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 capture projects include: The Shanxi International Energy Group (SIEG) is working to construct a 350 MW super-critical coal-fired power plant in Taiyuan, Shanxi province in China. Set for construction in the 2020s, this plant will capture carbon dioxide using oxy-fuel combustion, aiming for the capture of over 2 million tons of carbon dioxide per year. SIEG has been working with the US-based company Air Products since 2010 to perform feasibility testing and adapt its oxy-fuel technology to a proposed plant design. Captured carbon dioxide will be both sequestered and used for other applications. This project has also been included in