Carbon dioxide (chemical formula CO2) is a colorless and odorless gas that is vital to life on Earth. This naturally occurringchemical compound is made up of a carbonatomcovalentlydouble bonded to two oxygen atoms. Carbon dioxide exists in Earth's atmosphere as a trace gas at a concentration of about 0.04 percent (400 ppm) by volume. Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, in ice caps and glaciers and also in seawater. It is present in deposits of petroleum and natural gas.
Atmospheric carbon dioxide is the primary source of carbon in life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by photosynthetic organisms and geological phenomena. As part of the carbon cycle, plants, algae, and cyanobacteria use lightenergy to photosynthesizecarbohydrate from carbon dioxide and water, with oxygen produced as a waste product.
Carbon dioxide (CO2) is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy byrespiration. It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals, including humans. Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread,beer and winemaking. It is produced by combustion of wood and other organic materials and fossil fuels such as coal, peat,petroleum and natural gas.
It is a versatile industrial material, used, for example, as an inert gas in welding and fire extinguishers, as a pressurizing gas in air guns and oil recovery, as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee andsupercritical drying. It is added to drinking water and carbonated beverages including beer and sparkling wine to addeffervescence. The frozen solid form of CO2, known as "dry ice" is used as a refrigerant and as an abrasive in dry-ice blasting.
