Greenhouse in a Beaker Activity Source: Adapted with permission by The NEED Project. Carbon is naturally found in the atmosphere. Carbon dioxide, or CO2, itself is not considered a pollutant. The CO2 being released from burning fossil fuels was part of the atmosphere hundreds of millions of years ago before being captured by plants and sea organisms. Carbon atoms naturally cycle through the biosphere, the atmosphere, the hydrosphere, and the lithosphere in process known as the carbon cycle. [Read More]