Coal the heat and pressure of deep burial causes the loss of water, methane and carbon dioxide and an increase in the proportion of carbon. Thus first lignite (also called "brown coal"), then sub-bituminous coal, bituminous coal, and lastly anthracite (also called "hard coal" or "black coal") may be formed. The wide, shallow seas of the Carboniferous Period provided ideal conditions for coal formation, although coal is known from most geological periods. The exception is the coal gap in the Permian–Triassic extinction event, where coal is rare. Coal is known from Precambrian strata, which predate land plants—this coal is presumed to
Carbon, Iowa originally named Walters, after its first settler, but was renamed Carbon after the discovery of coal. The town was established in 1873, but was not incorporated until 1903. A post office was established in Carbon in 1874, but from 1877 to 1880, the name was changed to Shinn. By the time of the Civil War, there were small coal mines along the riverbanks near Carbon. In 1894, there were 9 coal mines in Carbon, of which 5 were in current use. Typical mine shafts were 80 feet deep, working a coal seam 12 to 20 inches (30 to 50 cm)