Smil explores the scientific kernel in the mystical shell of the Gaia hypothesis. He describes how living organisms assure their survival by actively participating in the complex cycling of carbon, nitrogen and sulphur. He updates us on what has been learned about the complex interplay of human beings, other organisms, chemical reactions and geological changes in the Earth's biosphere. Cycles of Life describes how biospheric cycles work, how we interfere in their natural flows, and how we could moderate or avert further deterioration.