ABSTRACT
Geologists believe that underground coal deposits formed about 290-360million years ago during Carboniferous geologic era, when much of Earth was covered with muddy ground, swamps and thick forests (Moore 1922, Jeffry 1924). As the plants and trees grew and perished, the plant debris was buried under Earth’s wet surface, where insufficient oxygen slowed their decay and led to the formation of peat. The plant debris converting into peat was through a biochemical process. Over millions of years, these layers of peat are altered physically and chemically; this process is called ‘coalification’. Covered by newly formed oceans and land masses, peat started to become a tightly packed and compressed sediment under combined effect of heat (from the Earth’s interior or near volcanic source) and pressure. The accumulation and sediment deposition continued repeatedly and was followed by geochemical process, i.e., biological and geological actions. This means, peat underwent several changes as a result of bacterial decay, compaction, heat, and time. Depending upon the extent of temperature, time, and pressure exerted, different types of coal (from peat to lignite coal, to sub-bituminous coal, to bituminous coal, and to anthracite coal) were formed and are mined today (e.g., Lieske 1930, Berl et al. 1932, Stadnikov 1937, Hendricks 1945, Fuchs 1952). The sequence of formation is represented in Figure 3.1 (Kentucky Geological Survey: How is coal formed?). It is estimated that three to seven feet of compacted plant matter is needed to form one foot of coal.
