"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...[Gaia can be defined] as a complex entity involving the Earth's biosphere, atmosphere, oceans, and soil; the totality constituting a feedback of cybernetic systems which seeks an optimal physical and chemical environment for life on this planet."
Dr James Lovelock -Gaia - A New Look at Life on Earth
The Gaia Hypothesis is the theory is that living organisms and inorganic material are part of a dynamic system that shape Earth's biosphere, in 
Lynn Margulis's words, a "super organismic system" The earth is a self-regulating environment; a single, unified, cooperating and living system - a superorganism that regulates physical conditions to keep the environment hospitable for life Evolution therefore is the result of cooperative not competitive processes.
It is an ironic fact that a theory about life on Earth should begin from an exploration of outer space.
In the mid-1960's, Dr James Lovelock was approached by NASA, who asked him for help in searching for life on Mars. In 1965, Lovelock proposed some physical tests for determining whether Mars held life or not. He proposed that a top-down view of the entire planet be employed. The test would analyze the composition of the planet's atmosphere. If it held no life, the planet should have an atmosphere close to the chemical equilibrium state, as determined by chemistry and physics. If the planet held life, the metabolic activities of life-forms would result in an atmosphere far from the equilibrium state.
Together with scientist Dian Hitchcock, Lovelock examined the atmospheric data for the Martian atmosphere and found it to be in a state of stable chemical equilibrium, while the Earth was shown to be in a state of extreme chemical disequilibrium. The two scientists concluded that Mars was probably lifeless; almost a decade later the Viking 1 and 2 landings conformed their conclusion.
In that same year, Lovelock began to think that such an unlikely combination of gases such as the Earth had, indicated a homeostatic of the Earth biosphere to maintain environmental conditions conducive for
life, in a sort of cybernetic feedback loop, an active (but non-teleological) control system. By the end of the 1960's, Lovelock had definitively organized his theory. The novelist William Golding, Lovelock's neighbor,
suggested he call the control system Gaia, after the ancient Greek Earth Goddess. First on his own in 1972, and then later in 1973 with American microbiologist Lynn Margulis, Lovelock
formally proposed the idea of Gaia as a control system. The name for the complex system of climate control has remained "Gaia" since then, and in 1979 his book, Gaia - a new look at life on Earth first presented the Gaia hypothesis to the wider public. Gaia has has become a very potentmeme in the humannoosphere
"The name of the living planet, Gaia, is not a synonym for the biosphere. The biosphere is defined as that part of the Earth where living things normally exist. Still less is Gaia the same as the biota, which is simply the collection of all individual living organisms. The biota and the biosphere taken together form part but not all of Gaia. Just as the shell is part of a snail, so the rocks, the air, and the oceans are part of Gaia. Gaia...has continuity with the past back to the origins of life, and extends into the future as long as life persists. Gaia, as a total planetary being, has properties that are not necessarily discernible by just knowing individual species or populations of organisms living together.
The Gaia hypothesis...suppose(s) that the atmosphere, the oceans, the climate, and the crust of the Earth are regulated at a state comfortable for life because of the behavior of living organisms. Specifically, the Gaia hypothesis said that the temperature, oxidation state, acidity and certain aspects of the rocks and waters are at any time kept constant, and that this homeostasis is maintained by active feedback processes operated automatically and unconsciously the biota. Solar energy sustains comfortable conditions for life. The conditions are only constant in the short term and evolve in synchrony with the changing needs of the biota as it evolves. Life and its environment are so closely coupled that evolution concerns Gala, not the organisms or the environment taken separately."
James Lovelock -
Oxygen
Dr Lovelock suggests that Gaia is at work to keep the oxygen content
of the atmosphere high and within the range that all oxygen-breathing animals
require. The atmospheres of our two nearest neighbors, Venus and Mars,
contain 0.00 percent and 0.13 percent respectively, of free oxygen.
Temperature
The Gaia hypothesis sees life regulating the surface temperature
of Earth. The average surface temperature of Earth has remained within
a narrow range - between 10 and 20 C - for over three billion years.
During that time the sun's output has increased by thirty or forty percent.
Even ignoring the long-term trend of the sun, the temperature would vary
far more, as it does for example every day on the surface of Mars
Carbon Dioxide
This stability of Earth's temperature is maintained by varying the
amount of carbon dioxide (a notorious greenhouse gas) in the atmosphere.
The drop in the atmosphere's ability to absorb solar radiation is due to
a global decline in carbon dioxide levels over that time. The biosphere
would have attempted to fix carbon dioxide in the form of the calcium carbonate
of marine shells. - The Carbon Cycle
Dimethyl Sulfide Production
Another form of temperature control is Dimethyl Sulfide Production.
Phytoplankton may have part of the control in that they produce dimethyl
sulfide. They release this dimethyl sulfide into the air, which is then
converted into drops sulfuric acid, which in turn become nuclei for cloud
condensation. These nuclei help to produce thicker clouds, blocking more
of the sun, and cooling the oceans.
Oceanic Salinity
Natural geological weathering releases salts into the oceans too
fast for life to adapt at the same rate. At the same time, geological
evidence indicates that the oceans have remained at a constant salinity
of 10% saturation for millions of years. Salt flats, which are hosts to
dense patches of bacteria, may be removing the salt from the oceans. The
bacteria, surviving in water too salty for any other life, trap salts and
other minerals to form a sheath within which the bacterial colonies live
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Books and Web Links |  |
The
Gaia Hypothesis - proposed by Dr. James Lovelock in collaboration with Dr. Lynn Margulis - an on-going project, by PRF Brown -Mountain Man Graphics - an excellent intro to the subject
, Gaia - some thoughts and musings on Gaia
MkzdK Earth Alive! - very good review of the Gaia hypothesis from the holistic perspective
Welcome
to our planet - a poetic site that covers a number of topics, includes the essay WHAT IS GAIA? by James Lovelock
GAIA-L mail list
The Living Earth - excerpt from The Global Brain Awakens by Peter Russel
Gaia : A New Look at Life on Earth by James Lovelock
The Ages of Gaia: A Biography of Our Living Earth by James Lovelock
Gaia's Body : Toward a Physiology of Earth by Tyler Volk
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