Gaia Hypothesis: Could Earth Really be a Single Organism?

by Ian O'Neill on April 30, 2008

The Earth as viewed from the ISS (NASA)
Can a planet like Earth be considered a single living organism? After all, the human body is composed of hundreds of billions of bacteria, and yet we consider the human body to be a single organism. The Gaia Hypothesis (or popularly known as “Gaia Theory”) goes beyond the individual organisms living on Earth, it encompasses all the living and non-living components of Earth’s biosphere and proposes that the complex interacting systems regulate the environment to a very high degree (here’s a biosphere definition). So much so, that the planet may be viewed as a single organism in its own right. What’s more this hypothesis was developed by a NASA scientist who was looking for life on Mars…

When you stop to think about it, our planet does act like a huge organism. If you look at the interrelationship between plants and atmospherics, animals and humans, rocks and water, a complex pattern of symbiotic processes seem to complement each other perfectly. Should one system be pushed out of balance by some external force (such as a massive injection of atmospheric carbon dioxide after a volcanic event), other processes are stimulated to counteract the instability (more phytoplankton appear in the oceans to absorb the carbon dioxide in the water). Many of these processes could be interpreted as a “global immune system”.

James Lovelock (

The hypothesis that our planet could be a huge organism was the brain child of British scientist Dr James Lovelock. In the 1960’s when Lovelock was working with NASA on methods to detect life on the surface of Mars, his hypothesis came about when trying to explain why Earth has such high levels of carbon dioxide and nitrogen. Lovelock recently defined Gaia as:

…organisms and their material environment evolve as a single coupled system, from which emerges the sustained self-regulation of climate and chemistry at a habitable state for whatever is the current biota.” – Lovelock J. (2003) The living Earth. Nature 426, 769-770.

So, Lovelock’s work points to interwoven ecological systems that promote the development of life currently living on Earth. Naturally, the statement that Earth itself is actually one living organism encompassing the small-scale mechanisms we experience within our biosphere is a highly controversial one, but there are some experiments and tests that have been carried out to support his theory. Probably the most famous model of the Gaia hypothesis is the development of the “Daisyworld” simulation. Daisyworld is an imaginary planet whose surface is either covered in white daisies, black daisies or nothing at all. This imaginary world orbits a sun, providing the only source of energy for the daisies to grow. Black daisies have a very low albedo (i.e. they do not reflect the sun’s light), thereby getting hot and heating up the atmosphere surrounding them. White daisies have a high albedo, reflecting all the light back out of the atmosphere. The White daisies stay cool and do not contribute to atmospheric warming.
Java applet of the Daisyworld simulation »

When this basic computer simulation runs, a rather complex picture emerges. In the aim of optimizing the growth of daisies on Daisyworld, the populations of white and black daisies fluctuate, regulating the atmospheric temperatures. When the simulation starts, there are huge changes in population and temperature, but the system quickly stabilizes. Should the solar irradiance suddenly change, the white:black daisy ratio compensates to stabilize atmospheric temperatures once more. The simulated Daisyworld plants are self-regulating atmospheric temperature, optimizing their growth.

This is an oversimplified view of might be happening on Earth, but it demonstrates the principal argument that Gaia is a collection of self-regulating systems. Gaia helps to explain why atmospheric gas quantities have remained fairly constant since life formed on Earth. Before life appeared on our planet 2.5 billion years ago, the atmosphere was dominated by carbon dioxide. Life quickly adapted to absorb this atmospheric gas, generating nitrogen (from bacteria) and oxygen (from photosynthesis). Since then, the atmospheric components have been tightly regulated to optimize conditions for the biomass. Could it also explain why the oceans aren’t too salty? Possibly.

This self-regulatory system is not a conscious process; it is simply a collection of feedback loops, all working to optimize life on Earth. The hypothesis also does not interfere with the evolution of species or does it point to a “creator”. In its moderate form, Gaia is a way of looking on the dynamic processes on our planet, providing an insight to how the seemingly disparate physical and biological processes are actually interlinked. As to whether Gaia exists as an organism in it’s own right, it depends on your definition of “organism” (the fact that Gaia cannot reproduce itself is a major drawback for viewing Earth as an organism), but it certainly makes you think…

Original source: Guardian


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Hello! My name is Ian O'Neill and I've been writing for the Universe Today since December 2007. I am a solar physics doctor, but my space interests are wide-ranging. Since becoming a science writer I have been drawn to the more extreme astrophysics concepts (like black hole dynamics), high energy physics (getting excited about the LHC!) and general space colonization efforts. I am also heavily involved with the Mars Homestead project (run by the Mars Foundation), an international organization to advance our settlement concepts on Mars. I also run my own space physics blog:, be sure to check it out!

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