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How is Coal & other Fossil Fuel Formed?

Fossil fuels such as coal and oil form the very bedrock of today's industrial economy. Yet, for a process as far from nature as is industrialization, the substances which drive it are completely natural. Here is a brief glimpse into the fascinating process of fossil fuel formation.

As their name suggests, fossil fuels are derived from fossilized organisms. In general terms, organisms decay and are subjected to immense heat and pressure within the earth's surface. Over thousands of years, these fossils are transformed into either coal, oil or natural gas. The organisms involved and necessary conditions vary based on the specific fuel.

Coal, for instance, is comprised of plants and trees that decayed in marshy terrain. The vegetation sank deep into the muddy ground, forming layers of peat. Layers upon layers of peat compacted over many years before the marshy surface dried, becoming instead areas of clay and sand. Over time, more weight on the earth's surface pressed down upon the layers, driving out the water and compacting the peat under tons of rock and other materials. In addition to pressure from above, the peat was cooked by heat from the earth's core, effectively baking it over thousands of years into the material we now know as coal.

Coal is categorized into different types based on the amount of pressure to which the peat has been subjected. In general, coal becomes more efficient and valuable if it has been subjected to more pressure. The least valuable coal, lignite, has a brownish appearance. If more pressure is applied, lignite transforms into subbituminous, the lowest quality of coal that is used for electricity and heating. The next two grades are bituminous and anthracite, both of which are commonly used for electricity production and heating in the United States. In addition to being of the highest quality, anthracite also burns more cleanly than does any other type of coal.

Natural gas and petroleum are formed slightly differently, although the process is much the same. Millions of years ago, many plants and animals died and sank to the bottom of the ocean. These organisms were soon buried in sand and silt which applied immense pressure, in addition to that provided by the water. Over millions of years, the pressure from above and heat from below transformed the organisms into oil and natural gas. This process is why oil is commonly drilled off shore, or why oil wells are commonly found in locations that were once under water before the earth's surface transformed.

The process for producing oil and natural gas are the same. Into which fossil fuel the organisms are ultimately transformed depends on the amount of heat to which they were exposed. If nearer the earth's surface, and thus exposed to less heat, the organisms tend to produce more oil. If buried deeper toward the core, and thus exposed to more heat, natural gas is produced. Deposits of oil and natural gas are often found close to each other, usually because natural gas deposits are deeper layers of any oil deposits that have been located.