The Gaia Theory was the result of collaboration between the British scientist, James Lovelock, and the American biologist, Lynn Margulis. They proposed the Gaia “hypothesis” in their 1974 paper entitled Atmospheric homeostasis by and for the biosphere: the Gaia hypothesis and was published in Tellus, Volume 26.

According to the Gribbin’s account, Lovelock and Margulis first met at a conference at Princeton University in 1968. It was at this conference that Lovelock presented his idea of the “earth system.” At the time Margulis was a professor of biology at Boston University and was married to Carl Sagan. Margulis was interested in the “oddity” of the oxygen rich atmosphere and asked Sagan whom she should discuss this with. He suggested James Lovelock. Margulis, who is now Distinguished University Professor of Microbial Evolution and Organelle Heredity at the University of Massachusetts, worked with Lovelock and together they developed the Gaia hypothesis. Here is abstract of this pioneering paper:

During the time, 3.2 x 109 years, that life has been present on Earth, the physical and chemical conditions of most of the planetary surface have never varied from those most favourable for life. The geological record reads that liquid water was always present and that the pH was never far from neutral. During this same period, however,the Earth’s radiation environment underwent large changes. As the sun moved along the course set by the main sequence of stars its output will have increased at least 30% and possibly 100%. It may also have fluctuated in brightness over periods of a few million years. At the same time hydrogen was escaping to space from the Earth and so causing progressive changes in the chemical environment. This in turn through atmospheric compositional changes could have affected the Earth’s radiation balance.It may have been that these physical and chemical changes always by blind chance followed the path whose bounds are the conditions favouring the continued existence of life. This paper offers an alternative explanation that, early after life began it acquired control of the planetary environment and that this homeostasis by and for the biosphere has persisted ever since. Historic and contemporary evidence and arguments for this hypothesis will be presented. (Emphasis mine)

In this groundbreaking paper Lovelock and Margulis argue that the total “ensemble of living organisms which constitute the biosophere can act as a single entity to regulate chemical composition, surface pH and possibly also climate.” Then they state:

The notion of the biosphere as an active adaptive control system able to maintain homeostasis we are calling the ‘Gaia’ hypothesis.

Lovelock was introducing a new way to look at life on Earth and was affirming in a scientific theory that “all things are connected.” Lovelock was urged to use the name Gaia by his neighbor, the novelist William Golding. Gaia, the Greek goddess of the Earth was to become the name of his and Margulis’ theory.

The implications of Gaia and the idea of connectedness are profound. Rachel Carson had written Silent Spring in the preceding decade which showed how DDT cycled through the food chain and had the potential of causing cancer and genetic damage. Now, Lovelock, in his 1979 book, Gaia: A New Look at Life on Earth provides us with a theory which explains that

Gaia is a complex entity involving the Earth’s biosphere, atmosphere, oceans, and soil; the totality constituting a feedback or cybernetic system which seeks an optimal physical and chemical environment for life on this planet. The maintenance of condtions on Earth may be conveniently described by the term ‘homeostatsis.’

Reading:

Here are fundamental readings on the Gaia Theory by Lovelock and Margulis.

James Lovelock, Gaia: A New Look at Life on Earth. Oxford University Press, 1979

James Lovelock, The Ages of Gaia: A Biography of Our Living Earth. W.W. Norton, 1988

Lynn Margulis, Symbiotic Planet: A New Look at Evolution. Basic Books, 1999.

James Lovelock, The Revenge of Gaia: Earth’s Climate Crisis & The Fate of Humanity. Basic Books, 2006

John Gribbin & Mary Gribbin. James Lovelock: In Search of Gaia. Princeton University Press, 2009