The Gaia Hypothesis
We are natural creatures which have evolved inside a great life system. Whatever we do that is not good for life, the rest of the system will try to undo or balance in any way it can.
- Elisabet Sahtouris
One of the major proponents of the theory that the planet behaves like a living system is British chemist and inventor Dr. James Lovelock. His ideas, which have fundamentally altered many people's perception of the planet, were another fortuitous spin-off from the space race.
In the early 1960s Lovelock served as a consultant to a team at the California Institute of Technology working on plans for the investigation of life on Mars. One problem they faced in looking for Martian life-forms was not knowing exactly what they were looking for. Other life-forms might be based on completely different chemistries—on silicon rather than carbon, for instance—and might not reveal themselves to tests based on Earthly life.
Lovelock theorized that however strange the chemistry and life-form might be, there would be one very general characteristic: any life-form would take in, process, and cast out matter and energy, and this would have detectable effects upon its physical surroundings. On a planet devoid of life, the chemical constituents of its atmosphere, oceans, and soil, through their interactions over millions of years, would settle into equilibrium; the proportions of the various constituents could be predicted roughly by the laws of physical chemistry. If, however, life were present, then whatever chemical processes it was based on almost certainly would leave the environment in a state recognizably different from that predicted by physical chemistry alone.
As a very simple example of this principle, consider a jar containing a mixture of sugar and water. Physical chemistry predicts that the sugar will dissolve until a given concentration is reached. If life in the form of yeast cells were added and left to grow, however, the resulting mix would be very different: there would be a lower concentration of sugar than predicted and much higher levels of alcohol and other organic products. We would determine, then, whether there was (or had been) life in the jar by measuring the sugar and alcohol concentrations.
The beauty of Lovelock's approach to life detection is that one need not visit another planet to know whether or not life is there. The basic chemistry of the atmosphere can be deduced from Earth-bound examination of the infrared, light, and radio waves coming from the planet. In the 1960s enough was known about the Martian atmosphere to suggest that it was very close to the state of chemical equilibrium; it showed no signs of the exotic chemistry characteristic of the presence of life. So, Lovelock concluded, it was extremely unlikely that there was life on Mars.
Applying a similar approach to the atmosphere, oceans, and soil of our own planet, Lovelock found that the chemical constituents were far removed from equilibrium. To the casual observer it might seem that he had merely shown that there was, after all, life on Earth. But Lovelock began to see far greater significance in these disequilibria.
First, the concentration of gases in the Earth's atmosphere differs by factors of millions from the levels predicted by physical chemistry. The predicted level of oxygen in the air, for example, would be virtually zero, yet the actual concentration is about 21 percent. This is puzzling because oxygen is a highly reactive gas, combining readily with many other chemical elements; it should therefore be rapidly absorbed. Second, and even more puzzling, the actual composition of the atmosphere has for aeons remained at a level that is optimal for the continuance of life.
After pondering many such unlikely characteristics, Lovelock came to "the only feasible explanation": the atmosphere is being manipulated on a day-to-day basis by the many living processes on Earth. The entire range of living matter on Earth, from viruses to whales, from algae to oaks, plus the air, the oceans, and the land surface all appear to be a part of a giant system able to regulate the temperature and composition of the air, sea, and soil so as to ensure the survival of life. This concept Lovelock termed the "Gaia Hypothesis" in honor of the Ancient Greek "Earth Mother," Gaia (or Ge). In this context Gaia signifies the entire biosphere—everything living on the planet—plus the atmosphere, the oceans, and the soil.
In maintaining the optimal conditions for life, Gaia manifests a characteristic that all living systems have in common: homeostasis. Derived from the Greek for "to keep the same", the term was coined by Claude Bernard, a nineteenth-century French physiologist, who stated that "all the vital mechanisms, varied as they are, have only one object: that of preserving constant the conditions of life."
An example of homeostasis is the human body's maintenance of a temperature of about 98.6 degrees Fahrenheit, the ideal temperature for the majority of the body's processes. Although the external temperature may vary by scores of degrees, our internal temperature seldom varies by more than a degree or two, the body cooling itself through sweating and warming itself through physical activity and shivering. The regulation of the number of white blood cells, the control of acidity, salt content, and the delicate chemical balance of the blood are homeostatic processes as well. These and many others maintain the best internal environment for the continuance of your body's life processes. Such processes are found not only in the human body and in all living systems but also within Gaia herself.
Gaia appears to maintain planetary homeostasis in a variety of ways, monitoring and modifying many key components in the atmosphere, oceans, and soil. The data that Lovelock amassed in support of this contention is fascinating, and the interested reader should take a look at Lovelock's book Gaia: A New Look at Life on Earth, and his sequel The Ages of Gaia. In summary, some of the indications of Gaia's homeostatic mechanisms are:
The steadiness of the Earth's surface temperature: Although life is found to exist between the extremes of 20 and 220 degrees Fahrenheit, the optimal range is between 60 and 100 degrees Fahrenheit. The average temperature of most of the Earth's surface appears to have stayed within this range for hundreds of millions of years despite major changes in atmospheric composition and an increase in the heat received from the sun. If at any time in the Earth's history the overall temperature had gone beyond these limits, life, as we know it, would have been extinguished.
The regulation of the amount of salt in the oceans: At present the oceans contain about 3.4 percent salt, and geological evidence shows that this figure has remained relatively constant, despite the fact that salt is being washed in continually by the rivers. If the salt concentration had ever risen as high as 4 percent, life in the sea would have evolved very differently. If it had exceeded 6 percent, even for a few minutes, life in the oceans immediately would have come to an end, for at this level of salinity cell walls disintegrate. The oceans would have become like the Dead Sea.
The stabilization of the oxygen concentration of the atmosphere at 21 percent: This is the optimal balance for the maintenance of life. With a few percent less oxygen, the larger animals and flying insects could not have found enough energy to survive; with a few percent more, even damp vegetation would burn. (A forest fire started by lightning would burn fiercely and indefinitely, eventually burning all vegetation on the Earth's land surface.)
The presence of a small quantity of ammonia in the atmosphere: This is the amount needed to neutralize the strong sulfuric and nitric acids produced by the natural combination of sulphur and nitrogen compounds with oxygen (thunderstorms, for instance, produce tons of nitric acid). The result is that rain and soil remain at the optimal levels of acidity for the preservation of life.
The existence of the ozone layer in the upper atmosphere: This shields life on the surface from ultraviolet radiation, which damages the molecules essential for life, particularly the DNA molecules found in every living cell. Without it life on land is impossible.
On the basis of these and other "homeostatic" behaviors, Lovelock concludes that the climate and chemical properties of the Earth seem always to have been optimal for life as we know it.
Critics of the Gaia Hypothesis might argue that the origin and maintenance of life on this planet have resulted from a series of very lucky coincidences, rather than planetary homeostatic behavior. If, for example, the proportion of ammonia in the early atmosphere had been a little higher or lower, the Earth would have ended up too hot or too cold for life. They might argue that it has been a series of flukes that kept the planet's surface temperature roughly constant while the sun's output changed; a series of flukes that kept the levels of carbon dioxide, oxygen, salt and many other chemicals at optimal levels for the maintenance of life; and a fluke that there is an ozone layer to protect us from lethal quantities of ultraviolet light.
In the same way, a cell in the human body, observing the body's continued survival through heat, cold, and many other changes, might, if it were so inclined, put it all down to a series of lucky coincidences; the body just happens to sweat when it is hot, just happens to shiver when it is cold, just happens to take in the right amount of nutrients when they are needed. Perhaps by a fluke, blood sugar, acidity, and salinity stay at the optimal levels and red blood cells happen to bring along oxygen and take away wastes. From such a point of view, the body survives from one moment to the next as a result of an extremely fortunate series of coincidences.
This quite definitely is not the case. The body behaves in a well-ordered manner with a definite sense of purpose. It sweats, shivers, eats, breathes, and regulates its internal functions and chemical constituents in order to preserve homeostasis, and so survive.
Just as this self-regulating principle makes more sense of the body's activities, so it makes more sense of the planet's. Gaia appears to be a self-regulating system, continually adjusting its chemical, physical, and biological processes in order to support life in its continuing evolution.
Does the Gaia Hypothesis imply that the biosphere is a single living organism? Lovelock is cautious on this point. He sees the atmosphere to be similar to a beehive, a biological construction designed to maintain a chosen environment, though not actually living in itself. But if we take the atmosphere, oceans, and soil to be intrinsic parts of a complete biosystem, couldn't we then speculate that the system as a whole is alive? And if so, is humanity an intricate, inseparable part of a larger living system? Before we can answer these questions, we need to look more closely at the general characteristics common to all living systems and see to what extent Gaia satisfies them.