Coal is a fossil fuel formed in ecosystems where plant remains were preserved by water and mud from oxidization and biodegradation; its chemical and physical properties have been changed as a result of geological action over time, thus sequestering atmospheric carbon. Coal is a readily combustible black or brownish-black rock. It is a sedimentary rock, but the harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. It is mainly carbon and hydrogen with small quantities of other elements, notably sulfur. Coal is extracted from the ground by mining, either underground mining or open pit mining (surface mining). It is a nonrenewable resource.
Coal is the largest source of fuel for the generation of electricity worldwide, and the largest worldwide source of carbon dioxide emissions. Carbon dioxide is a greenhouse gas and the major contributor to an increase in global average temperature and related climate changes. Gross carbon dioxide emissions from coal usage is slightly more than that from petroleum and about double the amount from natural gas.
Outcrop coal was used in Britain (2000-3000 years BC), where it has been detected as forming part of the composition of funeral pyres. The earliest recognized use is from the Shenyang area, 4000 BC where people carved ornaments from black lignite, but it was not until the Han Dynasty that coal was also used for fuel. In Roman Britain, with the exception of two modern fields, â€œthe Romans were exploiting coals in all the major coalfields in England and Wales by the end of the second century AD.â€ Evidence of trade in coal (dated to about AD 200) has been found at the inland port of Heron bridge, near Chester, and in the Fenlands of East Anglia, where coal from the Midlands was transported via the Car Dyke for use in drying grain. Coal cinders have been found in the hearths of villas and military forts, particularly in Northumberland, dated to around AD 400. In the west of England contemporary writers described the wonder of a permanent brazier of coal on the altar of Minerva at Aquae Sulis (modern day Bath). Evidence of coalâ€™s use for iron-working in the city during the Roman period has been found.
There is no evidence that the product was of great importance in Britain until after about AD 1000. Mineral coal came to be referred to as â€œseacoal,â€ probably because it came to many places in eastern England, including London, by sea. This is accepted as the more likely explanation for the name than that it was found on beaches, having fallen from the exposed coal seams above or washed out of underwater coal seam outcrops. These easily accessible sources had largely become exhausted (or could not meet the growing demand) by the 13th century, when underground mining from shafts or adits was developed. In London there is still a Seacoal Lane and a Newcastle Lane (from the coal-shipping city of Newcastle) where in the seventeenth century coal was unloaded at wharves along the River Fleet. An alternative name was â€œpitcoal,â€ because it came from mines. It was, however, the development of the Industrial Revolution that led to the large-scale use of coal, as the steam engine took over from the water wheel.