Elsevier Encyclopedia of Geology - Vol II G-M

656 Pages·43.283 MB·English

GAIA 1
GAIA
GJ HMcCall, Cirencester, Gloucester,UK globe as an integrated system, with the atmosphere,
theseas,therivers,andtherocksinteractingtomodu-
(cid:1)2005,ElsevierLtd.AllRightsReserved.
latetheplanet’sphysicalstateandthustheenvironment
inwhichlifecanexist,withthepresenceoflifecontrib-
Introduction
utingsignificantlytotheinteractions.Gaiaisthusnota
synonym of ‘biosphere’ or ‘biota’: it is a much larger
TheGaiaconcepthasevolvedinthe30yearssinceit
entity.Whenthe Gaiamodelwasoriginallyproposed
wasfirstintroducedbyJamesLovelock,anindepend-
in the 1970s, it was considered that the atmosphere,
ent scientist and inventor. It was initially a rather
oceans, climate, and crust of Earth were regulated to
vague model relating to the climate and diversity of
maintainacomfortablestateforlifetoexist,byandfor
theplanetEarth,thoughlivingorganismswerecritical
the biota. Temperature, oxidation state, acidity, and
to it. The workings of the model were initially un-
certain aspects of the rocks and waters were kept, at
specified.Theconcept,however,wasoneofa‘super-
anytime,constant,maintainedinhomeostasis,bythe
organism’operatingto‘regulate’theplanet,especially
organismsatEarth’ssurface.Thisconceptisnowseen
itssurfacetemperature,yetlackingthe‘foresight’pos-
to have been incorrect, because both life, which is
sessed by intelligent animals. Lovelock updated his
continually evolving, and the geological environment
work in 2000, publishing The Ages of Gaia. The
are in a state of constant change, and the conditions
discussion here is based on this later book, and it is
needed to maintain life change very rapidly, with the
quiteunavoidabletoechomuchofwhatLovelockhas
changingneedsofthebiota,sohomeostasiscannotbe
said,becauseheistheonlyanddefinitivesource.
maintained for more than very brief periods in Earth
history.TheEarthisthusseenasbeinglikeahelicopter,
Gaia in the Twenty-First Century
which is, unlike a fixed-wing plane, never in stable
flight. The changing and evolving needs of the biota
Gaia is essentially about life, because life is seen to
requirethatthebriefperiodsofhomeostasisarequickly
combinewithinanimateprocessesonEarth,affecting
overtakenbynewrequirements.Theconceptnowisof
and even regulating the physical state of the bio-
asuperorganisminwhichtheactivefeedbackprocesses
sphere. Lovelock found it surprisingly difficult to
operate automatically, so that solar energy maintains
find a good definition of ‘life’. Of the definitions
comfortableconditionsforlife.
found in Webster – ‘‘the property of plants and
animals (ending in death and distinguishing them
from organic matter) which makes it possible Molecular Biology: The Laws of
for them to take in food, get energy from it, grow
the Universe
etc.’’–andinOxford–‘‘thepropertywhichdifferen-
tiates a living animal or plant or a living portion of Lovelock regarded the emergence of the science of
organic tissue, from dead or non-living matter; the molecular biology – embodied in the information-
assemblage of the functional activities by which this processing chemicals that underpin the genetic basis
property is manifested’’ – neither is satisfactory, and ofmostlifeonEarth–ashavingtakenlifescienceout
thesecond istautologicalintheextreme.Tothefirst ofaroutineclassificatoryanddescriptivepursuitintoa
mightbeadded,before‘‘etc.’’,thewords‘‘andmove, new and exciting study ofhow all the componentsin
inthecase ofanimals’’.Lovelockadded tohisdefin- lifeare related. Equally important are physiology, the
itionoflifethat‘‘livingthingsuseenergydirectlyfrom study of organisms seen holistically, and thermo-
theSunandindirectlyfromfood’’(seeOriginofLife). dynamics, a branch of physics dealing with time and
There is no difficulty in accepting that advanced energy,connectinglivingprocesseswithuniversallaws.
livinganimalorganisms,suchashumans,aremadeup Two fundamental universal laws of physics are that
of intricate communities of connecting cells, and, as (1)energyisconserved,howevermuchitisdispersed,
LynnMargolishasshown,thatcellsarederivedfrom and(2)energyisalwaysabating.Hotobjectscool,but
micro-organismsthatoncelivedfree(seePrecambrian: coolobjectsdonotheatupspontaneously;waterflows
ProkaryoteFossils;EukaryoteFossils).Largerentities, downhill,butnotuphill.Onceused,energycannotbe
suchasecosystems,arealsoaccepted,andspaceexplor- recovered.Naturalprocessesalwaysmovetowardsan
ationhascontributedtothisunderstandingbyallowing increase in disorder, which is measured by entropy;
the entire planet Earth to be viewed from space. The entropy expresses the tendency to burn out. Looking
Gaia concept likewise involves envisaging the entire attherelationshipbetweenlifeandentropy,Lovelock
2 GAIA
referredtoErwinSchro¨dinger’sconclusionthatlifehas their own destiny in an interesting and complex, but
theabilitytomoveupstreamagainsttheflowoftime, comprehensible,way.Thusthesumtotalofthephys-
apparently paradoxically and contrary to the second ical state of a planet, with life, is a combination
universal law. In fact, what is operating is a tightly oftheinanimateprocessesandtheeffectsoflifeitself.
coupled system to favour survival; energy is taken in JZ Young said that the entity that is maintained
(e.g., oxygen from the atmosphere is breathed), con- intact, and of which we all form part, is the whole
verted (e.g., stored body fats and sugars are trans- of life on the planet. This statement really provided
formed),andthenexcreted(e.g.,wasteproductssuch the link between theory and consensus, on the one
as carbon dioxide are released back into the atmos- hand,andGaiaconcept,ontheother,expressingasit
phere). If the entropy of excretion is larger than the does the view that the entire spectrum of life on the
entropyoftheoxygenconsumed,lifecontinues,despite planet has to be considered alongside the geological
theseconduniversallaw. andinanimatephysicalprocesses,ifwearetounder-
stand how the planet works. This, of course, has led
to the present preoccupation in educational circles
The Superorganism Concept
with ‘Earth System Science’ (see Earth System Sci-
There is difficulty in envisaging an eruptive planet ence). Gaia goes further than Earth System Science,
withamoltencoreandothercomplexinorganicpro- which is purely a holistic educational approach, in
cessesasalivingsuperorganism.However,theinspir- requiring a global system that has the capacity to
ing‘whole-planet’imageofEarthasseenfromspace regulate the temperature and composition of Earth’s
and the contrast between the environment on Earth surface, hydrosphere, and atmosphere, keeping it
andtheenvironmentsonthemoon,Mars,Venus,and comfortableforlivingorganisms.
Mercury have focused research on considering how
thesignificantplanetarydifferencesarose,andinpar-
Criticism of the Gaia Concept
ticular on the question of how and why the atmos-
pheres differ. The atmospheres of the Moon, Mars, CriticismoftheGaiaconcept,onceadvanced,wasby
Venus, and Mercury are a good starting point for no means slight, and the Gaia model was not taken
comparisons to Earth, because the atmospheres are seriously by scientists, at all, until the early 1970s.
the least complex and most accessible of the zones FredDoolittlecameoutwiththebeliefthat‘‘molecu-
of all these planets; indeed, the atmospheric com- lar biology could never lead to altruism on a global
positions on other planets were known before space scale’’–altruismbylivingorganismsbeingapparently
exploration commenced (see Solar System: Mars; inherent to the concept. Richard Dawkins in 1982
Moon;Mercury;Venus). supported him: ‘‘the selfish interests of living cells
TheEarthhasanatmosphereofNandO,withtraces couldnotbeexpressedatthedistanceoftheplanet’’.
ofcarbondioxide,methane,andnitrousoxide,notin ItwasalsoremarkedthatGaialackedafirmtheoret-
equilibrium, whereas the atmospheres of Mars and ical basis. Heinrich D Holland considered that biota
Venus are dominated by carbon dioxide and are in simply react to change in the state of Earth’s near-
equilibrium. If the atmospheres of Mars and Venus surfaceenvironmentandprocesses,geologicallypro-
wereheated,therewouldbenoreactionwiththesur- duced,andthosethatadaptbettersurvive:therestdo
face materials, whereas heating Earth’s atmosphere not. Many scientists saw Gaia as a teleological con-
wouldproducereactionsleadingtoacarbondioxide- cept, requiring foresight and planning by organisms,
dominated atmosphere. Lovelock concluded that the something that the model surely never represented.
improbableatmosphereofEarth‘‘revealstheinvisible However, a major step was taken at the Chapman
hand of life’’. The atmosphere contains oxygen and conference of the American Geophysical Union in
methane, which should react to form water vapour 1988,whennumerouspapersonGaiawerepresented:
andcarbondioxide:thatthisdoesnotoccur,andthat the question of the scientific testability of the Gaia
constant atmospheric compositions of these gases are hypothesiswasraised.
maintained, reveal, Lovelock believes, that there is Holland’s statement was really an oversimplifica-
regulationbylife(seeAtmosphereEvolution). tion,becausetheenvironmentalconstraintstowhich
Scientists as early as Eduard Suess and Vladimir an organism adapts can in no way be entirely inor-
Vernadsky accepted that there was continuous inter- ganic in origin – geological processes are a combin-
action between soils, rocks, oceans, lakes, rivers, the ation of the inorganic and the organic. Lovelock
atmosphere,and life.Muchlater,Stephen JayGould stated this when he objected that ‘‘life cannot have
stated that ‘‘organisms are not billiard balls, struck adapted solely to an inert world determined by the
in a deterministic fashion and rolling to optimal dead hand of chemistry and physics’’. The two main
positions on life’s table’’. Living things influence objections to Gaia were, first, the teleological one
GAIA 3
(forecast or clairvoyance seemed to be needed for
Gaia tobe true) and, second, thefact that ecological
regulationbylifecouldonlybepartial.Whatmustbe
operatingisacombinationofregulationbytheliving
and the inorganic, even though in the long term, a
wholly inorganic interference, such as an asteroidal
impact, would be reacted to by the biota, much of it
bydyingoff.However,someofthebiotamaysurvive,
regeneratingandexpandingtoagainaffectthephys-
icalenvironmentofthelifeformscontinuingtoexist
atornearthesurface.
Other objections to the Gaia concept have been a
creationist argument, based on Schro¨dinger’s conclu-
sionson‘life’,thatsomeorganismsdonotneedthesun, Figure 1 Regulation by white daisies. The helmet-shaped
andalsoasuggestionthatLovelock’simageofEarthas curve(B)depictstheresponseofdaisiestotemperature.Curves
a‘spaceship’ignoresthefactthat40000tonnesyear(cid:1)1 AandA1depicttheresponsesofplanetarytemperaturetothe
areacoveredbydaisies,curveA1beingforalowerheatinputby
ofextraterrestrialdustentersEarth’satmosphereand
theplanet’sstar.Intheabsenceofdaisies,thechangeinplanet-
isdepositedonEarth’ssurface. ary temperature (DT) would be nearly 15(cid:2)C, whereas in their
presence DT is only about 3(cid:2)C. Reproduced with permission
fromLovelockJ(2000) The Ages of GAIA: A Biography of Our Living
Lovelock’s Hypothesis Earth.Oxford:OxfordUniversityPress.
The‘Daisyworld’Model
be determined by the average shade of colour of the
Lovelocksawthatheneededasimplemodeltoillus-
daisy coverage. If the average is the dark colour
trate his point. The effect of snow cover on the
shade, the albedo is low, more heat is absorbed, and
ground,apurelyinorganicchange,hadalreadybeen
thesurfaceiswarmed;iftheaverageisthelightshade,
modelledtoshowhowsnowcoverchangesthealbedo
70–80%ofheatisreflectedandthesurfaceiscolder.
and thus the cooling in the atmosphere. Lovelock
In the scale 0–1, dark daisies will have an albedo of,
developed a simple model, the ‘Daisyworld’ model,
say,0.2;lightdaiseswillhaveanalbedoof0.7andthe
illustratingthewaylifecouldhaveasimilareffect.
bare ground, 0.4. The initial weak Sun will increase
TheDaisyworldparableof1982proposesaplanet
until 5(cid:2)C is attained and that will favour the dark
like Earth in size, mass, and orbital distance from
daisies, because they have greater absorption of sun-
a star that is like Earth’s sun in mass and density;
light and will warm up the temperature just beyond
like Earth’s Sun, the Daisyworld Sun increases its
5(cid:2)C.Thelightdaisieswillbedisadvantagedandwill
output as it ages (the nature of the H/He reaction
fadeanddie.Nextseason,therewillbemoreseedsof
meansthatourSunwas30%cooleratitsbeginning,
thedarkstrainanditwillbecomewarmerandsoon,
butwilleventuallyheatupsoastoconsumeMercury,
until most of the planet is colonized by the dark
Venus, and possibly Earth). The Daisyworld planet
strain.However,whentheupperlimittemperatureis
has more land than sea, compared to Earth, is well
approached, the light strain, because of their high
watered, and plants can grow anywhere on the land
albedo, will keep the temperature in check and so
surface if the climate is right. The sole plant is a
will take over from the dark strain. The growth of
daisy, which may be dark, neutral, or light in colour
the star’s heat flux will eventually be so great that
shade.Asingleparameter,variabletemperature,con-
nothing can keep the temperature below 40(cid:2)C and
trolswhetherthedaisycangrow–5(cid:2)Cisthegrowth
all the daisies will die off. Flower power will no
threshold, 20(cid:2)C is the optimum, and 40(cid:2)C is the
longer be enough. The planet will be barren and
upper limit. The mean temperatureof the planet isa
there will be no way back. Figure 1 reproduces
simple balance between the heat received from the
Lovelock’s most important Daisyworld diagram.
sun and the heat lost to the cold depths of space in
The Daisyworld parable was devised to counter the
the form of long-wave radiation. The complication
‘teleological’criticism.
on the real Earth of reflection upwards and blanket-
ing downwards of heat by clouds is avoided, by
TheFourComponentsofGaia
havingalltherainfallontheDaisyworldplanetoccur
at night and having no clouds present in daytime. Lovelock described Gaia as an automatic, non-
Thereisjustenoughcarbondioxideintheatmosphere purposeful, goal-seeking system, and considered it
for the plants to grow. The mean temperature will tobemadeupoffourcomponents:
4 GAIA
1. Living organisms that grow freely, exploiting any remain possibilities of abrupt extinction of life on
environmentalopportunitiesthatopenup. Earth through physical disasters. For example, the
2. OrganismsthataresubjecttotherulesofDarwin- entire planetary biota might have been extinguished
ian natural selection: the species that leave the in the latest Proterozoic; if glaciation, a complex
mostprogenysurvive. phenomenon attributed to Milankovitch cycles in
3. Organisms that affect their physical and chemical theSolarSystem,hadcoveredtheglobeinthe‘snow-
environment.Thus,animalschangetheatmosphere ball Earth’ episode, it might well have extinguished
by breathing, taking in oxygen and breathing out all life. Definition 2 begs the question, ‘‘what about
carbondioxide.Plantsandalgaedothereverse.In the long early period in the Archaean, when only
numerousways,allformsoflifeincessantlymodify very primitive forms of unicellular life apparently
thephysicalandchemicalenvironment. existed?’’Theplanetinfactgotonverywellthrough
4. Theexistenceofconstraintsorboundsthatestab- a vast period of time when it was only partially in-
lishthelimitsoflife.Itcanbetoohotortoocold; habited by life, and that being very primitive, com-
there is a comfortable warmth in between, the pared with now. Regarding definition 3, surely to
preferred state. It can be too acid or alkaline; the word ‘rocks’ the words ‘hydrosphere and bio-
neutrality is preferred. For almost all chemicals, sphere’should be added. Finally, in definition 4, the
there is a range tolerated or needed by life. For statement that ‘‘increased diversity leads to better
many elements, such as iodine, selenium, or iron, regulation’’ is questionable. The evidence for this
too much is a poison and too little causes starva- does not seem to be to be given by Lovelock: the
tion. Pure, uncontaminated water will support word ‘regulation’, which is fundamental to Gaia
little, but neither will the saturated brine of the concept,seemstobeaproblem.Theconceptappears
DeadSea. to be tantamount to accidental regulation: in the
realworld,asopposedtotheDaisyworld,thereality
would seem to be that the biota make a major con-
DefinitionsandCriticisms
tribution to the physical and chemical environment
Lovelockadvancedasetofdefinitions: of the biosphere, and that, throughout Earth history
since life appeared on the planet, the bounds of liv-
1. Life is a planetary phenomenon with a cosmo-
ability of the planetary biota as whole have never
logicallifespan.Onthisscale,itisnearlyimmortal
beenexceeded,despiteseveralmassextinctions–yet
andhasnoneedtoreproduce.
total extinction could happen at any time. Also, like
2. There can be no partial occupation of the planet
the inorganic physical and chemical (geological)
bylivingorganisms.Suchaconditionwouldbeas
changes,changesinducedbythebiotacanbebenign
impermanent as half an animal. Ineluctable phys-
or adverse. The biota can react to change to counter
ical and chemical forces would soon render (the
adverse changes; initially benign changes can lead
planet)uninhabitable.Thepresenceofasufficient
to adverse changes in the long run (e.g., overpop-
numberofanimalsontheplanetisneededforthe
ulation). There is no law of the sum total planetary
regulationoftheenvironment.
biota adjusting to regulate the environment, keeping
3. Our interpretation of Darwin’s great vision is
within bounds, but so far (luck?), the bounds have
altered. Gaia draws attention to the fallacy of the
not been overridden in the case of the overall biota,
concept of adaptation. It is no longer sufficient to
not at any time in geological history, since life first
saythat‘‘organismsbetteradaptedthanothersare
appeared.
likelytoleaveoffspring’’.Itisnecessarytoaddthat
thegrowthoftheorganismaffectsitsphysicaland
Gaia and the Geological Record
chemicalenvironment;theevolutionofthespecies
and,therefore,theevolutionoftherocksaretightly
Lovelock, in his second book, considered Gaia in
coupledinasingle,indivisibleprocess.
terms of the geological record, discussing the Ar-
4. Theoretical ecology is enlarged. By taking the
chaean, the Middle Ages, and the contemporary
species and the physical environment together as
environment. Before concluding, it seems apposite
a single system, we can, for the first time, build
to refer to a recent contribution to the discussion by
ecological models that are mathematically stable,
EuanNisbet.
andyetincludelargenumbersofcompetingspecies.
In these models, increased diversity among the Nisbet’sEssay
speciesleadstobetterregulation.
EuanNisbet,inawide-rangingFermorLecturetothe
There are criticisms of Lovelock’s definitions. Of Geological Society in 2002, explored the question
definition 1, it is perhaps better to admit that there whether the presence of life or inorganic processes
GAIA 5
had constituted the dominant factor in shaping the the global biota.One cannotescape thefact that the
physicaldevelopmentandincontrollingthephysical physical state of the near-surface zones of the planet
conditions at or near Earth’s surface since life ap- has, for more than 3500 million years, been suffi-
peared on the planet more than 3500 million years ciently benign for some life to continue to exist;
ago. He found that life had a dominant role in throughoutthedevelopmentoflife,fromprotozoans
controlling the condition of the atmosphere through to destructive humans, the physical state of Earth’s
this immensely long period, and that, in turn, the surfacehasneverledtoextinctionofthesumtotalof
surface temperature had a very significant control lifeontheplanet.Yetthehistoryhassurelybeenone
on the tectonic evolution, especially plate tectonics. of reactions by life to changes, including extremely
Evenso,Nisbetcouldnotruleastowhichprocesses, criticalsituations,bothinorganicallyandorganically
biological or inorganic, had been the dominant triggered; changes have never reached the point of
factor – the two kinds of processes had operated driving life over the edge to extinction, but even so,
together to control the physical conditions. That this is not regulation, because there is no rule in-
life had exerted a significant effect on the ongoing volved. The irretrievable end-point situation has just
physicalevolutioncouldnotbearguedagainst. not happened. In fairness to Lovelock, in his 1991
Nisbet based his conclusions on inorganic and or- book he did include a chapter entitled ‘‘The People
ganic models, and in them not all the assumptions Plague’’, inwhich heargued that humans, having no
made are necessarily correct. For instance, Nisbet predators, had in effect become a plague on the
tended to extend plate tectonics back through the planet, and could well take the life on the planet to
Archaean,whereastherearestrongargumentsagainst that irretrievable end-point situation. Of course, one
this (e.g., see the publications by Hamilton in 1998, by could argue that humans do have predators, even if
Bleeker in 2002, and by McCall in 2003). Considering minute ones – viruses and microbes that could blot
the real world, rather than models, Nisbet could not them out forever and leave behind an Earth smiling
decide which had beenin the driving seat,and he be- with other life forms, until the Sun fulfils its destiny
lievedthatthequestionwaspossiblynotquantifiable. andincineratestheplanet.
The atmosphere was,however, largely the product of Theinfluenceoftheexistenceoflifeonthephysics
theexistenceoflifeatornearEarth’ssurface. andchemistrynearthesurfaceoftheplanet,andthe
feedback to life from that – the essence of Gaia – is
well understood, but has obviously become more
Beyond Gaia
complexasthespectrumoflifeonEarthhasbecome
Gaia,attheleast,isabrilliantconcept,andLovelock more complex, starting with the primitive prokary-
has provided a stimulating basis for looking at otes in the Early Archaean. For example, a plant
the entire globe and for integration of the effects of population limited to algae must have left bare rock
theprogressivedevelopmentoflifeandpurelyinani- surfacesintheArchaean,whereasoncehigherplants
mategeologicaldevelopmentthroughtime.Thiscon- appeared, there must have been a much more com-
cept also encompasses the maintenance throughout plex reaction of the land surface to the Sun’s radi-
timeofconditionssuitableforlifetocontinuetoexist ation. In fact, these relationships, though complex
throughout3500millionormoreyears.However,at and possibly unquantifiable at the present state of
this minimal assessment, it is no more than Earth the planet, are less obscure than are other processes.
SystemScienceunderanothername,butemphasizing Forexample,howdoesananimalobtaininformation
thespecialcontributionoflifetothechangingstateof that another animal exists and has a character or
the atmosphere, hydrosphere, and geological pro- activitytowhichthefirstanimalcanadapt,toobtain
cesses, which in sum determine the physical condi- benefit? How does the information get into the gen-
tions under which life of some sort can continue to etic process? The present author, in an unpublished
‘operate’.TheGaiaconcept,however,isclaimedtobe work, The Vendian (Ediacaran) in the Geological
more than this, and the critical word is ‘regulate’. Record, has called this mysterious process ‘cogni-
Lovelock never intended Gaia to have a teleological zance’. An example of this is the case of eoforamini-
significance, but even so, to regulate something fera found in Uruguay, in latest Proterozoic rocks.
wouldseemtoimplyanelementofdesign.Itmaybe These organisms agglutinated fine mineral particles
that when an extreme condition occurs, such as an on theirsurface, and it has been glibly said that they
extreme greenhouse condition (Cretaceous) or a did this to make themselves less palatable to preda-
‘snowball Earth’ approximation (end Proterozoic), tors. But how did they know that their mates were
the reactions of the living plant and animal popula- beingeaten?Itwouldseemthatthisaspectofgenetics
tionsthatsurvivemaybebeneficial,butequallythey is what scientists should now be concentrating on,
couldactuallybeadverseandeliminateevenmoreof ratherthan‘regulation’bythesumtotalbiota.
6 GEMSTONES
See Also Lovelock J (1978) GAIA: A New Look at Life on Earth.
Oxford:OxfordUniversityPress.
Atmosphere Evolution. Biodiversity. Earth Structure LovelockJ(1991)GAIA:ThePracticalScienceofPlanetary
andOrigins.EarthSystemScience.Evolution.Origin Medicine.London:GaiaBooks.
of Life. Palaeoclimates. Precambrian: Eukaryote LovelockJ(2000)TheAgesofGAIA:ABiographyofOur
Fossils;ProkaryoteFossils.Solar System:Mars;Moon; LivingEarth.Oxford:OxfordUniversityPress.
Mercury;Venus.TraceFossils. McCall GJH (2003) A critique of the analogy between
Archaean and Phanerozoic tectonics based on regional
Further Reading mapping of the Mesozoic–Cenozoic plate convergent
zone on the Makran, Iran. Precambrian Research
BleekerW(2002)Archaeantectonics–areview.In:Fowler 127(1-3):5–17.
CMR,EbingerCJ,andHawkesworthCJ(eds.)TheEarly Myers N (1984) Gaia: An Atlas of Planet Management.
Earth: Physical, Chemical and Biological Development. NewYork:Doubleday.
Special Publications 199, pp. 151–181. London: Geo- Nisbet E (2002) The influence of life on the face of the
logicalSociety. Earth. In:Fowler CMR, Ebinger CJ, and Hawkesworth
GaucherCandSprechmannP(1999)UpperVendianskel- CJ (eds.) The Early Earth: Physical, Chemical and
etal fauna of the Arroyo del Soldado Group, Uruguay. Biological Development. Special Publications 199, pp.
Beringeria23:55–91. 275–307.London:GeologicalSociety.
Hamilton WB (1998) Archaean magmatism and deform-
ationwerenotproductsofplatetectonics.Precambrian
Research91:131–175.
GEMSTONES
COldershaw, St.Albans, UK Quantifying Gemstone Mining
(cid:1)2005,ElsevierLtd.AllRightsReserved. While mineral exploration is generally well docu-
mented and statistics are available, providing figures
for production for most minerals on a country-
Introduction
by-country basis, this is generally not the case with
There are almost 4000 minerals known, of which gemstones (except perhaps for diamonds), which
only about 50 are commonly used as gemstones. have always been difficult to quantify. Much gem-
Thosethatformcrystalsofsufficientsizeandquality stone mining is carried out in remote places, with
to be cut and fashioned as gems are referred to as secrecy and security to protect the interests (and
‘gem quality’ or ‘cuttable’ pieces; other minerals or sometimes the lives) of the owners (Table 1). In
rocks with particularly attractive features (colour, some areas, families or groups of villagers purchase
texture,orpattern)maybecalled‘decorative’pieces. alicence tomine;inother areasthere islittle regula-
Crystalsareusuallyfaceted(cutandpolished)togive tion,andminingmaybecontrolledbylocalleadersor
agemstonewithanumberofflatfaces,whiledecora- warlords, with all the problems associated with
tivestonesaremainlytumbledorpolishedtoproduce regionsofconflictandpoliticalunrest.
piecesforpersonaladornmentorobjetsd’art. Over large regions it is difficult to assess the pro-
Gemstones are formed in each of the three main duction figures for particular gemstones, although
rock types: igneous, sedimentary, and metamorphic. general trends in availability and value (which could
Miningmethodsdependonthetypeofgemstoneand be as much a product of fashion as of supply) give
itsopticalandphysicalqualitiesandonwhetheritis some indication of production figures. On a smaller
beingminedfromtherockinwhichitwasformedor scale, a specialist gemstone buyer (such as a ruby
retrieved from secondary (placer) deposits produced or sapphire buyer) will, by building relationships
byweatheringanderosion. with miners, mine owners, and local traders, gain
A study of modern-day gemstone mining and expertise and some knowledge of the volume and
retrievalcovers every miningmethod,from the trad- quality of gemstones being mined in that region.
itional searches in streams and rivers using a pan As new localities are identified and new gemstones
or sieve to the ultra-high technology and research reach the markets, previously known localities or
models used in diamond mines deep underground. gemstones may lose their appeal or a region may
Ultimately, any source of gemstones will be mined become unproductive – so the market can be quite
andexploitedonlyifisfinanciallyviable. changeable.
GEMSTONES 7
Table1 Themainlocalitiesofsomeofthebest-knowngemstones(diamond,ruby,sapphire,emerald,aquamarine,chrysoberyl,
topaz,tourmaline,peridot,garnet,pearl,opal,spinel,zircon,turquoise,nephritejade,andjadeitejade)
USA Egypt Russia Myanmar(formerlyBurma)
Aquamarine Emerald Demantoidgarnet Chrysoberyl
Emerald Peridot Diamond Jadeitejade
Jadeitejade Turquoise Emerald Peridot
Nephritejade Nigeria Nephritejade Ruby
Peridot Aquamarine Topaz Sapphire
Ruby Sapphire Tourmaline Spinel
Sapphire Spinel Afghanistan Topaz
Topaz Topaz Aquamarine Tourmaline
Tourmaline Zaire,Angola,andNamibia Ruby Zircon
Turquoise Diamond Spinel Thailand
Canada Zambia Pakistan Almandinegarnet
Diamond Chrysoberyl Aquamarine Ruby
Emerald Emerald Sapphire
Nephritejade
Botswana Grossulargarnet Zircon
Mexico
Opal Diamond Ruby China
SouthAfrica Spinel Aquamarine
Topaz
Diamond Topaz Diamond
Tourmaline
Emerald India Nephritejade
Turquoise
Peridot Almandinegarnet Peridot
Honduras
Ruby Aquamarine Ruby
Opal
Tourmaline Chrysoberyl Sapphire
Colombia
EastAfrica Diamond Turquoise
Emerald
Aquamarine Emerald JapanandTaiwan
Brazil
Diamond Ruby Jadeitejade
Chrysoberyl
Emerald Sapphire Topaz
Diamond
Ruby SriLanka Australia
Emerald
Sapphire Chrysoberyl Diamond
Opal
Tanzanite Garnet Emerald
Topaz Tourmaline Ruby Nephritejade
Tourmaline Madagascar Sapphire Opal
Germany Aquamarine Spinel Sapphire
Topaz Chrysoberyl Topaz NewZealand
Italy Topaz Tourmaline Nephritejade
Tourmaline Tourmaline Zircon Guatemala
FormerCzechoslovakia Jadeitejade
Garnet Iran
Opal Turquoise
Gem-testing laboratories, museums, and specialist gemmological journals such as the Journal of Gem-
gemstone collectors are often the first to hear of a mology, Gems and Gemmology, and Australian
new find. Some gemstones will be mined in suffi- Gemmologist.
cientlylargevolumestoreachthemarketplaceworld-
wide, for example tanzanite (the blue variety of the
Alluvial and Eluvial Deposits
mineral zoisite), which was discovered in 1967 in
Tanzania and is now available through many retail Gems formed in igneous or metamorphic rock may
outlets.Othersmaybeminedoutfairlyquickly,with be subject to weathering and erosion, breaking
most of the gemstones going to a few specialist down the rock and releasing the gemstones (see
buyers. Weathering). The gems may remain where they are
Some particularly rare finds are found only in or be transported by ice, wind, or water and de-
museums or private collections. Other gems are cut posited elsewhere. Eluvial gem deposits are form-
for collectors but, because of their rarity or physical ed as a result of the weathering of rock that has
properties (for example they may be too soft remained in the same place. Alluvial deposits
for everyday wear), do not reach the retail market. are deposited by flowing water (see Sedimentary En-
New localities and new gemstone finds of vironments: Alluvial Fans, Alluvial Sediments and
interest,suchasaparticularlyfine-colouredgemstone Settings).
or a mine that is producing particularly clean large Gemstones are generally harder and heavier than
specimens of a gemstone, are usually reported in thesurroundingminerals.Theyarenotcarriedasfar
8 GEMSTONES
by flowing water and tend to sink faster, becoming
concentrated inpockets orareas along riverbanks or
withingravels(gemgravels).Therefore,alluvialgem-
stonedepositscontaingemstonesthataresufficiently
hardanddurabletowithstandtheconditionswithout
breaking, rather than those that are heavily included
orpronetofractureorcleavage.
Because nature has already partially eliminated
theweakerspecimens,thepercentageofgem-quality
gemstones in gem gravels is usually high, with the
result that more gemstones are retrieved from
gem gravels than from any other type of deposit.
Alluvial deposits, such as the gem gravels of Sri
Lanka and Myanmar (formerly Burma), contain a
wide range of gemstones including ruby, sapphire,
spinel,chrysoberyl,topaz,tourmaline,andgarnet.
Becausegemstonesassociatedwithgemgravelsare
often found together, the discovery of one type of
gemstone from a gem association (sometimes called
a tracer gem) can be used by exploration teams and
prospectors to ‘trace’ potential gemstone mining
areas. Another technique is to map the courses of
ancient river beds or present-day rivers and streams
andthenfollowtracergemsdownstreamtofindareas
where the gemstones are present in large enough
concentrationstoberetrieved.
The oldest and most traditional mining methods
arestillpracticedinareaswheregemstonesarenear
the surface and relatively easy to find and retrieve
Figure 1 A lady river panning, washing gravel in search of
and where labour is cheap. In Indonesia, Malaysia, chrysoberyl cat’s-eyes (Kerala, India). Printed with permission
Sri Lanka, and India, for example, local people fromAlanJobbins.
search rivers and streams and excavate the gravels
andsedimentsfromnow-buriedriverbeds.
RubyandSapphireDeposits
Panning for gems works on the principle that the
gemsaregenerallyheavierthanthesurroundingmud, TherubiesandsapphiresofThailandandCambodia
pebbles, or rock fragments. As the pan of water and are found in alluvial and eluvial gravels, derived
sedimentis‘jiggled’,thegemstonessettletowardsthe from highly alkaline basalt (Figure 5). The main
bottom of the pan while the lighter constituents and mining area is near the border between Thailand
waterarewashedoverthepan’sedge(Figure1).The andCambodia,aroundChantaburi.
heavier concentrate may be sieved to separate larger Sri Lanka is a source of alluvial sapphires, which
gemsoritmaybespreadoutontablesorclothstobe arederivedfrompegmatiteandgneissandarefound
hand-sorted. in a wide range of colours, including the pinkish-
Alluvial deposits are generally mined by similar orange padparadscha. Padparadscha is particularly
methods wherever they are found in the world, usu- rareandisnamedafterthesinhaleseforlotusflower,
ally by digging shafts or pits or by collecting the whosecolouritresembles.
alluvium from rivers and streams using sieves and Rubies and sapphires are members of the corun-
pans. Dams may be constructed to manage the dumfamily,anddifferenttraceelementswithinthem
water flow, and water may be diverted to wash the giverisetothecolourrange.Rubiesarered(coloured
gem gravels (Figures 2 and 3). Final sorting is done by chromium and possiblyvanadium); blue sapphire
byhand. is coloured by iron and titanium. Other sapphires,
Often the mining and retrieval of gems in these such as green sapphire, pink sapphire, and mauve
traditional ways is a family project, varying only sapphire, result from the addition of various trace
slightly from country to country. The men and boys elements during the gem’s formation. Colourless
may work in the rivers or dig the pits, while women (white)sapphirehasthesimplechemicalcomposition
andgirlssieveorsortthegems(Figure4). aluminiumoxide(Al O ).
2 3
GEMSTONES 9
Figure 2 A young worker carries the gemstone concen- Figure 3 Washing gemstone concentrate in a small pond
tratecalled‘paydirt’or‘rai’in‘Burmese-style’baskets(Pailin, (Pailin,Cambodia).(cid:1)AlanJobbins.
Cambodia).(cid:1)AlanJobbins.
Thecolourdoes,tosomeextent,affectthemining, therehavebeenfindsofprehistorictoolsthatsuggest
as the more popular and valuable colours are thatmininghasbeencarriedoutformanythousands
more sought after. It should be noted, however, that ofyears.
some gemstones, including corundum, may have Traditional methods involve digging a narrow pit
their colour changed or enhanced with heat treat- or vertical shaft, just wide enough for the miner to
ment, irradiation (electrons, X-rays, etc.), or other be lowered down to dig out the layer of weathered
techniques. metamorphosed crystalline limestone (marble) that
Kashmir sapphires, which are famous for their contains the rubies. The miner removes rock (often
cornflowercolour,areminedinSanskar,aninhospit- 2–3m below the surface) and placesit in abasket to
ablemountainousareaoftencoveredbysnow,north- behauledtothesurfaceandsorted.
west of the Himalayas. The sapphires are found in Following the establishment of the Burma Ruby
feldspar pegmatites or in gravels derived from the Mine Company in Victorian times, some mining
pegmatites.Therehasbeenintermittentminingsince techniques were modernized. Water pumps were
the 1920s; however, little is known about present introducedtospeedthewashingprocess,andintricate
miningbecauseofthepoliticalsituation. channelswereconstructedfromwoodenplanks,along
which water was sluiced to separate the rubies from
MogokRubies
rockfragments.Asaresultofthecollapseofthemarket
The most famous rubies are the ‘pigeon blood’- followingtheintroductionofsyntheticrubiesandsap-
coloured rubies from the Mogok Stone Tract area of phiresintheearlytwentiethcentury,theBritishCom-
northern Myanmar, about 110km north of Manda- panyfailedandtraditionalmethodswerereintroduced.
lay. Documentary evidence shows that mining has Inthe1990snewmineswereestablishedintheMong
been carried out since the sixteenth century, but Hsuarea,about250kmeastofMandalay.
10 GEMSTONES
Figure4 Girlssortinggemstoneconcentrate(Pailin,Cambodia).(cid:1)AlanJobbins.
Gemstones in Igneous Rocks
Where rock is harder, picks and drills may be suffi-
cient to prise loose the gemstones from the parent
rock (the host); otherwise the rock has to be mined,
crushed, washed, and sorted to retrieve the gem-
stones. Diamonds are mined on a larger scale and
with more highly mechanized methods than any
othergemstone.
ExtrusiveIgneousRocks
Alluvialgemdepositsderivedfrombasalticlavashave
been mentioned above. The basaltic lavas (extrusive
igneous rock, where magma has been erupted from
volcanoes as lava) may also be mined. Peridot is
commonly formed in basaltic lava. The peridot gen-
erallyformsassmallcrystalsorwithinvesicles(small
bubbles)andvoidsinthelava.Othergemsthatcrys-
tallize from lavas as they cool include zircon, ruby,
andsapphire.
IntrusiveIgneousRocks
Some of the largest crystals form where the magma
isnoteruptedbutrisessufficientlyintheEarth’scrust
tocoolslowly.Theslowerthecooling,thelargerthe
crystals that can form. Igneous rocks formed in this
wayaresaidtobeintrusive.
Gemsmayformindykes(smalligneousintrusions)
intruded into surrounding rocks, which may crop
Figure 5 Eluvialworkingsinweathered(decomposed)basalt
abovebasaltlava(Pailin,Cambodia).(cid:1)AlanJobbins. out at the surface as a result of weathering. Mining