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Gaia Hypothesis

Gaia hypothesis

The Gaia (pronounced GAY-ah) hypothesis is the idea that Earth is a living organism and can regulate its own environment. This idea argues that Earth is able to maintain conditions that are favorable for life to survive on it, and that it is the living things on Earth that give the planet this ability.

Mother Earth

The idea that Earth and its atmosphere are some sort of "superorganism" was actually first proposed by Scottish geologist (a person specializing in the study of Earth) James Hutton (17261797), although this was not one of his more accepted and popular ideas. As a result, no one really pursued this notion until some 200 years later, when the English chemist James Lovelock (1919 ) put forth a similar idea in his 1979 book, Gaia: A New Look at Life on Earth. Gaia is the name of the Greek goddess of Earth and mother of the Titans. In modern times, the name has come to symbolize "Earth Mother" or "Living Earth." In this book, Lovelock proposed that Earth's biosphere (all the parts of Earth that make up the living world) acts as a single living system that if left alone, can regulate itself.

As to the name Gaia, the story goes that Lovelock was walking in the countryside surrounding his home in Wilshire, England, and met his neighbor, English novelist William Golding (19111993), author of Lord of the Flies and several other books. Telling Golding of his new theory, he then asked his advice about choosing a suitable name for it, and the result of this meeting was that the term "Gaia" was chosen because of its real connection to the Greek goddess who pulled the living world together out of chaos or complete disorder.

Origin of Earth's atmosphere

Lovelock arrived at this hypothesis by studying Earth's neighboring planets, Mars and Venus. Suggesting that chemistry and physics seemed to argue that these barren and hostile planets should have an atmosphere just like that of Earth, Lovelock stated that Earth's atmosphere is different because it has life on it. Both Mars and Venus have an atmosphere with about 95 percent carbon dioxide, while Earth's is about 79 percent nitrogen and 21 percent oxygen. He explained this dramatic difference by saying that Earth's atmosphere was probably very much like that of its neighbors at first, and that it was a world with hardly any life on it. The only form that did exist was what many consider to be the first forms of lifeanaerobic (pronounced ANN-ay-roe-bik) bacteria that lived in the ocean. This type of bacteria cannot live in an oxygen environment, and its only job is to convert nitrates to nitrogen gas. This accounts for the beginnings of a nitrogen build-up in Earth's atmosphere.

Words to Know

Biosphere: The sum total of all lifeforms on Earth and the interaction among those lifeforms.

Feedback: Information that tells a system what the results of its actions are.

Homeostasis: State of being in balance; the tendency of an organism to maintain constant internal conditions despite large changes in the external environment.

Photosynthesis: Chemical process by which plants containing chlorophyll use sunlight to manufacture their own food by converting carbon dioxide and water to carbohydrates, releasing oxygen as a by-product.

Symbiosis: A pattern in which two or more organisms live in close connection with each other, often to the benefit of both or all organisms.

The oxygen essential to life as we know it did not start to accumulate in the atmosphere until organisms that were capable of photosynthesis evolved. Photosynthesis is the process that some algae and all plants use to convert chemically the Sun's light into food. This process uses carbon dioxide and water to make energy-packed glucose, and it gives off oxygen as a by-product. These very first photosynthesizers were a blue-green algae called cyanobacteria (pronounced SIGH-uh-no-bak-teer-eea) that live in water. Eventually, these organisms produced so much oxygen that they put the older anaerobic bacteria out of business. As a result, the only place that anaerobic bacteria could survive was on the deep-sea floor (as well as in heavily water-logged soil and in our own intestines). Love-lock's basic point was that the existence of life (bacteria) eventually made Earth a very different place by giving it an atmosphere.

Lovelock eventually went beyond the notion that life can change the environment and proposed the controversial Gaia hypothesis. He said that Gaia is the "Living Earth" and that Earth itself should be viewed as being alive. Like any living thing, it always strives to maintain constant or stable conditions for itself, called homeostasis (pronounced hoe-mee-o-STAY-sis). In the Gaia hypothesis, it is the presence and activities of life that keep Earth in homeostasis and allow it to regulate its systems and maintain steady-state conditions.

Cooperation over competition

Lovelock was supported in his hypothesis by American microbiologist Lynn Margulis (1918 ) who became his principal collaborator. Margulis not only provided support, but she brought her own scientific ability and achievements to the Gaia hypothesis. In her 1981 book, Symbiosis in Cell Evolution, Margulis had put forth the then-unheard of theory that life as we know it today evolved more from cooperation than from competition. She argued that the cellular ancestors of today's plants and animals were groups of primitive, formless bacteria cells called prokaryotes (pronounced pro-KAR-ee-oats). She stated that these simplest of bacteria formed symbiotic relationshipsrelationships that benefitted both organismswhich eventually led to the evolution of new lifeforms. Her theory is called endosymbiosis (pronounced en-doe-sim-bye-O-sis) and is based on the fact that bacteria routinely take and transfer bits of genetic material from each other.

Margulis then argued that simple bacteria eventually evolved into more complex eukaryotic (pronounced you-kar-ee-AH-tik) cells or cells with a nucleus. These types of cells form the basic structure of plants and animals. Her then-radical but now-accepted idea was that life evolved more out of cooperation (which is what symbiosis is all about) than it did out of competition (in which only the strong survive and reproduce). The simple prokaryotes did this by getting together and forming symbiotic groups or systems that increased their chances of survival. According to Margulis then, symbiosis, or the way different organisms adapt to living together to the benefit of each, was the major mechanism for change on Earth.

Most scientists now agree with her thesis that oxygen-using bacteria joined together with fermenting bacteria to form the basis of a type of new cell that eventually evolved into complex eukaryotes. For the Gaia hypothesis, the Margulis concept of symbiosis has proven to be a useful explanatory tool. Since it explains the origin and the evolution of life on Earth (by stating that symbiosis is the mechanism of change), it applies also to what continues to happen as the process of evolution goes on and on.

Gaia explained

The main idea behind the Gaia hypothesis can be both simple and complex. Often, several similar examples or analogies concerning the bodies of living organisms are used to make the Gaia concept easier to understand. One of these states that we could visualize Earth's rain forests as the lungs of the planet since they exchange oxygen and carbon dioxide. Earth's atmosphere could be thought of as its respiratory system, and its streams of moving water and larger rivers like its circulatory system, since they bring in clean water and flush out the system. Some say that the planet actually "breathes" because it contracts and expands with the Moon's gravitational pull, and the seasonal changes we all experience are said to reflect our own rhythmic bodily cycles.

Many of these analogies are useful in trying to explain the general idea behind the Gaia hypothesis, although they should not be taken literally. Lovelock, however, has stated that Earth is very much like the human body in that both can be viewed as a system of interacting components. He argues that just as our bodies are made up of billions of cells working together as a single living being, so too are the billions of different lifeforms on Earth working together (although unconsciously) to form a single, living "superorganism." Further, just as the processes or physiology of our bodies has its major systems (such as the nervous system, circulatory system, respiratory system, etc.), so, says Lovelock, Earth has its own "geophysiology." This geophysiology is made up of four main components: atmosphere (air), biosphere (all lifeforms), geosphere (soil and rock), and hydrosphere (water). Finally, just as our own physiological health depends on all of our systems being in good working condition and, above all, working together well, so, too, does Earth's geophysiology depend on its systems working in harmony.

Life is the regulating mechanism

Lovelock claims that all of the living things on Earth provide it with this necessary harmony. He states that these living things, altogether, control the physical and chemical conditions of the environment, and therefore it is life itself that provides the feedback that is so necessary to regulating something. Feedback mechanisms can detect and reverse any unwanted changes. A typical example of feedback is the thermostat in most homes. We set it to maintain a comfortable indoor temperature, usually somewhere in the range between 65°F (18°C) and 70°F (21°C). The thermostat is designed so that when the temperature falls below a certain setting, the furnace is turned on and begins to heat the house. When that temperature is reached and the thermostat senses it, the furnace is switched off. Our own bodies have several of these feedback mechanisms, all of which are geared to maintaining conditions within a certain proper and balanced range.

For Earth's critical balance, Lovelock says that it is the biosphere, or all of life on Earth, that functions as our thermostat or regulator. He says that the atmosphere, the oceans, the climate, and even the crust of Earth are regulated at a state that is comfortable for life because of the behavior of living organisms. This is the revolutionary lesson that the Gaia hypothesis wants to teach. It says that all of Earth's major components, such as the amount of oxygen and carbon dioxide in the atmosphere, the

saltiness of the oceans, and the temperature of our surface is regulated or kept in proper balance by the activities of the life it supports. He also states that this feedback system is self-regulating and that it happens automatically. As evidence that, if left alone, Earth can regulate itself, he asserts that it is the activity of living organisms that maintain the delicate balance between atmospheric carbon dioxide and oxygen. In a way, Love-lock argues that it is life itself that maintains the conditions favorable for the continuation of life. For example, he contends that it is no accident that the level of oxygen is kept remarkably constant in the atmosphere at 21 percent. Lovelock further offers several examples of cycles in the environment that work to keep things on an even keel.

Lovelock also warns that since Earth has the natural capacity to keep things in a stable range, human tampering with Earth's environmental balancing mechanisms places everyone at great risk. While environmentalists insist that human activity (such as industrial policies that result in harming Earth's ozone layer) is upsetting Earth's ability to regulate itself, others who feel differently argue that Earth can continue to survive very well no matter what humans do exactly because of its built-in adaptability.

Earth as seen from space

An important aspect about the Gaia hypothesis is that it offers scientists a new model to consider. Most agree that such a different type of model was probably not possible to consider seriously until humans went into space. However, once people could travel beyond the atmosphere of Earth and put enough distance between them and their planet, then they could view their home from an extra-terrestrial viewpoint. No doubt that the 1960s photographs of the blue, green, and white ball of life floating in the total darkness of outer space made both scientists and the public think of their home planet a little differently than they ever had before. These pictures of Earth must have brought to mind the notion that it resembled a single organism.

Although the Gaia hypothesis is still very controversial and has not been established scientifically (by being tested and proven quantitatively), it has already shown us the valuable notion of just how interdependent everything is on Earth. We now recognize that Earth's biological, physical, and chemical components or major parts regularly interact with and mutually affect one another, whether by accident or on purpose. Finally, it places great emphasis on what promises to be the planet's greatest future problemthe quality of Earth's environment and the role humans will play in Earth's destiny.

[See also Biosphere; Ecosystem ]

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Gaia Hypothesis

Gaia hypothesis

The Gaia hypothesis is a recent and controversial theory that views Earth as an integrated, pseudo-organismic entity, and not as a mere physical object in space . Gaia, Earth, was believed by the ancient Greeks to be a living, fertile ancestor of many of their important gods. 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. According to the Gaian hypothesis, evolution is the result of cooperative, not competitive processes. The Gaian hypothesis holds that evolution of life on Earth was enhanced by two processes: sexual reproduction, which introduced enormous variety in the gene pool, and the development of consciousness, which enabled genetic methods of evolution to be replaced with more efficient social mechanisms.

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 experimentationthere 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.

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

All 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. Hopefully, the changes wrought by humans will not exceed the limits of homeostatic tolerance and repair of the planet and its ecological components. If these possibly Gaian limits of tolerance are exceeded, some scientists assert the consequences could be catastrophic for life on Earth.

See also Earth (planet); Evolutionary mechanisms; Evolution, evidence of

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Gaia Hypothesis

Gaia Hypothesis


Gaia is the name of the Greek goddess of the Earth. The Gaia hypothesis is that the Earth is more worthy of the respect and reverence once shown to Gaia than modern people have supposed. According to this hypothesis, the Earth is a self-regulating system, of which humans are an unruly part. In particular, the organisms on the Earth's surface play a major role in determining the composition of the atmosphere to ensure that it is favorable to life. Some proponents judge from the scientific evidence that the Earth has its own intelligence and depict it in almost personal, quasi-divine, terms. This provides religious support for concern about particular features of the global ecosystem.


See also Animal Rights; Biological Diversity; Deep Ecology; Ecofeminism; Ecology; Ecology, Ethics of; Ecology, Religious and Philosophical Aspects; Ecology, Science of; Ecotheology; Sacramental Universe


Bibliography

lovelock, james e. gaia: a new look at life on earth. oxford: oxford university press, 1979.


john cobb

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Gaia hypothesis

Gaia hypothesis The theory, based on an idea put forward by the British scientist James Ephraim Lovelock (1919– ), that the whole earth, including both its biotic (living) and abiotic (nonliving) components, functions as a single self-regulating system. Named after the Greek earth goddess, it proposes that the responses of living organisms to environmental conditions ultimately bring about changes that make the earth better adapted to support life; the system would rid itself of any species that adversely affects the environment. The theory has found favour with many conservationists.

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Gaian hypothesis

Gaian hypothesis A hypothesis, formulated by James E.Lovelock and Lynn Margulis and first advanced by Lovelock in 1968. It holds that the presence of living organisms on a planet leads to major modifications of the physical and chemical conditions pertaining on the planet, and that subsequent to the establishment of life the climate and major biogeochemical cycles are mediated by living organisms themselves.

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Gaian hypothesis

Gaian hypothesis Hypothesis, formulated by James E. Lovelock and Lynn Margulis, that the presence of living organisms on a planet leads to major modifications of the physical and chemical conditions pertaining on the planet, and that subsequent to the establishment of life the climate and major biogeochemical cycles are mediated by the living organisms themselves.

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Gaian hypothesis

Gaian hypothesis A hypothesis, formulated by James E. Lovelock and Lynn Margulis, that the presence of living organisms on a planet leads to major modifications of the physical and chemical conditions pertaining on the planet, and that, subsequent to the establishment of life, the climate and major biogeochemical cycles are mediated by living organisms themselves.

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Gaia hypothesis

Gaia hypothesis The hypothesis, formulated by James E. Lovelock and Lynn Margulis, that the presence of living organisms on a planet leads to major modifications of the physical and chemical conditions pertaining on the planet, and that subsequent to the establishment of life the climate and major biogeochemical cycles are mediated by living organisms themselves.

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Gaia hypothesis

Gaia hypothesis Scientific theory interrelating the Earth's many and varied processes – chemical, physical, and biological. Popular in the 1970s, when it was proposed by James Lovelock, it showed the Earth as a single, living organism.

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Gaia Hypothesis

Gaia Hypothesis

Evidence in support of a Gaian Earth

Resources

Gaia, the Earth conceived as a supernatural entity, 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. In science, the Gaia hypothesis is a recent and 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 experimentationthere 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.

Evidence in support of a Gaian Earth

One supporting line of reasoning for the Gaia hypothesis concerns the presence of oxygen in Earths 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 pho-tosynthetic 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 Earths 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 nonliving 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 Earths 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 Earths 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 planets 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, Earths 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 homeo-static 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 Earths 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 Earths environments and ecosystems.

See also Biosphere; Chemical evolution; Ecological pyramids; Ecosystem; Homeostasis; Origin of life.

Resources

BOOKS

Lovelock, James, et al. The Revenge of Gaia: Earths Climate Crisis and the Fate of Humanity. New York: Basic Books, 2006.

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

Torres, Pedro Ruiz, et al. Scientists Debate Gaia: The Next Century. Cambridge, MA: MIT Press, 2004.

PERIODICALS

Lovelock, James. Gaia: The Living Earth. Nature. 426 (2003): 769-770.

Bill Freedman

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Gaia Hypothesis

Gaia hypothesis


The Gaia hypothesis was developed by British biochemist James Lovelock, and it incorporates two older ideas. First, the idea implicit in the ancient Greek term Gaia, that the earth is the mother of all life, the source of sustenance for all living beings, including humans. Second, the idea that life on earth and many of earth's physical characteristics have coevolved, changing each other reciprocally as the generations and centuries pass.

Lovelock's theory contradicts conventional wisdom, which holds "that life adapted to the planetary conditions as it and they evolved their separate ways." The Gaia hypothesis is a startling break with tradition for many, although ecologists have been teaching the coevolution of organisms and habitat for at least several decades, albeit more often on a local than a global scale.

The hypothesis also states that Gaia will persevere no matter what humans do. This is undoubtedly true, but the question remains: in what form, and with how much diversity? If humans don't change the nature and scale of some of their activities, the earth could change in ways that people may find undesirableloss of biodiversity , more "weed" species , increased desertification , etc.

Many people, including Lovelock, take the Gaia hypothesis a step further and call the earth itself a living being, a long-discredited organismic analogy. Recently a respected environmental science textbook defined the Gaia hypothesis as a "proposal that Earth is alive and can be considered a system that operates and changes by feedbacks of information between its living and nonliving components." Similar sentences can be found quite commonly, even in the scholarly literature, but upon closer examination they are not persuasive. A furnace operates via a positive and negative feedback systemdoes that imply it is alive? Of course not. The important message in Lovelock's hypothesis is that the health of the earth and the health of its inhabitants are inextricably intertwined.

See also Balance of nature; Biological community; Biotic community; Ecology; Ecosystem; Environment; Environmentalism; Evolution; Nature; Sustainable biosphere

[Gerald L. Young ]


RESOURCES

BOOKS

Schneider, S. H., and P. J. Boston, eds. Scientists on Gaia. Cambridge: MIT Press, 1991.

Joseph, L. E. Gaia: The Growth of an Idea. New York: St. Martin's Press, 1990.

Lovelock, J. E. Gaia: A New Look at Life on Earth. Oxford: Oxford University Press, 1979.

. The Ages of Gaia: A Biography of Our Living Earth. New York: Norton, 1988.

PERIODICALS

Lyman, F. "What Gaia Hath Wrought: The Story of a Scientific Controversy." Technology Review 92 (July 1989): 5461.

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Gaia Hypothesis

Gaia Hypothesis

Introduction

The term Gaia hypothesis is based on the Greek word meaning land or earth, and the name of the Greek goddess. The Gaia hypothesis contends that all constituents of Earth, living and nonliving, are part of an interconnected system (the biosphere), and that every living thing can affect Earth’s environment.

When Gaia is operating efficiently, according to the hypothesis proposed by British scientist James Lovelock with great collaborative help from American biologist Lynn Margulis, the net effect of all living things on the environment is beneficial and sustains the environment, which makes continued life possible.

The Gaia hypothesis has been interpreted by some as implying that Earth itself is an organism. Rather, Lovelock has maintained, Earth’s atmosphere can be more accurately viewed as a beehive—something constructed from a biological basis, which is designed to support an environment, but which is not itself alive.

Whether the Gaia hypothesis is correct will likely never be proven or refuted. Yet, the hypothesis has been and remains valuable for its proposal that a properly functioning Earth is in homeostasis—that processes of an organism can adjust to maintain the organism equilibrium.

Global warming may be demonstrating that changing processes of Earth can disrupt the equilibrium. According to the 2007 report of the Intergovernmental Panel on Climate Change (IPCC), human-activities such as the production of carbon dioxide (CO2) are driving the detrimental warming of the atmosphere.

Historical Background and Scientific Foundations

The early form of the Gaia hypothesis proposed by James Lovelock was prompted by his affiliation with the U.S. National Aeronautics and Space Administration (NASA). In the 1960s, Lovelock, a chemist and physician by training, was involved in a NASA project to design instrumentation that would be part of robotic payloads sent on explorations of the planet Mars. The intent of the instruments was to examine Martian samples for chemical indications of life.

Since life on other planets could be different from that on Earth, Lovelock needed to ponder how to detect the variety of life that might be possible. Two constants that were identified for any form of life were the need for energy and the production of waste. Lovelock reasoned that, similar to life on Earth, the atmosphere would always be used as an energy source and for waste disposal, providing potentially detectable chemical signals of life.

To properly design instruments that could function on the surface of Mars or even from the surface of Earth, it was necessary to know the composition of the Martian atmosphere. Comparison with Earth’s revealed differences. Mars was incapable of supporting life similar to that on Earth and had reached an equilibrium—compounds were not being added or removed. In contrast, Earth’s atmosphere contained gases that reacted with one another and yet the composition of the atmosphere remained constant, indicating that the atmosphere was being replenished. The basis of the replenishment, reasoned Lovelock, was the life on the planet.

The idea that the planet and its variety of life were interconnected prompted the suggestion of the name Gaia from Lovelock’s neighbor, novelist William Goldin.

In 1979, Lovelock wrote the book Gaia: A New Look at Life on Earth. In it, he summarized the Gaia hypothesis: “the physical and chemical condition of the surface of 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.”

In the 1980s, Lovelock began a collaboration with the American microbiologist Lynn Margulis, who is well known in her own right as the proponent of the now-proven theory that cell components such as mitochondria originated from bacteria. Margulis was instrumental in refining the Gaia hypothesis by clarifying the possible mechanisms by which Earth’s atmosphere could be regulated by life. Having tangible mechanisms that supported the theory made the Gaia hypothesis more powerful and a more seriously considered scientific theory.

One outcome of the collaboration with Margulis and others was the Daisyworld model. The model, which envisioned a planet containing only a light-colored species of daisy that tended to reflect sunlight and a dark-colored species of daisy that tended to absorb light, was used to show that self-regulation of the atmosphere by the growing flowers was possible. The model also pointed out that the atmospheric regulation is not intentional, but results inevitably from the survival and growth of life on the planet.

Several aspects of Earth’s environment support the implication of the Gaia hypothesis that the planet operates in homeostasis. One aspect is the steadiness of the planet’s temperature. Although microbial life can exist at temperature extremes, from below the freezing point of liquid water to above the boiling temperature of water, the majority of life on Earth exists between 60 and 100°F (15.5 and 37.8°C). The average temperature of much of the planet’s surface has remained in this range for hundreds of millions of years in spite of great changes in the composition of the atmosphere and has increased from the sun. Shifting of the planet’s temperature outside of the 60-100°F range would have ended almost all life.

Another supporting aspect is the constant level of salt in the oceans. The concentration of salt (sodium) in the global ocean is approximately 3.4%. Geological evidence is consistent with this concentration having remained fairly constant, despite the continual addition of salt washing from the land to the sea. Even a marginally higher salt level would affect the type of life in the sea, and a salt concentration of 6% or more would eliminate much of the microbial life in the sea, since their cell walls would rupture. Because microbes are an important basis of the ocean’s food chain, most of the fish and mammals in the ocean would be unable to survive.

The Gaia hypothesis remains contentious. Critics still argue that evolution selected for life that could exist in the conditions present, and that other atmospheric conditions would have selected for the development of different forms of life. Thus, the atmosphere determines life and not the reverse.

WORDS TO KNOW

BIOMASS: The sum total of living and once-living matter contained within a given geographic area; or, organic matter that can be converted to fuel and is regarded as a potential energy source.

ECOLOGY: The branch of science dealing with the interrelationship of organisms and their environments.

GLOBAL WARMING: Warming of Earth’s atmosphere that results from an increase in the concentration of gases that store heat, such as carbon dioxide (CO2).

GREENHOUSE GAS: A gas that accumulates in the atmosphere and absorbs infrared radiation, contributing to the greenhouse effect.

These opposing views of Earth will likely always be debated. However, what is clear from the atmospheric record through Earth’s history is that changes in one or several aspects of the environment have had a more substantial effect on the atmosphere and global climate.

One example is the series of ice ages that have occurred beginning almost three billion years ago and ending only 10,000 years ago. Examinations of rocks, fossils, and the chemistry of glacial ice have revealed that the climate of northern regions of Earth has warmed and cooled at least four times. The causes of the ice ages are debatable, but the consensus among climatologists is that they reflect changes in the composition of the atmosphere, the orbit of Earth around the sun, and catastrophes including meteorite impacts and huge volcanic eruptions that diminished the amount of sunlight reaching the surface.

A second example is the influence of human activities. According to the 2007 IPCC report, the evidence for the influence of human activities on Earth’s climate since the growth of industrialization in the mid-nineteenth century is unequivocal.

Impacts and Issues

From its beginning, the Gaia hypothesis has created a great deal of interest and has prompted much debate. Some of the criticism is directed at Lovelock’s early writing, which was interpreted as implying that life has a predetermined purpose. In the decades since the hypothesis was first proposed, Lovelock has strived to affirm that atmospheric regulation by life is not purposeful, as exemplified by the Daisyworld model. Still, the idea that the planet’s life can act in a coordinated way to regulate climate remains contentious.

Despite this continuing controversy, the Gaia hypothesis has become useful in understanding how climate change and environmental degradation might be addressed, since these are linked to human activities. For example, climate change strategies such as the reduction of the production and emission of greenhouse gases such as CO2 and fossil fuel exhaust, and reforestation to provide more opportunities to trap carbon from escaping to the atmosphere are based on the knowledge that the production of certain compounds changes the atmosphere, and that the changes are to some extent reversible.

With the publication of the 2007 IPCC report, the influence of human activities to global warming has become accepted by many people. The significance of these changes remains unclear. Modeling studies indicate that depending on the location, the climate change that is inevitable for the next century could be beneficial (longer growing season), merely inconvenient (cooler and damper winters), or serious (increased flooding, coastline loss due to rising sea levels, or increased transmission of insect-borne diseases in warming regions).

See Also Climate Change; Ecosystems; Global Warming

BIBLIOGRAPHY

Books

Jang, Hwee-Yong. Gaia Project: 2012; The Earth’s Coming Great Changes. Woodbury: Llewellyn Publications, 2007.

Kump, Lee R., James F. Kasting, and Robert G. Crane. The Earth System. New York: Prentice-Hall, 2003.

Lovelock, James. The Revenge of Gaia: Earth’s Climate Crisis and the Fate of Humanity. New York: Basic Books, 2006.

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Gaia Hypothesis

Gaia hypothesis

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.


Evidence in support of a Gaian Earth

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.

See also Biosphere; Chemical evolution; Ecological pyramids; Ecosystem; Homeostasis; Origin of life.


Resources

books

Lovelock, J. The Ages of Gaia: A Bibliography of Our LivingEarth. 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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Gaia Hypothesis

Gaia Hypothesis


The Gaia (pronounced guy-ah) hypothesis is the idea that Earth is a living organism and can regulate its own environment. This idea argues that Earth is able to maintain conditions that are favorable for life to survive on it, and that it is the living things on Earth that give the planet this ability.

The idea that Earth and its atmosphere are some sort of "superorganism" was actually first proposed by the Scottish geologist (a person specializing in the study of the Earth) James Hutton (1726–1797), although this was not one of his more accepted and popular ideas. As a result, no one really pursued this notion until some two hundred years later, when the English chemist, James Lovelock (1919– ), put forward a similar idea in his 1979 book, Gaia: A New Look at Life on Earth. Gaia is the name of the Greek goddess of the Earth, and in modern times has come to symbolize "Earth Mother" or "Living Earth." In this book, Love-lock proposed that Earth's biosphere (all the parts of Earth that make up the living world) acts as a single living system that if left alone, can regulate itself.

Lovelock arrived at this hypothesis (theory) by studying Earth's neighboring planets, Mars and Venus. Suggesting that chemistry and physics seemed to argue that these barren and hostile planets should have an atmosphere just like that of Earth, Lovelock stated that Earth's atmosphere is different because it has life on it. Both Mars and Venus have an atmosphere with about 95 percent carbon dioxide (gas), while Earth's is about 79 percent nitrogen (gas) and 21 percent oxygen. He explained this dramatic difference by saying that Earth's atmosphere was probably very much like that of its neighbors at first, and that it was a world with hardly any life on it. The only form that did exist was what many consider to be the first forms of life—anaerobic bacteria that lived in the ocean. This type of bacteria cannot live in an oxygen environment, and its only job is to convert nitrates to nitrogen gas. This accounts for the beginnings of a nitrogen buildup in Earth's atmosphere.

The oxygen essential to life as we know it did not start to accumulate in the atmosphere until organisms that were capable of photosynthesis evolved. Photosynthesis is the process that some algae and all plants use to chemically convert the Sun's light into food. This process uses carbon dioxide and water to make energy-packed glucose (sugar), and it gives off oxygen as a by-product. These very first photosynthesizers were a blue-green algae called cyanobacteria that live in water. Eventually, these organisms produced so much oxygen that they put the older anaerobic bacteria out of business. As a result, the only place that anaerobic bacteria could survive was on the deep-sea floor (as well as in heavily water-logged soil and in our own intestines). Lovelock's basic point was that the existence of life (bacteria) eventually made the Earth a very different place by giving it an atmosphere.

Lovelock eventually went beyond the notion that life can change the environment, and proposed the controversial Gaia hypothesis. He said that Gaia is the "living Earth" and that Earth itself should be viewed as being alive. Like any living thing, Earth always strives to maintain homeostasis (constant, or stable, conditions) for itself. In the Gaia hypothesis, it is the presence and activities of life that keeps Earth in homeostasis and allows it to regulate its systems and maintain steady-state conditions.

Lovelock claims that it is the living things on Earth that provide it with the feedback so necessary to regulating something. (A feedback mechanism is something that can detect and reverse any unwanted changes.) Lovelock offers several examples of cycles in the environment that work to keep things on an even keel. He also warns that since Earth has the capacity to keep things in a stable range, human tampering with Earth's environmental balancing mechanisms places everyone at great risk. While environmentalists insist that human activity is upsetting Earth's ability to regulate itself, others argue that Earth can continue to survive very well no matter what humans do exactly because of its builtin adaptability. An important aspect of the Gaia hypothesis is that it offers scientists a new model to consider. It places great emphasis on what promises to be the planet's greatest future problem—the quality of Earth's environment.

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