Right now, carbon is a biogeochemical cycle in transition, possibly even upheaval. The prehistoric earth had a much higher concentration of carbon dioxide in the atmosphere, and considerably more carbon was cycling in the vegetation and animals of ancient jungles and swamps, and in the sea creatures that lived at the time.

Slowly, this reservoir of organic carbon was converted into coal, oil, and natural gas, where it remained for millions of years. The Industrial Revolution began freeing that tied-up carbon and pumping it back into the atmosphere through the combustion of fossil fuels.