Carbon dioxide (chemical formula CO2) is a colorless and odorless gas vital to life on Earth. This naturally occurring chemical compound is composed of a carbon atom covalently double bonded to two oxygen atoms. Carbon dioxide exists in the 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. Since carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, in ice caps and glaciers and in seawater. It is present in deposits of petroleum andnatural 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 light energy to photosynthesize carbohydrate from carbon dioxide and water, with oxygen produced as a waste product. Carbon dioxide is produced by plants during respiration.
Carbon dioxide (CO2) is a product of respiration of all aerobic organisms. 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, carbohydrates andfossil fuels such as coal, peat, petroleum and natural gas.