Fossil fuels are derivatives of biologically degradable materials but only after millions of years of biological, chemical, pressure and heat reactions. They occur at different underground depths in three forms: as gases, liquids and solids. Natural gas is a gaseous fossil fuel, which is essentially a mixture of various hydrocarbons including butane, propane, ethane and methane. Liquid fossil fuels include mineral oil, fuel oil, aviation fuel, diesel, kerosene and petrol. Coal is a solid fossil fuel that occurs in three main types, including lignite, bituminous and anthracite.
Main sources of fossil fuels are marine organic matter and terrestrial trees, Paul Ih-fei Liu states in the book "Energy, Technology, and the Environment." Coal is the byproduct of prehistoric vegetation, including ferns, trees and other woody plants; liquid fossil fuels are formed from the remains of buried marine organisms; and natural gas, which is usually found near petroleum reserves, is formed from the decomposed remains of sea life and plankton.
R. Gieré and Peter Stille report in the book "Energy, Waste and the Environment" that fossil fuels provide approximately 86 percent of the global supply of fuel. Electricity generation is one of the primary uses of fossil fuels, accounting for more than 50 percent of all fossil fuel uses. Energy derived from fossil fuels is used extensively in the mining, construction, manufacturing and mineral production industries; commercial and residential cooling, heating and lighting purposes; and in the transportation sector.
Burning of fossil fuels releases carbon and other air pollutants, including volatile organic compounds, sulfur dioxide, smog, particulate matter, lead, carbon monoxide and nitrogen oxides. These substances have a host of negative environmental impacts, including greenhouse gases, acid rain and global warming. Indirect effects of carbon emissions from fossil fuel burning include erratic weather patterns, polar ice cap melting, droughts and floods. Health effects of fossil fuel combustion include central nervous system damage, digestive problems, damage to the respiratory system and cancer.