You are mixed up. The Gaea hypothesis has nothing to do with Gaea, the mythical Goddess. It has to do with the scientific theory that life can self regulate and enjoy homeostasis through evolutionary "cooperation" and competition--without recourse to teleological explanation. It is simply a theory about how "life", writ large, both cooperates and competes to the survival of the entire system or set which contains that life. At least, that is my understanding of Lovelock's theory. It has huge and increasing scientific support and it has nothing whatsoever to do with afterlife, Goddesses--or any superstitious or religious elements or connotations. The Daisyworld models have demonstrated the value of the theory.
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"The Gaia hypothesis postulates that the Earth's surface environment is maintained in a habitable state by self-regulating feedback mechanisms involving organisms tightly coupled to their environment. The Earth's atmospheric composition, climate, much of the chemical composition of the ocean, and the cycling of many elements essential to life are hypothesized to be regulated. The idea arose from the involvement of the British independent scientist and inventor James Lovelock in the 1960s space program and was developed during the early 1970s in collaboration with the American microbiologist Lynn Margulis .
Lovelock was employed by NASA as part of the team that aimed to detect whether there was life on Mars. Lovelock's interest in atmospheric chemistry led him to seek a general, physical basis for detecting the presence of life on a planet. He recognized that most organisms shift their physical environment away from equilibrium. In particular, organisms use the atmosphere to supply resources and as a repository for waste products. In contrast, the atmosphere of a planet without life should be closer to thermodynamic equilibrium, in a state attributable to photochemistry (chemical reactions triggered by solar ultraviolet radiation). Thus, the presence of abundant life on a planet might be detectable by atmospheric analysis.
Such analysis can be conducted from Earth using an infrared spectrometer (which detects the characteristic absorption of infrared radiation by specific gases) linked to a telescope. Using this technique, it was discovered that the atmospheres of Mars and Venus are dominated by carbon dioxide and are relatively close to chemical equilibrium, suggesting that they are lifeless. In contrast, the atmosphere of the Earth is in an extreme state of disequilibrium because of the activities of life, in which highly reactive gases such as methane and oxygen coexist many orders of magnitude from the photochemical steady state. Remarkably, despite this disequilibrium, the composition of the Earth's atmosphere was known to be fairly stable over geologic periods of time. Lovelock concluded that life must regulate the composition of the Earth's atmosphere.
Interestingly, the composition of the Earth's atmosphere is particularly suited to the dominant organisms. For example, nitrogen maintains much of the atmospheric pressure and serves to dilute oxygen, which at 21% of the atmosphere is just below the level at which fires would disrupt land life. Yet oxygen is sufficiently abundant to support the metabolism of large respiring organisms such as humans. Both oxygen and nitrogen are biological products—oxygen is the product of past photosynthesis, while the gaseous nitrogen reservoir is largely maintained by the actions of denitrifying organisms (which use nitrate as a source of oxygen and release nitrogen gas). Furthermore, the oxygen content of the atmosphere has remained within a narrow range for over 350 million years.
It is also remarkable that life on Earth has persisted despite major changes in the input of matter and energy to the Earth's surface. Most notably, the Sun is thought to have warmed by about 25% since the origin of life on Earth over 3.8 billion years ago. This increase in solar output alone should raise the Earth's surface temperature by about 20°C. Yet the current average temperature is only 15°C. The continuous habitability of the Earth in the face of a warming Sun suggested to Lovelock that life may have been regulating the Earth's climate in concert with its atmospheric composition.
The idea was named “Gaia” after the Greek goddess of the Earth and was first published in 1972 . Lovelock then sought an understanding of the organisms that might be involved. Lynn Margulis was already developing the theory of symbiogenesis—that eukaryotic cells (those with genetic material contained within a distinct nucleus) evolved from the symbiotic merger of previously free-living prokaryotes (organisms, including bacteria, whose genetic material is not enclosed within a cell nucleus). Margulis contributed her intimate knowledge of microorganisms and the diversity of chemical transformations that they mediate to the development of what became the Gaia hypothesis of “atmospheric homeostasis by and for the biosphere.”
The Gaia hypothesis was used to make predictions (for example, that marine organisms would make volatile compounds that can transfer essential elements from the ocean back to the land). Lovelock and colleagues tested this ancillary hypothesis on a scientific cruise between England and Antarctica in 1972 . They discovered that the biogenic gases dimethyl sulfide and methyl iodide are the major atmospheric carriers of the sulfur and iodine cycles. Later, the Gaia hypothesis was extended to include regulation of much of the chemical composition of the ocean.
Daisyworld
The Gaia hypothesis was greeted with hostility from many scientists and leading scientific journals, partly because of its mythological name. The first scientific criticism of the hypothesis was that it implies teleology, some conscious foresight or planning by the biota. Most subsequent criticisms have focused on the need for evolutionary mechanisms by which regulatory feedback loops could have arisen or been maintained. As Richard Dawkins pointed out ( Dawkins , 1983 ) the Earth is not a unit of selection, so Gaian properties cannot be adaptations in a strict neo-Darwinian sense since they cannot be refined by natural selection. This poses the challenge of explaining how such properties could arise.
The Daisyworld model (Figure 1) was formulated to demonstrate that planetary self-regulation does not necessarily imply teleology. It provides a hypothetical example of climate regulation emerging from competition and natural selection at the individual level. Daisyworld is an imaginary gray world orbiting, at a similar distance to the Earth, a star like our Sun, which gets warmer with time. The world is seeded with two types of life, black and white daisies. These share the same optimum temperature for growth, 22.5°C, and limits to growth of 5°C and 40°C. When the temperature reaches 5°C, the first seeds germinate. The paleness of the white daisies makes them cooler than their surroundings, hindering their growth. The black daisies, in contrast, warm their surroundings, enhancing their growth and reproduction. As they spread, the black daisies warm the planet. This further amplifies their growth and they soon fill the world. At this point, the average temperature has risen close to the optimum for daisy growth. As the sun warms, the temperature rises to the point where white daisies begin to appear in the daisy community. As it warms further, the white daisies gain a selective advantage over the black daisies and gradually take over. Eventually, only white daisies are left. When the solar forcing gets too high, regulation collapses.
Daisyworld illustrates that both positive and negative feedback are important for self-regulation. While the solar input changes over a range equivalent to 45°C, the surface of the planet is maintained within a few degrees of the optimum temperature for daisy growth. The initial spread of life is characterized by positive feedback—the more life there is, the more life it can beget. This is coupled to an environmental positive feedback—the warming due to the spread of black daisies enhances their growth and reproduction rates. The long period of stable, regulated temperature on Daisyworld represents a predominance of negative feedback. If the temperature of the planet is greatly perturbed by the removal of a large fraction of the daisy population, then positive feedback acts rapidly to restore comfortable conditions and widespread life. The end of regulation on Daisyworld is characterized by a positive feedback decline in white daisies—solar warming triggers a reduction in their population that amplifies the rise in temperature.
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Gaia Hypothesis. Figure 1. The Daisyworld Model.
A thought experiment to demonstrate that planetary self-regulation can emerge from natural selection at the individual level between types of life with different environment-altering traits. In this case the traits are “darkness” (albedo = 0.15) and “paleness” (albedo = 0.65) of black and white daisies on a gray planet (albedo = 0.4). Left panel: Planetary temperature as solar luminosity increases. The bold line is within daisies and the faint line without daisies. Right panel: Areal cover of black and white daisies.
The modeling approach pioneered in Daisyworld provided the beginnings of a mathematical basis for understanding self-regulation. It was soon adapted to study the regulation of atmospheric composition and climate on the early Earth. With this work, Lovelock began to refer to Gaia as a theory, in which self-regulation is understood as a property of the whole system of life tightly coupled to its environment. This replaced the original suggestion that regulation is “by and for the biota” (which is often interpreted as teleological, although never intended as such). The term “homeostasis,” which refers to regulation around a fixed set point, has also been revised: more appropriate is Margulis's suggestion of “homeorrhesis,” which describes regulation around an evolving set point.
The Gaian view of Earth history is one of periods of stability—of the environment and life, coupled together—with intervening periods of rapid change. Such a pattern of punctuated equilibria appears consistent with the geologic record of both environmental proxies (accessible data used to represent less readily measurable characteristics of a system) and species. Furthermore, evidence that the Earth has remained habitable despite major, periodic disruptions, including the impact of planetesimals and massive volcanic outbursts, supports the notion that the Earth is self-regulating. These events appear to have caused mass extinctions and climate change and yet, in all cases, diverse, widespread life and a tolerable climate soon returned.
Climate Regulation
Climate feedbacks somewhat analogous to those in Daisyworld can be found in the real world. For example, the trees of the boreal forests can be likened to the dark daisies. They possess the traits of shedding snow and dark foliage that give them a low albedo (reflectivity) and make them warmer than their surroundings. The presence of forest warms the high northern latitudes by approximately 4°C in winter. Over much of the surface of the Earth and over longer time scales, the Gaia theory predicts, given the relatively high solar input at present, that the predominant effect of organisms should be to cool the planet.[See Albedo.]
A Gaian mechanism for long-term climate regulation, involving the biological amplification of rock weathering, was proposed in the early 1980s. Over million-year time scales, the carbon dioxide content of the Earth's atmosphere and the resulting greenhouse effect on the Earth's temperature is determined by the balance of carbon dioxide input and removal fluxes. Removal occurs in the process of weathering of silicate rocks on land and the subsequent formation of carbonate rocks in the ocean. A chemical negative-feedback mechanism exists whereby, for example, increases in planetary temperature are counteracted by increases in the rate of rock weathering and the uptake of carbon dioxide. However, the rate of rock weathering is greatly enhanced by the activities of soil microbes, plants, and lichens. This offers the potential for more responsive stabilization of the Earth's temperature. For example, rising temperature may trigger increased plant growth and microbial respiration, which reduces the carbon dioxide content of the atmosphere. The evolution of biological amplification of rock weathering is estimated to have progressively reduced the level of carbon dioxide in the Earth's atmosphere and counteracted the warming Sun, so that this process now cools the Earth by roughly 20°C. [See Carbon Cycle.]
In the mid-1980s, Gaian thinking led to the hypothesis that production of dimethyl sulfide (DMS) by marine phytoplankton also cools the climate. DMS is oxidized in the atmosphere to form sulfate aerosol particles that can grow, often in combination with ammonium (NH4+, another biological product), to become cloud condensation nuclei (CCNs). Increases in the number density of CCNs make clouds more reflective, increasing the scattering of solar radiation back to space and thus causing cooling. Temperature affects phytoplankton growth directly and also determines the degree of stratification in the ocean water-column and hence the supply of nutrients to the surface layers. Hence there is potential for climate feedback involving the growth of DMS-emitting phytoplankton. The nature of this feedback is the subject of intensive ongoing research.
A regional example of self-regulation is the Amazon rainforest, where the trees, by generating a high level of water cycling, maintain the moist environmental conditions in which they can persist. Nutrients are also effectively retained and recycled, in contrast to the nutrient-poor soil. If too much forest is removed, the water-regulation system can collapse, the topsoil is washed away, and the region reverts to arid semidesert. Such change may be irreversible.
Current Work
In recent years, the implications of Gaian feedback for ecology and evolution have been explored. The Daisyworld model has been extended to include different types of “daisy” as well as herbivores and carnivores. Studies of biodiversity within this context (of plant life tightly coupled to climate) suggest that the potential for biodiversity is an essential part of an ecosystem's capacity to respond to perturbation. Different herbivore-feeding strategies have been found to have different effects on the self-regulating capacity of the system. Increases in the number of connections in a Daisyworld food web have been found to increase the stability of both population dynamics and climate, as has the introduction of carnivores to a model with only herbivores and plants. Simulations of habitat fragmentation in Daisyworld have revealed that a critical threshold exists at which the plants become geographically isolated and regulation breaks down. This emphasizes the importance of spatial interaction for self-regulation.
The challenge of reconciling the theories of Gaia and natural selection is now being addressed again, and evolutionary biologists are showing renewed interest in Gaia. When random mutation of the albedo of the daisies is incorporated in Daisyworld, the range of temperature regulation is extended. However, Daisyworld represents only one special case of a direct connection between the effect of a trait on its bearer and on the global environment. To test further the effect of natural selection on environmental regulation, new models are being developed that incorporate the random generation of environment-altering traits.
Fresh emphasis is also being placed on the importance of life in increasing the cycling of nutrient elements, both on land and in the ocean. For example, it has long been recognized that phosphate and nitrate are available in ocean waters in just the ratio required by phytoplankton. The effects of nitrogen fixation, denitrification, preferential recycling of phosphorus from ocean sediments, and the resultant feedbacks are being modeled to test whether they can account for such regulation. This is generating a new focus on the molecular biology of Gaia—the enzymes responsible for the regulation and the trace elements crucial to their functioning.
Gaian hypotheses concerning the mechanisms responsible for gradual onset and rapid termination of ice ages have been put forward and modeled. These may help us to understand and predict the biosphere's response to global change. Contemporary observations indicate that members of both the marine and terrestrial biota are involved in removing a significant fraction of the excess carbon dioxide released to the atmosphere by human activities. However, this negative feedback is not sufficient to prevent the carbon dioxide content of the atmosphere from rising. Furthermore, Lovelock has predicted that increasing temperature and resultant stratification of the ocean will trigger a decline in phytoplankton and their cooling effect via DMS emissions, providing a positive feedback on global warming. [See Global Warming.]
The Gaia hypothesis has contributed greatly to our understanding of the Earth as a unitary system. The previous view that life is merely a passenger on a dead planet has largely been replaced with recognition of the coevolution of organisms and their environment. The degree to which organisms are involved in regulating conditions at the surface of the Earth remains a subject of controversy, but the concept has proved its worth in stimulating valuable research. It may thus offer a new paradigm for environmental science.
Bibliography and More Information about Gaia Hypothesis
* General References
* Bunyard, P., ed. Gaia in Action: Science of the Living Earth. Edinburgh: Floris Books, 1996. Collected papers from three meetings on the scientific and philosophical implications of the Gaia hypothesis.
* Lovelock, J. E. Gaia: A New Look at Life on Earth. New York and Oxford: Oxford University Press, 1979. The classic exposition of the hypothesis, born out of the frustration of censorship from scientific journals. A rare and inspiring blend of science and poetry.
* Lovelock, J. E. The Ages of Gaia: A Biography of our Living Earth. New York and Oxford: Oxford University Press, 1988. The definitive scientific exposition of what the author now describes as the Gaia theory. A thorough response to the criticisms triggered by the original hypothesis, seeking consistency with natural selection, and replete with suggested and, to a lesser degree, tested regulatory mechanisms.
* Lovelock, J. E. Gaia: The Practical Science of Planetary Medicine. London: Gaia, 1991. An accessible and well-illustrated introduction to the subject for the general reader.
* Lovelock, J. E. The Revenge of Gaia: Earth's Climate in Crisis and the Fate of Humanity. New York: Basic Books, 2006.
* Margulis, L., and D. Sagan. Microcosmos: Four Billion Years of Evolution from Our Microbial Ancestors. London: Allen and Unwin, 1987. The history of microbial life and evolution. Stresses the importance of microbes in regulating the Earth's surface environment.
* Margulis, L., and D. Sagan Slanted Truths: Essays on Gaia, Symbiosis, and Evolution. New York: Copernicus/Springer, 1998. Provides a varied introduction to the work and thought of Lynn Margulis and colleagues.
* Schneider, S. H., and P. J. Boston, eds. Scientists on Gaia. Cambridge, Mass.: MIT Press, 1991. Scientific and philosophical papers from the 1988 Chapman Conference on the Gaia hypothesis, sponsored by the American Geophysical Union. Covers a broad spectrum of views on the subject.
* Volk, T. Gaia's Body: Toward a Physiology of the Earth. New York: Copernicus/Springer, 1998. Emphasizes the greatly amplified cycling of essential elements resulting from the existence of life.
* Williams, G. R. The Molecular Biology of Gaia. New York: Columbia University Press, 1996. Focuses on the biochemistry of the enzymes that catalyze matter transfers between organisms and their environment as a route to understanding the regulation of global biogeochemical cycles.
* Scientific Papers
* Charlson, R. J., et al. “Oceanic Phytoplankton, Atmospheric Sulphur, Cloud Albedo and Climate.” Nature 326 (1987), 655–661. A much cited paper, proposing both a mechanism of climatic cooling due to phytoplankton and (more speculatively) a resulting regulatory feedback. DOI: 10.1038/326655a0.
* Kump, L. R., and J. E. Lovelock. “The Geophysiology of Climate.” In Future Climates of the World: A Modelling Perspective, edited by A. Henderson-Sellers, pp. 537–553. Amsterdam, Oxford, and New York: Elsevier, 1995. An accessible review of postulated climate feedback mechanisms involving life.
* Lovelock, J. E. “Gaia as Seen through the Atmosphere.” Atmospheric Environment 6.8 (1972), 579–580. The first “Gaia” paper. DOI: 10.1016/0004-6981(72)90076-5.
* Margulis, L., and J. E. Lovelock. “Biological Modulation of the Earth's Atmosphere.” Icarus 21 (1974), 471–489. One of a collection of jointly authored papers that clarified the Gaia hypothesis and proposed regulatory mechanisms.
* Watson, A. J., and J. E. Lovelock. “Biological Homeostasis of the Global Environment: The Parable of Daisyworld.” Tellus 35B (1983), 284–289. Gives the equations, mathematical analysis, and an interesting variant of the Daisyworld model.
* Whitfield, M. “The World Ocean: Mechanism or Machination?” Interdisciplinary Science Reviews 6 (1981), 12–35. A comprehensive review that extends the Gaia hypothesis to include biological control of aspects of the chemical composition of the ocean.
* Contrasting Vews
* Dawkins, R. The Extended Phenotype. Oxford and New York: Oxford University Press, 1983.
* Doolittle, W. F. “Is Nature Really Motherly?” CoEvolution Quarterly 29 (1981), 58–63. A thoughtful critique of Lovelock's first book (Lovelock, 1979). The author argues that the Gaia hypothesis is inconsistent with natural selection. For a response, see Watson and Lovelock, 1983, and Lovelock, 1988.
* Holland, H. D. The Chemical Evolution of the Atmosphere and Oceans. Princeton: Princeton University Press, 1984. A thorough textbook on the Earth's geochemical history. The author also argues that the Gaia hypothesis is not necessary to explain the continuity of life on Earth for 3.8 billion years.
* Recent Work
* Lenton, T. M. “Gaia and Natural Selection.” Nature 394 (1998), 439–447. DOI: 10.1038/28792. A review and synthesis; clarifies the types of environmental feedback and explores their implications at levels from the individual to the global.
Tim Lenton
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