OLogy Cards > carbon dioxide

Carbon Cycle
Like water moves through the water cycle,
carbon moves through the carbon cycle.

Carbon moves through the air, water, soil, and even living things. Oceans absorb carbon dioxide from the atmosphere. Plants use carbon dioxide and sunlight to make their own food. Animals and plants alike release carbon dioxide through respiration and when they decay. Marine animals use carbon dissolved in water to make their shells. Shells build up to form rocks. Rocks release carbon dioxide through weathering. Different parts of this cycle can take anywhere from hours to tens of millions of years.

This cycle has kept a healthy balance of carbon dioxide in the atmosphere--just enough to keep Earth's temperatures within a certain range and for life to exist. But now, human actions are disturbing the balance. When we burn fossil fuels, we are rapidly releasing carbon that had been locked within Earth into the atmosphere. The carbon combines with oxygen in the air to form carbon dioxide.