Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere?
The atmosphere is composed of a mix of several different gases in different amounts. The permanent gases whose percentages do not change from day to day are nitrogen, oxygen and carbon dioxide. The cycling of oxygen, nitrogen and carbon dioxide between the atmosphere and the biosphere results in relatively constant proportions of these compounds in the atmosphere over time. For example, the carbon cycle, as it relates to the biosphere, is simple. Inorganic carbon (carbon dioxide) is converted to organic carbon (the molecules of life). To complete the cycle, organic carbon is then converted back to inorganic carbon. The nitrogen cycle begins with the fixing of inorganic atmospheric nitrogen () into organic compounds. These nitrogen-containing compounds are used by organisms and, through the process of denitrification, are converted back to inorganic atmospheric nitrogen.