| Carbon, used by all living organisms, continuously circulates in the earth’s ecosystem. In the atmosphere, it exists as colorless, odorless carbon dioxide gas, which is used by plants in the process of photosynthesis. Animals acquire the carbon stored in plant tissue when they eat and exhale carbon dioxide as a by-product of metabolism. The carbon cycle continues after plants and animals die, when bacteria contribute to the decay process and release carbon dioxide. Although some carbon is removed from circulation temporarily as coal, petroleum, fossil fuels, gas, and limestone deposits, respiration and photosynthesis balance to keep the amount of atmospheric carbon relatively stable. Industrialization, however, has contributed additional carbon dioxide to the environment. |
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