How is the carbon cycle disturbed by human activities?
Carbon is the fourth most abundant element in the universe, and is absolutely essential to life on earth. In fact, carbon constitutes the very definition of life, as its presence or absence helps define whether a molecule is considered to be organic or inorganic. Every organism on Earth needs carbon either for structure, energy, or, as in the case of humans, for both. Discounting water, you are about half carbon. Additionally, carbon is found in forms as diverse as the gas carbon dioxide (CO2), and in solids like limestone (CaCO3), wood, plastic, diamonds, and graphite. The movement of carbon, in its many forms, between the atmosphere, oceans, biosphere, and geosphere is described by the carbon cycle (Figure 1). This cycle consists of several storage pools of carbon (black text) and the processes by which the various pools exchange carbon (purple arrows and numbers). If more carbon enters a pool than leaves it, that pool is considered a net carbon sink. If more carbon leaves a pool tha
