| Themes > Science > Earth Sciences > Geology > Coal > About Coal, Generalities > The Origin of Coal |
Coal is a combustible, black sedimentary rock composed predominantly of carbon. It is formed out of plant matter that accumulated at the bottom of swamps millions of years ago, during the Carboniferous Period. At this time, the earth's climate was extremely favourable for plant growth. Organic matter accumulated in stagnant swamps which were low in oxygen and thus inhibited decomposition. Eventually, seas rose or the land subsided and the swamps were submerged. Sand, clay and other debris at the bottom of the seas buried the organic material. Over thousands of years, the organic material was compacted under the weight of the overlying sediments and was transformed into coal (Figure 1). Coal deposits are now found buried beneath layers of sandstone, limestone and shale all over the world. The United States, the former Soviet Union, China and India have the largest reserves of coal, but large deposits also exist in South Africa, Australia Germany and Eastern Europe. Canada has about 0.6% of worldwide coal reserves and these are concentrated in western Canada. FIGURE 2: Canadian coal deposits (39K). The mining of coal is carried out in a variety of different methods depending upon how close the coal is to the ground surface. Where coal is located at a shallow depth mining is accomplished by digging a large open pit or strip mine. This is the case in much of western Canada. In areas like eastern Canada (Nova Scotia) coal is found at greater depths and is mined using a system of underground rooms and tunnels. In the past and in some parts of the world today, coal mining has been responsible for a large number of deaths, both directly through mine accidents and indirectly through respiratory diseases caused by years of exposure to coal dust. New automated, mechanized methods of mining coal, the and strict safety regulations have greatly improved the safety record of coal mining in countries like Canada. |
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