Geophysiology, the science of Gaia

The Gaia hypothesis postulates that the climate and chemical composition of the Earth's surface environment is, and has been, regulated at a state tolerable for the biota. This notion was introduced in 1972 and 1973 (Lovelock, 1972; Margulis and Lovelock, 1974; Lovelock and Margulis, 1973). The wording of these early papers was sometimes poetic, rather than scientific, but Gaia has matured and might be better stated as a theory that views the evolution of the biota and of their material environment as a single, tightly coupled process, with the self‐regulation of climate and chemistry as an emergent property. It is a theory that makes “risky” predictions, for example, that oxygen is and has been regulated during the existence of land plants, within ±5% of its present level; it is therefore falsifiable. Numerical models are used to illustrate the potential for stable self‐regulation of tightly coupled systems of organisms and their environments.