a) Hypothesis developed by James Lovelock and Lynn Margulis stating that life on a planet will maintain suitable conditions for life; that “the biotic community plays the major role in biospheric homeostasis” – Odum, 1993.
b) Extension of the above hypothesis stating that the Earth is a living creature, a “super organism”.
Dr. James E. Lovelock was a British specialist in atmospheric gases employed by NASA in the early 1960s. His life’s work on the Gaia hypothesis stems from this time. The Mars Viking probes required life detection instruments, to determine whether any life existed on the planet. Lovelock was required to develop atmospheric tests for the presence of life.
Lovelock considered Earth’s atmosphere – asking what it was about our planet that, studied from space, would tell us that life existed here. He concluded that the nature of Earth’s atmosphere (especially the high levels of oxygen – a gas which chemistry suggests would normally not exist in such high concentration) was sufficient proof of life. The fact that our near neighbours Mars and Venus have such high levels of carbon dioxide in a low energy equilibrium was, for James Lovelock, sufficient proof that the planets were lifeless.
These findings were communicated to NASA, though the Viking probes were still considered necessary to investigate the Martian landscape. James Lovelock, however, moved his focus to investigating the postulation he had made about life on Earth.
In this he was assisted by prominent microbiologist Dr. Lynn Margulis (at the time the wife of Lovelock’s office mate – Carl Sagan).
The hypothesis was named by author William Golding – a near neighbour of Lovelock’s. The name of the ancient Greek goddess of the Earth seemed fitting for the theory, but makes a rather inflammatory statement about the Earth itself.
The nature of the Earth’s atmosphere and temperature indicates that some form of regulation is occurring. The following observations illustrate this fact:
Methane and Hydrogen concentrations: If not continuously replaced through biotic activity, Methane and Hydrogen gas would be unknown in our atmosphere.
Carbon dioxide levels: also far higher than chemistry alone would allow.
Temperature: though the sun has steadily increased in strength (by around 30% in the last 3.5 billion years), the average temperature has only fluctuated by approximately 5% from the current average of 15 degrees Celsius. Studies suggest that a 30% reduction in solar strength would result in a drastic drop in average temperature.
Oceanic salinity levels: geological weathering releases salts into the oceans, however, salinity levels have remained the same for millions of years. Bacteria in salt flats may be removing the salt from the oceans..
Life on Earth:
The Earth’s primary atmosphere was most likely formed through the process of outgassing: gases rising from the hot core of the Earth. Considering the warm climate in Earth’s early years, despite the weaker sun, a higher level of carbon dioxide at that time seems likely.
With the first anaerobic life on earth, the atmosphere began to change. These microbes released oxygen into the air as a byproduct of their respiration. As oxygen built up in the atmosphere, the aerobes evolved, and much carbon dioxide was trapped in the oceans by limestone forming marine organisms.
This reduction in carbon dioxide – a greenhouse gas – gives a reason for Earth’s relatively stable temperature when compared with the changing strength of the Sun.
Lovelock published his first book in 1979, though he and Margulis had previously written papers on the Gaia hypothesis.
“...the physical and chemical condition of the surface of the Earth, of the atmosphere, and of the oceans has been and is actively made fit and comfortable by the presence of life itself. This is in contrast to the conventional wisdom which held that life adapted to the planetary conditions as it and they evolved their separate ways.''
-James Lovelock: “Gaia: A New Look at Life on Earth” (1979)
“…the Gaia hypothesis says that the temperature, oxidation, state, acidity, and certain aspects of the rocks and waters are kept constant, and that this homeostasis is maintained by active feedback processes operated automatically and unconsciously by the biota."
-James Lovelock: “The Ages of Gaia” (1988)
Lovelock and Margulis’ hypothesis attracted no little criticism. Lovelock appeared to suggest that the Earth was in itself a living entity, and the hypothesis was seen as hinting at some form of altruism in nature, as well as consciousness, as the environment was altered for the good of all.
Lovelock developed Daisyworld as a counter argument to the latter comments. The gaia hypothesis does not require altruism or forethought, but relies of the activity, completely unconscious as it is, of all life in order to alter the environment.
Daisyworld is a hypothetical Earth-like planet, where only black and white daisies grow. By their nature, black daisies absorb most of the Sun’s heat, whereas white daisies reflect it back into space.
In the early years of the planet, when the atmosphere was very cool and the sunlight not strong, small colonies of black daisies would flourish at the equator. The colonies would, by absorbing heat, form warmer spots where the plants could flourish.
As the black daisies started to keep the earth’s atmosphere at a suitable temperature, white daisies would start to take advantage of the favourable temperature.
Slowly, the sun’s heat would increase to the point where the black daisies at the equator would absorb such quantities of heat as to preclude their survival. The black populations would retreat to the poles.
As the sun continued to heat up, the white daisy populations would flourish, reflecting the sun’s heat out of the atmosphere, and helping to maintain a temperature suitable for daisy life.
The daisies do not act for the good of all, they are not altruistic or conscious, they simply exist, and by existing, alter their environment.
Other examples of the hypothesis:
Attractive though the daisyworld model is, it seems simpler to take examples of this kind of homeostasis from real life.
Consider the current concerns as to global warming and the build up of carbon dioxide in our atmosphere. A result of this may well be the increased well being of plant populations, resulting in more plant respiration, thus having more oxygen fed back into the atmosphere.
The outbreaks of cyanobacteria (commonly known as blue-green algae) in extremely hot and nutrient rich waters may have a similar effect. The toxic substance will, through photosynthesis, produce more oxygen while trapping carbon dioxide.
One of the seven characteristics of life is the ability of the organism to alter its environment. Earth exists in a balanced homeostasis – some species producing oxygen, some producing carbon dioxide. Plants fix nitrogen as ammonia in the soil, counteracting the acidity that would otherwise build up. Trees flourish in areas where there is ample rainfall, only to have us find, when we fell the area for wheat, that the rainfall was in part caused by the transpiration of those trees.
All kinds of feedback can be seen as supporting the Gaia hypothesis. Perhaps my favourite is the notion that in overpopulated areas, disease is far more likely to break out – reducing population strain.
The Gaia Groupies:
Ever since its conception, the Gaia hypothesis has been taken up by environmental and religious groups for its portrayal of the Earth as a living being.
How literally Lovelock intended for his analogy of a living earth to be taken is hard to tell. He seems to present it quite literally, referring to “the Living Earth”. Margulis, on the other hand, has always seemed to rather distance herself from the more mystic side of the hypothesis, confining her studies to the nature of the Earth’s homeostasis.
Religious groups are known to call on the “spirit of Gaia” for guidance and healing. The hypothesis has been taken to extremes – making it easy for its detractors to criticize.
Lovelock and Margulis’ hypothesis has become widely accepted in the scientific community, overcoming the disadvantages of its original “wacko” stigma. The science behind the hypothesis seems accurate, and the question that remains is how far the analogy of a living Earth should be stretched.
“Ecology and our Endangered Life Support Systems” – Eugene P. Odum, 1993.