Precursors of Coal

Coal formation began during the Carboniferous Period, which is known as the first coal age and major coal deposits were formed in every geological period since the Upper Carboniferous Period, 270-350 million years ago. 

The concept that coal evolved from the organic debris of plant material is not new and came into being during the latter part of the eighteenth century (Moore, 1940 Hendricks, 1945). Precisely how this theory came about is still open to some speculation but the observation of plant imprints within the coal obviously would give rise to the idea of coal being associated with plant material. From that premise, it is one small step to the concept of plant material as the organic precursor to coal. 

Indeed, in order to emphasize the complexity of coal and the complexity of the coal-forming processes, some consideration of the potential precursors are worthy of consideration. However, there is also cautious assumption that there are little, if any, differences (natural selection notwithstanding) between the natural product chemicals known now and those in existence at the time of deposition of the coal beds perhaps a reasonable assumption, but it is fraught with uncertainties. 

On the other hand, the term organic debris is used globally in this text to mean any of the material after degradation or decay has commenced but before coaliflcation proper has ensued. 

Types of Macromolecules (Other than Proteins) in Plants 

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Peat Peat is partially decomposed plant matter that has accumulated underwater or in a water-saturated environment. It is the precursor of coal but is not classified as coal. Sold under the term peat moss or moss peat, peat is used in the United States mainly for horticultural and agricultural apphcations, but interest is growing in its use as a fuel in certain local areas (e.g.. North Carolina). Peat is used extensively as a fuel primarily in Ireland and the former Soviet Union. Although analyses of peat vary widely, a typical high-grade peat has 90 percent water, 3 percent fixed carbon, 5 percent volatile matter, 1.5 percent ash, and O.IO percent sulfur. The moisture-free heating value is approximately 20.9 MJ/kg (9000 Btu/lb). 

Humic substances in subaqueous sediments, such as peats and aquatic sediments, are generally considered to be precursors of coal (Flaig et al., 1975) and kerogen (Hue and Durand, 1977), respectively. Consequently, interest has been focused on the diagenetic changes that humic substances undergo in the course of their transformation to such bioliths. 

Humic acids in coal may have at least two origins. Humic acid remaining in coal may be the residue of the geological precursors of coal, or, the humic... 

Giving consideration to (1) the different chemical precursors of coal (as presented later), (2) the varied geological environment, (3) the maturation conditions, and (4) the variation of coal analysis within a seam, the rationale for an average structure of coal defeats itself. 

There is little hard evidence to support the theory that lignin is the major organic precursor of coal. The nature of lignin has been well researched but there are still many unknowns. Thus, the concept of... 

Smith and Smoot, 1990). This may be due to not only the deposition of a variety of different organic compounds that are believed to be the precursors of coal (Chapter 3) but also the accumulation of different parts of the plant (as well as different plants, e.g., trees, ferns, mosses, etc.) during the formation of the sediment (Murchison, 1991 Puttmann et al., 1991). Each compound type, tissue type, or plant type then progresses through the various maturation stages that eventually lead to coal. 

Coal originated from the remnants of various forms of plant life (trees, bushes, ferns, mosses, vines, etc.) that flourished in swamps and bogs millions of years ago during prolonged periods of abundant rainfall. Peat, the precursor of coal, was formed by bacterial and chemical action on accumulations of plant debris. Given has presented an excellent review on the origin and formation of coal. 

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