Gaia Hypothesis

The Gaia hypothesis, developed by James Lovelock and Lynn Margulis beginning in the 1970s, proposes that the Earth's living organisms and their inorganic environment form a single self-regulating system that maintains atmospheric composition, ocean salinity, and surface temperature within ranges suitable for life. Photosynthetic organisms produce oxygen; respiring organisms consume it; the balance stabilizes atmospheric oxygen at approximately twenty-one percent — high enough to support complex metabolism, low enough to prevent runaway combustion. Ocean salinity is regulated by the weathering of rocks, itself influenced by the root exudates of plants and the metabolic activities of soil microorganisms. The system works not through intentional coordination but through feedback loops: organisms modify their environment, the modified environment selects for organisms adapted to it, and the process produces stability at the planetary scale. Margulis's contribution was microbiological: she demonstrated that the regulatory mechanisms are primarily microbial, that bacteria engineered the planet's atmosphere and ocean chemistry long before complex life appeared, and that Gaia is not a metaphor but an empirical claim about