Soil

When plants and animals die, their remains are decomposed by organisms in the soil.  The nutrients in the previously living organism then become available to plants to support their growth. Part of this decomposed material is carbon, which at one time was carbon dioxide in the air. Soil organisms release some of this carbon as carbon dioxide during the decomposition process, while a portion of the carbon remains in the soil. Over long periods of time, this carbon can become ‘locked up’ in the form of coal, oil, and natural gas, forms that historically were not part of the carbon cycle. Only when we humans extract and burn these fossil fuels does that carbon return to the atmosphere as carbon dioxide, shifting the balance of carbon dioxide uptake and release by plants and animals, causing the atmosphere to trap more of the sun’s energy, and warming our planet.