The document discusses the carbon cycle. It begins by explaining that carbon is exchanged among the biosphere, atmosphere, hydrosphere, geosphere, and pedosphere. It then provides details on the global carbon budget, noting that the oceans contain 71% of the world's carbon while terrestrial ecosystems hold around 3%. The atmosphere contains around 1% of total carbon. It concludes by outlining the main components of the carbon cycle as the atmosphere, terrestrial biosphere, oceans, and sediments.