Gaia theory is a class of scientific models of the geo-biosphere in which life as a whole fosters and maintains suitable conditions for itself by helping to create an environment on Earth suitable for its continuity. The first such theory was created by the atmospheric scientist and chemist, Sir James Lovelock, who developed his hypotheses in the 1960s before formally publishing the concept, first in the New Scientist (February 13, 1975) and then in the 1979 book "Quest for Gaia". He hypothesized that the living matter of the planet functioned like a single organism and named this self-regulating living system after the Greek goddess, Gaia, using a suggestion of novelist William Golding.
Gaia "theories" have non-technical predecessors in the ideas of several cultures. Today, "Gaia theory" is sometimes used among non-scientists to refer to hypotheses of a self-regulating Earth that are non-technical but take inspiration from scientific models. Among some scientists, "Gaia" carries connotations of lack of scientific rigor, quasi-mystical thinking about the planet arth, and therefore Lovelock's hypothesis was received initially with much antagonism by much of the scientific community. No controversy exists, however, that life and the physical environment significantly influence one another.
Gaia theory today is a spectrum of hypotheses, ranging from the undeniable (Weak Gaia) to the radical (Strong Gaia).
At one end of this spectrum is the undeniable statement that the organisms on the Earth have radically altered its composition. A stronger position is that the Earth's biosphere effectively acts as if it is a self-organizing system, which works in such a way as to keep its systems in some kind of meta-equilibrium that is broadly conducive to life. The history of evolution, ecology and climate show that the exact characteristics of this equilibrium intermittently have undergone rapid changes, which are believed to have caused extinctions and felled civilisations.
Biologists and earth scientists usually view the factors that stabilize the characteristics of a period as an undirected emergent property or entelechy of the system; as each individual species pursues its own self-interest, for example, their combined actions tend to have counterbalancing effects on environmental change. Opponents of this view sometimes point to examples of life's actions that have resulted in dramatic change rather than stable equilibrium, such as the conversion of the Earth's atmosphere from a reducing environment to an oxygen-rich one. However, proponents will point out that those atmospheric composition changes created an environment even more suitable to life.
Some go a step further and hypothesize that all lifeforms are part of a single living planetary being called Gaia. In this view, the atmosphere, the seas and the terrestrial crust would be results of interventions carried out by Gaia through the coevolving diversity of living organisms. While it is arguable that the Earth as a unit does not match the generally accepted biological criteria for life itself (Gaia has not yet reproduced, for instance), many scientists would be comfortable characterising the earth as a single "system".
The most extreme form of Gaia theory is that the entire Earth is a single unified organism; in this view the Earth's biosphere is consciously manipulating the climate in order to make conditions more conducive to life. Scientists contend that there is no evidence at all to support this last point of view, and it has come about because many people do not understand the concept of homeostasis. Many non-scientists instinctively see homeostasis as an activity that requires conscious control, although this is not so.
Much more speculative versions of Gaia theory, including all versions in which it is held that the Earth is actually conscious or part of some universe-wide evolution, are currently held to be outside the bounds of science.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Gaia".