by M. Alan Kazlev


The 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 Earthís 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 Earthís 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 that living organisms and inorganic material are part of a dynamic system that shape Earthís biosphere, in Lynn Margulisís 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.

The Origin of the Gaia Hypothesis
It is an ironic fact that a theory about life on Earth should begin from an exploration of outer space.

In the mid-1960ís, 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 planetís 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 1960ís, Lovelock had definitively organized his theory. The novelist William Golding, Lovelockís 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 human

The nature of Gaia

"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

The Ages of Gaia, p.19

Examples of Gaian Processes

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.

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 sunís 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 Earthís temperature is maintained by varying the amount of carbon dioxide (a notorious greenhouse gas) in the atmosphere. The drop in the atmosphereís 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