Gaia hypothesis

Gaia hypothesis

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The Gaia hypothesis, also known as Gaia theory or Gaia principle, proposes that all organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s and their inorganic
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 surroundings on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 are closely integrated to form a single and self-regulating complex system
Complex system
A complex system is a system composed of interconnected parts that as a whole exhibit one or more properties not obvious from the properties of the individual parts....

, maintaining the conditions for life
Life
Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...

 on the planet.

The scientific investigation of the Gaia hypothesis focuses on observing how the biosphere
Biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...

 and the evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

 of life forms contribute to the stability of global temperature
Paleoclimatology
Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...

, ocean salinity
Paleosalinity
Paleosalinity is the salinity of the global ocean or of an ocean basin at a point in geological history.- Importance :From Bjerrum plots, it is found that a decrease in the salinity of an aqueous fluid will act to increase the value of the carbon dioxide-carbonate system equilibrium constants,...

, oxygen in the atmosphere
Geological history of oxygen
Before photosynthesis evolved, Earth's atmosphere had no free oxygen . Oxygen was first produced by photosynthetic prokaryotic organisms that emitted O2 as a waste product. These organisms lived long before the first build-up of oxygen in the atmosphere, perhaps as early as...

 and other factors of habitability
Planetary habitability
Planetary habitability is the measure of a planet's or a natural satellite's potential to sustain life. Life may develop directly on a planet or satellite or be transferred to it from another body, a theoretical process known as panspermia...

 in a preferred homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

. The Gaia hypothesis was formulated by the chemist James Lovelock
James Lovelock
James Lovelock, CH, CBE, FRS is an independent scientist, environmentalist and futurologist who lives in Devon, England. He is best known for proposing the Gaia hypothesis, which postulates that the biosphere is a self-regulating entity with the capacity to keep our planet healthy by controlling...

 and co-developed by the microbiologist
Microbiologist
A microbiologist is a scientist who works in the field of microbiology. Microbiologists study organisms called microbes. Microbes can take the form of bacteria, viruses, fungi, and protists...

 Lynn Margulis
Lynn Margulis
Lynn Margulis was an American biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst. She is best known for her theory on the origin of eukaryotic organelles, and her contributions to the endosymbiotic theory, which is now generally accepted...

 in the 1970s. Initially received with hostility by the scientific community, it is now studied in the disciplines of geophysiology
Geophysiology
Geophysiology is the study of interaction among living organisms on the Earth operating under the hypothesis that the Earth itself acts as a single living organism ....

 and Earth system science
Earth system science
Earth system science seeks to integrate various fields of academic study to understand the Earth as a system. It considers interaction between the atmosphere, hydrosphere, lithosphere , biosphere, and heliosphere....

, and some of its principles have been adopted in fields like biogeochemistry
Biogeochemistry
Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment...

 and systems ecology
Systems ecology
Systems ecology is an interdisciplinary field of ecology, taking a holistic approach to the study of ecological systems, especially ecosystems. Systems ecology can be seen as an application of general systems theory to ecology. Central to the systems ecology approach is the idea that an ecosystem...

. This ecological
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

 hypothesis has also inspired analogies and various interpretations in social sciences, politics, and religion under a vague philosophy
Gaia philosophy
Gaia philosophy is a broadly inclusive term for related concepts that living organisms on a planet will affect the nature of their environment in order to make the environment more suitable for life. This set of theories holds that all organisms on an extraterrestrial life-giving planet regulate...

 and movement
Gaia Movement
The Gaia Movement is an international network of individuals and groups that share a concern for living more sustainably on the earth. The term "Gaia" comes from Greek mythology, where it is the name of the Goddess of the Earth...

.

Overview


The Gaia theory posits that the Earth is a self-regulating complex system
Complex system
A complex system is a system composed of interconnected parts that as a whole exhibit one or more properties not obvious from the properties of the individual parts....

 involving the biosphere
Biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...

, the atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

, the hydrosphere
Hydrosphere
A hydrosphere in physical geography describes the combined mass of water found on, under, and over the surface of a planet....

s and the pedosphere
Pedosphere
The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The sum total of all the organisms, soils, water and air is termed as the "pedosphere"...

, tightly coupled as an evolving system. The theory sustains that this system as a whole, called Gaia, seeks a physical and chemical environment optimal for contemporary life.

Gaia evolves through a cybernetic feedback
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...

 system operated unconsciously by the biota
Biota (ecology)
Biota are the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales. The biota of the Earth lives in the biosphere.-See...

, leading to broad stabilization of the conditions of habitability in a full homeostasis. Many processes in the Earth's surface essential for the conditions of life depend on the interaction of living forms, especially microorganisms, with inorganic elements. These processes establish a global control system that regulates Earth's surface temperature, atmosphere composition and ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

, powered by the global thermodynamic desequilibrium state of the Earth system.

The existence of a planetary homeostasis influenced by living forms had been observed previously in the field of biogeochemistry
Biogeochemistry
Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment...

, and it is being investigated also in other fields like Earth system science
Earth system science
Earth system science seeks to integrate various fields of academic study to understand the Earth as a system. It considers interaction between the atmosphere, hydrosphere, lithosphere , biosphere, and heliosphere....

. The originality of the Gaia theory relies on the assessment that such homeostatic balance is actively pursued with the goal of keeping the optimal conditions for life, even when terrestrial or external events menace them.

Regulation of the salinity in the oceans


Ocean salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

 has been constant at about 3.4% for a very long time.
Salinity stability in oceanic environments is important as most cells require a rather constant salinity and do not generally tolerate values above 5%. Ocean salinity constancy was a long-standing mystery, because river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 salts should have raised the ocean salinity much higher than observed. Recently it was suggested that salinity may also be strongly influenced by seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...

 circulation through hot basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

ic rocks, and emerging as hot water vents on mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...

s. However, the composition of seawater is far from equilibrium, and it is difficult to explain this fact without the influence of organic processes. One suggested explanation lies in the formation of salt plains throughout Earth's history. It is hypothesised that these are created by bacteria colonies that fix ions and heavy metals during life processes.

Regulation of oxygen in the atmosphere




The atmospheric composition remains fairly constant providing the ideal conditions for contemporary life. All the atmospheric gases other than noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

es present in the atmosphere are either made by organisms or processed by them. The Gaia theory states that the Earth's atmospheric composition is kept at a dynamically steady state by the presence of life.

The stability of the atmosphere in Earth is not a consequence of chemical equilibrium
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

 like in planets without life. Oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 is the second most reactive element after fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...

, and should combine with gases and minerals of the Earth's atmosphere and crust. Traces of methane
Atmospheric methane
Atmospheric methane levels are of interest due to its impact on climate change. Atmospheric methane is one of the most potent and influential greenhouse gases on Earth. The 100-year global warming potential of methane is 25, i.e...

 (at an amount of 100,000 tonnes produced per annum) should not exist, as methane is combustible in an oxygen atmosphere.

Dry air in the atmosphere of Earth contains roughly (by volume) 78.09% nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, 20.95% oxygen, 0.93% argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

, 0.039% carbon dioxide
Carbon dioxide in the Earth's atmosphere
The concentration of carbon dioxide in Earth's atmosphere is approximately 392 ppm by volume and rose by 2.0 ppm/yr during 2000–2009. 40 years earlier, the rise was only 0.9 ppm/yr, showing not only increasing concentrations, but also a rapid acceleration of concentrations...

, and small amounts of other gases including methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

. While air content and atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 varies at different layers, air suitable for the survival of terrestrial plant
Terrestrial plant
A terrestrial plant is one that grows on land. Other types of plants are aquatic , epiphytic , lithophytes and aerial ....

s and terrestrial animal
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

s is currently known only to be found in Earth's troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

 and artificial atmospheres. Oxygen is a crucial element for the life of organisms, who require it at stable concentrations.

Regulation of the global surface temperature



Since life started on Earth, the energy provided by the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 has increased by 25% to 30%; however, the surface temperature of the planet has remained within the levels of habitability, reaching quite regular low and high margins. Lovelock has also hypothesised that methanogens produced elevated levels of methane in the early atmosphere, giving a view similar to that found in petrochemical smog, similar in some respects to the atmosphere on Titan. This, he suggests tended to screen out ultraviolet until the formation of the ozone screen, maintaining a degree of homeostasis. The Snowball Earth
Snowball Earth
The Snowball Earth hypothesis posits that the Earth's surface became entirely or nearly entirely frozen at least once, some time earlier than 650 Ma . Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical...

 research, as a result of "oxygen shocks" and reduced methane levels, that led during the Huronian
Huronian
The Huronian glaciation extended from 2400 Mya to 2100 Mya, during the Siderian and Rhyacian periods of the Paleoproterozoic era, triggered by the oxygen catastrophe, which oxidised the atmospheric methane...

, Sturtian and Marinoan/Varanger
Cryogenian
The Cryogenian is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran...

 Ice Ages the world to very nearly become a solid "snowball" contradicts the Gaia hypothesis somewhat, although the ending of these Cryogenian
Cryogenian
The Cryogenian is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran...

 periods through bio-geophysiological processes accords well with Lovelock's theory.

Processing of the greenhouse gas CO2, explained below, plays a critical role in the maintenance of the Earth temperature within the limits of habitability.

The CLAW hypothesis
CLAW hypothesis
The CLAW hypothesis proposes a feedback loop that operates between ocean ecosystems and the Earth's climate. The hypothesis specifically proposes that particular phytoplankton that produce dimethyl sulfide are responsive to variations in climate forcing, and that these responses lead to a negative...

, inspired by the Gaia theory, proposes a feedback loop
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...

 that operates between ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

s and the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

. The hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...

 specifically proposes that particular phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

 that produce dimethyl sulfide
Dimethyl sulfide
Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...

 are responsive to variations in climate forcing, and that these responses lead to a negative feedback loop
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...

 that acts to stabilise the temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 of the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

.

Currently this Gaian homeostatic balance is being pushed by the increase of human population and the impact of their activities to the environment. The multiplication of greenhouse gases may cause a turn of Gaia's negative feedback
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...

s into homeostatic
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

 positive feedback
Positive feedback
Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...

. According to Lovelock, this could bring an accelerated global warming and mass human mortality.

Daisyworld simulations


James Lovelock and Andrew Watson
Andrew Watson (scientist)
Andrew James Watson FRS is a British marine and atmospheric scientist and an expert in processes affecting atmospheric carbon dioxide and oxygen concentrations...

 developed the mathematical model Daisyworld
Daisyworld
Daisyworld, a computer simulation, is a hypothetical world orbiting a star whose radiant energy is slowly increasing. It is meant to mimic important elements of the Earth-Sun system, and was introduced by James Lovelock and Andrew Watson in a paper published in 1983 to illustrate the plausibility...

, that shows how temperature regulation can arise from organisms interacting with their environment. The purpose of the model is to demonstrate that feedback mechanisms can evolve from the actions or activities of self-interested organisms, rather than through classic group selection
Group selection
In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....

 mechanisms.

Daisyworld examines the energy budget
Earth's energy budget
The Earth can be considered as a physical system with an energy budget that includes all gains of incoming energy and all losses of outgoing energy. The planet is approximately in equilibrium, so the sum of the gains is approximately equal to the sum of the losses.Note on accompanying images:...

 of a planet populated by two different types of plants, black daisies and white daisies. The colour of the daisies influences the albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 of the planet such that black daisies absorb light and warm the planet, while white daisies reflect light and cool the planet. Competition between the daisies (based on temperature-effects on growth rates) leads to a balance of populations that tends to favour a planetary temperature close to the optimum for daisy growth.

Biodiversity and stability of ecosystems


The importance of the large number of species in an ecosystem, led to two sets of views about the role played by biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

 in the stability of ecosystems in Gaia theory. In one school of thought labelled the "species redundancy" hypothesis, proposed by Australian ecologist Brian Walker
Brian Walker (ecologist)
Brian H. Walker is a scientist specialized in ecological sustainability and resilience in socio-ecological systems.-Education and academic career:...

, most species are seen as having little contribution overall in the stability, comparable to the passengers in an aeroplane who play little role in its successful flight. The hypothesis leads to the conclusion that only a few key species are necessary for a healthy ecosystem. The "rivet-popper" hypothesis put forth by Paul R. Ehrlich
Paul R. Ehrlich
Paul Ralph Ehrlich is an American biologist and educator who is the Bing Professor of Population Studies in the department of Biological Sciences at Stanford University and president of Stanford's Center for Conservation Biology. By training he is an entomologist specializing in Lepidoptera , but...

 and his wife Anne H. Ehrlich
Anne H. Ehrlich
Anne Howland Ehrlich is the co-author of several books on overpopulation and ecology with her husband, Stanford University professor Paul R...

, compares each species forming part of an ecosystem as a rivet on the aeroplane (represented by the ecosystem). The progressive loss of species mirrors the progressive loss of rivets from the plane, weakening it till it is no longer sustainable and crashes.

Later extensions of the Daisyworld simulation which included rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...

s, fox
Fox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...

es and other species, led to a surprising finding that the larger the number of species, the greater the improving effects on the entire planet (i.e., the temperature regulation was improved). It also showed that the system was robust and stable even when perturbed. Daisyworld simulations where environmental changes were stable gradually became less diverse over time; in contrast gentle perturbations led to bursts of species richness. These findings lent support to the idea that biodiversity is valuable.

This finding was later proved in a eleven-year old study of the factors species composition, dynamics and diversity in successional and native grasslands in Minnesota by David Tilman and John A. Downing wherein they discovered that "primary productivity in more diverse plant communities is more resistant to, and recovers more fully from, a major drought." They go on to add "Our results support the diversity stability hypothesis but not the alternative hypothesis that most species are functionally redundant."

Processing of CO2



Gaia scientists see the participation of living organisms in the Carbon cycle
Carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...

 as one of the complex processes that maintain conditions suitable for life. The only significant natural source of atmospheric carbon dioxide (CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

) is volcanic activity, while the only significant removal is through the precipitation of carbonate rocks. Carbon precipitation, solution and fixation
Carbon fixation
In biology, carbon fixation is the reduction of carbon dioxide to organic compounds by living organisms. The obvious example is photosynthesis. Carbon fixation requires both a source of energy such as sunlight, and an electron donor such as water. All life depends on fixed carbon. Organisms that...

 are influenced by the bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 and plant roots in soils, where they improve gaseous circulation, or in coral reefs, where calcium carbonate is deposited as a solid on the sea floor. Calcium carbonate is used by living organisms to manufacture carbonaceous tests and shells. Once dead, the living organisms' shells fall to the bottom of the oceans where they generate deposits of chalk and limestone.

One of these organisms is Emiliania huxleyi
Emiliania huxleyi
Emiliania huxleyi, often abbreviated "EHUX", is a species of coccolithophore with a global distribution from the tropics to subarctic waters. It is one of thousands of different photosynthetic plankton that freely drift in the euphotic zone of the ocean, forming the basis of virtually all marine...

, an abundant coccolithophore
Coccolithophore
Coccolithophores are single-celled algae, protists, and phytoplankton belonging to the division of haptophytes. They are distinguished by special calcium carbonate plates of uncertain function called coccoliths , which are important microfossils...

 algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 which also has a role in the formation of clouds. CO2 excess is 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 necessary for terrestrial plants. Lately the atmospheric CO2 concentration has increased and there is some evidence that concentrations of ocean algal bloom
Algal bloom
An algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...

s are also increasing.

Lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...

 and other organisms accelerate the weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...

 of rocks in the surface, while the decomposition of rocks also happens faster in the soil, thanks to the activity of roots, fungi, bacteria and subterranean animals. The flow of carbon dioxide from the atmosphere to the soil is therefore regulated with the help of living beings. When CO2 levels rise in the atmosphere the temperature increases and plants grow. This growth brings higher consumption of CO2 by the plants, who process it into the soil, removing it from the atmosphere.

From hypothesis to theory


James Lovelock called his first proposal the Gaia hypothesis. but the term established nowadays is Gaia theory.
Lovelock explains that the initial formulation was based on observation, but still lacked a scientific explanation.
The Gaia Hypothesis has since been supported by a number of scientific experiments and provided a number of useful predictions, and hence is properly referred to as the Gaia theory. In fact, wider research proved the original hypothesis wrong, in the sense that it is not life alone but the whole Earth system that does the regulating.

In 2001, a thousand scientists at the European Geophysical Union meeting signed the Declaration of Amsterdam, starting with the statement "The Earth System behaves as a single, self-regulating system with physical, chemical, biological, and human components." In 2005 the Ecological Society of America
Ecological Society of America
The Ecological Society of America is a professional organization of ecological scientists. Based in the United States, ESA publishes a suite of publications, from peer-reviewed journals to newsletters, fact sheets and teaching resources. It holds an annual meeting at different locations in the...

 invited Lovelock to join their Fellowship, and in 2006 the Geological Society of London
Geological Society of London
The Geological Society of London is a learned society based in the United Kingdom with the aim of "investigating the mineral structure of the Earth"...

 awarded Lovelock with the Wollaston Medal
Wollaston Medal
The Wollaston Medal is a scientific award for geology, the highest award granted by the Geological Society of London.The medal is named after William Hyde Wollaston, and was first awarded in 1831...

 for his work on the Gaia theory.

Nowadays the Gaia theory is being researched further, mainly in the multidisciplinary fields of Earth system science
Earth system science
Earth system science seeks to integrate various fields of academic study to understand the Earth as a system. It considers interaction between the atmosphere, hydrosphere, lithosphere , biosphere, and heliosphere....

 and biogeochemistry
Biogeochemistry
Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment...

. It is also being applied increasingly to studies of climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

.
Predictions, tests and results relevant to the Gaia theory. Source: James Lovelock
Prediction Test Result
Mars is lifeless (1988) Atmospheric compositional evidence shows lack of disequilibrium Strong confirmation, Viking mission 1975
Biogenic gases transfer elements from ocean to land (1971) Search for oceanic sources of dimethyl sulphide and methyl iodide Found 1973
Climate regulation through biologically enhanced rock weathering (1973) Analysis of ice-core data linking temperature and CO2 abundance Confirmed 2008, by Zeebe and Caldeira
Gaia is aged and is not far from the end of its development (1982) Calculation based on generally accepted solar evolution Generally accepted
Climate regulation through cloud albedo control linked to algal gas emissions (1987) Many tests have been made but the excess of pollution interferes Probable for southern hemisphere
Oxygen has not varied by more than 5 percent from 21 percent for the past 200 million years (1974) Ice-core and sedimentary analysis Confirmed for up to 1 million years ago
Boreal and tropical forests are part of global climate regulation Models and direct observation Generally accepted
Biodiversity a necessary part of climate regulation By models but not yet in the natural ecosystems Jury still out
The current interglacial is an example of systems failure in a physiological sense (1994) By models only Undecided
The biological transfer of selenium from the ocean to the land as dimethyl selenide Direct measurements Confirmed 2000, Liss

Criticism


After initially being largely ignored by most scientists, (from 1969 until 1977), thereafter for a period, the initial Gaia hypothesis was ridiculed by a number of scientists, such as Ford Doolittle
Ford Doolittle
Dr. W. Ford Doolittle is a biochemist., he is a professor at Dalhousie University in Halifax, Nova Scotia. He received his BA in Biochemical Sciences from Harvard University in 1963 and his PhD from Stanford University in 1967.Since joining the biochemistry department at Dalhousie in 1971, Dr...

, Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...

 and Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....

. Lovelock has said that by naming his theory after a Greek goddess, championed by many non scientists, the Gaia hypothesis was derided as some kind of neo-Pagan New Age
New Age
The New Age movement is a Western spiritual movement that developed in the second half of the 20th century. Its central precepts have been described as "drawing on both Eastern and Western spiritual and metaphysical traditions and then infusing them with influences from self-help and motivational...

 religion
Religion
Religion is a collection of cultural systems, belief systems, and worldviews that establishes symbols that relate humanity to spirituality and, sometimes, to moral values. Many religions have narratives, symbols, traditions and sacred histories that are intended to give meaning to life or to...

. Many scientists in particular also criticised the approach taken in his popular book "Gaia, a New look at Life on Earth" for being teleological
Teleology
A teleology is any philosophical account which holds that final causes exist in nature, meaning that design and purpose analogous to that found in human actions are inherent also in the rest of nature. The word comes from the Greek τέλος, telos; root: τελε-, "end, purpose...

; a belief that all things have a predetermined purpose. Responding to this assertion in 1990, Lovelock stated "Nowhere in our writings do we express the idea that planetary self-regulation is purposeful, or involves foresight or planning by the biota
Biota (ecology)
Biota are the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales. The biota of the Earth lives in the biosphere.-See...

."

Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....

 criticised Gaia as merely a metaphorical description of Earth processes. He wanted to know the actual mechanisms by which self-regulating homeostasis was regulated. David Abram argued that Gould was unaware that mechanism was itself only metaphorical. Lovelock argues that no one mechanism is responsible, that the connections between the various known mechanisms may never be known, that this is accepted in other fields of biology and ecology as a matter of course, and that specific hostility is reserved for his own theory for other reasons.

Aside from clarifying his language and understanding of what is meant by a life form, Lovelock himself ascribes most of the criticism to a lack of understanding of non-linear mathematics by his critics, and a linearizing form of greedy reductionism
Greedy reductionism
Greedy reductionism is a term coined by Daniel Dennett, in his 1995 book Darwin's Dangerous Idea, to refer to a kind of erroneous reductionism...

 in which all events have to be immediately ascribed to specific causes before the fact. He notes also that his theory suggests experiments in many different fields, but few of them in biology, which most of his critics are trained in. "I'm a general practitioner in a world where there's nothing but specialists... science in the last two centuries has tended to be ever-dividing" and often rivalrous, especially for funding, which Lovelock describes as overly abundant and overly focused on institutions rather than original thought. He points out that Richard Feynman
Richard Feynman
Richard Phillips Feynman was an American physicist known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics and the physics of the superfluidity of supercooled liquid helium, as well as in particle physics...

 not only shared this opinion (coining the term cargo cult science
Cargo cult science
Cargo cult science refers to practices that have the semblance of being scientific, but are missing "a kind of scientific integrity, a principle of scientific thought that corresponds to a kind of utter honesty". The term was first used by the physicist Richard Feynman during his commencement...

) but also accepted a lack of general cause and effect explanation as an inevitable phase in a theory's development, and believed that some self-regulating phenomena may not be explainable at all mathematically.

The Earth alive


The concept of a living Earth has caused a lot of controversy, partly due to the different attributes and connotations given to this hypothetical life, partly because of the straightforward language used by Lovelock in his writings. For instance, evolutionary biologists such as the late palaeontologist Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....

 and the ethologist Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...

 attacked his statement in the first paragraph of his book (1979), that "the quest for Gaia is an attempt to find the largest living creature on Earth." James Lovelock sustains that agreeing on a rational answer is not possible because science has not yet formulated a full definition of life.

A basic criterion of the empirical definition of a life-form is its birth out of natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

 and its ability to replicate and pass on its genetic information to a succeeding generation. Dawkins stressed that, consequently, an argument against the idea that Gaia as a living organism is the fact that the planet is not the offspring of any parents and is unable to reproduce.

Lovelock, however, defines life as a self-preserving, self-similar system of feedback loops like Humberto Maturana
Humberto Maturana
Humberto Maturana is a Chilean biologist and philosopher. He is considered a member of the second wave of cybernetics, known for developing a theory of autopoiesis about the nature of reflexive feedback control in living systems.- Biography :After completing secondary school at the Liceo Manuel de...

's autopoiesis; as a self-similar system, life could be a cell as well as an organ embedded into a larger organism as well as an individual in a larger inter-dependent social context. The biggest context of interacting inter-dependent living entities is the Earth. The problematic empirical definition is getting "fuzzy on the edges": Why are highly specialized bacteria, such as E. coli, unable to thrive outside their habitat considered "life", while mitochondria, which have evolved independently from the rest of the cell, are not?

William Irwin Thompson
William Irwin Thompson
William Irwin Thompson is known primarily as a social philosopher and cultural critic, but he has also been writing and publishing poetry throughout his career and received the Oslo International Poetry Festival Award in 1986. He describes his writing and speaking style as "mind-jazz on ancient...

 suggests that the Chilean biologist Humberto Maturana
Humberto Maturana
Humberto Maturana is a Chilean biologist and philosopher. He is considered a member of the second wave of cybernetics, known for developing a theory of autopoiesis about the nature of reflexive feedback control in living systems.- Biography :After completing secondary school at the Liceo Manuel de...

 and James Lovelock, with the deductive definition of autopoiesis, have provided an explanation for the phenomenon of life. Reproduction becomes optional: bee swarms reproduce, while the biosphere has no need to. Lovelock himself states in the original Gaia book that even that is not true; given the possibilities, the biosphere may multiply in the future by colonizing other planets, as humankind may be the primer by which Gaia will reproduce. Humanity's exploration of space, its interest in colonizing and even terraforming other planets, lends some plausibility to the idea that Gaia might in effect be able to reproduce.

Natural selection and evolution


Lovelock accepts a process of systemic Darwinian evolution for such biological feedback mechanisms: creatures that improve their environment for their survival do better than those that damage their environment. However, some scientists dispute the existence of such mechanisms. In 1981, W. Ford Doolittle
Ford Doolittle
Dr. W. Ford Doolittle is a biochemist., he is a professor at Dalhousie University in Halifax, Nova Scotia. He received his BA in Biochemical Sciences from Harvard University in 1963 and his PhD from Stanford University in 1967.Since joining the biochemistry department at Dalhousie in 1971, Dr...

, in the CoEvolution Quarterly
CoEvolution Quarterly
CoEvolution Quarterly is a descendant of Stewart Brand's Whole Earth Catalog. It eventually became the Whole Earth Review.-History:...

article "Is Nature Motherly" argued that nothing in the genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 of individual organisms could provide the feedback mechanisms Gaia theory proposed, and therefore the Gaia hypothesis was an unscientific theory of a maternal type without any explanatory mechanism. In Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...

' 1982 book, The Extended Phenotype
The Extended Phenotype
The Extended Phenotype is a biological concept introduced by Richard Dawkins in a 1982 book with the same title. The main idea is that phenotype should not be limited to biological processes such as protein biosynthesis or tissue growth, but extended to include all effects that a gene has on its...

, he argued that organisms could not act in concert as this would require foresight and planning from them. Like Doolittle he rejected the possibility that feedback loops could stabilize the system.

Lynn Margulis
Lynn Margulis
Lynn Margulis was an American biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst. She is best known for her theory on the origin of eukaryotic organelles, and her contributions to the endosymbiotic theory, which is now generally accepted...

, a microbiologist who collaborated with Lovelock in supporting the Gaia hypothesis, argued in 1999, that “Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...

's grand vision was not wrong, only incomplete. In accentuating the direct competition between individuals for resources as the primary selection mechanism, Darwin (and especially his followers) created the impression that the environment was simply a static arena.” She wrote that the composition of the Earth's atmosphere, hydrosphere, and lithosphere are regulated around "set points" as in homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

, but those set points change with time.

She also wrote that there is no special tendency of biospheres to preserve their current inhabitants, and certainly not to make them comfortable. According to her, the Earth is a kind of community of trust that can exist at many discrete levels of integration. All multicellular organisms do not live or die all at once: not all cells in the body die instantaneously, nor are homeostatic "set points" constant through the life of an organism.

W. D. Hamilton
W. D. Hamilton
William Donald Hamilton FRS was a British evolutionary biologist, widely recognised as one of the greatest evolutionary theorists of the 20th century....

, one of the greatest evolutionary theorists of the 20th century, called the concept of Gaia Copernican
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....

, adding that it would take another Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

 to explain how Gaian self-regulation takes place through Darwinian natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

.

Range of views


Some have found James Kirchner
James Kirchner
James W. Kirchner is professor of Earth and Planetary Science at University of California, Berkeley. His current research spans the fields of geomorphology, hydrology, environmental geochemistry, evolutionary ecology, and paleobiology...

's suggested spectrum, proposed at the First Gaia Chapman Conference, useful in suggesting that the original Gaia hypothesis could be split into a spectrum of hypotheses, ranging from the undeniable (Weak Gaia) to the radical (Strong Gaia).

Weak Gaia


At one end of this spectrum is the undeniable statement that the organisms on the Earth have 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
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

s and felled civilization
Civilization
Civilization is a sometimes controversial term that has been used in several related ways. Primarily, the term has been used to refer to the material and instrumental side of human cultures that are complex in terms of technology, science, and division of labor. Such civilizations are generally...

s (see climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

).

Weak Gaian hypotheses suggest that Gaia is co-evolutive. Co-evolution
Co-evolution
In biology, coevolution is "the change of a biological object triggered by the change of a related object." Coevolution can occur at many biological levels: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different...

 in this context has been thus defined: "Biota
Biota (ecology)
Biota are the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales. The biota of the Earth lives in the biosphere.-See...

 influence their abiotic environment, and that environment in turn influences the biota
Biota (ecology)
Biota are the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales. The biota of the Earth lives in the biosphere.-See...

 by Darwinian process
Darwinism
Darwinism is a set of movements and concepts related to ideas of transmutation of species or of evolution, including some ideas with no connection to the work of Charles Darwin....

." Lovelock (1995) gave evidence of this in his second book, showing the evolution from the world of the early thermo-acido-philic
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 and methanogenic bacteria towards the oxygen enriched atmosphere today that supports more complex life
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...

.

The weakest form of the theory has been called "influential Gaia". It states that biota
Biota (ecology)
Biota are the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales. The biota of the Earth lives in the biosphere.-See...

 minimally influence certain aspects of the abiotic world, e.g. temperature and atmosphere.

The weak versions are more acceptable from an orthodox science perspective, as they assume non-homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

. They state the evolution of life and its environment may affect each other. An example is how the activity of photosynthetic
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

 bacteria during Precambrian times have completely modified the Earth atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

 to turn it aerobic, and as such supporting evolution of life (in particular eukaryotic life). However, these theories do not claim the atmosphere modification has been done in coordination and through homeostasis. Also such critical theories have yet to explain how conditions on Earth have not been changed by the kinds of run-away positive feedbacks that have affected Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

 and Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

.

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 reference examples of lives' 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
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

-rich one. However, proponents argue these atmospheric changes improved the environment's suitability for 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
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 criteria for life
Life
Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...

 itself (Gaia has not yet reproduced, for instance; it still might spread to other planets through human space colonization
Space colonization
Space colonization is the concept of permanent human habitation outside of Earth. Although hypothetical at the present time, there are many proposals and speculations about the first space colony...

 and terraforming
Terraforming
Terraforming of a planet, moon, or other body is the hypothetical process of deliberately modifying its atmosphere, temperature, surface topography or ecology to be similar to those of Earth, in order to make it habitable by terrestrial organisms.The term is sometimes used more generally as a...

), many scientists would be comfortable characterizing the earth as a single "system
System
System is a set of interacting or interdependent components forming an integrated whole....

".

Strong Gaia


A version called "Optimizing Gaia" asserts that biota manipulate their physical environment for the purpose of creating biologically favorable, or even optimal, conditions for themselves. "The Earth's atmosphere is more than merely anomalous; it appears to be a contrivance specifically constituted for a set of purposes". Further, "... 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".

Another strong hypothesis is the one called "Omega Gaia". Teilhard de Chardin claimed that the Earth is evolving through stages of cosmogenesis
Cosmogenesis
Cosmogenesis is the origin and development of the cosmos. This term "Cosmogenesis" was used by Helena P. Blavatsky to describe the content of Volume I of her two-volume The Secret Doctrine, published in 1888; volume II was called "Anthropogenesis" or the origin of humanity.-Teilhard...

, affecting the geosphere
Geosphere
The term geosphere is often used to refer to the densest parts of Earth, which consist mostly of rock and regolith. The geosphere consists of the inside of the Earth or other planets or bodies....

, biogenesis
Biogenesis
Biogenesis is the law that living things come only from other living things, e.g. a spider lays eggs, which develop into spiders. It may also refer to biochemical processes of production in living organisms.-Spontaneous generation:...

 of the biosphere
Biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...

, and noogenesis
Noogenesis
Noogenesis is the emergence of intelligent forms of life. The term was first used by Pierre Teilhard de Chardin in regard to the evolution of humans...

 of the noosphere
Noosphere
Noosphere , according to the thought of Vladimir Vernadsky and Teilhard de Chardin, denotes the "sphere of human thought". The word is derived from the Greek νοῦς + σφαῖρα , in lexical analogy to "atmosphere" and "biosphere". Introduced by Pierre Teilhard de Chardin 1922 in his Cosmogenesis"...

, culminating in the Omega Point
Omega point
Omega Point is a term coined by the French Jesuit Pierre Teilhard de Chardin to describe a maximum level of complexity and consciousness towards which he believed the universe was evolving....

. Another form of the strong Gaia hypothesis is proposed by Guy Murchie
Guy Murchie
Guy Murchie , the son of Ethel A. and Guy Murchie Sr., was a Chicago Tribune photographer, staff artist and reporter, who had served as a war correspondent in England and Iceland from 1940 to 1942. He was briefly married to Barbara Cooney , with whom he shared two children...

 who extends the quality of a holistic lifeform to galaxies. "After all, we are made of star dust. Life is inherent in nature." Murchie describes geologic phenomena such as sand dunes, glaciers, fires, etc. as living organisms, as well as the life of metals and crystals. "The question is not whether there is life outside our planet, but whether it is possible to have "nonlife".

There are speculative versions of the Gaia hypothesis, including versions that hold that the Earth is conscious or part of some universe-wide evolution such as expressed in the Selfish Biocosm hypothesis strain of a larger speculative Gaia philosophy
Gaia philosophy
Gaia philosophy is a broadly inclusive term for related concepts that living organisms on a planet will affect the nature of their environment in order to make the environment more suitable for life. This set of theories holds that all organisms on an extraterrestrial life-giving planet regulate...

. These extreme forms of the Gaia hypothesis, that the entire Earth is a single unified organism that is consciously manipulating the climate to make conditions more conducive to life, are metaphysical
Metaphysics
Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...

 or mystical
Mysticism
Mysticism is the knowledge of, and especially the personal experience of, states of consciousness, i.e. levels of being, beyond normal human perception, including experience and even communion with a supreme being.-Classical origins:...

 views for which no evidence exists, and that cannot be tested scientifically. The political branch of Gaia theory is the Gaia Movement
Gaia Movement
The Gaia Movement is an international network of individuals and groups that share a concern for living more sustainably on the earth. The term "Gaia" comes from Greek mythology, where it is the name of the Goddess of the Earth...

, 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".

Precedents



The holistic idea of the Earth as an integrated whole, a living being, has a long tradition. The mythical Gaia
Gaia (mythology)
Gaia was the primordial Earth-goddess in ancient Greek religion. Gaia was the great mother of all: the heavenly gods and Titans were descended from her union with Uranus , the sea-gods from her union with Pontus , the Giants from her mating with Tartarus and mortal creatures were sprung or born...

 was the primal Greek
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

 goddess
Goddess
A goddess is a female deity. In some cultures goddesses are associated with Earth, motherhood, love, and the household. In other cultures, goddesses also rule over war, death, and destruction as well as healing....

 personifying the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

, the Greek version of "Mother Nature
Mother Nature
Mother Nature is a common personification of nature that focuses on the life-giving and nurturing aspects of nature by embodying it in the form of the mother. Images of women representing mother earth, and mother nature, are timeless...

," or the Earth Mother. James Lovelock gave this name to his hypothesis after a suggestion from the novelist William Golding
William Golding
Sir William Gerald Golding was a British novelist, poet, playwright and Nobel Prize for Literature laureate, best known for his novel Lord of the Flies...

, who was living in the same village as Lovelock at the time (Bowerchalke
Bowerchalke
Bowerchalke or Bower Chalke is a village and civil parish in Wiltshire, England, about southwest of Salisbury. It is in the south of Wiltshire, about from the county boundary with Dorset and from that with Hampshire. It is in the Cranborne Chase and West Wiltshire Downs Area of Outstanding...

, Wiltshire
Wiltshire
Wiltshire is a ceremonial county in South West England. It is landlocked and borders the counties of Dorset, Somerset, Hampshire, Gloucestershire, Oxfordshire and Berkshire. It contains the unitary authority of Swindon and covers...

, UK). Golding's advice was based on Gea, an alternative spelling for the name of the Greek goddess, which is used as prefix in geology, geophysics and geochemistry.

In the eighteen century, as Geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 consolidated as a modern science, James Hutton
James Hutton
James Hutton was a Scottish physician, geologist, naturalist, chemical manufacturer and experimental agriculturalist. He is considered the father of modern geology...

 maintained that geological and biological processes are interlinked. Later, the naturalist
Naturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...

 and explorer Alexander von Humboldt
Alexander von Humboldt
Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...

 recognized the coevolution of living organisms, climate, and Earth crust. Already in the twentieth century, Vladimir Vernadsky
Vladimir Vernadsky
Vladimir Ivanovich Vernadsky was a Russian/Ukrainian and Soviet mineralogist and geochemist who is considered one of the founders of geochemistry, biogeochemistry, and of radiogeology. His ideas of noosphere were an important contribution to Russian cosmism. He also worked in Ukraine where he...

 developed theory of the Earth's development that is now one of the foundations of Ecology. The Ukrainian geochemist was one of the first scientists to recognize that the oxygen, nitrogen and carbon dioxide in the Earth's atmosphere result from biological processes. During the 1920s he published works arguing that living organisms could reshape the planets as surely as any physical force. Vernadsky was an important pioneer of the scientific bases for the environmental sciences. His visionary pronouncements were not widely accepted in the West, and some decades after the Gaia hypothesis received the same type of initial resistance from the scientific community.

Also in the turn to the XXth century Aldo Leopold
Aldo Leopold
Aldo Leopold was an American author, scientist, ecologist, forester, and environmentalist. He was a professor at the University of Wisconsin and is best known for his book A Sand County Almanac , which has sold over two million copies...

, pioneer in the development of modern environmental ethics
Environmental ethics
Environmental ethics is the part of environmental philosophy which considers extending the traditional boundaries of ethics from solely including humans to including the non-human world...

 and in the movement for wilderness
Wilderness
Wilderness or wildland is a natural environment on Earth that has not been significantly modified by human activity. It may also be defined as: "The most intact, undisturbed wild natural areas left on our planet—those last truly wild places that humans do not control and have not developed with...

 conservation, suggested a living Earth in his biocentric or holistic ethics regarding land.
Another influence for the Gaia theory and the environmental movement
Environmental movement
The environmental movement, a term that includes the conservation and green politics, is a diverse scientific, social, and political movement for addressing environmental issues....

 in general came as a side effect of the Space Race
Space Race
The Space Race was a mid-to-late 20th century competition between the Soviet Union and the United States for supremacy in space exploration. Between 1957 and 1975, Cold War rivalry between the two nations focused on attaining firsts in space exploration, which were seen as necessary for national...

 between the Soviet Union and the United States of America. During the 1960s, the first humans in space could see how the Earth looked alike as a whole. The photograph Earthrise
Earthrise
Earthrise is a famous photograph taken on the 1968 Apollo 8 space mission.Earthrise may also refer to:* Earthrise , a computer game by Interstel...

 taken by astronaut William Anders
William Anders
William Alison Anders is a former United States Air Force officer, NASA astronaut, businessman, and engineer. He is, along with Apollo 8 crewmates Frank Borman and Jim Lovell, one of the first three persons to have left Earth orbit and traveled to the Moon .-Biography:Anders was born to Arthur...

 in 1968 during the Apollo 8
Apollo 8
Apollo 8, the second manned mission in the American Apollo space program, was the first human spaceflight to leave Earth orbit; the first to be captured by and escape from the gravitational field of another celestial body; and the first crewed voyage to return to Earth from another celestial...

 mission became an early symbol for the global ecology movement.

Formulation of the hypothesis


James Lovelock started defining the idea of a self-regulating Earth controlled by the community of living organisms in September 1965, while working at the Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...

 in California on methods of detecting life on Mars
Life on Mars
Scientists have long speculated about the possibility of life on Mars owing to the planet's proximity and similarity to Earth. Fictional Martians have been a recurring feature of popular entertainment of the 20th and 21st centuries, but it remains an open question whether life currently exists on...

. The first paper to mention it was Planetary Atmospheres: Compositional and other Changes Associated with the Presence of Life, co-authored with C.E. Giffin. A main concept was that life could be detected in a planetary scale by the chemical composition of the atmosphere. According to the data gathered by the Pic du Midi observatory
Pic du Midi de Bigorre
The Pic du Midi de Bigorre or simply Pic du Midi is a mountain in the French Pyrenees famous for its astronomical observatory, the Observatoire du Pic du Midi de Bigorre , part of the Observatoire Midi-Pyrénées .-Pic du Midi Observatory:Construction of the observatory began in 1878 under the...

, planets like Mars or Venus had atmospheres in chemical equilibrium
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

. This difference with the Earth atmosphere was considered as a proof that there was no life in these planets.

Lovelock formulated the Gaia Hypothesis in journal articles in the 1970s followed by a popularizing 1979 book Gaia: A new look at life on Earth. Until 1975 the hypothesis was almost totally ignored. An article in the New Scientist
New Scientist
New Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...

of February 15, 1975, and a popular book length version of the hypothesis, published in 1979 as The Quest for Gaia, began to attract scientific and critical attention.

Lovelock called it first the Earth feedback hypothesis, and it was a way to explain the fact that combinations of chemicals including oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 persist in stable concentrations in the atmosphere of the Earth. Lovelock suggested detecting such combinations in other planets' atmospheres as a relatively reliable and cheap way to detect life. Later, other relationships such as sea creatures producing sulfur and iodine in approximately the same quantities as required by land creatures emerged and helped bolster the theory.

In 1971 microbiologist
Microbiologist
A microbiologist is a scientist who works in the field of microbiology. Microbiologists study organisms called microbes. Microbes can take the form of bacteria, viruses, fungi, and protists...

 Dr. Lynn Margulis
Lynn Margulis
Lynn Margulis was an American biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst. She is best known for her theory on the origin of eukaryotic organelles, and her contributions to the endosymbiotic theory, which is now generally accepted...

 joined Lovelock in the effort of fleshing out the initial hypothesis into scientifically proven concepts, contributing her knowledge about how microbes affect the atmosphere and the different layers in the surface of the planet. The American biologist had also awaken criticism from the scientific community with her theory on the origin of eukaryotic
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

 organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....

s and her contributions to the endosymbiotic theory
Endosymbiotic theory
The endosymbiotic theory concerns the mitochondria, plastids , and possibly other organelles of eukaryotic cells. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts...

, nowadays accepted. Margulis dedicated the last of eight chapters in her book, The Symbiotic Planet, to Gaia. She resented the widespread personification of Gaia and stressed that Gaia is "not an organism", but "an emergent property of interaction among organisms". She defined Gaia as "the series of interacting ecosystems that compose a single huge ecosystem at the Earth's surface. Period." Yet still she argues, "the surface of the planet behaves as a physiological system in certain limited ways". Margulis seems to agree with Lovelock in that, in what comes to these physiological processes, the Earth's surface is "best regarded as alive". The book's most memorable "slogan" was actually quipped by a student of Margulis': "Gaia is just symbiosis as seen from space". This neatly connects Gaia theory to Margulis' own theory of endosymbiosis.

First Gaia conference


In 1985, the first public symposium on the Gaia Hypothesis—Is The Earth A Living Organism? -- was held at the University of Massachusetts August 1–6. The principal sponsor was the National Audubon Society Expedition Institute. Speakers included James Lovelock, George Wald
George Wald
George Wald was an American scientist who is best known for his work with pigments in the retina. He won a share of the 1967 Nobel Prize in Physiology or Medicine with Haldan Keffer Hartline and Ragnar Granit.- Research :...

, Mary Catherine Bateson
Mary Catherine Bateson
Mary Catherine Bateson is an American writer and cultural anthropologist.A graduate of the Brearley School, Bateson is the daughter of Margaret Mead and Gregory Bateson. Since 1960, she has been married to Barkev Kassarjian, a professor of business management at Babson College...

, Lewis Thomas
Lewis Thomas
Lewis Thomas was a physician, poet, etymologist, essayist, administrator, educator, policy advisor, and researcher.Thomas was born in Flushing, New York and attended Princeton University and Harvard Medical School...

, John Todd
John Todd (biologist)
John Todd is a biologist working in what is sometimes considered the general field of ecological design, in that his ideas often involve applications that become the basis of alternative technologies. His principal professional interests have included solving problems of food production and...

, Donald Michael, Christopher Bird
Christopher Bird
Christopher Bird was a best-selling author, specialising in unconventional beliefs. His notable works included The Secret Life of Plants which was co-authored with Peter Tompkins and The Divining Hand: The 500-Year-Old Mystery of Dowsing...

, Thomas Berry
Thomas Berry
Thomas Berry, C.P. was a Catholic priest of the Passionist order, cultural historian and ecotheologian ....

, Michael Cohen
Michael Cohen (academic)
Michael Cohen is Director of the at The New School. He also works as Advisor to the Dean of the Faculty of Architecture, Design, and Urban Planning of the University of Buenos Aires.- History :...

, and William Fields. Some 500 people attended and a concert by Paul Winter concluded the program. The symposium was produced by James A. Swan and Roberta Swan.

Second Gaia conference


In 1988, to draw attention to the Gaia hypothesis, the climatologist
Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...

 Stephen Schneider
Stephen Schneider
Stephen Henry Schneider was Professor of Environmental Biology and Global Change at Stanford University, a Co-Director at the Center for Environment Science and Policy of the Freeman Spogli Institute for International Studies and a Senior Fellow in the Stanford Woods Institute for the Environment...

 organised a conference of the American Geophysical Union
American Geophysical Union
The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...

's first Chapman Conference on Gaia, held at San Diego in 1989, solely to discuss Gaia.

At the conference James Kirchner
James Kirchner
James W. Kirchner is professor of Earth and Planetary Science at University of California, Berkeley. His current research spans the fields of geomorphology, hydrology, environmental geochemistry, evolutionary ecology, and paleobiology...

 criticised the Gaia hypothesis for its imprecision. He claimed that Lovelock and Margulis had not presented one Gaia hypothesis, but four -
  • CoEvolutionary Gaia — that life and the environment had evolved in a coupled way. Kirchner claimed that this was already accepted scientifically and was not new.
  • Homeostatic Gaia — that life maintained the stability of the natural environment, and that this stability enabled life to continue to exist.
  • Geophysical
    Geophysics
    Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...

     Gaia — that the Gaia theory generated interest in geophysical cycles and therefore led to interesting new research in terrestrial geophysical dynamics.
  • Optimising Gaia — that Gaia shaped the planet in a way that made it an optimal environment for life as a whole. Kirchner claimed that this was not testable and therefore was not scientific.


Of Homeostatic Gaia, Kirchner recognised two alternatives. "Weak Gaia" asserted that life tends to make the environment stable for the flourishing of all life. "Strong Gaia" according to Kirchner, asserted that life tends to make the environment stable, to enable the flourishing of all life. Strong Gaia, Kirchner claimed, was untestable and therefore not scientific.

Lovelock and other Gaia-supporting scientists, however, did attempt to disprove the claim that the theory is not scientific because it is impossible to test it by controlled experiment. For example, against the charge that Gaia was teleological Lovelock and Andrew Watson offered the Daisyworld
Daisyworld
Daisyworld, a computer simulation, is a hypothetical world orbiting a star whose radiant energy is slowly increasing. It is meant to mimic important elements of the Earth-Sun system, and was introduced by James Lovelock and Andrew Watson in a paper published in 1983 to illustrate the plausibility...

 model (and its modifications, above) as evidence against most of these criticisms. Referring to the Daisyworld Simulations, Kirchner responded that these results were predictable because of the intention of the programmers — Lovelock and Watson, who selected examples that produced the responses they desired. Many of these issues were later answered by Lovelock which showed the "Daisyworld model demonstrates that self-regulation of the global environment can emerge from competition amongst types of life altering their local environment in different ways".

Lawrence E. Joseph in his book Gaia: The Growth of an Idea argued that Kirchner's attack was principally against Lovelock's integrity as a scientist. Lovelock did not attack Kirchner's views for ten years, until his autobiography "Homage to Gaia", where he calls Kirchner's position sophistry.

Lovelock was careful to present a version of the Gaia Hypothesis that had no claim that Gaia intentionally or consciously maintained the complex balance in her environment that life needed to survive. It would appear that the claim that Gaia acts "intentionally" was a metaphoric statement in his popular initial book and was not meant to be taken literally. This new statement of the Gaia hypothesis was more acceptable to the scientific community.

The accusations of teleologism
Teleology
A teleology is any philosophical account which holds that final causes exist in nature, meaning that design and purpose analogous to that found in human actions are inherent also in the rest of nature. The word comes from the Greek τέλος, telos; root: τελε-, "end, purpose...

 were largely dropped after this conference.

Third Gaia conference


By the time of the 2nd Chapman Conference on the Gaia Hypothesis, held at Valencia, Spain, on 23 June 2000, the situation had developed significantly in accordance with the developing science of Bio-geophysiology
Geophysiology
Geophysiology is the study of interaction among living organisms on the Earth operating under the hypothesis that the Earth itself acts as a single living organism ....

. Rather than a discussion of the Gaian teleological views, or "types" of Gaia Theory, the focus was upon the specific mechanisms by which basic short term homeostasis was maintained within a framework of significant evolutionary long term structural change.

The major questions were:
  1. "How has the global biogeochemical/climate system called Gaia changed in time? What is its history? Can Gaia maintain stability of the system at one time scale but still undergo vectorial change at longer time scales? How can the geologic record be used to examine these questions?"
  2. "What is the structure of Gaia? Are the feedbacks sufficiently strong to influence the evolution of climate? Are there parts of the system determined pragmatically by whatever disciplinary study is being undertaken at any given time or are there a set of parts that should be taken as most true for understanding Gaia as containing evolving organisms over time? What are the feedbacks among these different parts of the Gaian system, and what does the near closure of matter mean for the structure of Gaia as a global ecosystem and for the productivity of life?"
  3. "How do models of Gaian processes and phenomena relate to reality and how do they help address and understand Gaia? How do results from Daisyworld transfer to the real world? What are the main candidates for "daisies"? Does it matter for Gaia theory whether we find daisies or not? How should we be searching for daisies, and should we intensify the search? How can Gaian mechanisms be investigated using process models or global models of the climate system that include the biota and allow for chemical cycling?"


In 1997, Tyler Volk argued that a Gaian system is almost inevitably produced as a result of an evolution towards far-from-equilibrium homeostatic states that maximise entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...

 production, and Kleidon (2004) agreed stating: "...homeostatic behavior can emerge from a state of MEP associated with the planetary albedo"; "...the resulting behavior of a biotic Earth at a state of MEP may well lead to near-homeostatic behavior of the Earth system on long time scales, as stated by the Gaia hypothesis." Staley (2002) has similarly proposed "...an alternative form of Gaia theory based on more traditional Darwinian principles... In [this] new approach, environmental regulation is a consequence of population dynamics, not Darwinian selection. The role of selection is to favor organisms that are best adapted to prevailing environmental conditions. However, the environment is not a static backdrop for evolution, but is heavily influenced by the presence of living organisms. The resulting co-evolving dynamical process eventually leads to the convergence of equilibrium and optimal conditions."

Fourth Gaia conference


A fourth international conference on the Gaia Theory, sponsored by the Northern Virginia Regional Park Authority and others, was held in October 2006 at the Arlington, VA campus of George Mason University. Martin Ogle, Chief Naturalist, for NVRPA, and long-time Gaia Theory proponent, organized the event. Lynn Margulis, Distinguished University Professor in the Department of Geosciences, University of Massachusetts-Amherst, and long-time advocate of the Gaia Theory, was a keynote speaker. Among many other speakers: Tyler Volk, Co-director of the Program in Earth and Environmental Science at New York University; Dr. Donald Aitken, Principal of Donald Aitken Associates; Dr. Thomas Lovejoy, President of the Heinz Center for Science, Economics and the Environment; Robert Correll, Senior Fellow, Atmospheric Policy Program, American Meteorological Society and noted environmental ethicist, J. Baird Callicott. James Lovelock, the theory’s progenitor, prepared a video specifically for the event.

This conference approached Gaia Theory as both science and metaphor as a means of understanding how we might begin addressing 21st century issues such as climate change and ongoing environmental destruction.

See also


  • Autopoiesis
  • Biocoenosis
    Biocoenosis
    A biocoenosis , coined by Karl Möbius in 1877, describes the interacting organisms living together in a habitat . This term is rarely used in English, as this concept has not been popularized in Anglophone countries...

  • Creation
    Creation
    Creation may refer to:In religion and philosophy:*Creation myth, stories of the supernatural creation of the Earth and its inhabitants*Genesis creation narrative, The Biblical account of creationIn science and technology:...

  • Earth Science
    Earth science
    Earth science is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, the Earth being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth sciences...

  • Environmentalism
    Environmentalism
    Environmentalism is a broad philosophy, ideology and social movement regarding concerns for environmental conservation and improvement of the health of the environment, particularly as the measure for this health seeks to incorporate the concerns of non-human elements...

  • Gaia spore
    Gaia spore
    Gaia spore is a subset of the Gaia hypothesis, the concept that Earth's ecosystems can be treated as a single unified organism. The Gaia spore concept states that Gaia can reproduce via space colonization...

  • Gaia philosophy
    Gaia philosophy
    Gaia philosophy is a broadly inclusive term for related concepts that living organisms on a planet will affect the nature of their environment in order to make the environment more suitable for life. This set of theories holds that all organisms on an extraterrestrial life-giving planet regulate...

  • Geophysiology
    Geophysiology
    Geophysiology is the study of interaction among living organisms on the Earth operating under the hypothesis that the Earth itself acts as a single living organism ....

  • Holism
    Holism
    Holism is the idea that all the properties of a given system cannot be determined or explained by its component parts alone...

  • Hylozoism
    Hylozoism
    Hylozoism is the philosophical point of view that all matter is in some sense alive. This may include the view that "inanimate" matter has latent powers of abiogenesis, a widely held position in the scientific community...

  • Medea Hypothesis
    Medea Hypothesis
    The Medea Hypothesis is a term coined by paleontologist Peter Ward for the anti-Gaian hypothesis that multicellular life, understood as a superorganism, is suicidal; in this view microbial-triggered mass extinctions are attempts to return the Earth to the microbial dominated state it has been for...

  • SimEarth
    SimEarth
    SimEarth: The Living Planet, the second life simulation computer game designed by Will Wright in which the player controls the development of a planet. The game was published in 1990 by Maxis...


General




External links