The document discusses the carbon cycle and how carbon moves between organic and inorganic forms through photosynthesis and cellular respiration. It describes how producers convert carbon dioxide into organic compounds through photosynthesis, and how consumers and producers return carbon dioxide to the atmosphere through cellular respiration. It also discusses how carbon is absorbed by oceans and sediments, and incorporated into shells, coral, and limestone over long periods of time. The document then explains how humans disrupt the natural carbon cycle by burning fossil fuels, releasing carbon that has been fixed for thousands of years back into the atmosphere as carbon dioxide. This increased carbon dioxide is contributing to rising global temperatures and global warming.