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Gaia theory (biology)

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Gaia theory (biology) is a broadly inclusive name for a group of ideas that living organisms on a planet modify the nature of the planet to make it more suitable for life. This set of theories holds that all organisms on a planet regulate the biosphere to the benefit of the whole.

While there were a number of precursors to Gaia theory, the first scientific form of this idea was proposed as the Gaia Hypothesis by James Lovelock, a U.K. chemist, in 1970. While controversial at first, various forms of this idea became accepted to some degree by many within the scientific community.

Gaia theory is a spectrum of hypotheses, ranging from the undeniable to radical. At one end is the undeniable statement that the organisms on the Earth have radically altered its composition. A stronger position is that the Earth's biosphere effectively acts as if it is a self-organizing system which works in such a way as to keep its systems in some kind of equilibrium that is conducive to life. Biologists usually view this activity as an undirected emergent property of the ecosystem; as each individual species pursues its own self-interest, their combined actions tend to have counterbalancing effects on environmental change. Proponents of this view sometimes point to examples of life's actions in the past that have resulted in dramatic change rather than stable equilibrium, such as the conversion of the Earth's atmosphere from a reducing environment to an oxygen-rich one.

An even stronger claim is that all lifeforms are part of a single planetary being, called Gaia. In this view, the atmosphere, the seas, the terrestrial crust would be the result of interventions carried out by Gaia, through the coevolving[?] diversity of living organisms. Most scientists do not hold this view; however such a view is considered within scientific possibility.

The most extreme form of Gaia theory is that the entire Earth is a single unified organism; in this view the Earth's biosphere is consciously manipulating the climate in order to make conditions more conducive to life. Scientists contend that there is no evidence at all to support this last point of view, and it has come about because many people do not understand the concept of homeostasis. Many non-scientists instinctively see homeostatis as an activity that requires conscious control, although this is not so.

Much more speculative versions of Gaia, including all versions in which it is held that the Earth is actually conscious or part of some universe-wide evolution, are currently held to be outside the bounds of science. These are discussed in the Gaia theory article.

Table of contents

Strong Gaia theories

Several types of strong theories may be defined. Lovelock's core initial 1979 hypothesis was that the biomass modifies the conditions on the planet to make conditions on the planet more hospitable - the Gaia Hypothesis proper defined this "hospitality" as a full homeostasis. Lovelock's initial teleological hypothesis was that Gaia atmosphere is kept in homeostasis by and for the biosphere.

Lovelock suggested that life on Earth provides a cybernetic, homeostatic feedback system operated automatically and unconsciously by the biota, leading to stabilization of global temperature and chemical composition.

With his initial hypothesis, Lovelock claimed the existence of a global control system of surface temperature, atmosphere composition and ocean salinity. His arguments were:

  • The global surface temperature of the Earth has remained constant, despite an increase in the energy provided by the sun
  • Atmospheric composition remains constant, even though it should be unstable
  • Ocean salinity is constant

Since life started on Earth, the energy provided by the sun has increased by 25%; however the surface temperature of the planet has remained constant when measured on a global scale. Furthermore, he argued, the atmospheric composition of the Earth is constant. The Earth's atmosphere consists of 79% nitrogen, 20.7% oxygen and 0.03% carbon dioxide. This composition should be unstable, according to Lovelock, and its stability can only have been maintained with removal or production by living organisms.

Ocean salinity has been constant at about 3.4% for a very long time. Salinity stability is important as most cells require a rather constant salinity degree and do not tolerate much values above 5%. Salinity is partially controlled by evaporation processes, which mostly take place in lagoons.The only significant natural source of atmospheric carbon dioxide is volcanic activity, while the only significant removal is throught the weathering of some rocks. During weathering, a reaction causes the formation of calcium carbonate. This chemical reaction is enhanced by the bacteria and plant roots in soils, where they improve gazeous circulation. The calcium carbonate can be washed to the sea where it is used by living organisms with carboneous tests and shells. Once dead, the living organisms shells fall at the bottom of the oceans where they generate deposits of chalk and limestones. In short, a rock was weathered, the resulting carbon dioxide processed by a living organism, and returned to a rock through sedimentation process. Part of the organisms with carboneous shells are the coccolithophores (algua), which also happen to participate in the formation of clouds. When they die, they release a sulfurous gaz (DMS), which act as particles on which water vappor condense to make clouds.

Lovelock sees this as one of the complex processes that maintain conditions suitable for life. The volcanoes make the CO2 enter the atmosphere, CO2 participate in limestocks weathering, itself accelerated by temperature and soil life, the dissolved CO2 is then used by the algua and releasd on the ocean floor. CO2 excess can be compensated by an increase of coccolithophoride life, increasing the amount of CO2 locked in the ocean floor. Coccolithophoride increase the cloud cover, hence control the surface temperature, help cool the whole planet and favor precipitations which are necessary for terrestrial plants. For Lovelock, coccolithophoridees are one stage in a regulatory feedback loop. Lately the atmospheric CO2 concentration has increase and there is some evidence that concentrations of ocean algal blooms are also increasing.

The initial Gaia Hypothesis was highly criticized by orthodox scientists for being teleological.

An even stronger claim states that biota manipulate their physical environment to creat optimal conditions. It is sometimes refers to as optimizing Gaia.

"the Earth's atmosphere is more than merely anomalous; it appears to be a contrivance specifically constituted for a set of purposes". (Lovelock and Margulis 1974).

Optimizing Gaia asserts that the biota manipulate their physical environment for the purpose of creating biologically favorable, or even optimal, conditions for themselves.

"...it is unlikely that chance alone accounts for the fact that temperature, pH and the presence of compounds of nutrient elements have been, for immense periods, just those optimal for surface life. Rather, ... energy is expended by the biota to actively maintain these optima". (Lovelock and Margulis 1974)

Another strong theory is the one called Omega Gaia, and proposed by Teilhard de Chardin's. Teilhard de Chardin claims that the Earth is evolving through stages of geosphere[?], biosphere, and noosphere, culminating in the Omega Point.

Standard Gaia theories

In 1988, Lovelock presented a new version of the Gaia Hypothesis which was abandoning any attempt to argue that Gaia intentionally or consciously maintained the complex balance in her environment that life needed to survive. This new hypothesis was more acceptable by the scientific community. He supported his new hypothesis with the metaphor of Daisyworld. Using computer simulations of the Daisyworld parameters (no atmosphere, taking into account different albedos for each daisy type) and a mathematical approach, Lovelock proved that the controlled stability of the climate by life was not being teleological. The new Gaia hypothesis stated that Gaia was homeostatic, ie that the biota influence the abiotic world in a way that involves homeostatic feedback.

Weak Gaia theories

A version of Gaia theory was developed by Lynn Margulis, a microbiologist, in 1979. Her model is more limited in scope than the one that Lovelock proposed. In particular, that only homeorhetic and not homeostatic balances are involved, and that there is no special tendency of biospheres to preserve their current inhabitants, and certainly not to make them comfortable. Accordingly, the Earth is not a living organism which can live or die all at once, but rather a kind of community of trust which can exist at many discrete levels of integration.

Coauthor of the original Gaia Hypothesis, "Lynn Margulis, tells us that Earth is not homeostatic but homeorhetic: that is, the composition of Earth's atmosphere, hydrosphere and lithosphere are regulated around "set points" as in homeostasis, but those set points change with time... Gaia is just symbiosis as seen from space." - from Greenpeace (http://cybercentre.greenpeace.org//t/s//996755792/1007012854/1007026932/1013059381) apparently in reference to Lynn Margulis, Symbiotic Planet: A New View of Evolution.

A system in homeostasis tends to move towards constant values for its parameters, whereas a system in homeorhesis will always exhibit similar dynamic behavior, without necessarily converging to a constant state. There is strong evidence that plants are selected for the microclimate effects which they can have locally to themselves, and good evidence that these patterns also exist on some wider scales, with symbiotic relationships existing for larger scale climate modification.

Other reductionist theories suggest that Gaia is co-evolutive. Co-evolution in this context has been thus defined: "Biota influence their abiotic environment, and that environment in turn influences the biota by Darwinian process."

The weakest form of the theory has been called influential Gaia. It barely states that biota influence certain aspects of the abiotic world, e.g. temperature and atmosphere.

All of these theories are more acceptable from an orthodox sience perspective, as they assume non-homeostasis. It states the evolution of life and its environment may affect each other. An example is how the activity of photosynthetic bacteria during precambrion times have completely modified the Earth atmosphere to turn it aerobic, and as such supporting evolution of life (in particular eucaryotic life) . However, these theories do not claim the atmosphere modification has been done in coordination and though homeostasis.

Semantic debate

The argument is that these symbiotic organisms, being unable to survive apart from each other and their climate and local conditions, form an organism in their own right, under a wider conception of the term organism than is conventionally used. It is a matter for often heated debate whether this is a valid usage of the term, but ultimately it appears to be a semantic dispute. In this sense of the word organism, it is argued under the theory that the entire biomass of the Earth "is a single organism".

Unfortunately, many supporters of the various Gaia theories do not state exactly where they sit on this spectrum; this makes discussion and criticism difficult.

Much effort on behalf of those analyzing the theory currently is an attempt to clarify what these different hypotheses are, and whether they are proposals to 'test' or 'manipulate' outcomes. Both Lovelock's and Margulis's understanding of Gaia are considered valid scientific theories, and are now a part of biology proper.


put this here for now

A simple model that is often used to illustrate the original Gaia hypothesis is the so-called Daisyworld simulation.

Whether this sort of system is present on Earth is still open to debate. Some relatively simple homeostatic mechanisms are generally accepted. For example, when atmospheric carbon dioxide levels rise, plants are able to grow better and thus remove more carbon dioxide from the atmosphere, but the extent to which these mechanisms stabilize and modify the Earth's overall climate are not known.

The Gaia hypothesis is sometimes viewed from significantly different philosophical perspectives. Some environmentalists view it as an almost conscious process, in which the Earth's ecosystem is literally viewed as a single unified organism. Some evolutionary biologists, on the other hand, view it as an undirected emergent property of the ecosystem; as each individual species pursues its own self-interest, their combined actions tend to have counterbalancing effects on environmental change. Proponents of this view sometimes point to examples of life's actions in the past that have resulted in dramatic change rather than stable equilibrium, such as the conversion of the Earth's atmosphere from a reducing environment to an oxygen-rich one.

Depending on how strongly the case is stated, the hypothesis conflicts with mainstream neo-Darwinism. Most biologists would accept Daisyworld-style homeostasis as possible, but would not accept the idea that this equates to the whole biosphere acting as one organism.

See also

keystone species, climate engineering, gardening, urban ecology[?], industrial ecology, arcology, places to intervene in a system, James Kirchner[?]

External links



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