Gaia Hypothesis

“The entire range of living matter on Earth from whales to viruses and from oaks to algae could be regarded as constituting a single living entity capable of maintaining the Earth’s atmosphere to suit its overall needs and endowed with faculties and powers far beyond those of its constituent parts.”

James Lovelock – Gaia: A New Look at Life on Earth, 1979

The beginnings of the Gaia hypothesis came not from a study of Earth, but from the search for alien life. In the 1960’s, NASA set up its planetary exploration program with a mission to determine whether there was life on Mars. Observing planets beyond our own forces a new perspective on our position on Earth. From space, the Earth is one self contained entity, with clear boundaries containing our oceans, atmosphere, rocks and all known life.

“…it dawned on me that life was regulating climate as well as chemistry. Suddenly the image of the Earth as a living organism able to regulate its temperature and chemistry at a comfortable steady state emerged in my mind.”

James Lovelock – Homage to Gaia: The life of an independent scientist, 2001

James Lovelock was hired by NASA to design life-detection experiments for Mars. Many suggested experiments focused on finding organisms or by-products of life on the Martian surface and requiring sending robots to Mars. Lovelock realised that a visit to Mars was not necessary to determine whether the planet hosted life. He recognised that the presence of life left fingerprints all over Earth; that the high degree of chemical disequilibrium in our atmosphere was largely due to life processes on our planet and that such a feature in the atmospheres of other planets could be used a ‘bio-signature’ – a marker for an inhabited world¹.

Without life’s influence, Earth’s atmosphere would be drastically different to what it is today; a lifeless Earth would have an atmosphere consisting of mostly CO2 and be almost entirely devoid of O². With this realisation, Lovelock determined that Mars, with its atmosphere being (in contrast to Earth’s) very close to chemical equilibrium, was almost certainly devoid of life. Lovelock, together with microbiologist Lynn Margulis, developed these realisations into the Gaia Hypothesis.

The Gaia Hypothesis2. 3. proposes that the Earth, with its biosphere, hydrosphere, lithosphere, and atmosphere, can be thought of as a single entity that self regulates within the narrow parameter limits that allow for life to survive and thrive; the whole Earth system – Gaia – can herself be thought of as somewhat like a living organism.

Evidence for Gaia extends to all parts of the Earth – Life plays a part in regulating atmospheric CO2 levels4. 5., the salt content of the oceans6. – 8., life is even thought to impact the formation of plate tectonics 9..

Gaia attracted widespread criticism from the scientific community with accusations of teleology, and of being incompatible with Darwinian selection. These criticisms were addressed with numerical models, most famously – the Daisyworld model 10. 11.. Daisyworld is a simple model ‘planet’ host to two species of life – white daisies which cool their local environment, and black daisies which warm their local environment. Daisyworld orbits a star like our own which warms as it ages. The interplay between the daisy species and their environment act to maintain a stable temperature on the Daisyworld planet in the face of a warming sun.

Numerous books have been written by Lovelock on Gaia12. – 17. exploring and expanding the hypothesis, and today it is well accepted by the scientific community that the Earth system does indeed self-regulate. The Gaia hypothesis offers answers to the questions on why Earth has remained habitable, and inhabited despite the increasing luminosity of the Sun and changing tectonic activity over geological timescales. It informs our understanding on our impacts on our planet with man made climate change, and understanding Gaia will be critical for understanding and mitigating the climate changes yet to come.

More information on the work and achievements of James Lovelock, including key papers, can be found on his personal website at:

‘There’s a danger of losing our tenure on this planet’

BBC interview with James


1. Lovelock, James E (1965). “A physical basis for life detection experiments”. In: Nature 207.997, pp. 568–570

2. Lovelock, James E. and Lynn Margulis (1974). “Atmospheric homeostasis by and for the biosphere: the Gaia hypothesis”. In: Tellus 26, pp. 2–10

3. Margulis, Lynn and J. E. Lovelock (1974). “Biological modulation of the Earth’s atmosphere”. In: Icarus 21.4, pp. 471–489

4. Schwartzman, David W and Tyler Volk (1989). “Biotic enhancement of weathering and the habitability of Earth”. In: Nature 340: 6233, pp. 457–460

5. Schwartzman, David W and Tyler Volk (1991). “Biotic enhancement of weathering and surface temperatures on Earth since the origin of life”. In: Palaeogeography, Palaeoclimatology, Palaeoecology 90.4, pp. 357–371

6. Kennett, James P (1982). Marine Geology. Prentice-Hall, Englewood Cliffs, NJ

7. Holland, Heinrich D. (1984). The chemical evolution of the atmosphere and oceans. Princeton University Press

8. Baerlocher, F. (1990). “The Gaia hypothesis: A fruitful fallacy?” In: Experientia 46.3, pp. 232–238

9. Höning, Dennis et al. (2014). “Biotic vs. abiotic Earth: A model for man- tle hydration and continental coverage”. In: Planetary and Space Science 98, pp. 5–13.


10. Watson, Andrew J. and James E. Lovelock (1983). “Biological homeostasis of the global environment: the parable of Daisyworld”. In: Tellus 35B, pp. 284–289

11. Wood, Andrew J. et al. (2008). “Daisyworld: A review”. In: Review of Geo- physics 46.1

12. Lovelock, James E. (1979). Gaia, a new look at earth. Oxford: Oxford University Press

13. Lovelock, James (1988). The ages of Gaia. Oxford University Press

14. Lovelock, James E. (1991). Gaia The practical science of planetary medicine. Oxford University Press

15. Lovelock, James E. (2007). The revenge of gaia: earth’s climate crisis & the fate of humanity. Penguin.

16. Lovelock, James E. (2009). A Final Warning: The Vanishing Face of Gaia. Penguin London

17. Lovelock, James E. (2015). A rough ride to the future. The Overlook Press