THE FOSSIL FUELS
John J. Fagan
Department of Geology City College of New York
Source of information: 1974 by Prentice-Hall, Ins.,Englewood Cliffs, New Jersey.
Millions of Years of Sunlight
Almost all of the energy we use comes from the solar radiation of the sun. Plants use this energy by the vital process of photosynthesis, and animals use it indirectly by eating plants or other creatures which deŽpend on plants. Thus, by domesticating animals and by burning wood, man uses concentrated solar energy. If he burns a very old tree, like a redwood giant, the heat energy released represents some of the solar radiŽation which reached the earth's surface during the centuries that passed as the tree grew and built its thick trunk, layer by layer. Living plants temporarily store the energy derived from solar energy; this energy is eventually released as heat to the atmosphere during the decay of the dead plants. The heat given off by decay is approximately equal to that produced and stored by the living plants so that a balance is maintained. But in any given year a very small fraction of the photo-synthesized energy is held back from decay in a few unusual situations, such as in a swamp or in certain protected bodies of water. In such environments, the lack of oxygen retards decay and allows the accumulation of organic matter and its preservation amid layers of mud or other sediments. This is the preservation process that produces the fossil fuels: coal, petroleum, and natural gas. It is quite rare, most living matter being wholly destroyed soon after death. But during the last half billion years of earth's history, enough matter has been preŽserved to provide us with the fuels on which we so heavily depend on today.
Man's Use of Coal
It is believed that the Chinese used small amounts of coal as long as 2000 years ago, and there is clear evidence that some of the Indians of northern Arizona burned coal prior to the arrival of Europeans. In England, coal was first used in the 12th century, having been found as scattered lumps weathering out of the rocky coastline, where they were called sea coals (or coles). For hundreds of years such coal was gathered and used for cooking and heating, but it was not until the early 18th century that it was recognized that coal occurred in extensive beds or seams inter layered with other sedimentary rocks. In this country, coal was being mined in Virginia by the middle of the 18th century. From the middle of the 19th century on, the use of coal increased rapidly. In the United States, usage by railroads, industry, and homes was heavy until the close of World War II. At this time, a slight levelŽing off of demand occurred as railroads and home furnaces stopped burnŽing coal, but a new demand arose as water power was inadequate for the increasing demand for electricity. The use of coal by steam-electric plants soared and the rate of consumption of this fuel is now greater than ever and rising rapidly.
Fuel from the Swamps.
A coal bed is a greatly compacted layer of plant matter that originally accumulated in a swamp or bog, generally along the edge of the sea. Under such stagnant conditions, the plant remains that fall to the ground year after year, century after century, are kept from decaying completely by the low oxygen content of the wet ground. Thus, a thick layer of peat is built up. This spongy mass of vegetal matter becomes covered by layers of mud or other sediment when a change occurs in the environŽment of deposition. Often the change is a result of the sea flooding the land. The new sediment layers slowly build up; the peat is slowly compacted under their growing weight and more and more of the cellulose of the twigs, branches, and leaves is converted chemically to carbon dioxide, water, methane, and carbon. With continued pressure and time, the first three of these are gradually volatilized, the carbon remaining behind. The carbon content increases relative to other components. We distinguish between varieties of coal on the basis of their carbon content. The most commonly used coal, called bituminous or soft coal, contains 50 percent or more carbon, greater carbon content characterizŽing the higher ranks of bituminous. In a few regions, such as eastern Pennsylvania, a very hard, especially desirable but rare coal called anthracite is found. This variety is usually found as part of a sequence of layers that have been deeply buried and intensely folded. Because of the pressure or heat involved, anthracite contains over 95 percent carbon with little remaining volatile matter. It is hard to ignite but burns with almost no smoke. Most modern coal-forming environments are relatively small areas like the Irish peat bogs where Ice Age glacial deposits have dammed streams to produce shallow, swampy basins. Thick and extensive accumulation of peat, similar to those which gave rise to the major coal layers of the world, are not widespread today. Perhaps, the best American example of modern environment of swamps and peat on a large scale is that of the Great Dismal Swamp that covers over 2000 square miles of Virginia and North Carolina. Coal formation has been occurring ever since the middle Paleozoic Era (see Appendix) when the evolutionary development of land plants had sufficiently progressed to form forests and peat bogs. However, coal was formed in the greatest quantities during the late Paleozoic period known as the Pennsylvania (late Carboniferous of Europe), which began about 320 million years ago. Most of the coal in Europe and eastern North America is Pennsylvania. Strata of the next younger, or Permian period, include coal deposits in the U.S.S.R., China, South Africa, India, and Australia. Cretaceous (late Mesozoic) coal is abundant in a number of regions, especially in the Rocky Mountain states. These three periods, which account for the formation of most of the world's coal deposits, must have been times of vast, long-enduring swamplands in many regions throughout the world.
Energy in Layers
Individual coal beds (or seams) range in thickness from a fraction of an inch to several tens of feet. It has been estimated that about 30 feet of peat must be compressed in order to produce each foot of bituminous coal. Studies of rates of peat accumulation suggest that each foot of accumulation required about a century. Thus it appears that each foot of coal represents some 3000 years of plant growth. A valuable ten-foot-thick bed of coal would represent about 30,000 years of continuous plant growth during which trees and other plant debris gradually accumulated in Paleozoic or Mesozoic swamps. It is clear from the above estimates of the time required for coal formaŽtion that new coal is being formed too slowly even to be considered as fuel for mankind. In practical terms, the world's present coal layers are all the coal available to us. Geologists believe that all the major coal fields of the world are now discovered. The total recoverable amount of coal beds over one-foot thick and within working distance of the surface has been estimated at over 8000 billion tons, with Asia, North America, and Europe, in that order, accounting for over 95 percent of the total. The continents of South America, Africa, and Australia together account for the remainder, less than five percent of the world's reservoirs. Clearly, the southern hemisphere is coal-poor. In spite of the thousands of billions of tons of coal reserves, if we conŽtinue to use coal and increase our consumption at the rates predicted by various experts, the time required to exhaust most of the coal supplies in the world is somewhere between one and four centuries. And in order for most of these reserves actually to be mined, the strip type of operaŽtion is almost certain to be employed on so vast a scale as to seriously alter the world's landscapes Strip mining is rapidly becoming one of the most spectacularly visible forms of environmental alteration in the United States. In Kentucky, West Virginia, and Pennsylvania, vast areas of the landscape are now being devastated by bulldozers in order to remove the layers of coal beneath. Various corporations, including the giant oil companies, are already involved and heavily invested in strip mining plans for fuŽture power production in these regions and in most of the other 23 states that have strippable coal deposits.