The Earth is a complex physical-chemical-biological system that is driven in large part by energy from the Sun and from the Earth's interior. The history of the System, its arrows and its cycles, reflect the evolution of these energy sources and the evolution of the biosphere.<BR><BR>This collection of chapter from the Treatise on Geochemistry describes the present and the past operation of the major Earth surface systems. Chapters on volcanic and hydrothermal systems are followed by descriptions of the geochemical cycles of carbon and sulfur, the nature of weathering, the composition of river waters, the operation of the oceans, and the evolution of sedimentary rooks. The final chapter on the behavior of volatiles in subduction zones closes the cycle that is opened in the first two chapters.