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Gaia Hypothesis - Evidence in support of a Gaian Earth

oxygen organisms ecosystems life

Gaia, Earth, was believed by the ancient Greeks to be a living, fertile ancestor of many of their important gods. The Romans, who adopted many Greek gods and ideas as their own, also believed in this organismic entity, who they renamed Terra. The Gaian notion has been personified in more recent interpretations as "Mother Earth." The Gaia hypothesis is a recent and highly controversial theory that views Earth as an integrated, pseudo-organismic entity and not as a mere physical object in space. The Gaia hypothesis suggests that organisms and ecosystems on Earth cause substantial changes to occur in the physical and chemical nature of the environment, in a manner that improves the living conditions on the planet. In other words, it is suggested that Earth is an organismic planet, with homeostatic mechanisms that help to maintain its own environments within the ranges of extremes that can be tolerated by life.

Earth is the only planet in the universe that is known to support life. This is one of the reasons why the Gaia hypothesis cannot be tested by rigorous, scientific experimentation-there is only one known replicate in the great, universal experiment. However, some supporting evidence for the Gaia hypothesis can be marshaled from certain observations of the structure and functioning of the planetary ecosystem. Several of these lines of reasoning are described in the next section.


One supporting line of reasoning for the Gaia hypothesis concerns the presence of oxygen in Earth's atmosphere. It is believed by scientists that the primordial atmosphere of Earth did not contain oxygen. The appearance of this gas required the evolution of photosynthetic life forms, which were initially blue-green bacteria and, somewhat later, single-celled algae. Molecular oxygen is a waste product of photosynthesis, and its present atmospheric concentration of about 21% has entirely originated with this biochemical process (which is also the basis of all biologically fixed energy in ecosystems). Of course, the availability of atmospheric oxygen is a critically important environmental factor for most of Earth's species and for many ecological processes.

In addition, it appears that the concentration of oxygen in the atmosphere has been relatively stable for an extremely long period of time, perhaps several billions of years. This suggests the existence of a long-term equilibrium between the production of this gas by green plants, and its consumption by biological and non-living processes. If the atmospheric concentration of oxygen were much larger than it actually is, say about 25% instead of the actual 21%, then biomass would be much more readily combustible. These conditions could lead to much more frequent and more extensive forest fires. Such conflagrations would be severely damaging to Earth's ecosystems and species.

Some proponents of the Gaia hypothesis interpret the above information to suggest that there is a planetary, homeostatic control of the concentration of molecular oxygen in the atmosphere. This control is intended to strike a balance between the concentrations of oxygen required to sustain the metabolism of organisms, and the larger concentrations that could result in extremely destructive, uncontrolled wildfires.

Another line of evidence in support of the Gaian theory concerns carbon dioxide in Earth's atmosphere. To a substantial degree, the concentration of this gas is regulated by a complex of biological and physical processes by which carbon dioxide is emitted and absorbed. This gas is well known to be important in the planet's greenhouse effect, which is critical to maintaining the average temperature of the surface within a range that organisms can tolerate. It has been estimated that in the absence of this greenhouse effect, Earth's average surface temperature would be about -176°F (-116°C), much too cold for organisms and ecosystems to tolerate over the longer term. Instead, the existing greenhouse effect, caused in large part by atmospheric carbon dioxide, helps to maintain an average surface temperature of about 59°F (15°C). This is within the range of temperature that life can tolerate.

Again, advocates of the Gaia hypothesis interpret these observations to suggest that there is a homeostatic system for control of atmospheric carbon dioxide, and of climate. This system helps to maintain conditions within a range that is satisfactory for life.

Scientists agree that there is clear evidence that the non-living environment has an important influence on organisms, and that organisms can cause substantial changes in their environment. However, there appears to be little widespread support within the scientific community for the notion that Earth's organisms and ecosystems have somehow integrated in a mutually benevolent symbiosis (or mutualism), aimed at maintaining environmental conditions within a comfortable range.

Still, the Gaia hypothesis is a useful concept, because it emphasizes the diverse connections of ecosystems, and the consequences of human activities that result in environmental and ecological changes. Today, and into the foreseeable future, humans are rapidly becoming a dominant force that is causing large, often degradative changes to Earth's environments and ecosystems.

Resources

Books

Lovelock, J. The Ages of Gaia: A Bibliography of Our Living Earth. New York: Norton & Co., 1988.

Margulis, L., and L. Olendzenski. Environmental Evolution. Effects of the Origin and Evolution of Life on Planet Earth. Cambridge, MA: MIT Press, 1992.

Smith, L. E. Gaia. The Growth of an Idea. New York: St. Martin's Press, 1991.

Periodicals

Huggett, R.J. "Ecosphere, Biosphere, Or Gaia? What To Call The Global Ecosystem." Global Ecology And Biogeography 8, no. 6 (1999): 425-432.

Bill Freedman

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about 7 years ago

Why on Earth must you bring God into this, Ty and Jeff? Gaia is about the way the Earth maintains itself and the way life interacts with its environment so that it can benefit over long periods of time. It has nothing to do with belief or religion: it is just Earth Science.

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over 4 years ago

It is true that geological studies show changes of the environment that contradicts the strong Gaia hypothesis of ecosystems working towards an optimum state. It is also true that there is evidence that ecosystems have collapsed from within. However, the frequency of such ecosystem collapses through geological history is many orders of magnitude lower than the extremely high frequency predicted by the Malthusian model of maximum reproduction. So evolution must be driven by something other than maximization of reproduction. The selfish gene model (the theoretical mechanism basis of the Medea hypothesis of life destroying itself) appears to be supported by simple computer simulations, but so does strong Gaia hypothesis. The strong Gaia hypothesis failed scale-up to more complex systems, and the missing frequency of Medean ecosystem collapses can be explained if the selfish gene model also fails scale-up to the greater complexity of real life because real life is too complex to be livable to such rigid, unselfcritical entities as the selfish gene model claims that living organisms are. In other words, the selfish gene model is based on the same methodological error as is the strong Gaia hypothesis. This is explained in greater detail on the pages "Moderating the Gaia/Medea debate" and "Self-organization" on Pure science Wiki, a wiki devoted to the scientific method unaffected by academic prestige obsession. I recommend Pure science Wiki!

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about 6 years ago

"One supporting line of reasoning for the Gaia hypothesis concerns the presence of oxygen in Earth's atmosphere".



The WHOLE section about Oxygen is NOT supporting the Gaia Theory!



It is just a fact that the atmosphere changed, saying that this fact is supporting the theory doesn't make any support.



Next, the oxygen level is 21% but has been turned to 21% by organisms, so life is able to live without this "optimal level of O2". maybe if it had evolved in an other way, we would have 23% instead.



And "Destructive Fires" are destructive in human mind only, on a evolutionary scale they are part of the nature, not to be judged "bad".

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over 7 years ago

Not to be argumentative, but the article doesn't really say anything debunking the Judeo-Christian God. It appears to me that the Bible and the Gaia theory can live together in harmony, rather than being mutually exclusive. If I were you, I think I would prefer to think that God designed the world to be self-reliant, ie "teach a man to fish," but "teach the earth to homeostasis".



I am certainly not claiming expertise on either subject, but I don't think you have left either open enough to interpretation.

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almost 5 years ago

From what I have learned, you actually have it backwards. It is not that Earth is perfectly suited to life, but life, over time, has become perfectly suited to it. Climate has fluxuated over geologic periods and eras, though in different areas of the globe, and the global average also tends to fluxuate, so the Earths climatary equilibrium is not truly present. Therefore, creatures that inhabit the earth have to constantly adapt to the new climates that form over millions of years. Also, as for the stability of the carbon cycle, oxygen-using organisms and oxygen-creating organisms have have been keeping the carbon cycle moving for billions of years, so it only makes sense that eventually things would balance outover these long periods of time.

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almost 8 years ago

I think this whole this whole hypothesis or theory is bunk. Plants replentish our air, this is known today so why does something have to be different & then "it" stabalizes enough to support human or life in general. The old Romans & Greeks believed the earth was held up by a turtle or elephant but the Bible says the Earth "hangs in the air", & we have pictures to prove that today. Your article does provde an interesting counter for the anthropic principal but all these things have to be in place in order to support life & does not have the ability to know precisly when to stop "evolving" because there is no intelegent being that can set those perfect perameters,say like the God of the Bible. You People go to such great lengths to support your own belief systems. Try believing in God. His word is true, its been proven & we will all be accountable to it. Thank You.

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over 4 years ago

The link to Pure science Wiki is http://purescience.wikia.com

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almost 5 years ago

From what I have learned, you actually have it backwards. It is not that Earth is perfectly suited to life, but life, over time, has become perfectly suited to it. Climate has fluxuated over geologic periods and eras, though in different areas of the globe, and the global average also tends to fluxuate, so the Earths climatary equilibrium is not truly present. Therefore, creatures that inhabit the earth have to constantly adapt to the new climates that form over millions of years. Also, as for the stability of the carbon cycle, oxygen-using organisms and oxygen-creating organisms have have been keeping the carbon cycle moving for billions of years, so it only makes sense that eventually things would balance outover these long periods of time.

Vote down Vote up

almost 5 years ago

From what I have learned, you actually have it backwards. It is not that Earth is perfectly suited to life, but life, over time, has become perfectly suited to it. Climate has fluxuated over geologic periods and eras, though in different areas of the globe, and the global average also tends to fluxuate, so the Earths climatary equilibrium is not truly present. Therefore, creatures that inhabit the earth have to constantly adapt to the new climates that form over millions of years. Also, as for the stability of the carbon cycle, oxygen-using organisms and oxygen-creating organisms have have been keeping the carbon cycle moving for billions of years, so it only makes sense that eventually things would balance outover these long periods of time.