Global dynamics: Gaia or geochemistry?

Summary The nature and evidence of the gaia and geochemical hypotheses describing the dynamics of the ecosphere are reviewed. In particular, the ways in which the unorthodox gaia hypothesis challenges the orthodox global models of geochemistry are discussed in the context of the logic and sociology of science. It is argued that the gaia hypothesis offers environmental scientists a working hypothesis of unusual promise, especially for understanding the processes underlying the long-term dynamics of the global environmental system.Dr Ian Moffatt is a member of the staff of the Department of Environmental Science at the University of Stirling.