Carbon can be found in many different places on Earth. You can find it in rocks, trees, oceans and in groundwater. It is also found as a gas in carbon dioxide, or CO2.
Just as H2O circulates between the atmosphere, the ground, and ocean waters in the water cycle, CO2 also circulates between these three reservoirs, solidifing as rock, dissolving out of rock into the water, baked out of rock into the air, or being absorbed directly into the waters at the Earth's surface. The transfer of CO2 between the air, water, and the ground is called the carbon cycle.