The Breathing of the Biosphere
Life, all life, from single-celled bacteria to entire ecosystems, shares common features, the most fundamental of which is metabolism. Most life is driven by the energy of the sun, captured by photosynthesis within the chemical bonds of organic materials. Organisms, including you, consume these organic materials with oxygen, producing CO2 . Just as you breathe, so does the biosphere.
This is a presentation from J. W. Raich, "The Breathing of the Biosphere," based on Raich, Potter & Bhagawati (2002) Global Change Biology 8:800-812.