Coalification is the formation of coal over a three hundred million year process. During the initial periods of Coalification the Earth’s surface was covered mainly by swamps. These conditions, much like those in the tropical rain forests of South America today, facilitated dense vegetation growth.
As this vegetation died and fell into nearby water deposits, the absence of air prevented any further decay of the material. Over thousands of years this accumulated into layers of vegetation residue many meters thick.
Drastic changes in the Earth’s crust over millions of years took place which resulted in the creation of coal. Had these changes not occurred to the earth’s surface then a peat like substance found in Ireland, Scotland and Yorkshire today would be much more common and widespread.
However, great volcanic eruptions did occur vastly changing the landscape creating mountain ranges and lower ground. These highs and lows over a time span of millions of years, coupled with dramatic atmospheric changes with great winds, ice ages and thaws resulted in the erosion of the mountain tops. These erosions created hundreds of meters of sand, shale and rock minerals being deposited on top of the vegetation. Large pressure on the vegetation, in addition to heat and great lengths of time changed the peat like matter into the coal product used extensively today.
When burning fuel such as coal, ash deposits are made requiring the user to clean the fire or appliance before its next use. Ash exists within coal because of the vegetation which it is initially formed from. Ash is present within the vegetation and appears much like the residue from a cigarette or wood fire. During Coalification the ash content in the vegetation is trapped and becomes part of the final coal product. Residue level in coal varies around the world because of the changes in the composition of vegetation.