Letter from James Lovelock to Lynn Margulis dated 11 December 1972, forming part of the Margulis-Lovelock correspondence, in which James Lovelock discusses why he thinks the Gaia hypothesis is on its way to becoming a theory. The letter is typed on verso and has punched holes.

The Gaia hypothesis, devised by James Lovelock, describes the Earth as a self regulating system that maintains conditions suitable for life. This letter was written seven years before Lovelock published his first book on Gaia, yet reveals his growing confidence in his hypothesis: ‘The logic of the atmospheric life detection experiment ... can only mean kthat [sic] Gaia exists.’ He worked on Gaia from 1965, and six years later collaborated with Lynn Margulis, a respected American microbiologist, to develop it further. She contributed important ideas about how microbes affect the atmosphere and surface of the planet.