UNIT 12 ENERGY RESOUCES:

One of the most striking differences between the developed and less-developed nations is found in their patterns of energy use, with industrialized nations using far more energy per capita, of very different types. Oil and gas constitute the most important energy fuels in the United States today, and you will have a chance to examine their nature and origin along with the techniques being employed in the search for new oil and gas fields. World reserves of oil are dominated by those of the Persian Gulf region, but even with these huge fields the total supply is finite and some estimates put peak production only a decade or so away. Production in the United States already appears to have peaked. Tar sands and oil shales may extend petroleum reserves considerably if technological advances make them more profitable to work.

Coal, on the other hand, is present in large quantities. Its utilization is more likely to be impeded by environmental factors than those related to supply. You will consider the origin of coal, and relate its worldwide distribution to conditions that persisted in the Carboniferous world.

Uranium for use in nuclear power reactors is a finite resource in the type of reactor currently in use, but the development of breeder reactors could greatly extend the usefulness of existing fuel supplies. Public fears concerning reactor safety and security of nuclear fuel have virtually crippled the nuclear industry in the United States, however. Research in controlled thermonuclear fusion reactors continues, offering hopes of an alternative source of energy that may become available in the next century.

Renewable energy sources such as geothermal and solar energy, hydropower, and energy derived from wind, tides, and the thermal stratification of the oceans are all being investigated or developed as supplemental energy sources. As oil and gas production diminish in the future, alternative energy sources must be developed to take their place.

One of the principal ways in which the developed countries are distinguished from the less-developed ones is in their use of energy. A poor farmer in a less-developed country must rely on humanpower and beastpower. Oxen or some equivalent are still used in many parts of the world to draw plows and provide motive power beyond the strength of men. In contrast, developed countries consume large quantities of energy for transportation, for industrial uses, and for heating or cooling of building space.

Stop for a moment and look around you, and think of how many energy-consuming devices are in your home or apartment building. Then consider how you would have lived if you had been born a thousand years ago -- or even two hundred years ago. Much of your present lifestyle is dependent upon abundant and affordable energy along with the devices that utilize it.

Figure 12-1 shows how energy is used in the industrial countries of the Organization for Economic Co-operation and Development. Three broad areas -- industry, buildings, and transportion -- have comparable shares of total energy use. Two of the most dominant uses of energy within the latter two areas are automotive and space heating and cooling.

The energy used in the United States is supplied by a number of fuels, as shown in Figure 12-2. Most of it is supplied by oil, natural gas, and coal. These are the fossil fuels, so-called because they are derived from energy that in most cases was emplaced in the ground millions of years ago. The heavy dependence on natural gas, by the way, is a peculiarity of North America, due to extensive domestic gas fields linked to many parts of the continent by a truly remarkable grid of gas lines. Other developed regions generally show a heavier reliance on oil and coal and a lesser use of natural gas.

This pattern of fuel use is quite recent; only a hundred years ago, the dominant fuel by far was wood, with coal contributing a much smaller proportion of the total. By 1900, coal became the most heavily used fuel, but in the 1940s, oil and gas use began an explosive growth.

The quantities of fossil fuels that are consumed today are so great that even minor imbalances between supply and demand can cause considerable societal disruption. The 1973 oil embargo by OPEC (Organization of Petroleum Exporting Countries) caused considerable distress in the United States even though total oil consumption was cut by less than five percent. As it turned out, much of the problem was in the political and public response to the apparent shortage. Many people tried to keep their automobile gas tanks as full as possible, making more visits to service stations and so creating long lines, and creating temporary shortages by increasing the amount of gasoline stored in individual gas tanks. Political attempts to ration and allocate supplies also contributed to local product shortages. Even without these multiplying effects, though, small disturbances in energy supplies can have profound effects on a society so dependent upon them.

Worldwide use of energy for several decades appeared to be increasing dramatically, but in recent years it has leveled off and even dropped somewhat, as shown in Figure 12-3. All forms of energy use are represented in the diagram in terms of the amount of coal that would provide the equivalent energy.

This turnaround in energy demand was virtually unforeseen in the 1970s; most predictions made at that time assumed that demand would continue to accelerate, causing severe energy shortages. Instead, today we find a surplus of energy on the worldwide market, which has resulted from economic downturn coupled with a tenfold increase in the price of oil during the past two decades. In the United States, for example, new automobiles are smaller and more fuel-efficient, and many people have cut back on energy use. Whether energy consumption will remain depressed or will resume something more like its historical rise is quite unknowable at this point. Many observers, however, expect some resumption of increased demand due, at least in part, to the pressures of an expanding population.

Figure 12-4 shows the effect for the United States. Energy use is plotted on a per capita basis, and it can be seen that individual energy use began to decline between 1970 and 1980 in the United States. The figure also shows the enormous discrepancy in per capita energy use between the United States, with its high state of industrialization, and less developed countries, represented by an average for the whole African continent and by India.

Let us examine each of the major energy resources, and some minor ones as well. We shall be most concerned with how they are formed, how they are distributed, and how they are found.

Today we must expend millions of dollars to prospect and drill for oil that is buried deep below ground, but there are a number of places where small quantities of crude oil find their way to the surface and are exposed as oil seeps. The famous La Brea Tar Pits in Los Angeles formed a natural trap for unwary creatures of past ages. Mired in the tarry pools, they died and their bones were preserved in the bitumen that still can be seen welling up from the ground.

Natural seeps occur in many parts of the world, and were used by Stone Age people in construction, by ancient Egyptians as an aid to the preservation of their mummies, and by seafaring people everywhere for caulking. Kerosene became popular for use in lamps, and in 1857 commercial oil production began in Romania. Two years later, .;Edwin L. Drake sank the first oil well at Titusville, Pennsylvania, to a depth of 21 meters (69 feet), beginning our modern age of oil consumption. That region is still producing. In the intervening century and a third, the availability of oil as a concentrated and portable source of energy has become a major influence in determining the life styles of people living in the industrialized nations.

Petroleum is composed primarily of organic compounds made from carbon and hydrogen (hydrocarbons) that occur in a variety of mixes. Hydrocarbons can take a number of different forms, occurring as gases (natural gas, mostly methane), liquids (gasoline, kerosene), and solids (paraffin). Crude oil is "cracked" in refineries, a process of breaking complex organic molecules into simpler ones, to produce a wide variety of products. These include gasoline, kerosene, fuel oil, lubricants, paraffin, and raw material for the chemical industry. Referring to the latter uses, an oil minister of Saudi Arabia was once quoted as saying, "Oil is too precious to burn." Indeed, the chemical industry is heavily dependent on petroleum in the production of plastics and pharmaceuticals. Differing hydrocarbon mixes produce different grades of crude oil. Some, like the light oils of Pennsylvania, are suited for the production of lubricants, while heavier grades are better suited for the production of fuels.

Oil and natural gas are found almost exclusively in sedimentary rocks. Oil begins to form with the burial of organic remains from plants and animals (usually microscopic in size) in an oxygen-deficient or anaerobic environment. Where oxygen is plentiful and supplies of organic material are slow in accumulating, decay, (which is largely oxidation) sets in and returns the hydrogen to water and the carbon to carbon dioxide. In these environments, potential sources for production of oil and gas are destroyed. In certain geological settings, however, accumulations of organic materials in sediments rapidly deplete the oxygen supply, and if no external sources of oxygen are present, the formation of hydrocarbons can begin. This appears to happen most often for oil and gas in marine sediments. River deltas and other near-shore environments are rich sources of both organic debris and sediment, and the source rocks of many important oil deposits are associated with them.

Bacterial action on the organic material during and after burial is probably a part of the oil-forming process. As the organic material becomes buried deeper beneath the accumulating sediments, pressure and temperature rise and a natural form of the cracking process begins to occur, reducing the complexity of the organic remains and converting them into hydrocarbons. The deeper the burial and the longer the process goes on, the lighter the crude oil becomes, accounting for some of the different types that are found.

Natural gas is formed in much the same way, with methane being formed almost as soon as organic material is buried and continuing to be produced throughout the cracking process.

Both liquid crude oil and natural gas are less dense than water and are much less dense than rock. As a result, they have a strong tendency to migrate upward from their points of origin, provided that they can find permeable rock in which to do so. Some sedimentary rocks are relatively porous in that there are open spaces between sediment grains and small channels connecting them. A coarse sandstone may be so porous that a drop of water placed on it can be seen to spread out and be absorbed as though the rock were a sponge. It may be a slow process, but given enough time, oil can migrate through porous or fractured rock layers. Other sedimentary rocks, shales for instance, may be relatively solid and impermeable to oil and gas. These can form barriers to further upward migration of oil. In this way, pools of oil can accumulate beneath impermeable rocks and form economically important deposits.

Most of the oil that has been produced throughout geologic time has probably succeeded in migrating to the surface where it has oxidized to carbon dioxide and water. This is seen in the relative scarcity of oil in very old rocks. The majority of large oil pools are found in rocks less than 200 million years old.

A wide variety of techniques have been developed to aid in the search for oil and gas. Because they are fluids and are contained within the pore spaces and fractures of rock, their presence deep underground is very difficult to detect. As a result, most exploration techniques are aimed at detecting the underground geological structures that serve to trap oil and gas in their upward journey. Figure 12-5 shows two such structural traps that are common sites for oil and gas deposits -- anticlines and salt domes.

An anticline is formed when rock strata are folded into an arch. If permeable rock is present beneath impermeable layers and the latter have not been so fractured that the oil or gas can leak through, then a concentration might form if hydrocarbon fluids are working their way upwards through the permeable rock. The odds are against a significant oil accumulation, however. In order for oil to form, there must be present a suitable source rock, an appropriate maturation history, a migration pathway, a sufficiently porous rock to form a reservoir, a structural trap, and the top of that trap must be sealed with an impermeable rock to prevent the oil's escape.

The lower part of the diagram shows another situation that has provided the setting for significant oil and gas finds. In the previous unit we referred to the formation of salt domes when evaporite beds become deeply buried. Because of its low density, the salt may force its way through the overlying strata, buckling them upwards and forming structural traps in which oil and gas may accumulate. Large oil deposits near the mouth of the Mississippi River and in the Gulf of Mexico and elsewhere have been found in association with salt domes.

The presence of a structural trap does not by any means guarantee that it contains oil. Most do not, but these are the most likely places to begin looking in a region that appears to have potential for oil production. In order to locate them, the structure and kind of rock layers must be worked out in considerable detail. Petroleum geologists apply a wide variety of techniques to this task. Precise surveys of the Earth's gravity and magnetic fields may serve to locate large subsurface features of interest, while seismic surveys provide more detailed views of the underground structure. In the seismic reflection method, sound waves generated by a small explosion or other artificial source near the surface travel down into the ground and are reflected from rock layers. The recorded echoes from these layers are then processed by computers to provide diagrams of structures such as those shown in Figure 12-5. Test holes are drilled to look for traces of oil or gas and to obtain rock cores or chips that allow the geologist to identify the different strata. In addition, sensitive instruments are lowered down the drill holes to aid in the identification of rock layers.

Oil and gas exploration is extremely expensive. The drilling of a single oil well may cost many millions of dollars, and more millions may be expended in the careful scientific work that precedes any substantial drilling.

Sedimentary rocks are widely distributed over the Earth and so one might expect that the same would hold true for petroleum resources. To a certain extent this is true in that every continent contains major oil fields, but distribution on a finer scale turns out to more capricious. Of the 600 or so sedimentary basins known to exist, only about three dozen contain giant oil fields, which account for a sizable portion of worldwide reserves. These giant fields may occur in clusters and cover only a fairly small geographical area within an individual basin.

The distribution of estimated reserves, shown in Figure 12-6, contains one very great anomaly -- the producing areas of the Middle East. This region, measuring only about 1,500 by 700 kilometers (900 by 400 miles) in and around the Persian Gulf, accounts for nearly 57% of total world reserves. Throughout long stretches of geologic time, all the factors involved in the generation of oil and gas -- proximity to sources of sediment and organic material, nearly enclosed oxygen-deficient seas, and the production of structural traps -- have been optimized to produce a series of giant oil fields that even today are not fully explored. Other large oil fields are found in the Arctic regions of the former U.S.S.R. and Alaska, in the Gulf of Mexico region, and in the North Sea.

The major portion of the continental shelves have not yet been fully explored and some may have considerable potential for substantial new discoveries. Even though offshore drilling brings with it a host of new difficulties, not the least of which is coping with severe weather conditions at sea and preventing oil spills during drilling and during transportation of oil to its destination, drilling has taken place offshore from more than 100 countries and in water depths as great as 7,000 feet (2,100 m) off the east coast of the United States.

How long will the oil last? This is a question frequently asked, but one whose answer depends on so many unknowable factors-such as future oil demand, future exploratory success, future technological developments, and future economic conditions-that no definitive answer can be given. For example, worldwide-proved reserves at current rates of consumption equates to a 32-year lifetime, but if estimates for undiscovered recoverable resources are included, a value of 70 years is obtained. However, both these estimates are based on a recovery of about 35% of the original oil in place, and new technology will certainly increase this factor to 50% or more. With this addition, the number becomes 100 years. If improved efficiency of usage and fuel-switching possibilities are considered, the time period becomes even longer. Furthermore, these observations don't include the potential additions from tar sands and heavy oils discussed below.

Clearly, oil is a finite resource and if viewed with respect to the totality of human history, the "oil age" may cover only a relatively brief period. There are many known sources of energy that will be developed to supplant oil in response to our ever-changing technologies and economic conditions.

In addition to crude oil pumped from oil fields, there are also substantial amounts of hydrocarbons found in heavy oils and tar sands. Tar sands contain heavy oil in the form of tar or very viscous oil that are incapable of migrating from the reservoir rock. As a result, these deposits cannot be pumped from the ground like crude oil. To make the oil fluid enough to flow, it may be heated with steam, and once recovered, it can be refined to recover the lighter oil components. Tar sands may also be utilized by mining tar sand rocks, which are then crushed and treated to recover the tar, which is then refined.

Two large tar-sand and heavy-oil deposits are known: the Athabasca tar sands in Alberta, Canada, and the Orinoco deposit in Venezuela. Their total resources have been estimated at around one trillion barrels, or about half as much as worldwide crude oil resources. Commercial mining operations of tar sand deposits in Canada are ongoing. Recovery of heavy oil deposits by using in situ methods such as steam drive is becoming common, especially in the United States.

Another potential petroleum resource is oil shale. These are fine-grained sediments containing organic matter that can be distilled to yield oil. They must be mined and then heat treated on the surface, requiring that the energy equivalent of about 40 liters of oil must be expended to recover the oil from a ton of shale. As a result, only shales that will yield in excess of 75 liters of oil-per-ton are worthwhile for development. Particularly rich oil shales have been used for commercial production of oil in the former U.S.S.R. and in China for many years, but the largest oil shale deposits known are found in the United States. Worldwide reserves from oil shales are estimated to be comparable to those of tar sands. Whether these petroleum resources are ever utilized to any great extent will probably depend on the development of new lower-cost technology for mining and refining. At present, large-scale surface mining and disposal of residues left over from retorting the shale can pose environmental difficulties. These will need to be addressed if the cost of oil recovery from oil shale becomes competitive with that of crude oil.

During the Middle Ages, wood was the dominant energy fuel, and in areas of high population density, the forests began to suffer from overcutting. In the twelfth century A.D., so-called "sea coles" were found on the beaches of northeast England, and with the discovery that they were flammable, widespread use for home heating began. These were chunks of coal that had weathered from coastal cliffs and, traced to their source, were later mined directly from coal seams underground.

Coal use expanded rapidly with the invention of the steam engine in the eighteenth century. As the principal energy source for this new form of motive power, it was the essential fuel that ignited the industrial revolution in Europe. It can hardly be a coincidence that two nations that led this revolution, Great Britain and Germany, were the European nations most endowed with coal deposits.

Of all mineral deposits, the origin of coal is among the best understood. Coal is a rock composed largely of carbon that is organic in origin. Within coal may be found fossil imprints of thousands of species of plants that flourished at the time that coal formed. These tell us that, unlike oil, which is largely marine in origin, coal formed entirely on the continents from a wide variety of plant life. In order for this organic matter to be preserved, however, a particular environment is necessary.

When a tree or other plant dies in a forest environment, it falls to the ground and immediately begins to decay, attacked by insects and microorganisms that aid in the processes of decomposition. In this process, the complex carbohydrates that make up plant tissues are broken down into, primarily, water and carbon dioxide-both of which are returned to the environment. The carbon is recycled to carbon dioxide and not trapped, and so the usual forest environment is not likely to result in the formation of coal.

The preservation of carbon requires an oxygen-deficient, or anaerobic, setting, such as that found in stagnant waters. Swamps are good environments for carbon preservation, as may be demonstrated by turning up a few inches of the muck at the bottom of a stagnant swampy pool. If you do this, you will generally find that old leaves, twigs, and stems are matted in layers and that the sediment is dark in color, indicating high levels of carbonaceous material.

Even at such shallow depths, the coal-making process has begun. Bacteria attack the wood and plant tissues, reducing the hydrogen and oxygen content and concentrating the carbon. The result is a carbon-rich humus that is called peat, generally regarded as the first stage in the making of coal. Though peat is not yet coal, it is in fact a low-grade fuel. For centuries, peat has been cut from bogs and dried for domestic use in cooking and heating.

Many coal deposits extend over large areas, indicating that the original coal swamps were quite extensive. Today, we might go to a place like the Everglades of Florida for a similar environment. Because running water brings in new supplies of oxygen, swamps in low, flat terrain with sluggish circulation of water serve the purpose best. In addition, incorporation of inorganic sediments such as sand or mud are minimized in flat regions, leading to the generation of high-purity coal.

Another environment in which peat may form is that of the tidewater region of coastal zones. A long, thin barrier island of sand takes the brunt of the sea's waves and storms, protecting shallow tidal pools behind it. If the coastal terrain is flat, freshwater marshes and swamps are commonly built between the streams that feed the tidewaters. Many of today's major coal seams appear to have originated in such an environment.

With an increasing overburden of sediment, the peat becomes progressively more compacted and dehydrated. Biological action largely ceases, and further changes are brought about by increasing pressure, temperature, and chemical changes. In this step, peat is changed into lignite, sometimes called "brown coal." It is woody in character and brown or brown-black in color. Because of its high moisture content, it tends to disintegrate when it dries. Lignite is often burned as a power-plant fuel.

With further heat, compaction, dehydration, and chemical action, lignite turns into sub-bituminous coal and then into bituminous coal. These are the most abundant and commonly used forms of coal. They are dense and stable when dry and produce a large amount of heat when they burn.

A further step may be taken when coal seams are exposed to metamorphic processes that occur in tectonic regions. Coal seams that have been subjected to intense folding and heating from nearby igneous activity are often found in the form of anthracite, a dark and brittle jet-black coal that burns with a blue flame, has high heating value, and contains little sulfur, a major contaminant of many bituminous coals.

The earliest coals appear in Devonian rocks because, prior to this time, the land plants that form coal had not yet evolved. It was, however, in the Carboniferous period that the coal swamps reached their greatest development. In tropical regions of the Carboniferous world, conditions must have optimized in the luxuriance of vegetation, climate, rainfall, and the geographical setting that produced enormous peat bogs that would later be preserved as coal. When oil and gas are produced, they have a high probability of escaping to the surface, but coal seams are destroyed only when they are uncovered by erosion. It has been estimated that most of the coal produced in the past 350 million years is still in existence.

The origin of coal in broad, shallow swamps and bogs produces coal seams that are widespread but thin. They appear sandwiched between strata of other sedimentary rocks, frequently in groups one above another. Because of this, coal seams are not hard to find, and it is likely that most of the world's major coal deposits are known at this time. For this reason, the major involvement of the coal scientist is not in finding new coal seams to develop, but in determining the value and properties of known deposits and in aiding the coal mining industry in carrying out its task with safety and efficiency.

On a global basis, coal is the most abundant fossil fuel, and known recoverable reserves would last for over 200 years at present rates of consumption. Estimated resources are truly huge, and if it should become necessary and profitable to use these as well, present consumption rates could be maintained for more than 1,500 years.

The distribution of coal reserves is shown in Figure 12-7. The most striking feature of this distribution is the relative scarcity of coal in the continents of the southern hemisphere. Keeping in mind that the most favorable climate for coal-swamp formation is temperate to subtropical, turn to Figure 3-27 and look again at the geography of the Carboniferous world. The large coal deposits of Appalachia in the eastern United States, of England and Wales, and of Germany in Europe were all located very near the equator at that time. Now look at the maps for succeeding geological periods and note how these regions have moved from the tropics into the northern temperate zone, carrying their coal deposits with them. Indeed, this pattern of distribution of Paleozoic coal was used as evidence by Alfred Wegener in his reconstruction of the supercontinent that we call Pangea.

In the Carboniferous period, much of the African and South American portions of Gondwana were situated at high southern latitudes, and the rest of Gondwana covered the South Pole. In fact, Permian-Carboniferous times marked one of the prominent periods of glaciation in world history, but with only the south polar region covered by continental ice sheets. The southern portions of South America and Africa were thus covered in ice and devoid of vegetation.

It is fascinating to speculate that the emergence of the Industrial Revolution in the northern hemisphere and the present asymmetric division between the developed and affluent northern nations and the less-developed and generally poorer southern nations may have been influenced by the geography of the Carboniferous world that existed 300 million years ago.

Bituminous coal constitutes an obvious source of energy that could last for the next century or more. Unfortunately, there are severe problems associated with increased dependence on the burning of coal. We have already investigated the climatic implications of increasing the carbon dioxide concentration of the atmosphere in Unit 5, Climates of Earth. The fossil fuel reserves of the world constitute an enormous store of carbon that is safely locked away in the rocks below ground. Burning them combines carbon with oxygen to form carbon dioxide that is released to the atmosphere. Even at present rates of fossil fuel consumption, the carbon dioxide level of the atmosphere is increasing at rates which show that the natural processes that would normally dissolve excess carbon dioxide in the waters of the oceans cannot maintain equilibrium.

The carbon dioxide problem is common to all the fossil fuels, of course, and so as oil and natural gas resources are used up, simply replacing their usage with coal burning may not aggravate the situation. If we are to avoid adding to the buildup of CO₂ in the atmosphere, we must avoid an increase in the total production of energy from fossil fuels.

HM 12-4: United States air pollution related to various sources

(this figure from Natural Resources Defense Council).

A common contaminant of bituminous coal is sulfur, and when coal is burned it is released into the environment as sulfur oxides (SO₂ and SO₃), which are major air pollutants. Once in the atmosphere, the sulfur oxides (along with nitrogen oxides from other sources) may react with water to form acids. Many observers believe this to be a contributor to the phenomenon of acid rain, which seems to be particularly prevalent in regions downwind of concentrations of coal-fired power generation plants. In some of these places rainfall has been measured to have an acidity greater than that of vinegar, and damaging acidification of lakes and soil has been blamed on coal burning. At the present time, the relative importance of the different contributors to acid rain is not known with certainty.

Air-pollution devices installed in power plants can cut back substantially on sulfur emissions (but not on carbon dioxide emissions). These devices are costly to operate and maintain, and they produce a waste-disposal problem in the sludges that remain from the process of scrubbing the sulfur gases from smokestack emissions. Taken together with the fact that underground mining of coal is dangerous and unhealthy, these problems and the regulations that have resulted from attempts to mitigate them have worked to hold coal consumption down in recent decades. Perhaps even more important as a constraint on coal production has been the relatively low price of oil and gas, which are competing sources of energy. Nonetheless, coal production in the countries such as China and the United States continues to rise, and the sheer abundance of coal will make it more attractive as time goes on and the limited reserves of oil and gas become more depleted.

Although most uranium ore concentrations occur in a variety of sedimentary rocks, there is one important type of uranium deposit also occurring in igneous rocks. Deposits in Ontario, Canada and in Namibia in Africa are examples. As mentioned in the previous unit, there is still some controversy over the exact concentration mechanism, but it is thought that some are deposited at the same time as the enclosing sediments and some are deposited later by circulating uranium-bearing groundwater.

Figure 12-8 depicts the distribution of uranium reserves, recoverable at current prices. North America holds the greatest reserves, with significant additional reserves in Europe, Africa, and Australia.

Once separated from its ore, uranium consists of three isotopes: U-238, which accounts for 99.3%, U-235, which accounts for only 0.7%, and U-234, which is very short-lived and accounts for less than 0.006%. U-235 is fissionable and hence is usable in nuclear reactors, while U-238 is not. Before being used as fuel, uranium is processed to enrich its U-235 concentration. It is then made into pellets, ready for use in nuclear reactors.

While the fuel pellets are in a light-water reactor, the type commonly in use today, the U-235 nuclei are bombarded with neutrons that cause fissioning, in which the U-235 nuclei are split into two smaller nuclei, releasing additional neutrons and a large amount of energy. The neutrons just produced can then strike other U-235 nuclei, causing them to fission in a chain reaction that can be controlled and sustained. The heat energy released is used to create steam that drives turbines attached to electric generators.

Because U-235 is such a small part of naturally occurring uranium, most of the uranium goes to waste, severely limiting the total amount of energy that can be derived from existing uranium reserves. However, U-238 can be converted into Plutonium-239 by absorption of neutrons. Plutonium-239 is fissionable and so may also be used as a fuel in reactors.

This circumstance has led to the development of the breeder reactor. In this reactor, U-235 or Plutonium-239 is fissioned in the usual way, but some of the neutrons produced are used to convert U-238 to Plutonium-239. With proper design, the breeder reactor using Plutonium-239 as fuel will convert 130 U-238 nuclei into Plutonium-239, while using up only 100 Plutonium-239 nuclei. This opens up the possibility for converting much of the existing U-238 reserves into fissionable Plutonium-239.

The tremendous multiplying effect that the breeder reactor would bring about means that existing reserves of uranium in the United States could supply all electricity needed by the country for several hundred years. In fact, the U-238 presently stored in uranium waste stockpiles could meet electrical needs for nearly a century.

In spite of such promise, the nuclear industry in the United States is in a state of severe depression. In the wake of the Three-Mile Island accident in Pennsylvania in 1979, public confidence in the safety of nuclear power plants plunged in the U. S. A. Six years after the accident, extremely expensive cleanup operations were still in progress. While nuclear reactors are incapable of exploding like a nuclear bomb, a severe accident resulting in a meltdown of the fuel assembly could release dangerous amounts of radioactivity into the surrounding countryside.

Just such a catastrophe occurred in a nuclear reactor in Chernobyl in the former U.S.S.R. (now the Ukraine) in 1986. A runaway chain reaction blew the lid off the containment vessel and spread heavy radioactive contamination over the surrounding countryside, killing 31 people immediately and forcing an evacuation of hundreds of square miles around the power plant.

Public fear of accidents and possible terrorist attacks on nuclear plants have combined with extremely high construction costs and delays caused by litigation to create an unfavorable environment for the nuclear power industry at the present time. As a result, new orders for nuclear power plants in the United States have effectively ceased during the past decade, though new plant construction continues in other countries.

Many scientists feel that the hazards of nuclear power generation have been exaggerated to the point of hysteria in the popular press. They point out that the safety record of the industry in general has been excellent and that reliance instead on coal burning carries with it far greater hazards in mining accidents and black-lung deaths, and in environmental problems such as air pollution, water pollution, and CO2 generation. Others feel that problems unique to the nuclear industry make it undesirable for major expansion. Of considerable concern is possible proliferation of nuclear weapons as a result of reprocessing of spent fuel to recover weapons-grade plutonium.

The disposal of radioactive wastes that have already accumulated or that will result from future reactor operation is a major problem that has not yet been solved. In the past, wastes have been stored in tanks and barrels below ground, encased in concrete and dumped into the sea, or stockpiled above ground. The question of how to safely dispose of these wastes without contaminating the environment has been given a great deal of study in recent years, and experimental sites are now being chosen in the United States for this purpose.

Among the most likely disposal sites are salt formations and stable igneous rocks deep underground. Salt formations have the advantage that groundwater does not move through them rapidly (if it did, they would have dissolved a long time ago), but salt is mobile and the effects of heat generated by the stored wastes on the salt are not fully understood. Igneous rocks are very stable, but it is hard to guarantee that groundwater would not invade the storage area during the hundreds or even thousands of years that radioactivity in the wastes would persist. A major related problem is the design of waste containers that will not degrade over long periods of time.

Oceanic sediments far from spreading ridges or other tectonic zones on the sea floor contain very little circulating water, and it has been suggested that burial in these sediments would be safe, especially in areas of rapid sediment accumulation. An interesting suggestion has been made to bury radioactive wastes in deep ocean trenches where they eventually would be subducted. In both of these schemes, though, it is very hard to guarantee that the waste containers will remain intact until they are sufficiently buried, or that disturbances to the sea-floor sediments will not occur that might expose the wastes to circulating ocean waters.

At this point in time, it is very hard to separate the scientific from the social and economic difficulties that now beset the further development of nuclear power.

In a democratic society, the ultimate decision must be made by the citizenry, who must take the time and trouble to listen carefully to arguments on both sides and then come to a reasoned conclusion.

HM 12-7 (A-C): Different modes of power generation are shown in this comparision of electricity production by the counties of France, the United States and People's Republic of China

A) (Upper figure) France, B) (Middle figure) United States, and C) (Bottom figure) People's Republic of China (data from US Department of Energy, years vary between 1991 and 1995). Note the high use of nuclear power by France. Thermal generation refers to burning of material, such as oil, gas, coal, or other combustibles, in produce power.

With recognition that oil and gas supplies are finite, increasing attention is going to sources of energy that are renewable in the sense that they can be used without exhausting the source of the energy. Among these are hydropower, geothermal, and solar energy in its various forms.

The traditional forms of hydropower make use of the energy of the Sun that goes to power the hydrologic cycle. Low-lying water from the sea is evaporated, carried to high elevations in the atmosphere, and then falls as rain onto the continental highlands. Energy is released by the water as it makes its way to lower elevations and, ultimately, back to the sea. Hydropower is generally utilized by damming rivers and streams and using the energy of falling water to turn electric generator turbines. This is a well-established technology that has been in use throughout the past century and indeed, water power has been used directly, without the intermediary of electric power generation, for thousands of years.

The potential for expansion of hydropower in the industrialized countries is limited, since most of the best sites have already been developed. In energy-poor continents of South America and Africa, however, hydroelectric projects may be able to provide substantial amounts of economical electrical energy. However, even if all potential sites were developed, hydropower would supply no more than 13% of current world energy demands. In addition, dams and reservoirs eventually fill with sediment, losing their storage capacity and becoming useless after lifetimes that extend typically for 50 to 100 or 200 years. Finally, dams alter streamflow and destroy habitats, landscape, and agricultural land along rivers and streams.

Another form of hydropower uses tidal energy instead of solar energy. In some coastal areas, tides are exceptionally large in amplitude, with the sea surface rising and falling five to ten meters (16 to 33 ft) twice each day. Two small tidal power generating plants have been constructed in France and in the former U.S.S.R., but because in most places tides are much lower in amplitude, tidal power is unlikely ever to be more than a useful local option.

Among the renewable energy sources, solar energy has particular appeal because it is probably the most environmentally benign. A substantial technology has already developed, but actual employment has been hampered by inefficiencies and high initial costs.

The Greenhouse Effect, this time using actual glass instead of gases in the atmosphere, is the basis for operation of passive solar heating systems, so-called because they have no moving parts. Large, south-facing windows allow sunlight to enter an enclosed space where suitable surfaces are heated by sunlight. Heat so produced is stored in walls, floors, or water containers and is then circulated to the rest of the space to be heated. Many houses in sunny climes can derive all of their heating requirements from such a system, but in cloudier regions a supplemental heat source may be required. Careful attention must be paid to insulation and reducing air leaks in solar-heated homes.

Active solar heating uses a collecting system, usually panels mounted on roofs or in fields. A circulating fluid is heated by sunlight within the panels and heat is transferred by it to a storage tank. The system is well-suited to production of hot water for domestic use, and millions of these units are in use throughout the world. Note in Figure 12-1 that hot-water heating accounts for a significant part of total energy use in the United States.

Solar energy use for space heating will almost certainly increase dramatically as oil and gas supplies become more scarce and expensive, but the future for large-scale power generation using solar energy is less clear. Steam may be produced by collecting sunlight over a large area with mirrors and focusing it on a small boiler, but the costs of construction and maintenance for this type of installation compared to its power production are still very high. In addition, energy produced during the day must be stored for use at night, and electrical energy storage technology is extremely expensive at present.

Direct conversion of sunlight into electricity is possible using photovoltaic solar cells, but at the present time these are inefficient and expensive to manufacture. New technological developments in this area promise to increase efficiency dramatically, but a fundamental limitation is the rate of energy input from the Sun to a given area of the Earth's surface. As an example, even if a 30% energy conversion efficiency might be obtained, it would still be necessary to cover eight square kilometers (2,000 acres) of ground in order to produce as much energy as a single modern nuclear power plant. Solar energy may best be used in small, distributed power systems provided that technological advances can increase efficiencies and lower costs. If this should occur, solar energy may prove to be a boon especially in underdeveloped tropical and subtropical countries that lack other resources.

Indirect solar energy is being explored in a variety of ways. Wind energy is being developed using new efficient designs for windmills in regions of persistent air currents. The same problems of efficiency and cost are the principal drawbacks to more widespread use.

The burning of wood has remained a prime energy source within undeveloped regions, but in all too many cases, the results have been disastrous in terms of deforestation and its resultant effects that will be explored in the final unit of this course. Utilization of other forms of biomass (literally all organic matter contained within plants and animals) for energy production is another field of active research, particularly in the production of synthetic fuels. Certain kinds of desert shrubs and even sunflower seeds may eventually be used to provide synthetic oil.

A more speculative use of indirect solar energy employs temperature differences between the different layers of the ocean. Temperature differences across the thermocline between warm surface currents and colder intermediate or bottom waters may amount to as much as 22°C (40°F), and large floating power plants have been envisioned that would use this oceanic thermal gradient to produce electric power.

Finally, a proposal has been made to establish large satellites in Earth orbit that would collect solar energy unhindered by clouds or atmosphere, convert it directly to electrical energy and beam it to Earth receivers via microwaves. Huge costs, low efficiencies, and potential hazards associated with microwave transmissions are the principal difficulties with this scheme at present.

We have already raised the question of how long our present supplies of fossil fuels will last. To understand the kinds of problems that we face, it is necessary to understand the manner in which finite resources are used up. Look back at Figure 11-6, in which a rough model was established for the production of metal from a limited resource. The same model may be applied to oil produced within the United States, simply replacing the words "metal" and "mines" with "oil" and "oil wells."

Before the peak of production is reached, the number of oil wells drilled annually increases rapidly to meet the mounting demand. At about the time that the resource is half gone, the peak production rate is reached, and production declines thereafter. The reason for this decline is simply that the easy deposits to find and extract are the ones that are first exploited. As time goes on, smaller and less economical deposits are being developed. In the case of oil, the average depth of drilling has increased steadily, greatly adding to increased costs. Exploration costs are also increasing rapidly as smaller and more deeply buried deposits are sought. The result is that fewer wells are drilled and production falls. If the resource is still abundant elsewhere and domestic demand continues, the percentage of the resource that is imported will rise.

Figure 12-9 shows world and United States oil production over a forty-year period. Note that United States production peaked in about 1970, in good accord with predictions that had been made a decade earlier on the basis of estimates of the recoverable domestic oil resource. In 1970, it was felt, the United States would have used approximately half of its supply of recoverable oil. More recent estimates have not revised this figure significantly. In spite of an intense exploration effort, domestic production has declined somewhat since then, and until about 1980, imports of foreign oil grew. Economic downturn and the shift to smaller and more fuel-efficient automobiles has produced a lessened demand, as shown by the curve of United States consumption of oil. In addition, the number of wells drilled recently has increased again as oil companies have intensified their search for domestic oil. Importation of oil has decreased as a result.

The recent downturn of world oil production is due to economic factors rather than to a peak reached due to passing the halfway mark in resource supplies. If the world economy should improve and the upward trend in production is resumed, it is widely felt that the natural peak in world production will be reached during the 1990s, and that total production will begin to fall irreversibly. The picture for natural gas supplies is not so clear, and world supplies of it may last longer. Even so, we can see that the oil and gas burning age in which we live will be a very short episode in human history.

Because of this situation, pressure is growing to switch to alternative energy sources such as the ones that we have already discussed. At the present time, many of our energy needs in the developed countries are being met by the elaborate electrical power distribution system. The only immediate replacements that are available for oil and gas use within this system are nuclear and coal, both of which have their attendant difficulties. Energy for transportation is an even more difficult situation, because no alternative technology to the gasoline or diesel engine exists in an acceptable form. Switching from gasoline to alcohol produced from fermented biomass has been suggested as perhaps the least disruptive alternative, but many observers are concerned that fuel needs will compete with food production for valuable farmlands, decreasing food supplies to an increasingly hungry world population.

The problems of finding sufficient energy resources to fuel the needs of a modern industrialized society are legion, especially as the populations of the developing nations improve their standards of living, with an attendant increase in per capita consumption of energy. A glance at Figure 12-4 shows that it may be impossible for the rest of the world to increase their energy consumption to that found today in the United States, given the present energy supplies and the environmental problems that are already becoming manifest. But who would deny the people of the Third World the right to as high a standard of living as that enjoyed in the developed countries? And what implications does this have for world stability?

A development with the potential to substantially alter this scenario would be the successful harnessing of thermonuclear fusion. This, of course, is the process that fuels the Sun. We shall defer a more detailed discussion of it until Unit 13, The Sun, but you may wish to take a look at Figure 13-3. The process fuses four protons (hydrogen nuclei) to form one helium nucleus along with a large amount of energy. Rather than starting with hydrogen atoms, the process could use deuterium (heavy hydrogen) as a fuel. Deuterium is a minor but recoverable constituent of seawater, present in such huge total quantities that world energy needs could be supplied for perhaps a million years at present rates of use.

Unfortunately, the technology of fusion is still in a very primitive state and, unlike fission reactors currently in use, nothing approaching a commercially feasible fusion reactor has yet been produced. Even if good progress continues to be made in this line of research, it is widely assumed that commercial-scale fusion reactors would not become available for another 30 to 40 years. In the meantime, we will have to use existing alternatives.

Certainly one means of stretching our energy resources lies in more conservative use of what we already have. Upgrading the fuel efficiency of American automobiles and reduction in oil use because of increased prices have had a dramatic effect on oil consumption in the United States in a remarkably short period of time. Effecting even greater energy savings will require incentives and an increased awareness on the part of the public of the many ways in which energy is wasted or is used in an inefficient manner.

In this arena, effective energy conservation can literally start in the home. Turning out unneeded lights, turning down the thermostat in the winter (and turning it up in the summer if you have air conditioning), and purchasing energy-efficient appliances and automobiles that get high gas mileage not only are ways of conserving energy and holding down carbon dioxide releases to the atmosphere, but also can save you and your family substantial sums of money in utility and gasoline bills.

Explore Selley (1985) for an introductory level description of petroleum geology. Hunt (1979) present, in considerable detail, how petroleum forms from organic material in rocks and the many fine points to hydrocarbon deposits. For a description of Chernobyl refer to Park (1989) or Savchenko (1995).