The Gaia hypothesis, proposed by the chemist James Lovelock and developed with the microbiologist Lynn Margulis from the late 1960s and set out fully in Lovelock's 1979 book Gaia: A New Look at Life on Earth, is a scientific proposal that the Earth's biosphere, atmosphere, oceans and soil interact as a single, complex, self-regulating system that has actively maintained conditions favorable for life, including a stable global temperature and atmospheric chemistry, across immense spans of geological time.
Lovelock developed the hypothesis while working on methods for detecting life on other planets, reasoning that a planet's atmosphere in chemical disequilibrium, far from what non-living chemistry alone would produce, could itself be a signature of life actively maintaining that disequilibrium, an observation he then extended into the broader claim that Earth's whole biosphere functions as a coupled, self-regulating system. Lovelock and Margulis presented Gaia as a scientific hypothesis about feedback mechanisms in earth system science, subject to ordinary empirical testing and revision, and named it, at the suggestion of the novelist William Golding, a neighbor of Lovelock's, after the Greek earth goddess, a naming choice that would shape the hypothesis's reception considerably beyond what its authors intended scientifically.