In Cycles of Life, Vaclav Smil explores the crucial insight that, through their participation in biogeochemical cycles, living organisms act as a tremendously important agent of change in their environment. He shows, for example, how the composition of the atmosphere has been affected by microscopic organisms of the ocean; climate by the Earth's vegetation; soil chemistry by microbes teeming on and beneath the planet's surface. Smil argues that several of today's principal environmental concerns - such as possible global warming, acid rain, photochemical smog, and the degradation of ecosystems - are tied to human interference in the biospheric cycles of carbon, nitrogen, and sulfur. Human society has always interfered in this cycling of elements, but industrialization and development worldwide have intensified the disruption, as burning fossil fuels spew carbon, nitrogen, and sulfur oxides into the air and crop fertilizers overload waters and ecosystems with nitrogen. From the broader perspective offered by this book's examination of biogeochemical cycles, Smil is able to explore the links among environment, energy, food, population, economy, and society that will determine how these interferences shape the planet's future. Future human activity will inevitably disrupt further the flow of the biogeochemical cycles of carbon, nitrogen, and sulfur. By helping us understand how those cycles work and how we interfere with their flows and stores, Smil is arming us to meet one of modern society's great challenges - to prosper on this planet while still protecting it.