Summit; Environmental law in the United States; Gore, Al; Kyoto Protocol; United Nations climate change conferences; United Nations Convention on Long-Range Transboundary Air Pollution; United Na- tions Environment Programme. Greenpeace Category: Organizations, agencies, and programs Date: Established 1969 Greenpeace is an international environmental watch- dog organization concerned with protecting the Earth’s natural resources. Background Greenpeace evolved from activists’ concerns about nuclear testing near Alaska in the late 1960’s. Fearing catastrophic environmental damage, the organiza- tion’s founders relied on confrontational tactics to draw attention to their cause. Notably, Greenpeace members sought to “bear witness”: Simply being pres- ent where a wrongdoing was committed symbolized one’s objection to the act. This approach could entail such perilous and controversial tactics as sailing right up to a proposed nuclear test site and daring officials to set offdeviceswithhumans within the safety zone. Impact on Resource Use The idea of “bearing witness” expanded to include several other campaigns intended to protect the Earth’s natural resources and maintain biodiversity. Its activities on behalf of marine life, especially whales and seals, represented Greenpeace’s fight to protect wildlife from human destruction. Through showdown encounters with whaling vessels and seal hunters, Greenpeace joined an international call for a de- crease in—and ultimately the halting of—whale and seal hunting. Other environmental issues soon moved the orga- nization into new arenas. Campaigns emerged to arouse people’s concern and educate the world to the environmental dangersassociated with hazardous waste dumping, toxic chemical production, and global warming. Greenpeace’s techniques, although often contro - versial, brought international noticeto its causes. The organization proved successful in raising public awareness of threats to the Earth’s natural resources and calling for action to protect them. Jennifer Davis Web Sites Greenpeace Greenpeace International http://www.greenpeace.org/international/ Greenpeace Greenpeace USA http://www.greenpeace.org/usa/ See also: EarthFirst!; Environmental ethics; Environ- mental movement; Friends of the Earth Interna- tional; Hazardous waste disposal; National Audubon Society; Nuclear energy; Sea Shepherd Conservation Society. Groundwater Categories: Ecological resources; geological processes and formations; mineral and other nonliving resources Groundwater is that portion of the Earth’s subsurface water that is contained within the zone of saturation. It accounts for a much larger fraction of the total vol- ume of water in storage on the Earth than all of the combined fresh surface water. Background Groundwater is one of the most valuable natural re- sources: It serves as thesourceof a significant percent- age of the water used for all purposes. However, even though it is so widely used and so vital to the health and economy of all nations, the occurrence of ground- water is not only poorly understood butalso subject to many misconceptions. For example, one common misconception is that groundwater flows in large un- derground rivers that resemble surface streams. Folk- lore has it that these streams can be detected by cer- tain special individuals who practice “water dowsing.” Such misconceptions have hindered the development and conservation of groundwater and have negatively affected the protection of water quality. 548 • Greenpeace Global Resources Infiltration Groundwater is a majorcomponentof the hydrologic cycle, which is the constant movement of water above, on, and below the Earth’s surface. That fraction of pre- cipitation that can infiltrate the Earth’s surfacecan become part ofthesubsurface component of the hydrologic cycle. Infil- tration rates vary enormously, depending upon the intensityand duration of precip- itation, land use, and the physical charac- teristics and moisture content of the soil. For example, the infiltration rates can range from a high of 25 millimeters per hour in mature forests on sandy soils to only a few millimeters per hour in clayey and silty soils to zero in paved areas. The Unsaturated Zone Subsurface water occurs in two distinct zones in the ground. The uppermost zone contains both water and air and is called the unsaturated zone. It is divided into three parts: a soilzoneorsoil-water belt, an intermedi- ate zone, and the upper part of the capillary fringe. The soil-water belt extends from the top of the land surface to a maximum depth of about 1 to 2 meters. The porosity (the amount of openings in earth mate- rial) and the permeability (velocity of fluid flow within the Earth material) are higher in the soil-water belt than in the underlying intermediate zone. The capil- lary fringe is located in the lowest part of the unsatu- rated zone and results from the attraction between water and rocks. The thickness ordepthof the unsatu- rated zone varies from zero in swamps to a few meters in humid regions to more than 300 meters indeserts. The Saturated Zone The zone below theunsaturatedzone has all intercon- nected openings filled with water and is called the sat- urated zone. The top of the saturated zone is marked by the water table, which is the level at which the hy- draulic pressure is equal to atmospheric pressure. Water in the saturated zone is the only subsurface water that supplies wells, springs, and base flow to streams and is the only water which is properly called groundwater. Groundwater Movement In sharp contrast to surface water, groundwater moves very slowly. For example, surface water can move tens of kilometers per day, whereas groundwater flow ranges approximately from 1.5 meters per day to as low as1.5 metersper year. This slow movement means that any contaminant that gets into groundwater will be there for a long time. As part of the hydrologic cycle, groundwater also furnishes the stream with base flow or dry-weather flow. This is why streams in humid areas have water flowing in the channel days after precipitation has oc- curred. In fact, a large portion of streamflow is de- rived from base flow which is groundwater. Groundwater Recharge The source of groundwater is precipitation in the re- charge area that has percolated through the unsatu- rated zone and reached the water table. Once there, groundwater flows downthehydraulic gradient todis- charge areas along floodplains and streams. Average annual recharge ratesin the UnitedStates range from zero in desert areas to as much as 600 millimeters per year in rural areas in Long Island, New York, and simi- lar places along the Atlantic coastal plain that are un- derlain by permeable sands. These high recharge rates account for as much as 50 percent of average an- nual precipitation. The rate of groundwater movementfrom recharge areas to discharge areas depends upon the permeabil- ity and porosity of the Earth material. Shallow ground- water flow to discharge areas can be measured in days as compared with deep groundwater flow which can take decades, centuries, or even millennia to reach a discharge area. Global Resources Groundwater • 549 A standard aquifer system, featuring the flow times of different paths. (USGS) Groundwater Quality and Groundwater Pollution Water is often referred to as the universal solvent be- cause of its ability to dissolve at least small amounts of almost all substances that it contacts. Since groundwa- ter moves very slowly, it has plenty of time to dissolve earth materials. Thus, groundwater usually contains large amounts of dissolved solids. Groundwater pollution refers to any degradation of water quality that results from anthropogenic activ- ities. In urban and suburban areas, these activities in- clude disposal of industrial and municipal wastes in unlined landfills, leaking sewers, and application of lawn fertilizers, herbicides, and pesticides. Ground- water can be polluted in rural areas by septic tanks, an- imal feedlots, and application of crop fertilizers, her- bicides, and pesticides. Other sources of groundwater pollution include leaking gasoline and home-heating oil tanks, salt coming from unprotected stockpiles, and saltwater encroachment incoastal areas that have been overpumped. There have been numerous in- stances of groundwater pollution: Municipal wells on Long Island were forced to close because of a pre- World War II application of fertilizers to potato fields; public supply wells were closed in Massachusetts be- cause of excessive road salt applications; and well fields were contaminated by saltwater encroachment in Dade County, Florida, and Southern California (Manhattan Beach). Robert M. Hordon Further Reading Appelo, C. A. J., and D. Postma. Geochemistry, Ground- water, and Pollution. 2d ed. New York: Balkema, 2005. Fetter, C. W. Applied Hydrogeology. 4th ed. Upper Sad- dle River, N.J.: Prentice Hall, 2001. _______. Contaminant Hydrogeology. 2d ed. Upper Sad- dle River, N.J.: Prentice Hall, 1999. Palmer, Christopher M. Principles of Contaminant Hydrogeology. 2d ed. Boca Raton, Fla.: CRC Lewis, 1996. Price, Michael. Introducing Groundwater. 2d ed. New York: Chapman & Hall, 1996. Todd, David Keith, and Larry W. Mays. Groundwater Hydrology. 3d ed. Hoboken, N.J.: Wiley, 2005. Younger, PaulL. Groundwater in the Environment: An In- troduction. Malden, Mass.: Blackwell, 2007. Zektser, Igor S., and Lorne G. Everett, eds. Ground Water Resources of the World and Their Use. Paris: UNESCO, 2004. Reprint. Westerville, Ohio: Na - tional Ground Water Association Press, 2006. Web Sites Natural Resources Canada Groundwater http://atlas.nrcan.gc.ca/site/english/maps/ freshwater/distribution/groundwater/1 U.S. Environmental Protection Agency Aquatic Biodiversity: Groundwater http://www.epa.gov/bioiweb1/aquatic/ground- r.html U.S. Geological Survey USGS Groundwater Information Pages http://water.usgs.gov/ogw See also: Aquifers; Glaciation; Hydrology and the hydrologic cycle; U.S. Geological Survey; Water; Water pollution and water pollution control; Water supply systems; Wetlands. Guano Category: Plant and animal resources Accumulated bird excrement,rich in nitrogen, isknown as guano and offers a renewable source of fertilizers. Definition Guano is a renewable natural fertilizer. It is found in commercial quantities only on a few desert islands where millions of fish-eating sea birds roost undis- turbed. Overview There is archaeological evidence that guano was col- lected and used by prehistoric Peruvian farmers, who called it huano. Nineteenth century application of guano to the exhausted soils of Europe was first advo- cated by the German agronomist Georg Leibig after its introduction in the 1830’s by the noted scientist and South American explorer Alexander von Hum- boldt. The dramatic increases it caused in wheat, corn, and cotton production created enormous de- mand for this product, which was soon being dug by hundreds of Chinese laborers forced to work on the Chincha Islands south of Lima, Peru. 550 • Guano Global Resources These rain-free guano islands arepopulated by mil - lions of cormorants, gannets, and pelicans that fly out to sea daily to eat anchovies and sardines. The fish themselves feed on plankton they find in the cold, north-flowing Chile-Peru (Humboldt) Current. When this current is occasionally displaced by a warm (El Niño) countercurrent, the entire ecosystem collapses, and many sea birds begin to die of starvation. A guano boom began in 1851, when the U.S. Con- gress passed legislation allowing any American citizen to declare uninhabited guano islands as territory of the United States. Under the provisions of this little- known act, several Caribbean and South Pacific is- lands were so claimed. One of them, Navassa, located midway between Cuba and Haiti, remains an undis- puted U.S. territorial possession to this day under ju- risdiction of the U.S. Fish and Wildlife Service. Sub- fossil guano deposits found there are thought to be the excrement of a fish-eating bat. Although the Peruvian government recognized guano as a strategic and highly valuable natural re- source, little was done to protect the industry from foreign interests and political intrigue. In order to meet financial obligations and service debts, the gov- ernment mortgaged its guano resources for quick cash loans from foreign business firms selling the in- creasingly valuable Chincha guano. Failure to protect the guano-producing birds, as well as ignorance of the complex ecology of their hab- itat, eventually resulted in the decline of the industry in the face of overwhelming competition from Chil- ean sodium nitrate deposits discovered in the 1870’s. Not untilthe 1910’s wasany progress madein reviving the resource. Based on the advice of foreign ichthyol- ogists and the American ornithologist Robert Cush- man Murphy, good conservation practices were be- gun by Francisco Ballen, director of the newly created Compañía Administradora del Guano. Global Resources Guano • 551 A massive guano-collecting structure juts from the guano-covered, rocky shoreline of the Ballestas Islands off the coast of Peru. (©Jarnogz/ Dreamstime.com) The impact of several disastrous El Niño events beginning in 1925, together with severe overfishing of anchovy stocks, seriously retarded the buildup of new Peruvian guano deposits. No longer exported, Chincha guano is now used exclusively for the benefit of Peruvian agriculture. Guano is also collected elsewhere in the world and used locally; farmers in Baja California, Mexico, and some regions of western Africa, for example, use it as fertilizer. Bat-guano deposits oftenoccur in caves with sufficiently large bat populations. Seal excrement is also sometimes included in the definition of guano. Bird guano, however, has a higher concentration of fertilizing nutrients (notably nitrogen and phospho- ric acid) than either bat or seal guano. From the study of any deep undisturbed sequence of guano may come a valuable scientific record of environmental conditions that prevailed while it was accumulating. Identifying and dating ancient layers showing disturbed conditions can give statistical clues to hidden climatic cycles and the ability to predict fu- ture long-range changes in weather patterns. Alan K. Craig See also: El Niño and La Niña; Fertilizers; Nitrogen and ammonia. Guggenheim family Category: People The Guggenheims are an American family who domi- nated mining and refining operations worldwide in the first quarter of the twentieth century. Aggressively controlling and extracting metals and minerals in the United States and developing countries, the Guggen- heims built one of the world’sgreatfortunes,whichthey used for philanthropic enterprises in the latter half of the twentieth century. Biographical Background The founder of the family business, Meyer Guggen- heim (1828-1905), was a Jewish immigrant from a Swit- zerland ghetto. Accumulating capital from his Phila- delphia store, he bought shares in Colorado mines in 1880. When the mines struck a silver bonanza, the Guggenheims’ rise was launched on an empire of global resources. A partnership of Meyer and his seven sons, M. Guggenheim’s Sons, bought mines and smelting operations in Mexico and throughout the world. (Smelting is the refining operation that ex- tracts the valuable metal resources from the mined ore.) In 1899, Guggenheim and his sons started the Guggenheim Exploration Company (Guggenex) to consolidate and extend their interests. In 1901, after an epic business battle, the Guggen- heims took control of the American Smelting and Re- fining Company (ASARCO), a trust that dominated the mining industry. Second-oldest son Daniel (1856- 1930) became president of ASARCO and aggressively expanded Guggenheim ventures into zinc and cop- per mining and to other continents. Daniel’s son Harry Guggenheim (1890-1971) led a third genera- tion of Guggenheims in additional entrepreneurial and philanthropic enterprises; his palatial Sands Point estate is preserved in Port Washington, New York. Peggy Guggenheim (1898-1979) was a prominent art collector and socialite. Impact on Resource Use The Guggenheims dominated the worldwide mining and smelting industry in the beginning of the twenti- eth century through their ASARCO trust. Their oper- ations began with silver and lead mines and smelters in the western United States, and, in 1890, in Mon- terrey, Mexico. Contracting with autocratic Mexican president Porfirio Díaz and with low-wage Mexican workers, the Guggenheimsbecame the leadingindus- trialists of Mexico. Their ASARCO and Guggenex firms expanded into copper mines in Utah in 1905 and silver mines in Nevada and Ontario, Canada, in 1906. In 1910, they acquired extensive copper mines in Chile, adding the label “Copper Kings” to their so- briquet of “Silver Kings.” Pioneering large-scale mining operations through- out the globe, the Guggenheims mined for nitrates in Chile, tin in Bolivia, copper in Australia, diamonds in Africa, and gold in Peru and the Yukon. Their rubber plantations in the Congo were barely profitable and entangled the Guggenheims in the brutal colonial competition for African resources. In 1911, they were subjected to congressional scrutiny for their efforts to develop Alaskan resources. Their various firms were continually suspected of antitrust violations. The Gug- genheims didnot hesitate to use force against striking mineworkers but laterattained a reputation for better treatment of their employees and for steps to reduce the pollutants spewing from their refineries. 552 • Guggenheim family Global Resources After World War I, the extended Guggenheim clan sold many of their mining and smelting interests, in- creasing their vast liquid fortune and turning their at- tention to charitable and social matters. Among their many philanthropies were a foundation to provide dentistry for the poor, donations to the Mayo Clinic and Mount Sinai Hospital, and the support of various educational enterprises, most prominently the Gug- genheim Fellowships. The GuggenheimAeronautical Laboratory opened in 1926, and the magnificent Solomon Guggenheim Art Museum in Manhattan opened in 1959. Howard Bromberg See also: Copper; Diamond; Silver; Tin. Gypsum Category: Mineral and other nonliving resources Where Found Gypsum is the most common sulfate mineral. It is widely distributed in sedimentary rocks, frequently occurring with limestones and shales. It is commonly associated with minerals such as rock salt, anhydrite, dolomite, calcite, sulfur, pyrite, galena, and quartz. Gypsum is mined extensively in many parts of the world. Primary Uses Gypsum is used in the construction industry, espe- cially for the manufacture of plasters, wallboard, and tiles. It is also used in cements, as a filler in paper and paints, and as a fertilizer and soil conditioner. Technical Definition Gypsum is a hydrated calcium sulfate (CaSO 4 C 2H 2 O). Its average molecular weight is 172.18, and its specific gravity is 2.32. This mineral forms white or colorless prismatic crystals; impurities may add a grayish, red- dish, yellowish, bluish, or brownish tint. Its hardness on the Mohs scale is 1.5 to 2. Gypsum has a character- istic three-way cleavage; that is, it breaks along three different crystallographic planes. It is insoluble in water and soluble in acids. When heated to between 190° and 200° Celsius, gypsum loses three-quarters of its water of crystallization to become calcium sulfate hemihydrate (2CaSO 4 C H 2 O), also known as plaster of paris. Heating to more than 600° Celsius drives off all water to produce anhydrous or dead-burnedgypsum. Description, Distribution, and Forms Gypsum, a widely distributedsedimentary deposit, is a soft, colorless, or light-colored mineral that can be scratched with the fingernail. Its crystals often form arrowhead-shaped or swallowtail-shaped twins (two individual crystals joined along a plane). When heated to drive off much of its water of crystallization, gyp- sum istransformed into plaster of paris (so named be- cause of the famous gypsum deposits of the Mont- martre district of Paris, France). When reduced to a powder and mixed with water, plaster of paris forms a slurry that setsquickly and graduallyre-forms again as tiny interlocking crystals ofgypsum. Its properties asa natural plaster make gypsum an important resource for construction and other industries. In 2008, the United States produced about 12.7 million metric tons of gypsum, and total world production was about 151 million metric tons. Gypsum, the most common sulfate mineral, is widely distributed in sedimentary rocks. It forms thick, extensive evaporite beds, especially in rocks of Perm- ian and Triassic age. In the United States, gypsum is present in rocks of every geologicera except theCam- brian. Because gypsum is normally deposited before anhydrite and salt during theevaporation of seawater, it often underlies beds of these minerals. Other min- erals with which gypsum is frequently associated in- clude dolomite, calcite, sulfur, pyrite, galena, quartz, and petroleum source rocks. Massive layers ofgypsum frequently occur interbedded with limestones and shales, and lens-shaped bodies or scattered crystals are found in clays and shales. Gypsum is common in volcanic regions, particularly where limestones have been acted uponbysulfur vapors. It isalso found in as- sociation with sulfide ore bodies. Extensive gypsum deposits are found in many localities throughout the world, including the United States, Great Britain, Thailand, Iran, Canada,China, France, and Australia. In Arizona and New Mexico there are large deposits in the form of wind-blown sand. Gypsum occurs in nature in five varieties: gypsum rock, a bedded aggregate consisting mostly of the mineral gypsum; gypsite, an impure, earthy variety that is found in association with gypsum-bearing strata in arid regions; alabaster, a massive, fine-grained form, white or delicately shadedandoften translucent; satin spar, a white, translucent mineral with a fibrous struc - Global Resources Gypsum • 553 554 • Gypsum Global Resources Million Metric Tons Source: Mineral Commodity Summaries, 2009Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009. Algeria Australia Austria Brazil Canada China Egypt France Germany India Iran Italy Japan Mexico Poland Russia Spain Thailand United Kingdom United States Uruguay Other countries 1,300,000 4,100,000 1,000,000 1,700,000 7,300,000 40,700,000 2,000,000 4,700,000 1,700,000 2,800,000 12,000,000 5,500,000 5,700,000 5,800,000 1,700,000 2,400,000 11,300,000 8,800,000 1,700,000 12,700,000 1,100,000 14,900,000 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 Gypsum: World Mine Production, 2008 ture and a silky luster; and selenite, a transparent, col - orless, crystalline variety. Gypsum is rarely found in its pure form. Deposits may contain quartz, sulfide minerals, carbonates, and clayey and bituminous materials. Gypsum dehydrates readily in nature to form anhydrite (CaSO 4 ), a min- eral with which it is often associated; bassanite (2CaSO 4 C H 2 O) forms much more rarely. High-tem- perature and low-humidity environments favor the formation of anhydrite. Anhydrite can also hydrate to form gypsum. Gypsum deposits formed by the alter- ation of anhydrite may show folding due to the in- creased volume of the mineral in its hydrated state. History The Chinese, Assyrians, and Greeks made decorative carvings from gypsum. The Greek philosopher Theo- phrastus (371-287 b.c.e.) wrote of burning gypsum to create plaster. Gypsum’s properties as a plaster were also known to the early Egyptians, who used a crude gypsum plaster in such building projects as the pyra- mids. Gypsum gained widespread use as a soil condi- tioner in eighteenth century Europe. The develop- ment of a commercial method for retarding the setting of gypsum plaster in 1885 made it possible to use gypsum for more construction applications. Obtaining Gypsum Gypsum is generally obtained through open-pit min- ing, although some underground mining is per- formed where the material is of a high quality or is close to the consuming market. Gypsum may be crushed and ground for use in dihydrate form, heated to produce plaster of paris, or completely de- hydrated to form anhydrous gypsum. Uses of Gypsum Unaltered gypsum is commonly used to slow the rate of setting in portland cement. Other major uses in- clude the manufacture of wallboard, gypsum lath, and artificial marble products. Its sulfate contents make it useful for agriculture, where it serves as a soil conditioner and fertilizer. Gypsum is used as a white pigment, filler, or glaze in paints, enamels, pharma- ceuticals, and paper. It is also used in making crayons, chalk, and insulating coverings for pipes and boilers. Other uses are as a filtration agent and a nutrient in yeast growing. Plaster of paris is used for builder’s plaster and the manufacture of plaster building materials such as moldings and panels. In medicine, plaster of paris is used for surgical casts, bandages, and supports and for taking dental and other impressions. The anhy- drous formofgypsum is used incementformulations; in metallurgy; in the manufacture of tiles, plate glass, pottery, and paints;and as a paper filler. Because of its water-absorbing nature, it is also used as a drying agent. Alabaster, a form of gypsum that can be carved and polished with ease because of its softness, is fashioned into ornamental vessels, figures, and statuary. Satin spar is used in jewelry and other ornaments. Karen N. Kähler Further Reading Bates, Robert L. Geology of the Industrial Rocks and Min- erals. New York: Dover, 1969. Carr, Donald D., ed. Industrial Minerals and Rocks. 6th ed. Littleton, Colo.: Societyfor Mining, Metallurgy, and Exploration, 1994. Chatterjee, Kaulir Kisor. “Gypsum.” In Uses of Indus- trial Minerals, Rocks, and Freshwater. New York: Nova Science, 2009. Kogel, Jessica Elzea, et al., eds. “Gypsum and Anhy- drite.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration, 2006. Myers, Richard L. The One Hundred Most Important Chemical Compounds: A Reference Guide. Westport, Conn.: Greenwood Press, 2007. Pellant, Chris. Rocks and Minerals. 2d American ed. New York: Dorling Kindersley, 2002. Web Sites Natural Resources Canada Canadian Minerals Yearbook, Mineral and Metal Commodity Reviews http://www.nrcan-rncan.gc.ca/mms-smm/busi- indu/cmy-amc/com-eng.htm U.S. Geological Survey Gypsum: Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/gypsum See also: Australia; Canada; Cement and concrete; China; Evaporites; Fertilizers; France; Iran; Mexico; Mohs hardness scale; Sedimentary processes, rocks, and mineral deposits; Thailand. Global Resources Gypsum • 555 H Haber-Bosch process Category: Obtaining and using resources The Haber-Bosch process, named for Fritz Haber (1868-1934) and Carl Bosch(1874-1940), two Nobel Prize-winning German chemists, was the first commer- cially successful process to overcome the chemical inert- ness ofnitrogen gas and allow it to betransformed into ammonia, which can be utilizedas a nitrogen fertilizer for plant growth. Definition The Haber-Bosch process isa chemical process, devel- oped in Germany in the early twentieth century, that enables nitrogen tobe obtained from the atmosphere and transformed into ammonia. Afterward, it be- comes usable in products such as chemicals, pharma- ceuticals, and fertilizers. Overview All living things need nitrogen. It is an essential com- ponent of compounds such as proteins and amino ac- ids. However, although plants and animals live in a world surrounded by nitrogen gas (78 percent of the atmosphere is nitrogen gas, a relatively inert com- pound), little of it is available to them. The stability of nitrogen gas, because of the strength of the triple bond in the molecule, means that of all nutrients in the biosphere, nitrogen is one of the least available nutrients for plant and animal growth. Only a few spe- cialized bacteria, in a process called biological nitro- gen fixation, are able to utilize the nitrogen gas sur- rounding them. Fritz Haber developed the process of extracting ammonia from nitrogen in his laboratory at Karls- ruhe, Germany. Carl Bosch made its industrial appli- cation possible by scaling up the laboratory process for his employers at Badische Anilin und Soda Fabrik (BASF) in Ludwigshafen am Rhein, Germany. The Haber-Bosch process mimics biological nitro - gen fixation on an industrial scale. One molecule of nitrogen gas (N 2 ) and three molecules of hydrogen gas (H 2 ) are combined to yield two molecules of am- monia (NH 3 ): N 2 + 3H 2 ↔ 2NH 3 The reaction is reversible, and there is no tendency for ammonia to form unless an enzyme catalyst is used (as in biological nitrogen fixation) or the reac- tion is conducted at an extremely high temperature (450° Celsius) and extremely high pressure (200 at- mospheres or 20.2 million pascals) in the presence of an iron catalyst. More than 90 million metric tons ofnitrogen fertil- izer are produced by the Haber-Bosch process each year. Much is used directly for fertilizer. Most, how- ever, isused for otherprocesses,such as production of nitrogen-containing chemicals, pharmaceuticals,and explosives. The Haber-Bosch process, which became a commercial reality when the first plant began oper- ating in 1913, allowed Germany to continue making armaments and explosives despite a blockade of its ports by England in World War I. The nitrogen in the Haber-Bosch process comes from air, but the hydrogen generally comes from the reaction of natural gas or methane with steam at high temperatures. Consequently, most of the cost associ- ated with the process comes from the hydrocarbons used to heat the system and supply the hydrogen. As a result, the price of fertilizer nitrogen tends to fluctu- ate with the price of energy. The oil embargo insti- tuted in 1973 by the Organization of Petroleum Ex- porting Countries (OPEC) had a trickle-down effect on agriculture, since it raised the cost of energy re- quired for the Haber-Bosch process enormously. As a result, it had the unintended effect of stimulating research in biological nitrogen fixation as a cheaper alternative forimproving the nitrogen fertility of soil. Mark S. Coyne See also: Agriculture industry; Eutrophication; Fer- tilizers; Food shortages; Nitrogen and ammonia; Oil embargo and energy crises of 1973 and 1979; Organi - zation of Petroleum Exporting Countries; Soil man - agement. Halite. See Salt Hall, Charles Martin Category: People Born: December 6, 1863; Thompson, Ohio Died: December 27, 1914; Daytona Beach, Florida Aluminum was well known by the middle of the nine- teenth century, but it was expensive to obtain. Charles Martin Hall developed a method of reducing alumi- num oxide cheaply by electrolysis of a molten salt mix- ture—essentially the same method used in the twenty- first century. World production of aluminum by the electrolytic process has risen into the range of billions of kilograms annually. Biographical Background In 1873, Charles Martin Hall’s parents moved from Thompson to Oberlin, Ohio, where Hall studied at Oberlin College, graduating with a bachelor of arts degree in 1885. He became interested in the produc- tion of aluminum and started to do research in the college laboratory. After graduation, Hall continued his research in a woodshed behind the family home, assisted from time to time by his sister Julia. He con- structed his own equipment, even the voltaic cells, for a source of electricity. A key discovery was the use of the mineral cryolite (sodium hexafluoroaluminate) as a solvent for aluminum oxide at an elevated tem- perature. By the summer of 1886, Hall had obtained his first samples of aluminum and submitted a patent application for his process. The electrolytic method was discovered virtually simultaneously by Paul Hé- roult (1863-1914) in France. Hall went on to found an aluminum industry, first at the Pittsburgh Reduction Company and later at the Aluminum Company of America (ALCOA). He was awarded the Perkin Medal of the American Section of the Society of Chemical Industry in 1911. Impact on Resource Use Aluminum compounds are abundant in the Earth’s crust, firmly united with oxygen in minerals such as bauxite, clay, and feldspar. Bauxite is the only impor- tant ore. Freeing the metal from oxygen constitutes the essential problem for aluminum production. Elec - trolysis of water solutions of aluminum compounds failed to produce the metal. Early commercial pro- cesses involved electrolysis of sodium chloride toform sodium metal, which was then used to produce alumi- num from its chloride, a relatively inefficient and costly arrangement. Hall’s discovery of the direct electrolytic process, and its refinements over the years of 1889 to 1914, made possible a dramatic reduction of the price of aluminum to about $0.08 per kilogram. The process operates at about 1,220 kelvins (947° Celsius) and in- volves passage of electric current between carbon electrodes through a molten electrolyte of aluminum oxide (alumina) dissolved in the mineral cryolite (sodium hexafluoroaluminate). The alumina used is made from bauxite by the Bayer process. Resistive heating is sufficient tokeep the electrolyte liquid, and the aluminum metal is formed as a liquid at the cath- ode and tapped off periodically at the bottom of the electrolysis cell. Oxygen gas is formed at the anode and combines with the carbon of the electrode. The Global Resources Hall, Charles Martin • 557 Charles Martin Hall developed an inexpensive method of obtaining aluminum that is essentially the same method in use today. (Cour- tesy, Alcoa Inc.) . heated to drive off much of its water of crystallization, gyp- sum istransformed into plaster of paris (so named be- cause of the famous gypsum deposits of the Mont- martre district of Paris, France) little of it is available to them. The stability of nitrogen gas, because of the strength of the triple bond in the molecule, means that of all nutrients in the biosphere, nitrogen is one of the. constant movement of water above, on, and below the Earth’s surface. That fraction of pre- cipitation that can infiltrate the Earth’s surfacecan become part ofthesubsurface component of the hydrologic