Gaia Theory
The Idea of the Earth as a Living Whole Now Has Many Adherents
Gaia theory, elaborated by scientists James Lovelock and Lynn Margulis, holds that earth's biosphere is a living whole--in some ways an organism, or super-organism.
Gaia Theory
The Idea of the Earth as a Living Whole Now Has Many Adherents
According to Gaia theory, a term coined by atmospheric scientist James Lovelock in the 1960’s and later taken up by microbiologist Lynn Margulis, the earth’s biosphere is a sort of living whole, or “super-organism.” While initially dismissed by mainstream scientists, the theory has gained considerable prestige and credibility with its further elaboration. Scientists over a wide spectrum of disciplines now accept its validity.
The Gaia Organism
One of the prime characteristics of a living being is the presence of organization, of a system of parts all tending toward individual survival through cooperative interaction. The word organism itself reflects this. The earth’s biosphere (the 20 –30 kilometer-thick layer on the surface of the planet, where life occurs) possesses such organization. It is self-regulating. It has evolved to maintain an atmospheric temperature range and an ocean salinity (salt content) that are precisely right for the life forms present in it to survive.
The devices whereby the self-regulation is accomplished are complex in their operation and involve vast living subsystems. Before the advent of Gaia theory, the conditions of earth’s atmosphere and oceans were thought of as products of random distribution—accidents in other words—out of which life had randomly emerged through a fortuitous set of physical circumstances. But it turns out that earth’s life- forms and the physical properties of earth’s surface evolved together. It is no accident that the composition of the air we breathe, its temperature range, the salinity of the oceans and their temperature range encourage and support life rather than oppose it. The biosphere is not just a useful concept. It is a living entity, whose first priority—like that of all other living entities—is to go on living.
How the Living System Works: Algae and the Atmosphere
Our neighbor planets, Venus and Mars, both show evidence of having had water on their surfaces—oceans that were eventually dissipated into space through the sun’s radiance, so that both are now dry planets. Why did earth retain its water? Because, through the metabolism of photosynthesizing algae, it was able to keep its surface cool enough to prevent overwhelming evaporation. Photosynthesizing organisms such as algae remove carbon dioxide from the atmosphere. Carbon dioxide is a greenhouse gas. Its presence causes the atmosphere to heat up. Algae in the early biosphere reduced the buildup of carbon dioxide so that the immense oceans of that time remained relatively cool.
Coolness is also essential to algal growth itself. When surface waters grow too warm, the layer of warm water prevents nutrients from rising out of the deeper layers to fertilize the algae growing at the surface level. Thus the action of algae in removing the heat-causing carbon dioxide serves to help maintain optimal water temperatures for their own growth. The algae are regulating the air for their own benefit—a process that benefits humans and other organisms as well, since too much heat would soon make life impossible for all but a few.
There is a further amazing fact about temperature regulation by algae and terrestrial plants: solar radiance has increased by 30% over the last four billion years, yet the parameters of earth’s surface temperature have remained constant over most of that time.
The Place of Bacteria in Atmospheric Regulation
Soil bacteria also affect carbon dioxide levels. Another of the ways this greenhouse gas is removed from the atmosphere is through chemical decay of rocks. Atmospheric carbon dioxide dissolved in rainwater combines with rock to form carbonates. The rate of this chemical process is greatly accelerated by bacterial activity. The warmer the air becomes as a result of increased carbon dioxide, the more active the heat-loving soil bacteria become—and the more effectively the carbon dioxide is removed, cooling the atmosphere. Thus the temperature of Gaia benefits from the regulatory effect of both types of microorganism: algae and bacteria.
Due to the persuasive evidence of these and other forms of self-regulation, Gaia theory has received wide acceptance and is no longer so controversial as it was even 20 years ago. Though earth’s biosphere may not be an organism by all definitions, its status as a living being is hardly to be questioned, especially in view of its implications for global warming and other recent phenomena of global change.
Sources:
The Web of Life: A New Scientific Understanding of Living Systems. Fritjof Capra
The Ages of Gaia: A Biography of Our Living Earth. James Lovelock
Symbiotic Planet: A New Look a Evolution. Lynn Margulis
