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 pollution mitigation and 5000 tons globally. However, according to the United States Geological Survey, the trace amounts of mercury in coal by-products do not pose a threat to public health. A study in 2013 found that Mercury found in the fish in the Pacific Ocean could possibly be linked to coal-fired plants in Asia. Whether carbon capture and storage technology is adopted worldwide will “…depend less on science than on economics. Cleaning coal is very expensive.” Conversion of a conventional coal-fired power plant is done by injecting the into ammonium carbonate after which it is then transported and deposited underground (preferably in