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Since 1971, the noted microbiologist Lynn Margulis has been Lovelock's most important collaborator in developing Gaian concepts (Turney 2003). Gaia "theories" have Non-technical Predecessors in the ideas of several cultures. Today, "Gaia theory" is sometimes used among non-scientists to refer to hypotheses of a Self-regulating Earth that are non-technical but take inspiration from scientific models. Among some scientists, "Gaia" carries connotations of lack of scientific rigor and quasi-mystical thinking about the planet Earth, and therefore Lovelock's hypothesis was received initially with much antagonism by much of the scientific community. No controversy exists, however, about the fact that life and the physical environment significantly influence one another (see Ecology ). RANGE OF VIEWS The original Gaia hypothesis has split into a spectrum of hypotheses, ranging from the undeniable (Weak Gaia) to the radical (Strong Gaia). At one end of this spectrum 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 Meta- Equilibrium that is broadly conducive to life. The history of evolution, ecology and climate show that the exact characteristics of this equilibrium intermittently have undergone rapid changes, which are believed to have caused Extinction s and felled civilisations (see Climate Change ). Biologists and earth scientists usually view the factors that stabilize the characteristics of a period as an undirected Emergent Property or Entelechy of the system; as each individual species pursues its own self-interest, for example, their combined actions tend to have counterbalancing effects on environmental change. Opponents of this view sometimes point to examples of life's actions 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. However, proponents will point out that those Atmospheric composition changes created an environment even more suitable to life. Some go a step further and hypothesize that all lifeforms are part of one single living planetary being called ''Gaia.'' In this view, the atmosphere, the seas and the terrestrial crust would be results of interventions carried out by Gaia through the Coevolving diversity of living organisms. While it is arguable that the Earth as a unit does not match the generally accepted Biological criteria for Life itself (''Gaia'' has not yet reproduced, for instance; it still might ''spread'' to other planets through human Space Colonization and Terraforming ), many scientists would be comfortable characterising the earth as a single " System ". The most extreme form of Gaia hypothesis 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 Homeostasis as an activity that requires conscious control, although this is not so. Much more speculative versions of Gaia hypothesis, 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 Philosophy article. Also outside the bounds of science is the Gaia Movement , a collection of different organisations operating in different countries, but all sharing a concern for how humans might live more sustainably within the "living system". GAIA THEORIES Early modern parallels In ''Lives of a Cell'' (1974), the biologist, Lewis Thomas , makes an observation very similar to Lovelock's Gaia hypothesis: I have been trying to think of the earth as a kind of organism, but it is no go. I cannot think of it this way. It is too big, too complex, with too many working parts lacking visible connections. The other night, driving through a hilly, wooded part of southern New England, I wondered about this. If not like an organism, what is it like, what is it most like? Then, satisfactorily for that moment, it came to me: it is most like a single cell. Lovelock initial hypothesis Lovelock defined Gaia as: a complex entity involving the Earth's biosphere, atmosphere, oceans, and soil; the totality constituting a feedback or cybernetic system which seeks an optimal physical and chemical environment for life on this planet. His initial hypothesis was that the biomass modifies the conditions on the planet to make conditions on the planet more hospitable – the Gaia Hypothesis properly defined this "hospitality" as a full homeostasis. Lovelock's initial hypothesis, accused of being Teleological by his critics, 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 broad 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:
Since life started on Earth, the energy provided by the Sun has increased by 25% to 30%; however the surface temperature of the planet has remained remarkably constant when measured on a global scale. Furthermore, he argued, the atmospheric composition of the Earth is constant. The Earth's atmosphere currently consists of 79% nitrogen, 20.7% oxygen and 0.03% carbon dioxide. Oxygen is the second most reactive element after fluorine, and should combine with gases and minerals of the Earth's atomosphere and crust. Traces of methane (at an amount of 100,000 tonnes produced per annum), should not exist, as methane is combustible in an oxygen atmosphere. This composition should be unstable, 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%. Ocean salinity constancy was a long-standing mystery, because river salts should have raised the ocean salinity much higher than observed. Only recently have we learned salinity is controlled by seawater circulation through hot basaltic rocks, and emerging as hot water vents on ocean spreading ridges. The only significant natural source of atmospheric Carbon Dioxide (CO2) is volcanic activity, while the only significant removal is through 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 gaseous 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 to the bottom of the oceans where they generate deposits of chalk and limestone. 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 Coccolithophore s ( Algae ), which also happen to participate in the formation of clouds. When they die, they release a sulfurous gas (DMS), (CH3)2S, which act as particles on which water vapor Condenses 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 participates in limestone weathering, itself accelerated by temperature and soil life, the dissolved CO2 is then used by the algae and released 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. Coccolithophorides 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, coccolithophorides are one stage in a regulatory Feedback Loop . Lately the atmospheric CO2 concentration has increased and there is some evidence that concentrations of ocean Algal Bloom s are also increasing. CRITICAL ANALYSIS Basis This theory is based on the simple idea that the Biomass self-regulates the conditions on the planet to make its physical environment (in particular temperature and chemistry of the atmosphere) on the planet more hospitable to the species which constitute its "life". The Gaia Hypothesis proper defined this "hospitality" as a full Homeostasis . 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 yet known. Criticism The initial Gaia Hypothesis was highly criticized by many scientists for being Teleological , a belief that all things have a predetermined purpose. It was very critically received, in particular by Richard Dawkins and Ford Doolittle . These latter argue organisms could not act in concert as this would require foresight and planning from them. They rejected the possibility that feedback loops could stabilize the system. In 1982, Dawkins claimed "there was no way for evolution by natural selection to lead to Altruism on a Global scale". They find it impossible to see how the feedback loops which Lovelock says stabilise the Gaian system could have evolved. They argue that, as Gaia can't reproduce herself, she cannot be alive in any meaningful sense. They also claim that the theory is not scientific because it is impossible to test it by controlled experiment. Lovelock offered the Daisyworld model as mathematical evidence to refute most of these criticisms. The initial hypothesis was rather imprecise, and Lovelock later refuted accusation of Teleologism by stating "Nowhere in our writings do we express the idea that planetary self-regulation is purposeful, or involves foresight or planning by the Biota ." – (Lovelock, J. E. 1990) Another of the largest criticisms against the idea that Gaia is a "living" organism is the inability of the planet to reproduce. Certainly one of the hallmarks of living organisms is their ability to replicate and pass on their genetic information to succeeding generations. Others have proposed that man himself is the means by which Gaia will reproduce. Man's exploration of space, his interest in colonizing other planets, and the large body of sci-fi literature that describes terraforming, lend strong evidence to the idea that Gaia is planning to reproduce. DaisyWorld simulations Lovelock responded to criticisms with the mathematical Daisyworld model (1983), first to prove the existence of feedback mechanisms, second to demonstrate it was possible that control of the global biomass could occur without consciousness being involved. | ||
| Staley, M (2004) Darwinian Selection Leads To Gaia ''J Theoretical Biol'', 218(1): | "http://wwwncbinlmnihgov/entrez/queryfcgicmd=Retrieve&db=PubMed&list_uids=12297068&dopt=CitationM" class="copylinks" target="_blank">Staley abstract |
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