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
Coal-fired pizza Coal-fired pizza Coal-fired pizza is a pizza style in the United States. New York-style pizza and New Haven-style pizza are often cooked in coal-fired pizza ovens. A coal-fired oven can reach and cook a pie in two to three or five minutes. Pizzarias outside of the Northeastern United States that feature coal-fired oven are uncommon enough to be noted in travel guides: for instance, Black Sheep Pizza with the first coal-fired oven in Minneapolis, or URBN in San Diego. As of 2007, coal-fired ovens were quite uncommon in the Western United States with only five west of the Mississippi: four