The Gaia hypothesis, also known as Gaia theory or Gaia principle, proposes that organisms interact with their inorganic surroundings on Earth to form asynergistic self-regulating, complex system that helps to maintain and perpetuate the conditions for life on the planet. Topics of interest include how the biosphereand the evolution of life forms affect the stability of global temperature, ocean salinity, oxygen in the atmosphere, the maintenance of a hydrosphere of liquid water and other environmental variables that affect the habitability of Earth.
The hypothesis was formulated by the chemist James Lovelock and co-developed by the microbiologist Lynn Margulis in the 1970s. The hypothesis was initially criticized for being teleological and contradicting principles of natural selection, but later refinements resulted in ideas framed by the Gaia hypothesis being used in fields such as Earth system science, biogeochemistry, systems ecology, and the emerging subject of geophysiology.
Nevertheless, the Gaia hypothesis continues to attract criticism, and today some scientists consider it to be only weakly supported by, or at odds with, the available evidence. In 2006, the Geological Society of London awarded Lovelock the Wollaston Medal in part for his work on the Gaia hypothesis.