Gaia theory (science)
In science,Gaia theory isclassscientific models ofbiospherewhich life fostersmaintains suitable conditionsitself by affecting Earth's environment. The first such theory was created byEnglish atmospheric scientist James Lovelock1969. He hypothesized thatliving matter ofplanet functioned likesingle organismnamed this self-regulating living system afterGreek goddess Gaia.
Gaia theories have non-technical predecessors inideasseveral cultures. Meanwhile today, "Gaia theory"sometimes used among non-scientistsrefertheories ofself-regulating Earth thatnon-technical but take inspiration fromscientific models.
Among some scientists "Gaia" carries connotationsscientifically unrigorous quasi-mystical thinking about Earth,Lovelock's own hypothesis was received initiallymuch antagonism byscientific community. No controversy exists now, however, that life andphysical environment significantly influence one another.
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2 Rangeviews 3 Gaia theories 4 Semantic debate 5 Gaia hypothesisecology 6 New science 7 Early Modern Parallels 8 See also 9 External links |
Basis
This ideabased onidea thatbiomass self-regulateconditions onplanetmake its physical environment (in particular temperaturechemistry ofatmosphere) onplanet more hospitable tospecies which constitute its "life." The Gaia Hypothesis proper defined this "hospitality" asfull homeostasis. A simple model thatoften usedillustrateoriginal Gaia hypothesis isso-called Daisyworld simulation.
Whether this sortsystempresent on Earthstill opendebate. Some relatively simple homeostatic mechanismsgenerally accepted. For example, when atmospheric carbon dioxide levels rise, plantsablegrow betterthus remove more carbon dioxide fromatmosphere, butextentwhich these mechanisms stabilizemodifyEarth's overall climatenot known.
Rangeviews
Gaia theory today isspectrumhypotheses, ranging fromundeniable toradical.
At one end isundeniable statement thatorganisms onEarth have radically altered its composition. A stronger positionthatEarth's biosphere effectively acts as ifisself-organizing system which workssuchway askeep its systemssome kindequilibrium thatconducivelife. Biologists usually view this activity as an undirected emergent property ofecosystem; as each individual species pursues its own self-interest, their combined actions tendhave counterbalancing effects on environmental change. Opponentsthis view sometimes pointexampleslife's actions inpast that have resulteddramatic change rather than stable equilibrium, such asconversion ofEarth's atmosphere fromreducing environmentan oxygen-rich one; However, proponents will point out that preciselyatmospheric composition changes createdmuch more suitable environmentlife.
An even stronger claimthat all lifeformspart ofsingle planetary being, called Gaia. In this view,atmosphere,seas,terrestrial crust would beresultinterventions carried out by Gaia, throughcoevolving diversityliving organisms. Most scientists do not hold this view; however suchviewconsidered within scientific possibility.
The most extreme formGaia theorythatentire Earth issingle unified organism;this viewEarth's biosphereconsciously manipulatingclimateordermake conditions more conducivelife. Scientists contend that thereno evidence at allsupport this last pointview,it has come about because many people do not understandconcepthomeostasis. Many non-scientists instinctively see homeostasis as an activity that requires conscious control, although thisnot so.
Much more speculative versionsGaia, including all versionswhich itheld thatEarthactually conscious or partsome universe-wide evolution,currently heldbe outsideboundsscience. Thesediscussed inGaia philosophy article.
Gaia theories
Lovelock initial hypothesis
Lovelock defined Gaia as:
- "a complex entity involvingEarth's biosphere, atmosphere, oceans,soil;totality constitutingfeedback or cybernetic system which seeks an optimal physicalchemical environmentlife on this planet."
Lovelock suggested that life on Earth providescybernetic, homeostatic feedback system operated automaticallyunconsciously bybiota, leadingstabilizationglobal temperaturechemical composition.
With his initial hypothesis, Lovelock claimedexistence ofglobal control systemsurface temperature, atmosphere compositionocean salinity. His arguments were:
- The global surface temperature ofEarth has remained constant, despite an increase inenergy provided bysun
- Atmospheric composition remains constant, even thoughshould be unstable
- Ocean salinityconstant
Ocean salinity has been constant at about 3.4% forverytime. Salinity stabilityimportant as most cells requirerather constant salinity degreedo not tolerate much values above 5%. Salinitypartially controlled by evaporation processes, which mostly take placelagoons.The only significant natural sourceatmospheric carbon dioxidevolcanic activity, whileonly significant removalthroughweatheringsome rocks. During weathering,reaction causesformationcalcium carbonate. This chemical reactionenhanced bybacteriaplant rootssoils, whereimprove gaseous circulation. The calcium carbonate can be washed tosea where itused by living organismscarboneous testsshells. Once dead,living organisms' shells fall tobottom ofoceans wheregenerate depositschalklimestone. In short,rock was weathered,resulting carbon dioxide processed byliving organism,returned torock through sedimentation process. Part oforganismscarboneous shells arecoccolithophores (algae), which also happenparticipate informationclouds. Whendie,releasesulfurous gas (DMS), which act as particles on which water vapor condensesmake clouds.
Lovelock sees this as one ofcomplex processes that maintain conditions suitablelife. The volcanoes makeCO2 enteratmosphere, CO2 participatelimestone weathering, itself accelerated by temperaturesoil life,dissolved CO2then used byalgaereleased onocean floor. CO2 excess can be compensated by an increasecoccolithophoride life, increasingamountCO2 locked inocean floor. Coccolithophorides increasecloud cover, hence controlsurface temperature, help coolwhole planetfavor precipitations whichnecessaryterrestrial plants. For Lovelock, coccolithophoridesone stage inregulatory feedback loop. Latelyatmospheric CO2 concentration has increasedtheresome evidence that concentrationsocean algal bloomsalso increasing.
Criticism
The initial Gaia Hypothesis was highly criticized by many scientistsbeing teleological,belief that all things havepredetermined purpose.
It was very critically received,particular by Richard DawkinsFord Doolittle. These latter argue organisms could not actconcertation as this would require foresightplanning from them. They rejectedpossibility feedback loops could stabilizesystem. In 1982, Dawkins claimed "there was no wayevolution by natural selectionleadaltruism onGlobal scale". They findimpossiblesee howfeedback loops which Lovelock says stabiliseGaian system could have evolved. They argue that, as Gaia can't reproduce herself, she cannot be aliveany meaningful sense. They also claim thattheorynot scientific because itimpossibletestby controlled experiment. Lovelock offered The Daisyworld model as mathematical evidencerefute mostthese criticisms.
The initial hypothesis was rather imprecise,Lovelock later refuted accusationteleogism by stating "Nowhereour writings do we expressidea that planetary self - regulationpurposeful, or involves foresight or planning bybiota." - (Lovelock, J. E. 1990)
DaisyWorld simulations
Lovelock respondedcriticisms withmathematical Daisyworld model (1983), firstproveexistencefeedback mechanisms, seconddemonstratewas possible that control ofglocal biomass occur, without consciousness being involved.
Gaia conference
In 1988,climatologist Stephen Schneider organisedconference ofAmerican Geophysical Union solelydiscuss Gaia. The accusationsteleologism were dropped after that meeting.
Lovelock presentednew version ofGaia Hypothesis, which was abandoning any attemptargue that Gaia intentionally or consciously maintainedcomplex balanceher environment that life neededsurvive. This new hypothesis was more acceptable byscientific community. He supported his new hypothesis withmetaphorDaisyworld. Using computer simulations ofDaisyworld parameters (no atmosphere, taking into account different albedoseach daisy type) andmathematical approach, Lovelock proved thatcontrolled stability ofclimate by life was not being teleological. The new Gaia hypothesis stated that Gaia was homeostatic, ie thatbiota influenceabiotic world inway that involves homeostatic feedback.
DuringGaia conference, James Kirchner,physicistphilosopher tookopportunity ofmeetingexplain that therenot one Gaia hypothesis, but several ones. He then described fivethese : Influential Gaia, Coevolutionary Gaia, Homeostatic Gaia, Teleological Gaia, Optimising Gaia.
Strong Gaia theories
Several typesstrong theories may be defined.
An even stronger claim states that biota manipulate their physical environmentcreate optimal conditions. Itsometimes refersas optimizing Gaia.
- "the Earth's atmospheremore than merely anomalous;appearsbecontrivance specifically constituted forsetpurposes". (LovelockMargulis 1974).
- "...itunlikely that chance alone accounts forfact that temperature, pH andpresencecompoundsnutrient elements have been,immense periods, just those optimalsurface life. Rather, ... energyexpended bybiotaactively maintain these optima". (LovelockMargulis 1974)
Weak Gaia theories
A versionGaia theory was developed by Lynn Margulis,microbiologist,1979. Her modelmore limitedscope thanone that Lovelock proposed. In particular, that only homeorheticnot homeostatic balancesinvolved,that thereno special tendencybiospherespreserve their current inhabitants,certainly notmake them comfortable. Accordingly,Earthnotliving organism which can live or die all at once, but ratherkindcommunitytrust which can exist at many discrete levelsintegration.
Coauthor oforiginal Gaia Hypothesis, "Lynn Margulis, tells us that Earthnot homeostatic but homeorhetic: that is,compositionEarth's atmosphere, hydrospherelithosphereregulated around "set points" ashomeostasis, but those set points changetime... Gaiajust symbiosis as seen from space." - from Greenpeace apparentlyreferenceLynn Margulis, Symbiotic Planet: A New ViewEvolution.
A systemhomeostasis tendsmove towards constant valuesits parameters, whereassystemhomeorhesis will always exhibit similar dynamic behavior, without necessarily converging toconstant state. Therestrong evidence that plantsselected formicroclimate effects whichcan have locallythemselves,good evidence that these patterns also exist on some wider scales,symbiotic relationships existinglarger scale climate modification.
Other reductionist theories suggest that Gaiaco-evolutive. Co-evolutionthis context has been thus defined: "Biota influence their abiotic environment,that environmentturn influencesbiota by Darwinian process."
The weakest form oftheory has been called influential Gaia. It barely states that biota influence certain aspects ofabiotic world, e.g. temperatureatmosphere.
Allthese theoriesmore acceptable from an orthodox science perspective, asassume non-homeostasis. They stateevolutionlifeits environment may affect each other. An examplehowactivityphotosynthetic bacteria during Precambrian times have completely modifiedEarth atmosphereturnaerobic,as such supporting evolutionlife (in particular eucaryotic life) . However, these theories do not claimatmosphere modification has been donecoordinationthough homeostasis.
Semantic debate
The argumentthat these symbiotic organisms, being unablesurvive apart from each othertheir climatelocal conditions, form an organismtheir own right, underwider conception ofterm organism thanconventionally used. It ismatteroften heated debate whether this isvalid usage ofterm, but ultimatelyappearsbesemantic dispute. In this sense ofword organism, itargued undertheory thatentire biomass ofEarth "issingle organism".
Unfortunately, many supporters ofvarious Gaia theories do not state exactly wheresit on this spectrum; this makes discussioncriticism difficult.
Much effort on behalfthose analyzingtheory currentlyan attemptclarify what these different hypotheses are,whether theyproposals'test' or 'manipulate' outcomes. Both Lovelock'sMargulis's understandingGaiaconsidered valid scientific theories, andnowpartbiology proper.
Gaia hypothesisecology
After initial criticism, Gaia hypothesisnow considered an essential partecological science, proposingplanetbeobjectecological study. Most ecologists agreeassimilatebiosphere tosuper ecosystemconsider this hypothesis, thoughsimplification,consistent withmodern visionglobal ecology, relyingconceptbiospherebiodiversity.
New science
Gaia hypothesis led tonew science called biogeography, or even geophysiology, which take into accountinteractions between biota,oceans andatmosphere.
Early Modern Parallels
In Lives ofCell, Lewis Thomas makes an observation very much like Lovelock's Gaia hypothesis:
- "I have been tryingthink ofearth askindorganism, but itno go. I cannot thinkit this way. Ittoo big, too complex,too many working parts lacking visible connections. The other night, driving throughhilly, wooded partsouthern New England, I wondered about this. If not like an organism, whatit like, whatit most like? Then, satisfactorilythat moment,cameme: itmost likesingle cell."
See also
climate engineering, urban ecology, industrial ecology, arcology, placesintervene insystem, James Kirchner, geophysiology
External links
