Encyclopedia of Global Resources part 29 pptx

geared toward improving the water productivity in river basins. The emphasis of the program is to create synergies andpartnerships amongthe stakeholdersin ways that are pro-poor, gender equitable, and envi- ronmentally sustainable. Since the 1970’s, climate change has been a research area of interest to CGIAR scientists. They have been working on theeffects of climate change on natural resources, including water resources, and devel- oping crop varieties that can continue to provide the needed food to an ever-growing world population. The scientistshave also been active in identifyingpoli- cies and newapproaches forcommunities todeal with climate change and its consequences. All these years of research have led to the release of improved crop varieties, new farming techniques and crop production methods, and the development of policies to help rural populations, especially indeveloping countries, manage natural resources in a sustainable way. Lakhdar Boukerrou Web Site Consultative Group on International Agricultural Research http://www.cgiar.org See also: Agriculture industry; Agronomy; Green- house gases and global climate change; Land Insti- tute; Land-use planning. Copper Category: Mineral and other nonliving resources Where Found Copper deposits are found inseveral types of geologic environments. Most common are the porphyry copper ore deposits that formed in magmatic arcs associated with subduction zones. These types of ores are found in Canada, the western United States, Mexico, Peru, and Chile. Other important copper deposits were formed by different processes and are found in central Europe, southern Africa, Cyprus, Indonesia, and Japan. Primary Uses The major usesof copperare in the electricalindustry because of the substance’s ability to conduct electric - ity efficiently. Copper is also utilized extensively in the construction industry especially for plumbing. Most of the remaining copper is alloyed with other metals to make bronze (with tin), brass (with zinc), and nickel silver (with zinc and nickel, not silver). Technical Definition Copper (chemical symbol Cu) is a reddish mineral that belongs to Group IB of the periodic table. Cop- per has an atomic number of 29 and an atomic weight of 63.546, and it is composed of two stable isotopes, copper 63 (69.17 percent) and copper 65 (30.83 percent). Pure copper has a face-centered cubic crystal- line structure with a density of 8.96 grams per cubic centimeter at 20° Celsius. The melting point of copper is 1,083° Celsius, and the boiling point is 2,567° Celsius. Description, Distribution, and Forms Copper is a ductile metal and a good conductor of heat and electricity. It is not especially hard or strong, but these properties can be increased by cold working of the metal. Copper is a relatively rare element, making uponly 50 parts per billion in the Earth’s crustal rocks. It occurs in nature both in elemental form and incorporated into many different minerals. The primary minerals are the sulfides (chalcopyrite, bornite, covellite, and others), oxides (cuprite and others), and carbonates (malachiteand azurite). Copper has two valences (degrees ofcombining power), +1 and +2, and important industrial compounds have been synthesized using both oxidation states. The most useful industrial +1 (cuprous, or Cu I) compounds are cuprous oxide (Cu 2 O), cuprous sulfide (Cu 2 S), and cuprous chloride (Cu 2 Cl 2 ). Important +2 (cupric, or Cu II) compounds used by industry are cupric oxide (CuO), cupric sulfate (CuSO 4 ), and cupric chloride (CuCl 2 ). Although copper is relatively rare in the crust of the Earth, it has been concentrated into ore deposits by geologic processes. There are four major types of copper ore deposits, each formed by a different set of geologic events. Most of the copper mined is taken from porphyry copper deposits.These deposits are composedof copper minerals disseminated fairly evenly throughout porphyritic granitic rocks and associated hydrother- mal veins. The primary ore mineral is chalcopyrite, a copper/iron sulfide. Porphyry copper ore deposits are generally located in rocks that have been formed 250 • Copper Global Resources near convergent plate boundaries where the granites have been produced from magma generated during the subduction of an oceanic plate beneath a continental plate. This tectonic regime has existed along the western coastsof North America and South Amer- ica for more than 200 million years; consequently, gi- ant porphyry copper deposits are found in western Canada, the western UnitedStates, Mexico,Peru, and Chile. The world’s two largest producers of copper are Chile and the United States, and the largest copper ore deposit in the world is located in Chile. Other porphyry copper depositsare foundin Australia, New Guinea, Serbia, the Philippines, and Mongolia. A second kind of copper ore deposit is commonly called a Kupferschiefer type because of the large quantity of copper found in the Kupferschiefer shale of central Europe. Thecopper occursin a marineshale that is associated with evaporites and nonmarine sedi- mentary rocks. The origin of the copper in these ores is still debated. The Zambian-Democratic Republic of the Congo copper belt of southern Africa contains morethan 10 percent ofthe world’s copper reserves. Copper is also found in massive sulfide deposits in volcanic rocks, ophiolites, greenstone belts, and fumarolic deposits. Copper-bearing massive sulfide ores are found in Canada, Cyprus, and Japan. Global Resources Copper • 251 Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009.Source: Mineral Commodity Summaries, 2009 650,000 460,000 270,000 1,220,000 430,000 750,000 1,310,000 560,000 2,030,000 Metric Tons 6,000,0005,000,0004,000,0003,000,0002,000,0001,000,000 Zambia Poland Peru Mexico Kazakhstan Indonesia Russia United States Other countries China Chile Canada Australia 850,000 590,000 5,600,000 1,000,000 Copper: World Mine Production, 2008 A fourth type of copper deposit is found on the deep-ocean floors, where manganese nodules have formed very slowly inareas of unusuallyslow sedimen- tation. These nodules contain not only manganese but also copper, cobalt, and nickel in economically important concentrations. Since these nodules generally form in water depths of 900 to 2,000 meters, they are difficult to mine. They do, however, represent an important potential source of copper for the future. Copper is an essential trace element of life and is found in various concentrationswithin plantsand animals. For example, copper is found in many blue- blooded mollusks and crustaceans because it is the central element in hemocyanin, a molecule that trans- ports oxygen in the organisms. It is found in lesser concentrations in many other organisms, such as sea- weeds, corals, and arthropods. Copper can be found in most soils, and its absence or unavailability to plants will cause the soil to be relatively infertile. For example, many muck soils that are very rich in organic material cannot sustain plant life because the copper is bound to the organic matter and is therefore not available to plants. Some soils have suffered from copper pollution at- tributable to the excess of copper-bearing fertilizers and the application of copper-rich fungicides or sewage wastes tothe land. Researchhas shown thatthe ac- cumulations of copper in these soils will not be effec- tively leached from the land for decades or even centuries because the copper has an affinity for soil colloids that can tightly bind the copper. Copper is distributed throughout the Earth’s lithosphere, hydrosphere, atmosphere, and pedosphere in variousconcentrations. About 5 percent ofthe copper content of the lithosphere is found in sedimen- tary rocks, particularly shale, and only about 0.00004 percent in soils. Only about 0.001 percent of the copper of the lithosphere is in exploitable concentrations, and some of thesedeposits have been minedfor centuries. The total production of copper by mining is approximately 300 million metric tons, of which about 80 percent was mined in the twentieth century. Almost 30 percent of the entire world’s historic production of copper was mined in the 1980’s. The total copper mined amounts to about twice the total copper in the upper 2 centimeters of soil worldwide and nearly tentimes thetotal copper found in all living organisms. Much ofthe copper produced hasbeen used and thendisposed of on land or wasted inwater orthe atmosphere. The impact of the transfer of this much copper from the deposits of the crust to the surface of the Earth is not yet well understood. The total amountof copperreleased intothe atmosphere has been estimated to be almost three times the amount of carbon in the atmosphere today. The residence time of copper in the atmosphere is quite short, and there probably has not been a significant buildup of copper overtime, butthe atmosphere does act as a medium for transferring copper around the globe. Copper pollution of many local ecosystems has been well documented in areas near smelters and copper mines. Although it is clear that copper con- centrates in the soils andwaters near theareas, the impact of copper pollution is often hard to separate from the environmental effects resulting from increased levels of other heavy metals and from sulfur dioxides and other gases released from smelters. Research has also shown that urban areas generally have much higher levels of copper in the soils and air than are found in rural areas. In many cases the copper concentration in urban soils is more than ten times that of nearby rural areas. In addition, it is well established that the dumping of sewage into rivers, lakes, and the ocean can raise the concentrations of copper in the sediments by factors of two to one hundred times the background levels in unpolluted areas. However, distinguishing the environmental impact of copper from the effects of the associated metals found in sewage effluent is difficult. Copper is an essential element in the human diet. It is found in several oxidative enzymes, such as cyto- chromes a and a3, ferroxidase, and dopamine hy- droxylase. The copper is used by enzymes in the oxidation and absorption of iron and vitamin C. The level of copper in the body is primarily controlled by the excretion ofthe elementin bile. Absorbed copper is probably stored internally by some intracellular proteins. Generally, copper deficiencies in humans are rare. There are two known genetic diseases, Wilson’s disease and Menkesdisease, that disrupt coppermetabo- lism. In Wilson’s disease, an unknown mechanism re- stricts the excretion of copper in bile, and as a result copper builds up in various tissues in the body. Once diagnosed, Wilson’s disease can be treated by giving the patient a chelating agent to remove the accumu- lated copper. Menkes disease, commonly called steely or kinky hair syndrome, causes inefficient utilization of copper in the body. This lack of copper affects the normal formation of connective tissue and the loss of 252 • Copper Global Resources some widespread enzymatic activity. Death generally occurs within the first three years. History Copper was one of the first metals mined and usedby humans. It,along with gold and silver, occurs naturally as a free elemental metal and thus can be extracted and used without smelting or refining. Neolithic humans probably learned that this un- usual metal could be shaped by ham- mering with stone tools and that the copper tools could be hardened by continued cold working. The first use of copper probably predated 8000 b.c.e. By 6000 b.c.e. it was known that copper could be melted in crude furnaces and poured into casts to elaborate weapons and ornaments. Egyptian copper artifacts are dated as far back as 5000 b.c.e., and ancient Egyptians appear to have been the first to alloy copper with tin to make bronze. The earliest record of a bronze artifact dates to about 3700 b.c.e. Bronze makes better weapons and ornaments because it is much harder and tougher than pure copper. As a result, the bronze technology spread throughout the Middle East and into Asia. Bronze items at least as old as 2500 b.c.e. have been found in China, but the alloy may have been used earlier. Bronze was superseded by iron as the metal of choice for weapons and for structural uses. This tech- nological advance occurred after furnaces were devel- oped that could obtain temperatures high enough to smelt iron from its ores. After the introduction of iron and later steel into common use, copper and its alloys were used primarily for ornaments, utensils, pipes for plumbing, and coinage. Because of its natural resis- tance to most corrosion caused by air and seawater, copper wascommonly utilized for purposes requiring such protection. The discovery of electricity and the invention of the incandescent lightbulb and electric motors led to theextensive useof copperfor the trans- mission of electricity. This became the most common and most important use of copper. Obtaining Copper Copper is mined in fifty to sixty countries worldwide, with Chile accounting for about 35 percent of the production in 2008. The primary ore minerals of copper are chalcopyrite (copper-iron sulfide), chalcocite (copper sulfide), covellite (copper sulfide), azurite (copper carbonate), and malachite (copper carbonate). Other ore minerals of lesser importance are native copper, bornite, enargite, tetrahedrite, cuprite, tenorite, chalcanthite, and chrysocolla. The copper sulfide minerals are found in porphyry, massive sulfide, andKupferschiefer typedepos- its, and the copper carbonates and copper oxides are commonly found in the upper zones of such deposits that have been exposed to weathering and ground- water action. Much of the copper of the world is extracted from open-pit mines that expose the ore deposits. The overburden of surrounding rock or soil covering the ore is physically removed, and the ore extracted by drilling and detonating explosives to loosen the ore. Underground mining is done using standard techniques of tunneling and blasting. The ore from either underground mines or open-pit mines is then gath- ered and hauled to ore processing plants, where the ore is crushed and the copper and other metals are concentrated. The concentrated ore usually mea- sures 20 to 30 percent copper, and it is then either smelted or leached to produce a relatively high concentration of copper, which still contains some impu - rities. This smelted copper is then electrolytically re - fined to a purity of more than 99 percent. Global Resources Copper • 253 A worker in a Chinese factory guides a forklift loaded with rolls of copper tubes. (AP/ Wide World Photos) Uses of Copper Copper was one of the first metals used by humans because it can be found in nature as pure metal and can be worked easily by hand. Pure copper was probably first mined and used by humans around 8000 b.c.e. Through the ensuing ages, copper has remained an important metal and a component of such important materials as pewter, brass, and other bronzes. After the Industrial Revo- lution, copper became the second most used metal in the industrial world behind only iron. However, the discovery of aluminum, its properties, and its general availability made aluminummore useful in modern society. Copper is one of the most commonly used metals in the world, and, because of its special qualities of high ductility and electrical conductivity, it is used extensively in the electrical industries. Copper that has been refined electrolytically is up to 99.62 percent pure; the primary remaining material is oxygen. The oxygen helps to increase the density and conductivity of copper wire. Thewire canbe produced inlarge quantities by rolling the copper into rods, which are then drawn through tungsten carbide or diamond dies to form the wire. Copper is also produced in sheets or smaller strips by initially rolling hot copper, with later rollings done with cold copper. The resultant strips or sheets are generally of even thickness and uniform surface ap- pearance. This strip copper can be cut or pressed to be used in the electrical or construction industries. One of the earliest uses of copper was in the production of bronze. The early bronzes were copper/ arsenic alloys; later, tin was added at various concentrations. Modern bronzes are alloys of copper and tin, and they are used primarily for ornaments, bells, and musical instruments. The bronze used in making bells and musical instruments usually contains up to 20 percent tin to impart the proper tonal qualities to the sounds produced from these instruments. An- other traditional use for copper is in the production of pewter, which is an alloy of copper and lead. Since lead is highly toxic, the use of pewter has been re - stricted in recent times and is generally reserved for ornamental pieces. Brass is a widely used alloy of copper and zinc. Al- though the coppercontent of brasscan range from less than 5 percent to more than 95 percent, only brasses of at least 55 percent copper can be worked and used industrially. White brasses contain more than 45 percent zinc and are not at all malleable and thus are not useful for industrial purposes. The various relative concentrations of copper and zinc produce brasses of widely varying physical properties of hardness, ductility, and malleability. Many brasses can be drawn into wire, rolled into sheets, or formed into rods. Copper and nickel are completely miscible and therefore can be mixed in any relative concentration. The various mixturesproduce alloys with various physical properties and different industrialuses. The alloys using 2 percent to 45 percent nickel produce a material with a much higher hardness than pure copper, and the mixture of about 20 percent nickel produces an extremely ductile alloy that can be cold worked without annealing. This makes this mixture useful for drop forging, cold stamping, and pressing. Indus - trially this alloyis commonlyused forfittings in theau - tomobile industry and for bullet sheathing. Copper 254 • Copper Global Resources Source: Mineral Commodity Summaries, 2009 Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009. Building construction 49% Electrical & electronic products 21% Industrial machinery & equipment 9% Transportation equipment 10% Consumer &general products 11% U.S. End Uses of Copper and Copper Alloy Products and nickel occur together in some ores and can be smelted to produce a natural alloy called Monel metal. The natural ores usuallyalso contain somemanganese, which, withother impurities, is incorporated in theal- loy.It isalso producedartificially bymixing theappro- priate levelsof nickel, copper, and manganese.Monel metal is extremely strong at normal and high temperatures and thus has many engineering applications. Copper can also be alloyed with various metals to form other types ofbronzes. It can be mixedwith 9per- cent aluminum to form aluminum bronzes, which are corrosion-resistant metals. Manganese bronzes, which are high-strength alloys, usually contain copper, zinc, aluminum, and 2 to 5 percent manganese. The addition of 1 to 3 percent silicon and 1 percent manganese to copper produces the silicon bronzes, which have good welding and casting qualities. A very strong alloy of copper and about 2 percent beryllium can be strengthened by heat working and will produce a metal with a hardness equal to that of many of the harder steels. Many copper-containing compounds are used for industrial purposes. Cuprous oxide is used as an anti- fouling agent in some paints and to give some glass a red color. A green color can be imparted to glass by cupric oxide, and cupric chloride is usedin the manufacture of some pigments. Copper sulfate is commonly used as a desiccant and in the production of electrolytically refined copper. Like many other copper compounds, copper carbonates impart strong blue or green colors to solutions and are used in the production of many pigments. Copper can also be combined with arsenic; these compoundsare used asinsecticides. Jay R. Yett Further Reading Adriano, Domy C.“Copper.” In Trace Elementsin Terres- trial Environments: Biogeochemistry, Bioavailability, and Risks of Metals.2d ed. NewYork:Springer, 2001. Brookins, Douglas G. Mineral and Energy Resources: Oc- currence, Exploitation, and Environmental Impact.Co- lumbus, Ohio: Merrill, 1990. Greenwood, N. N., and A. Earnshaw. “Copper, Silver, and Gold.” In Chemistry of the Elements. 2d ed. Bos- ton: Butterworth-Heinemann, 1997. Joseph, Günter. Copper: ItsTrade, Manufacture, Use, and Environmental Status. Edited by Konrad J. A. Kundig. Materials Park, Ohio: ASM International, 1999. Krebs, Robert E. The History and Use of Our Earth’s Chemical Elements: A Reference Guide. Illustrations by Rae Déjur. 2d ed. Westport, Conn.: Greenwood Press, 2006. Linder, Maria C. Biochemistry of Copper. Vol. 10 in Bio- chemistry of the Elements. New York: Plenum Press, 1991. National Research Council. Copper in Drinking Water. Washington, D.C.: National Academy Press, 2000. Nriagu, Jerome O., ed. Copper in the Environment. 2 vols. New York: Wiley, 1979. Web Sites Copper Development Association, Inc. Copper.org: The Ultimate Source for Information on Copper and Copper Alloys http://www.copper.org 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 Copper: Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/copper See also: Alloys; Bronze; Metals and metallurgy; Mining wastes and mine reclamation; Plate tectonics; Plutonic rocks and mineral deposits; Secondary en- richment of mineral deposits. Coral reefs Categories: Ecological resources; plant and animal resources Where Found Typical coral reefs occur in shallow water ecosystems of the Indo-Pacific and Western Atlantic regions. Lesser known cold-water reefs are found at depths be- tween 40 and 3,000 meters along continental shelves, continental slopes, seamounts, andfjords worldwide. Primary Uses Reefs protect shorelines from wave action and storm damage. Historically, coral has been used in bricks and for mortar. Other uses include souvenirs, aquar - ium specimens, and even human bone grafts. Global Resources Coral reefs • 255 The diverse array of plants, invertebrate animals, and vertebrate life that a reef supports are used by humans as food, living and preserved displays, and traditional medicine. Bioprospecting has identified a promising chronic-pain treatment from a reef mol- lusk. Two possible cancer drugs and an anti-asthma compound have been isolated from reef sponges. Technical Definition Corals are animals in thephylum Cnidaria,kin to jelly- fish. As members of the class Anthozoa, they are closely related to sea anemones. Reef-building corals secrete calcium carbonate (CaCO 3 ) skeletons that surround the individual soft-bodied organisms com- prising the colony. The living layer mounts itself on layer upon layer of the unoccupied skeletons of its ancestors. Corals are carnivorous,capturing and stinging zooplankton with tentacles surrounding the single open- ing that serves as mouth and anus. Corals derive a greater amount of nourishment from photosynthetic algae living within cells lining their digestive cavity. Bleaching refers to the loss of these endosymbionts, called zooanthellae, from the coral host or loss of pig- ment from the algae. Coral may or may not recover from a bleaching episode. Description, Distribution, and Forms According to the Global Coral Reef Monitoring Net- work, 20 percent of reefs have been lost, 24 percent risk imminent collapse because of human pressure, and 26 percent are threatened with collapse over time. Threats to this diverse, productive, complex, and fragile ecosystem are wide-ranging. Some of the damage originates from imbalanceson land.Nutrient excesses run off farms and end up in the oceans,feed- ing explosive reproduction of bacteria. The bacteria use up the available oxygen, creating uninhabitable “dead zones.” Another chain reaction begins with de- forestation. Increased erosion washes large amounts of 256 • Coral reefs Global Resources This coral reef in Bonaire, the Netherlands Antilles, was badly damaged by a 2008 hurricane. (Roger L. Wollenberg/UPI/Landov) soil into thewaterway, increasing waterturbidity, which blocks light to the coral’s zooanthellae. Particulate matter also settles onto the corals, smothering them. Pollution from the construction and operation of ma- rinas, prawn farms, desalination plants, sewage treatment works, and hotels further degrades the reefs. Ship grounding, channel dredging, deep-water trawl- ing, oil and gas exploration, laying of communication cable, dynamite and cyanide fishing, and tourism each take a toll. Environmental stress renders corals more suscepti- ble to disease. Disproportionate changes in herbi- vores and predators further disrupt life on the reef. Reduced herbivoryby sea urchins or parrot fish allows algae to replace corals. When tritons, large predatory snails, are harvested for theirshowy shells,population explosions of the crown-of-thorns starfish can deci- mate reefs. Storms, such as the 2004 tsunami in the Indian Ocean, shatter and smother large numbers of corals. Climate changewill likely expose the reefs to intolera- ble temperature fluctuations. Low temperatures in 1968, high temperatures in 1987, and major El Niño and La Niña events in 1998 each caused wide-ranging bleaching. Rising levels of carbon dioxide, combined with warmer seawater, inhibit formation of the corals’ skeletons. Designating marine protected areas (MPAs), of which the United States has two hundred, is intended to enhance the management and monitoring of unique ocean ecosystems such as coral reefs. How- ever, fishing and resource extraction are allowed to continue in MPAs, so reef conservation requires stronger protection, such as “no-take areas.” Australia’s Global Coral Reef Monitoring Network publishes the Status of Coral Reefs of the World biannu- ally. It includes recommendations for reef conservation from morethan eightycountries. Nearly one-half of the coral reef countriesand states have populations under 1 million. Roughly half of those have less than 100,000 inhabitants. It stands to reason that with less international political clout, banding together ad- vances protection of the reefs. An area equal to 1 percent of the world’s oceans, 190 million kilometers, is coveredby coralreefs. Indo- nesia has the largest area of warm-water (18°-32° Cel- sius) reefs. Norway is estimated to have the most cold- water (4°-13° Celsius) coral reefs. Cold-water reefs occupy depths below light penetration. Rather than relying on photosynthetic algae, cold-water reefs are supplied particulate anddissolved organic matterand zooplankton by currents. Species diversity of coral and associated organisms is lower, and the reefs grow more slowly than their tropical counterparts. Individual corals are measured in millimeters. To- gether, billions of these animals form reef structures as imposing as Australia’s Great Barrier Reef, which is 2,000 kilometers longand 145 kilometerswide. Thisis even more impressive when one realizes that a reef may grow as little as 1 meter in one thousand years. Dependent upon coral species and physical environment, reefs can be branching, massive, lobed, or folded. On a larger scale, reefs are fringing, barrier, atoll, or platform. Fringing reefs extend from the shoreline. Barrier reefs run parallel to the coast, sepa- rated from shore by a lagoon. An atoll is a living reef around a central lagoon. Platform reefs lie far off- shore, in calm waters; they are flat-topped with shallow lagoons. History Coral reef history stretches back hundreds ofmillions of years. Coral larvae that gave rise to modern-day reefs settled on limestone during the Holocene ep- och, ten thousand years ago. Humans have been ex- ploiting reef resources for the past one thousand years. Atlantic warm-water reefs are less diverse than those of the Pacific. Reasons for this disparity include lower temperatures, younger geologic age of the ocean, and lower sea levels during the Ice Age in the Atlantic than in the Pacific. Charles Darwin published The Structure and Distri- bution of Coral Reefs in 1842. One hundred years ago, the world’s reefs were healthy. Pollutionand sedimen- tation had not emerged as problems, and natural fish populations were harvested sustainably. In the 1950’s, the geology of reef formation, reef zonation and productivity,and the role ofdisturbance were areas of study advanced considerably with the widespread use of scuba gear. During the 1980’s, research shifted to human impact and decline of coral reefs and how to conserve and restore reefs. The study of cold-water reefs awaited necessary in- strumentation and deep submersibles, available only since the late 1990’s. Within the same time frame, the Kyoto Protocol limited carbon emissions, one-third of the Great Barrier Reef was designated a no-take area, and sea urchins returned the balance to Carib - bean reefs, each a measure that promises to improve the health of coral reefs. Global Resources Coral reefs • 257 Obtaining Reef Resources Coral reefs support the marine aquarium trade and luxury live food markets. Fishes and reef organisms are captured by hand, hook and line, spear, nets, and trawl nets. Overfishing has ledto reliance on methods with indiscriminate by-catch and habitat destruction via dynamite andcyanide fishing. Handlingand transfer mortality drive extraction rates even higher in order to meet global demand. Uses of Reef Resources The main usesof coral reefs are theirin situecosystem services. The vivid interdependency of the diversity they support rivals that of tropical rain forests. Hun- dreds of species of coral support thousands of other organisms, including, but not limited to, algae, sea- grass, plankton, sponges, polychaete worms, mollusks, crustaceans, echinoderms, and fish. More than one- half of all marine fish species are found on coral reefs and reef-associated habitats. Largerpredators, such as sharks and moray eels, feed on the fish. The extensive coral reef food web cycles nutrients in oligotrophic (nutrient-poor) tropical waters. Over millennia, coral reefs have formed landmasses rising up from the sea. The Maldives, Tuvalu, theMar- shall Islands, and Kiribati are atoll countries sitting atop coral islands. The Florida keys are well-known coral islands. Calcification in corals, mollusks, and others se- questers one-third of human-induced CO 2 emissions. Loss of this carbon sink would exacerbate the effects of climate change. The value of that cannot be measured. Tourism, fishing, and ecosystem services are valued at hundreds of billions of dollars annually. Used in traditional medicine for centuries, reef organisms continue to be studied for use in Western medicine. Antiviral, antifungal, and anticancer products; inflammatoryresponse mediators;and evensun- block are under development, some of which have already been administered to patients. Marine biotechnology is amultibillion-dollar industry, withstrong growth potential. Ultimately, the health of humanity is tied to the health of the reefs. Sarah A. Vordtriede Further Reading Brennan, Scott R., and Jay Withgott. Environment: The Science Behind the Stories. San Francisco: Benjamin Cummings, 2005. Côté, Isabelle M., and John D. Reynolds, eds. Coral Reef Conservation. New York: Cambridge University Press, 2006. Feely, R. A., et al. “Impact of Anthropogenic CO 2 on the CaCO 3 System in the Oceans.” Science 305, no. 5682 (July 16, 2004): 362-366. Hare, Tony. Habitats. New York: Macmillan, 1994. Kricher, John C. A Neotropical Companion: An Introduc- tion to the Animals, Plants, and Ecosystems of the New World Tropics. Princeton, N.J.: Princeton University Press, 1997. Lalli, Carol M., and Timothy Richard Parsons. Biologi- cal Oceanography. Oxford, Oxfordshire, England: Butterworth Heinemann, 1997. Moyle, Peter B., and Joseph J. Cech, Jr. Fishes: An Intro- duction to Ichthyology. 2d ed. Englewood Cliffs, N.J.: Prentice-Hall, 1988. Pechenik, Jan A. Biology of the Invertebrates. 6th ed. New York: McGraw-Hill, 2010. Tunnell, John Wesley, Ernesto A. Chávez, and Kim Withers. Coral Reefs of the Southern Gulf of Mexico. College Station: Texas A&M University Press, 2007. Web Sites Coral Reef Alliance http://www.coral.org/ U.S. Environmental Protection Agency Habitat Protection: Coral Reef Protection http://www.epa.gov/OWOW/oceans/coral/ See also: Animals as a medical resource; Australia; Biotechnology; Calcium compounds; Clean Water Act; Coastal Zone Management Act; Ecosystems; El Niño and La Niña; Environmental degradation, resource exploitation and;Fisheries; Monsoons;Ocean- ography; Oceans. Corn Category: Plant and animal resources Where Found Corn grows as far north as Canada and Siberia (roughly 58° northlatitude) andas far southas Argen- tina and New Zealand (40° south). Although adapt- able toa widerange ofconditions, corn does best with at least 50 centimeters of rainfall (corn is often irri - gated in drier regions) and daytime temperatures be - 258 • Corn Global Resources tween 21° and 26° Celsius. Much of the United States meets thesecriteria, henceits ranking as the top corn- producing country in the world. Primary Uses Corn is the most important cereal in the Western Hemisphere. It is used as human food, as livestock feed, and for industrial purposes. Technical Definition Corn (Zea mays) is a coarse, annual plant of the grass family. It ranges in height from 1 to 5 meters, has a solid, jointed stalk, and grows long, narrow leaves. A stalk usually bears one to three cobs, which develop kernels of corn when fertilized. Description, Distribution, and Forms Corn no longer grows in the wild; it requires human help in removing and planting the kernels to ensure reproduction. In the United States and Canada, “corn” is the common name for this cereal, but in Eu- rope, “corn” refers to any of the small-seeded cereals, such as barley, wheat, and rye. “Maize” (or its transla- tion) is the term used for Zeamays in Europe and Latin America. History Christopher Columbus took corn back to Europe with him in 1493, andwithin one hundredyears it had spread through Europe, Asia, and Africa. Reportedly, a corn crop is harvested somewhere in the world each month. Corn’s exact origins remain uncertain, but most scholars agree that it is closely linked to a grass called teosinte, which is native to Mexico. Through unknown means a wild corn evolved with tiny, eight-rowed “ears” of corn about 2 centimeters long. Corncobs and plant fragments from this wild corn have been Global Resources Corn • 259 Data from United Nations Food and Agriculture Organization.Source: 52.1 151.9 14.5 84.0 18.9 13.3 23.5 67.2 333.1 Millions of Metric Tons 35030025020015010050 Nigeria India Hungary France China Brazil Indonesia Mexico United States 21.8Argentina Corn: Leading Producers, 2007 . causes inefficient utilization of copper in the body. This lack of copper affects the normal formation of connective tissue and the loss of 252 • Copper Global Resources some widespread enzymatic. in order to meet global demand. Uses of Reef Resources The main usesof coral reefs are theirin situecosystem services. The vivid interdependency of the diversity they support rivals that of tropical. organisms. Much ofthe copper produced hasbeen used and thendisposed of on land or wasted inwater orthe atmosphere. The impact of the transfer of this much copper from the deposits of the crust to

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