a Department of Cybernetics, University of Reading, Reading, England
b Department of Biology, Boston University, Boston, MA 02215, U.S.A.
Abstract:
The Gaia hypothesis states that the composition, oxidation-reduction potential and the temperature of the Earth's lower atmosphere are modulated by and for the biota living on the surface (Lovelock, 1972; Margulis and Lovelock, 1974). A corollary is that atmospheric oxygen is presently regulated at about 21% for the dominant life forms today: vascular plants and metazoa. We suggest that the enormous annual production of methane (of the order of 1014 mol) is directly related to the short term modulation of oxygen concentration. Atmospheric oxygen results from the burial of reduced carbon; methanogenesis and subsequent atmospheric oxidation of methane prevents that burial. We also present experimental work on the probability of ignition of vegetation as a function of increasing oxygen concentration (Watson, 1978). Both the experiments and consideration of the fossil record lead us to conclude that oxygen has been regulated by methane (and perhaps by N2O and others) at about 10–25% for very long periods relative to the atmospheric residence times of these reactive gases.