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 capture and storage and fossil fuel-based hydrogen production plants. Extracting from air is also possible, although the far lower concentration of in air compared to combustion sources presents significant engineering challenges. Organisms that produce ethanol by fermentation generate cool, essentially pure that can be pumped underground. Fermentation produces slightly less than ethanol by weight. Flue gas from the combustion of coal in oxygen has a large concentration of , about 10-15% whereas natural gas power plant flue gas is about 5–10% . Therefore, it is more energy and cost efficient to capture from coal-fired power plants. Impurities in streams, like sulfurs and water,