Earth_Science

Vocab List mineral- naturally occurring inorganic solid substance with a definite soil substance with a definite chemical composition and structure rock- a group of minerals bound together color- first and most easily observed mineral property luster- way the mineral shines in reflected light streak- the color of a mineral when powdered or rubbed on a streak plate hardness- the resistance of a mineral scratching cleavage-the tendency of mineral to split easily along planes parallel to the crystal faces, leaving smooth, flat surfaces in one or more directions crystal shape- the pattern mineral's ions or atoms form if there is enough time and room to grow specific gravity- the ratio of the weight of a substance to the weight of an equal volume of water taste- have flavor magnetism- attraction for iron acid reaction- a chemical reaction produced by an acid double refraction- division of a single incident light ray or other electromagnetic wave into two separate rays in an anisotropic medium Moh's Scale of Hardness- characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material silicates- compounds of the elements silica and oxygen; they include more than 90% of the mineral's in Earth's crust carbonate- ion group of one carbon atom combined with three oxygen atoms and having a negative charge of two sulphide- compound of bivalent sulfur with an electropositive element or group, especially a binary compound of sulfur with a native minerals- minerals composed of single elements; also called native elements oxide- any compound of oxygen with another element or a radical rock cycle- a fundamental concept in geology that describes the dynamic transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous igneous rocks- rocks formed by the solidification of hot molten rock material called magma intrusive- forced while molten into cracks between layers of other rock extrusive- forced out while molten through cracks in the earth's surface magma- the hot liquid rock beneath Earth's surface lava- molten rock that reaches Earth's surface sedimentary rocks- rocks formed from sediments bound together in some way clastic rocks- sedimentary rocks formed from fragments of other rocks chemical sediments- formed by the process of evaporation of water containing salts in solution biogenous sediments- sediment that is composed of the skeletons and shells of marine organisms, primarily plankton ferromagnesian silicate- a silicate mineral containing atoms of iron and magnesium and dark in color mafic rocks- dark-colored; low-silica rocks felsic rocks- light-colored; high-silica rocks foliation- the arrangement of leaflike layers in a rock metamorphic- denoting rock that has undergone transformation by heat, pressure, or other natural agencies crystal shape- the pattern a mineral's ions or atoms form if there is enough time and room to grow regional metamorphism- process of rock-forming that results from large areas of rocks being under intense heat and pressure of mountain-building movements contact metamorphism- process of rock-forming that results when hot magma forces its way into overlying rock and changes that rock resource- available source of wealth reserves- the amount of known deposits of a mineral in ores that are worth mining at the present time ore- a valuable mineral or metal that is mixed and worked open pit- denoting a method of mining in which coal or ore is extracted at or from a level near the earth's surface, rather than from shafts strip mine- obtain (ore or coal) by open-pit mining offshore platform- a lаrge structure used to house workers and machinery needed to drill wells in the ocean bed, extract oil and/or natural gas, process the produced fluids, and ship or pipe them to shore oil rig- a structure with equipment for drilling and servicing an oil well crude oil- a dark oil consisting mainly of hydrocarbons refining- process of purification of a substance or a form renewable resource- a resource that can be replaced in nature at a rate close to its rate of use non-renewable resource- a resource that is used up faster than it can be replaced in nature conservation- the action of conserving something pg.52 #1b,2abc,3abd,4ab,5,6a-f 1. (b) Minerals in rocks are usually identified by their physical properties. 2. (a) Color is the least useful property for mineral identification. One reason is that many different minerals have similar colors. Also, traces of impurities can turn colorless minerals into colored minerals. A third reason is that some minerals change color when exposed to air. (b) The luster of mineral is the way of the mineral shines in reflected light. Lusters are either metallic or nonmetallic. Examples of minerals with metallic luster are galena and pyrite. A mineral that doesn't shine like a metal has a nonmetallic luster. A vitreous luster, shinning glass, is seen in quartz. (c) Crystal shape is not usually helpful in mineral identification because crystal faces are rare. More often mineral grains in rocks lacked room to grow. The mineral grains in most rocks are so small or so imperfect that crystal faces are hard to find. 3. (a) The streak of a mineral is the color of its powder. The streak is obtained by rubbing the mineral on an unglazed white tile, called a streak plate. For many minerals, the streak is not the same color as the mineral. Although the color of a mineral may vary, its streak rarely does. As a rule, the streak of a metallic mineral is at least as dark as the hand specimen. The streak of a nonmetallic mineral is usually colorless or white. (b) The cleavage of a mineral is its tendency to split easily or to seperate along flat surfaces. Cleavage surfaces can be obsereved even on tiny mineral grains. Mica splits very easily, and always in the same direction. Mica is said to have one perfect cleavage. Feldspar splits readily in two different directions, at or near right angles. Calcite and galena cleave in three directions. (d) The hardness of mineral is its resistance to being scratched. It will scratch any other mineral againts which is rubbed. From Moh's scale you can find the approximate hardness of any common mineral. All you need is a copper penny, a knife blade or metal nail file, and a small glass plate. If a mineral is harder than number 5 but softer than number 6 in the hardness scale, it has a hardness about 5 1/2. 4. (a) Specific gravity is another property that is helpful in identifying a mineral. Specific gravity= weight of sample in air/weight of equal volume of water (b)Nearly all minerals are denser than water. Their specific gravities are greater than 1. Typical nonmetallic minerals have specific gravities of about to 5. Other metallic minerals are much denser. Gold has specific gravity as high as 19.3 when pure. 5. Calcite is the principle mineral in limestone and marble. Calcite is easily identified by simple chemical test. Calcite is calcium carbonate. If a drop of cold, weak hydrochloric acid is placed on calcite, the drop of acid fizzes. The bubbles are carbon dioxide gas. Other minerals also react to acid, but they are not reactive. They may require using stronger acid, heating the acid, or powdering the mineral. 6. (a) Magnetism- magnetite (b)Taste- halite (c)Flourescence- flourine, calcite (d) Phosphorescent- willemite, sphalerite (e)Radioactivity- uranium, carnotite (f) Double refraction- calcite pg. 57 #7bcdef, 8ab, 9ac 7. (b) Feldspars are divided into two major groups- the potassium feldspars and the sodium-calcide feldspars. The most common potassium feldspar is orthoclase. The color of the mineral varies but is usually a light colour such as white, cream, or pink. In orthoclase, the two cleavage surfaces meet at right angles. Like the mineral quartz, orthoclase is most commonly found in granite. The sodium-calcite feldspars are plagioclase feldspars. Albite and oligoclase are two common varieties. The plagioclase feldspar range in color from white to gray to reddish-brown. The two cleavage surfaces in plagioclase meet at slightly less than a right angle. Unlike orthoclase, one cleavage surface is often marked by fine parallel lines called striations. (c) Muscovite mica, also known as white mica, is silvery white. Biotite mica is dark brown or black. Both are soft- each has a hardness of about 2.5/ Each has one perfect cleavage. (d) Ferrimagnesian silicates are silicate minerals containing atoms of iron and magnesium and dark in colour. Hornblende, augite, and olivine are three examples. (e) Hornblende and augite are common minerals in many dark crystalline rocks. Hornblende and Augite are both a shiny dark green, brown, or black mineral. They both have two good cleavages and both have hardness between 5-6. Hornblende is in the amphilobles family and Augite is in the Pyroxenes family. (f) Quartz is made entirely of silica tetrahedrons bound tightly together. It has the chemical formula SiO2 and its chemical name is silicon dioxide. Quartz has a glassy or greasy luster. Its fracture is shell-like or irregular. Quartz is number 7 in Moh's scale of hardness. It is the hardest of the comment mineral. Pure quartz are colorless or white, but many colored varieties exist. Garnet may be dark red, brown, yellow, green, or black. They are very hard and are used as abrasives. Clear crystals are used as gems. They are found in many crystalline rocks. Kaoline is an aluminum silicate. It's formed by the weathering of feldspar and other silicate minerals. It's principal mineral in clay and in shale. Pure kaolin is white, but impurities usually make it yellow. Less often it's red, brown, green, or blue. It has an earthy fracture. Its hardness is between 1 and 2.5. It feels greasy and, when breathed on, it gives off a typical earthy odor. 8. (a) Carbonate minerals are different from silicate minerals. Carbonate mineral is made of carbonate groups joined with various metal ions. (b) The most common carbonate material is calcite. Calcite is calcium carbonate, chemical formula CaCO3. Pure calcite is colorless or white. Impurities may make it almost any color. Its hardness is 3. It has three part cleavages that meet at oblique angles. Its cleavages give it a very strong tendency to break into little flat-sided rhombs when dropped or struck. Dolomite is calcium magnesium carbonate. Its hardness is 3.5-4. Like calcite, it cleaves into rhombs. Dolomite is not as reactive to acidas calcite is, and does not easily bubble in the acid concentrated. Dolomite usually occurs as coarse or fine grainsin dolomitic limestones and marbles. 9. (a) Hematite is the most common iron oxide mineral. It has a hardness of 5-6. Most hematite is red and has an earthy luster and crumbly fracture. All hematite samples leave a red-brown streak on a streak plate. (c) Magnetite is a black magnetic iron oxide. It has a hardness of 5.5-6.5. It occurs in many rocks in the form of small grains or crystals. Its name refers to the fact that its attracted to a magnet. Lodestone is highly magnetic variety of magnetite. Its a natural magnet. The first magnetic compass needles were made from lodestone. pg.68 #1ab,2ab,3abc,4ab,5ac,6ab 1. (a) Before Hutton, most geologists thought that the physical features of earth had been formed by sudden spectacular events, or catastrophes. In their view, these catastrophes caused the formation of mountains, canyons, waterfalls, and almost all landforms. (b) James Hutton’s ideas were quite different. After years of studying landforms and rocks, he came to the conclusion that "the present is the key to the past." this statement included two concepts. One is that the geologic processes now at work were also active in the past. Two is that the present physical features of earth were formed by these same processes, at work over long periods of time. 2.(a) Hutton’s principals of uniform processes have been used by geologists to explain the origin of rocks. Geologists have noted, for example, that erupting lava hardens into rocks. These rocks are similar to others that have been found in many places on earth. Geologists have seen that sands and clays sometimes harden into rocklike materials. Such materials resemble present-day sandstone and shale. They have observed that when hot lava flows over other rocks, it changes those rocks. (b) Igneous rocks are formed by the cooling and hardening of hot molten rock from inside earth. This hot molten rock is called magma. Sedimentary rocks are formed by the hardening and cementing of layers of sediments. The sediments may consist of rock fragments, plant and animal remains, or chemicals that form on lake and ocean bottoms. Metamorphic rocks are formed when rocks that already exist are changed by heat and pressure into new kinds of rock. 3.(a) Magma is the hot liquid rock beneath earth’s surface. Lava is the molten rock that reaches Earth’s surface. (b) Rocks that form underground from cooled magma are called plutonic, or intrusive, igneous rocks. Such rocks are seen at the surface only after the rock that covers them is worn away. (c) The rock that forms when the lava cools is called volcanic, or extrusive, igneous rock. Volcanic rocks also form out of volcanic dust and ash. 4.(a) Felsic: high-silica magma is thick and slow flowing. When it hardens, it forms rocks that live mainly light-colored minerals. Mafic: low-silica magma is hotter, thinner, and more fluid than the felsic type. When it solidifies, it forms rocks that contain mostly dark ferromagnesian minerals. (b) Most plutonic rocks are felsic. Most volcanic rocks are mafic 5.(a) Crystal size is the most important factor affecting texture. The crystal size is an igneous rock depends mostly upon how fast the magma hardens. When rock is in the liquid state, its atoms are free to move around and arrange into crystals. The longer the magma stays liquid, the longer the atoms are free to move, and the larger the crystals become. A second factor that affects crystal size, and thus rock texture, is the amount of gas dissolved in the magma. Dissolved gases help ions move around in the magma. A high percentage of dissolved gases help crystals to grow faster. Thus the crystals grow large in a relatively short time. (c) In some cases magma flowing onto the surface hardens so rapidly that there is no time at all for crystals to develop. The rocks that form under these conditions, for example, obsidian- are as smooth as glass. They are said to have a glassy texture. 6.(a)Some igneous rocks have two distinctly different textures. In these rocks, large crystals are surrounded by a fine-grained mass of rock. A rock is called porphyry. pg.74 #9ab, 10bc, 11ab, 12abc, 13ab, 14, 16, 18b 9. (a)Although most of Earth’s crust is made of igneous rock, most of its surface is covered by sedimentary rocks. (b) Clastic sedimentary rocks are formed from fragments of other rocks. Examples of clastic sedimentary rocks are shale, sandstone, and conglomerate. Chemical sedimentary rocks are formed from mineral grains that fall out of a solution (precipitate) by evaporation or by chemical action. Rock salt and some limestones are examples or chemical sedimentary rocks. Organic sedimentary rocks are formed from the remains of plants and animals. Coal is an example. Limestones made of shell fragments are also examples. 10. (b)How do loose sediments become rock= in coarse sediments such as gravels and sands, the particles do not stick together unless they are cemented. Ocean water, lake water, and groundwater all contain natural cements in the form of dissolved minerals. These natural cements include silica, calcite, and iron oxide. When these dissolved minerals settle into the spaces between sand grains or pebbles, they bind the fragments together. The cement transforms loose sediments into firm, cemented rock. (c) The pressure of overlying sediments is sometimes enough to make fine sediments such as clay or silt together, even without cement. More often, however, cement is needed to hold the rock together. Cements give their own colors to rocks. Cemented rocks may be gray or white from silica or calcite, or red, brown, or rust-colored from iron cement. 11. (a)When a river flows into a ocean, it drops its sediment load as it slows down. The first sediments to be dropped are larger pebbles and gravels. These settle to the bottom in the shallow areas near shore. Next to settle are smaller sands and finally, in calm water, the silts and clays. (b) In time, the sediments become cemented together into sedimentary rock. Pebbles and gravels become conglomerate. Sands form sandstones. Slits and clays form shale. 12. (a)Conglomerate is the coarsest of the clastic rocks. It is a cemented mixture of rounded pebbles and sand grains that were deposited in rough water. The pebbles in conglomerate may be any rock material. Quartz is most common because it is so durable. (b) Most sandstone’s are made largely of grains of quartz. The cement is a rock seldom fills all the spaces between the grains. Sandstones may have up to 30 percent air space in them. The air spaces mean that sandstone is both porous and permeable. Sandstone’s are rough, gritty, and durable if well cemented. (c)The clays found in shale are usually tiny flakes of the mineral kaolin. The spaces between the clay particles in shale are so tiny that water cannot pass through the rock. This makes shale impermeable. Shale’s are smooth, soft, and easily broken. 13. (a)Sea, lake, swamp, or underground waters often contain dissolved minerals. Chemical sediments are formed when these minerals fall out of solution. This can occur through evaporation or though chemical action, the combining of dissolved ions to form new minerals. The most common chemical sediments are limestone, rock salt, and rock gypsum.(b) Limestones of chemical origin are formed from tiny grains of calcite deposited from sea or lake waters. These limestones are often gray to tan in color, compact and dense in appearance, and smooth to the touch. Rock salt is the natural form of common table salt. It occurs as a sedimentary rock in thick layers in many parts of the world. Rock salt is almost pure halite. Rock gypsum, like rock salt, occurs in layers. It also occurs as nearly pure veins of the mineral gypsum. 14. Organic sediments come from the remains of animals and plants. The most common rocks that come from organic sediments are limestone and coal. The “lime” in organic limestones is the mineral calcite. Calcite is dissolved out of the rocks on land, carried to the ocean by streams, and taken from the water by shell-producing organisms. Great number of animals and plants that use calcite live in the shallow ocean water near shore. These include clams, mussels, oysters, sea snails, corals, microscopic algae, and many others. When they die, their shells pile up on the shallow ocean floor. The shells may be whole but are more often broken into fragments by the grinding action of the waves. In time the shells become cemented into limestones. The limestones that form near the shore may contain a good deal of clay. Those that form farther from shore may be almost pure calcite. 16. Fossils are the remains, impressions, or any other evidence of plants and animals preserved in rock. The shells of clams, mussels, and snails are often found in layers of sandstone, limestone, and shale. More often, the shells themselves have dissolved but were replaces by other minerals that took the shape of the shells. Other fossils are formed when a shell or a skeleton, such as that of a fish, leaves an impression in the rock layer. These are seen when the rock layers are split apart. Plants can also form impressions in rocks. Plant remains or impressions are usually found in rocks formed from swamp sediments. 18. (b)Limestones sometimes contain small hollow spheres of silica rock. The hollows may be lined with crystals of quartz or calcite. These spheres are called geodes. Geodes seem to have been formed by groundwater. First, the water dissolved some of the limestone and formed cavities in it. Then the groundwater deposited quartz or calcite crystals in the cavities. pg.79 #21ab, 22ab, 23a 21. (a)When shale undergoes regional metamorphism, many changed can occur. The rock becomes more dense and more crystalline. The elements recombine to form new minerals that are not found in shale, such as mica and hornblende. The pressures on the rocks squeeze the flakes of mica or the needles of hornblende into parallel layers. The new rocks split easily along these layers. This new feature in the rocks is called flotation. (b) The first rock formed from shale during regional metamorphism is slate. In slate, the foliation layers are microscopically thin. If metamorphism goes further, a shiny rock called phyllite is formed. More intense metamorphism produced a flaky rock called schist, in which the flotation layers are easily seen. Schists can be formed many different rocks, such as shales, impure sandstones, and basalt. The result is that there are many varieties of schist. These are usually named for their principal mineral. Mica schist, talc schist, and hornblende schist are examples. Gneiss is another metamorphic rock that is formed from a variety of rocks. It can be formed from shale, granite, conglomerate, and many others. Gneiss has the coarsest foliation of all the metamorphic rocks. Its minerals are arranged in cardboard-thick parallel bands. Bands of light-colored minerals such as quartz and feldspar alternate with dark minerals such as hornblende or biotite. 22. (a) A second kind of metamorphism is contact metamorphism. This process occurs when hot magma forces its way into overlying rock. The heat of the magma bakes the rocks that are in contact with it. (b) The width of the affected area depends on the temperature of the intrusion. Hot liquids and gases from the magma also enter the intruded rock and react with its minerals. These effects rarely reach more than a hundred meters into the intruded rock. Much less rock is affected than in regional metamorphism. Changes in the rock are usually less drastic, and flotation is not produced. 23. (a)The igneous rocks may be thought of as the primary, or parent, rocks of the crust. As these are attacked by weathering and erosion, sediments form. The sediments are turned into sedimentary rocks. If these rocks are buried beneath other sediments and are involved in movements of Earth’s crust, they may become metamorphic rocks. If crustal movements force rocks deep into Earth’s crust, they may reach temperatures so high that they melt into magma. The magma may then harden into igneous rocks to complete the rock cycle. pg.92 #8ac,9abc,10abc 8. (a) If the rock has enough of the element to make the separation profitable, the rock is called an ore. Iron ore and copper ore are examples of rocks from which elements can be removed. The valuable mineral is called the ore mineral. (c) Mineral resources are nonrenewable. Thus, it is important to know how much of each resource is available for the future. Surveys have been made for this purpose. In these surveys, the amount of a resource is an estimate of the total amount of the mineral though to exist. Mineral reserves are the amount of known deposits of a mineral in ores that are worth mining at the present time. Knowing how fast a particular mineral is being used makes it possible to figure out about how long the supply will last. 9. (a) Reserves are resources that have been found and can be extracted at a profit using current technology. (b) Metals are used in a wide variety of ways. Iron is a metal essential to steel production. Copper is used in electrical wiring and in making brass. (c) Some metals are scarce in the United States and must be entirely imported. Examples of such metals include platinum, magnesium, cobalt, chromium, tin, and nickel. 10. (a) Unlike most metallic minerals, most nonmetallic mineral resources are used in the form in which they come out of the ground. Little treatment is needed to extract them from other compounds. (b) The main nonmetallic resources are such simple materials as sand, gravel, building stone, rock salt, talc, and graphite. (c) Materials used as soil fertilizers are also nonmetals. These include phosphate rock, potash, and nitrates. All are mined or produced in the United States. pg.97 #12ab,13ac 12. (a)Coal is formed from such a plant materials as mosses, ferns, and part of trees. All organic material contains the elment carbon, hydrogen, and oxygen. When plant or animal materials are buried in swamp waters- usually under sand of clay- they slowly decay. They gradually lose most of their oxygen and are left with most of their carbon. As the sediment ages and is compacted over time, it changes. A compressed mass of plant remains in which the mosses, leaves, and twigs can still be seen is called peat. During the time that is needed for peat to form, hydrogen and oxygen are lost. This concentrates the carbon remains. Lignite, is about 40% carbon. After millions of years of compression, bituminous coal may form. (b) The main use of coal in the US today is to run power plants that generate electricity. It is also used in making steel and as a raw material in many chemical factories. 13. (a) Petroleum means "rock oil". Petroleum, like coal, is a sedimentary material of organic origin. It's a mixture made many of liquid hydrocarbons. Scientists think that petroleum was formed by slow chemical changes in plant and animal materials buried under sand and clay in shallow coastal waters. Some of the hydrocarbons formed were liquids, and some were gases. As the sediments became compacted, the hydrocarbons were squeezed into pores and cracks of nearby sandstones and limestones. The lighter, mixed hydrocarbon liquids rose above the water, and the natural gas collected about the petroleum. (c) Petroleum are used as the raw material in making such substances as plastics, fertilizers, dyes, and medicines. G. Underground Mining: this refers to different types of subsurface mining techniques used to take out hard minerals, such as zinc, copper, gold, nickel, and lead. Declines, shafts, and adits are used to get to the ore. Miners have to go in and blast away all the waste rock to get to the ore. This causes many various impacts on the environment. Strip Mining: most commonly used to mine coal, drastically alters the landscape (strip mining involves removing large strips of land [overburden] to expose minerals underneath). Not only that, but the coal, once it has been mined, further harmed the environment when it is burned as a fuel, which creates toxic fumes. Open-Pit Mining: it is the most obvious and severe effect on the environment caused by open pit mines: the removal of huge chunks of land, creating craters. In addition to being a huge eyesore, these chunks of land used to be the habitat of many different organisms. By destroying them, the mine endangers the animals, forcing the creatures in the area to relocate. A link in the ecosystem chain is chopped out, and the entire biodiversity of the area suffers. Also, when the mine is no longer in operation, the area can no longer be used for anything else. pg.97 #11abc,12ab,13ac,14ac,15 11. (a)Energy is defined as the ability to do work.Water, wind, animals, and even human muscles can supply energy for work. (b) Fossil fuels are coal, petroleum, and natural gas. (c) Fossil fuels are are nonrenewable because they are burned at rates millions of times faster than they are forming today. 12. (a)Coal is formed from such a plant materials as mosses, ferns, and part of trees. All organic material contains the element carbon, hydrogen, and oxygen. When plant or animal materials are buried in swamp waters- usually under sand of clay- they slowly decay. They gradually lose most of their oxygen and are left with most of their carbon. As the sediment ages and is compacted over time, it changes. A compressed mass of plant remains in which the mosses, leaves, and twigs can still be seen is called peat. During the time that is needed for peat to form, hydrogen and oxygen are lost. This concentrates the carbon remains. Lignite, is about 40% carbon. After millions of years of compression, bituminous coal may form. (b) The main use of coal in the US today is to run power plants that generate electricity. It is also used in making steel and as a raw material in many chemical factories. 13. (a) Petroleum means "rock oil". Petroleum, like coal, is a sedimentary material of organic origin. It's a mixture made many of liquid hydrocarbons. Scientists think that petroleum was formed by slow chemical changes in plant and animal materials buried under sand and clay in shallow coastal waters. Some of the hydrocarbons formed were liquids, and some were gases. As the sediments became compacted, the hydrocarbons were squeezed into pores and cracks of nearby sandstones and limestones. The lighter, mixed hydrocarbon liquids rose above the water, and the natural gas collected about the petroleum. (c) Petroleum are used as the raw material in making such substances as plastics, fertilizers, dyes, and medicines. 14. (a)Uranium is used in nuclear reactors to generate electricity. Energy is obtained from certain kinds of uranium during a reaction that can be triggered within the nucleus of the uranium atom. (c) Uranium is the forth most important source of energy in the world today. 15. (a) Oil shale contains a high percentage of carbon compounds. When oil shale is heated, oil in vapor form is driven off. The oil vapor can be recovered as liquid oil. (b) Tar sand is another possible source of oil. (c) Gasohol is a mixture of gasoline and alcohol from corn or other grain crops. It can be used instead of 100% gasoline in auto engines. (d) Oil shale, tar sand, and gasohol are not commonly used at present because these are too expensive. pg. 100 #17ab,18ab,19abc,20c,21abcd 17. (a) Water power, wind power, solar energy, and geothermal energy are examples of renewable power. (b) Each of these energy resources is limited in some way. Water power can be used only in areas where dams can be built for water storage. Wind power can be used only in areas with strong, steady winds. Solar energy varies with the time of day, the season, and the location. Geothermal energy is presently useful only in areas with hot bedrock near the surface. 18. (a) Water power is a more efficient method of generating electricity than coal or nuclear energy because when burning coal or atomic fission is used, the energy must first heat water to change it into steam. The steam then turns the blades of turbine to generate electricity. With water power, the turbine blades are turned directly by the moving power. (b) Efforts are underway to generate electricity from tides. The water of Earth's oceans rises and falls with the tides. Water levels can differ from 1-10 metres in height. When this water is held back and released slowly, its motion can be used to spin a turbine to produce electricity. 19. (a)The amount of power produced depends on the speed of the wind, the diameter of the blades on the windmill, and the efficiency of the windmill. (b)Windmill farms are vast arrays of windmills. They produce significant amounts of electrical energy for their local area. (c)There are problems with using wind power. Windmills are noisy. They also interfere with television and radio reception. There is also the problem of energy storage. No good method has been found to store that energy produced during strong winds for use during calmer periods. 20. (c)Solar cell, also knows as photovoltaic cells, have been used to generate electricity for spacecraft since the start of the space age. These cells convert sunlight into electricity. 21. (a)Geothermal energy is heat from the interior of Earth. The heat may be brought to the surface by steam or hot water. If the steam or hot water can be piped into a power plant to run a generator, the geothermal energy is changed into electrical energy. Hot water from geothermal areas can also be piped into homes from heating and cooking. (b) The power plant in California is driven by superheated, highly pressurized steam. The steam rises naturally out of deep hot rock. Most other geothermal sources, however, are drilled and controlled like oil wells. (c) One plan at Fenton Hill, New Mexico involves pumping cold water into an underground reservoir hollowed out in the hot rocks. The water is left underground to warm. Then it's pumped back to the surface to generate electricity and heat homes. (d) Geothermal energy has many advantages. It needs no fuel, and it gives off little pollution. It also has disadvantages. Geothermal power plants are usually far from pollution centres. The energy must be moved a long way to be used. The superheated steam and superheated water is very corrosive. It requires expensive piping and other equipment. Hot water drawn from the ground must be returned to the ground to prevent cave-ins. For these reasons, geothermal energy presently provides much less than 1% of the world's total supply of energy.