The Gaia theory is a scientific hypothesis which originated with Dr. James Lovelock in the 1960s. Lovelock argues that the earth and its physical makeup, such as its geological and chemical properties, are tied to the world's ecosystems, and that their coexistence influences, if not governs completely, the geological, chemical, and biological circumstances, including the climate, of the earth. Many liken the Gaia theory to an understanding of the earth as a single organism. Originally referred to the Gaia hypothesis, Lovelock's idea has since been designated the Gaia theory, due to its ability to help predict some of the earth's behaviors.
Scientists know that most of the earth's processes are complex and interact with each other. Lovelock claims that all of the earth's ecosystems interact with each other, each one forming a vital component of the earth's structure and regulating the earth. This, Lovelock claims, is how the earth's many different processes, whether biological, geological, chemical, or climatic, remain stable.
Each process exists both in itself, in relation to other processes, and in relation to the earth as a whole. For example, hydrogen would disappear from the earth's atmosphere if it were not for certain biologically produced gases, such as methane. If it were not for some living organisms, the amount of carbon dioxide in the atmosphere would increase to approximately 30 times its current level, which would cause a greater greenhouse effect, increasing the temperature of the earth's atmosphere, as well as altering its chemical composition and rendering the earth much less suitable for living organisms.
Lovelock claims that the near-constant surface temperature of the earth supports the Gaia theory in another way. The sun's energy has increased by 30% since life first began, which should have also increased the earth's atmospheric temperature and changed its chemical makeup. The only major non-biological source of the carbon dioxide necessary for the greenhouse effect, a phenomenon which contributes substantially to the earth's temperature, is from volcanic activity, which is unpredictable, sporadic, and incapable of self-regulation.
The chemical makeup of the earth's atmosphere should, from the standpoint of chemistry, be unstable and in flux. Oxygen should combine with numerous other gases, while methane would be unstable and should combust in such an oxygen-rich environment. Lovelock postulates that only through regulation by living organisms can all of the earth's processes continue and remain so constant.