. Features further reading and a list of principal ore minerals and production figures.

Craig, James R., et al. Resources of the Earth. 4th ed. Upper Saddle River, N.J.: Prentice Hall, 2010. Includes numerous black-and-white photographs, color plates, tables, charts, maps, and line drawings. Provides an excellent overview of the metal, nonmetal, and energy resources of the earth. Covers Earth resources throughout history. Suitable for college-level readers or the interested layperson.

Cutter, Susan L., and William H. Renwick. Exploitation Conservation Preservation: A Geographic Perspective on Natural Resource Use. 4th ed. Hoboken, N.J.: John Wiley & Sons, 2003. Offers information on the social, economic, political, and environmental effects of resource use. Offers detailed content useful for graduate students. Presents and leaves open to discussion varying views on unresolved issues.

Davidson, Jon P., Walter E. Reed, and Paul M. Davis. Exploring Earth: An Introduction to Physical Geology.2d ed. Upper Saddle River, N.J.: Prentice Hall, 2001. An excellent introduction to physical geology. Explains the composition of the earth, its history, and its state of constant change. Intended for the layperson. Includes colorful illustrations and maps.

Grotzinger, John, et al. Understanding Earth. 5th ed. New York: W. H. Freeman, 2006. General text on all aspects of geology. Appropriate for advanced high school and college students.

Jensen, John R. Remote Sensing of the Environment: An Earth Resource Perspective. 2d ed. Upper Saddle River, N.J.: Prentice Hall, 2006. Discusses the principles of remote sensing and use in geology, as well as remote sensing instruments and methodology. Covers specific resources analyzed through remote sensing, such as vegetation, water, soil and rocks, and geomorphic features. Provides practical information for use by geologists and graduate students.

Jensen, M. L., and A. M. Bateman. Economic Mineral Deposits. 3d ed. New York: John Wiley & Sons, 1981. Includes detailed information on different metallic and nonmetallic mineral deposits and their modes of formation. Covers the history of mineral use and the exploration and development of mineral properties. Cross-sections of individual deposits are provided. For college-level readers.

Sinding-Larsen, Richard, and Friedrich-W. Wellmer, eds. Non-renewable Resource Issues: Geoscientific and Societal Challenges. New York: Springer, 2012. Discusses the use, overuse, and future needs of natural resources. Elaborates on the various possible resource needs of the future. Discusses concepts of land use, sustainability, and cultural needs.

Tarbuck, Edward J., et al. Earth: An Introduction to Physical Geology. 10th ed. Upper Saddle River, N.J.: Prentice Hall, 2010. Provides a clear picture of the earth’s systems and processes. Appropriate for the high school or college reader. Includes illustrations, graphics, and a computer disc. Bibliography and index.

Tennissen, Anthony C. The Nature of Earth Materials. 2d ed. Englewood Cliffs, N.J.: Prentice-Hall, 1983. Contains detailed descriptions of 110 common minerals, with corresponding black-and-white photographs. Discusses the modes of formation and the classification of igneous, sedimentary, and metamorphic rocks. Includes an overview of metallic and nonmetallic mineral resources. Appropriate for college-level readers.

Thompson, Graham R. Introduction to Physical Geology. Fort Worth, Tex.: Saunders College Publishing, 1998. Provides an easy-to-follow examination of physical geology and the phases involved. Covers each phase of the earth’s geochemical processes. Excellent for high school and college readers. Illustrations, diagrams, and bibliography included.

Warren, John K. Evaporites: Sediment, Resources and Hydrocarbons. Berlin: Springer-Verlag, 2006. Discusses a number of evaporitic minerals, with Chapters 4 and 6 focusing on salts. Discusses chemistry and hydrology, deposit locations, and mining. Includes many drawings of geological features.

"What Is U.S. Electricity Generation by Energy Source?" U.S. Energy Information Administration, US Dept. of Energy, 18 Apr. 2017, www.eia.gov/tools/faqs/faq.php?id=427&t=1. Accessed 5 Sept. 2017.

"World Development Indicators: Electricity Production, Sources, and Access." The World Bank, 2017, wdi.worldbank.org/table/3.7. Accessed 5 Sept. 2017.