The CourierJULY 1986 B French Irancs

A time to live . . .

45 Mexico

To the rescue

Earthquakes are a grim fact of life for thepeople of Mexico. Mexico City, one of theworld's largest and oldest capital cities, issituated on the southern Mexican plateau inan area of volcanic activity and faulting ofthe Earth's crust related to the shaping ofthe continental areas to the north and south.

In September 1985, Mexico City was shakenby a powerful earthquake which caused se¬vere damage in the heart of the metropolis.In an unprecedented effort of internationalsolidarity, rescue teams from many coun¬tries came to Mexico City to help in the w orkof rescuing and caring for the many victims.

TheCourierA window open on the world

Editorial

SEEN against the immensity of the Universe, the Earthwe live on is a tiny speck of rock and metal. The thirdplanet of the Solar System, counting outward from the

Sun round which it orbits at a speed of 29.8 kilometres persecond , the Earth is located between Venus and Mars , at justthe right distance from the Sun (149,573,000 kilometres) toavoid being baked in perpetual heat or frozen in unendingcold.

In this issue of the Unesco Courier our purpose is to offerour readers a simple description of the genesis of our planetand of the major geological mechanisms that regulate itsrestless churning. For though we call the land surface we liveon "terra firma", the great continental plates are in constantmotion. Sometimes these plates collide, buckling at thepoint of impact into mighty mountain ranges; at times theyare shaken by violent, shuddering earthquakes; at times theinternal furnaces spew out molten rock in awesome volcaniceruptions. And all the while new crust is forming on theocean floor and old crust is being sucked down to be recycledin the banked fires of the mantle.

In terms of geological time, man is a newcomer to thisplanet. If we imagine the 3,900 million years since theEarth's crust solidified as one calendar year, then Homosapiens only appeared on the scene on 31 December at about

_^¿ eight and a half minutes to midnight (100,000 years ago).' In the very last half second of our condensed time scale,

man has himself become a major geological force capable ofdeteriorating or even destroying the environment in whichhe lives. The damage that human beings inflict upon theenvironment is mainly due to ignorance. We still do notknow enough, for example, about the long-term effects ofthe widespread use of chemical fertilizers and pesticides,how to prevent the spread of man-induced desertification, orhow best to handle our newest energy source nuclearpower.

With its major international science programmes Unescois in the forefront of the battle to keep our planet habitable.Although there may well be other Earths in the vast ex¬panses of the Universe, if they exist they are well beyond ourreach. We must look after planet Earth; we have nowhereelse to go.

N. B. We suggest that this issue be read in conjunction with two other recent issues of theUnesco Courier: "The Story of the Universe" (September 1984), and "The New Worldof the Ocean" (February 1986).

' Several of the photographs and diagrams in this issue of the Unesco Courier arereproduced by courtesy of the Geological Museum, London, to whom we express ourgrateful thanks.

Cover: Océane Pyrénées, 1985, acrylic on canvas (116 x 73 cm), byGeorges Servat. Galerie jean-pierre lavignes, Paris.

Editor-in-chief : Edouard Glissant

July 198639th year

4 The genesis of the Earthby John Gribbin

6 Vital statistics

8 Inside the Earth

9 Our place in the Solar System

10 Wandering continents

12 Rocks around the clock

The concept of geological time

12 Shaping the land

15 A trilogy of rocks

16 Drilling into the unknownby Yevgeni Kozlovski

23 The restless Earth

The uncertain art of earthquake predictionby E.M. Foumier d'Albe

27 Volcanoes

by Haroun Tazieff

32 The evolution of life

33 Life from SpaceDoes life on Earth have its origins in comets?by Chandra Wickramasinghe

35 The hand of man

by Stephen Boyden and Malcolm Hadley

38 1986: Year of Peace/ 7

2 A time to live...

MEXICO: To the rescue

Published monthly in 32 languagesby UnescoThe United Nations Educational,

Scientific and Cultural Organization7, Place de Fontenoy, 75700 Paris.

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German Persian Korean BulgarianArabic Dutch Swahili Greek

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A selection in Braille is publishedquarterly in English, French,Spanish and Korean

ISSN 0041-5278

N° 7 - 1986 - CPD - 86 - 1 - 435 A

The genesis

IN the beginning there was nothing atall. Space, time and the matter of theUniverse we live in were created

together in a superdense fireball, some15,000 million years ago, a fireball whichwe call the "Big Bang". As the Universeexpanded and cooled, matter becamespread more thinly until huge clouds ofhydrogen gas began to clump together,breaking up and collapsing inwards toform stars and galaxies. By about 10,000million years ago, galaxies like our ownMilky Way system, each containing up toa few thousand million stars, were estab¬lished as the basic units of the Universe.

Within each galaxy stars are born, liveand die, wheeling their long orbitsaround the galaxy's centre, while thegalaxies themselves are carried everfarther apart as the Universe continues toexpand.

Our Sun and Solar System are typicalproducts of the galactic environment, butour Sun was not one of the first stars to

shine in the cosmic night. Those earlieststars contained only hydrogen and a littlehelium; all the other elements have been

created by nuclear reactions inside starsand scattered through space when thosefirst stars exploded. So when our Sunformed, only a little over 4,500 millionyears ago, it formed out of a cloud ofhydrogen gas well laced with other mate¬rials such as iron, carbon, oxygen and

nitrogen materials that settled out ofthe collapsing gas cloud to form theplanets.

The planets of the Solar System differfrom one another chiefly because of theirdistances from the Sun. Those closest to

the forming young Sun were subjected tothe greatest heat, and this drove off intospace many light materials. This is whyMercury, Venus, Earth and Mars aresmall, rocky objects. Far out from theSun's furnace, however, even light gasessuch as methane and ammonia could be

trapped and held by a forming planet. Sothe giant planets, Jupiter, Saturn, Uranusand Neptune, probably contain the sameamount of rocky material as the Earth,but this is buried deep beneath the vastlayers of their gaseous atmospheres.They need not concern us here, but it is

interesting and informative to make somecomparisons between our own home inspace, Planet Earth, and our nearestneighbours, Venus and Mars.

The small cloud of material that col¬

lapsed to form our planet, within thegreater cloud that was collapsing to formthe Solar System, was probably made upchiefly of silicon compounds, iron oxidesand magnesium oxides, with just a smalltrace of all the other elements, includingthose that are so important to life.

As the Earth formed, it grew hot. First,gravitational energy was turned to heat asparticles rained down and smashed intothe proto-planet. In addition, radioactiveelements inside the core of the growing

planet contributed their share of warmthas they decayed into stable elements aprocess which continues at a slower ratetoday.

The young, iron-rich planet must havebeen largely molten in the first tens orhundreds of millions of years after itformed, and as a result molten globules ofiron forced their way downwards to thecore of the Earth through the lighter,rocky material, which was left to float ontop and provide a solid skin as the crustcooled. The material of the crust on

which we live is not typical of the materialthat makes up the bulk of the Earth andthe material of the atmosphere that webreathe is even less representative of thewhole planet.

The crust of the Earth contains 6 percent iron, but the planet as a whole con¬tains 35 per cent; silicon, which makes uponly 15 per cent of the mass of the planet,forms 28 per cent of the crust, combinedwith oxygen to make silicate rocks. Thelightest rocks, chiefly granite, make upthe bulk of the continents, but the ocean

floor consists of basalt, which is ratherheavier.

From the surface to the centre, the

Earth is layered like an onion, with thelightest material on the outside and themost dense material at the core. And this

process of segregation was more or lesscompleted by 3,900 million years ago,just 600 million years after the planetformed. Geophysicists know this becausethey have been able to date the oldest

rocks of the Earth's crust, using measure¬ments of their residual radioactivity; andthey know about the layered structure ofthe planet from studies of earthquakewaves, which are bent and distorted by

the different layers.However, no more than the broad out¬

lines of the picture of the Earth's interiorcan be determined in this way. Thepioneering geophysicist Sir Edward Bul-lard once told me that "determining thestructure of the Earth by studying earth¬quakes is like a blind man trying to deter¬mine the structure of a grand piano solelyby listening to the sound it makes whenpushed down a flight of stairs". And it is ''^,.true that scientists know more about the '^

composition of distant stars than aboutthe Earth deep below our feet after all,we can actually see the stars!

But we do at least have the broad out¬

lines of a picture of the Earth's interior.Starting from the surface, we live on arocky ball with an average radius of 6,372kilometres, slightly flattened at the poles.The outer skin, or the crust, representsonly 0.6 per cent of the volume of theplanet. Below the crust, which varies inthickness from 5 to 35 kilometres, there is

a sharp boundary called the MohorovicicDiscontinuity, or Moho.

This marks the top of the mantle, alayer which goes down to a depth of 2,900kilometres and takes up 82 per cent of thevolume of the Earth. Near the top, the

mantle is partly molten, with a consisten¬cy like thick porridge, or slushy, meltingice. This region of weakness, called theasthenosphere, is of great importance be¬cause the crust above can move over it,

leaving the continents free to wanderaround the globe (see page 10). On abroader scale, the mantle seems to be

made up of three zones , the upper mantlebeing about 370 kilometres thick andseparated by a transition zone about 600kilometres thick from the lower mantle,

which is itself 1,900 kilometres in thick-ness.

Evolution of the Earth from a cloud ofgasand dust to a rocky planet

of the Earth by John Gribbin

^ Below the mantle lies the core an

outer core 2,100 kilometres thick and the

inner core itself, with a radius of just1,370 kilometres, at the centre of the

Earth. The outer core is the region ofliquid iron, where the Earth's magneticfield is generated.

Venus and Mars are rocky planets likethe Earth and formed in much the same

way. But our planet is covered by oceansof water, whereas Mars is a cold, dryplanet with a thin atmosphere and Venushas a superdense atmosphere covering abaking hot surface. These differencesseem to be a direct result of the differ¬

ences in the distance of the planets fromthe Sun.

All three planets, astronomers andgeophysicists now believe, had no atmos¬

phere immediately after they cooled.Any gases that were present as theyformed were driven off by the heat of theSun. Simple physics tells us the tempera¬ture of the surface of each of the three

rocky balls, at their different distancesfrom the Sun, once the Sun had settled

down to a steady brightness. For Venus,the stable temperature, where incomingheat from the Sun is exactly balanced byoutgoing radiation, is 87 degrees Centi¬grade, and for Mars the figure is -30degrees Centigrade. These figures, re¬member, are for airless planets. ^

Vital statisticsSource: National Geographic Society, Washington, D.C

THE EARTH

Weight: 5,973,502,000,000,000,000,000 tonnesCircumference at the Equator: 40,075 kmArea: 510,074,600 km2Land: 148,940,540 km2Water: 391,134,060 km2

THE CONTINENTS

Area JL Highest point V7 Lowest pointv (metres)

Population(km2) (metres)

Asia 43,998,920 1 Everest

8,8481 Dead Sea

-3962,048,898,000

Africa 29,800,540 2 Kibo

(Kilimanjaro)5,895

2 Lake Assal

-156344,000,000

North 24,320,100 3 McKinley 3 Death 314,970,000America 6,194 Valley

-86South 17,599,050 4 Aconcagua 4 Valdés 186,013,000America 6,960 Peninsula

-40

Europe 9,699,550 5 El'bruz

5,6425 Caspian Sea

-28637,943,000

Australia 7,687,120 6 Kosciusko

2,2286 Lake Eyre

-1612,200,000

Antarctica 14,245,000 7 Vinson

Massif

5,139

Not known

MAJOR WATERFALLS

Height(metres)

1 Angel 979

2 Tugela 9483 Yosemite 7394 Cuquenán 6105 Sutherland 5806 Mardalsfossen 5177 Ribbon 491

8 King George VI 4889 Gavarnie 422

10 Victoria 108

1 1 Iguazú 72

12 Niagara 59

LONGEST RIVERS

Length(kilometres)

1 Nile 6,6692 Amazon 6,4363 Mississippi-Missouri 5,9694 Ob'lrtysh 5,5675 Yangtze 5,4716 Huang 4,8277 Congo 4,3738 Amur 4,3449 Lena 4,312

10 Mackenzie-Peace 4,2401 1 Mekong 4,18312 Niger 4,18313 Paraná 4,02314 Murray-Darling 3,71715 Volga 3,685

A highest points

^7 lowest points

^¡¡f Earth's extremes

^ deepest points

A major seas

O largest lakes

| | longest rivers

major waterfalls

A

LARGEST LAKES O THE OCEANS

Area Greatest depth Area tar Deepest Point(metres)(km2) (metres) (km2)

1 Caspian Sea 371,795 995 Pacific 166,242,517 1 Mariana Trench 1 1 ,0332 Superior 82,362 406 Atlantic 86,557,800 2 Puerto Rico Trench 8,6483 Victoria 69,485 81 Indian 73,427,795 3 Java Trench 7,7254 Aral Sea 65,527 68 Arctic 13,223,763 4 Eurasia Basin 5,4505 Huron 59,570 229

6 Michigan 58,016 282

7 Tanganyika 32,893 1,4178 Great Bear 31,792 413

9 Baikal 30,510 1,62010 Nyasa 29,604 678

MAJOR SEAS #Area

(km2)Average depth

(metres)

EARTH'S EXTREMES ft

1

2

3

4

5

6

7

8

9

10

11

12

13

South China Sea

Caribbean Sea

Mediterranean Sea

Bering SeaGulf of Mexico

Sea of Okhotsk

Sea of JapanHudson BayAndaman Sea

Black Sea

Red Sea

North Sea

Baltic Sea

2,974,6152,515,9262,509,9692,261 ,0701,507,6391,392,1251,012,949

730,121564,879507,899452,991427,091

382,025

1,464

2,575

1,5011,4911,615

973

1,66793

1,1181,191

538

308

55

1. Rainiest spot: Mount Waialeale, Hawaii: average annual rainfall: 11,680 mm.2. Driest spot: Atacama Desert, Chile: rainfall barely measurable. (At Calama,

no rain has ever been recorded.)3. Coldest spot: Vostok, Antarctica: -88°C (recorded in August 1960).4. Hottest spot: AI'Aziziyah, Libya: 56°C (recorded in September 1922).5. Northernmost town: Ny Alesund, Spitsbergen, Norway.6. Southernmost town: Puerto Williams, Chile.7. Highest town: Aucanquilcha, Chile: 5,334 m8. Lowest town: Villages along the Dead Sea: -396 m9. Largest gorge: Grand Canyon, Colorado River, Arizona: 349 km long,

6 to 21 km wide, 1.6 km deep.10. Deepest gorge: Hells Canyon, Snake River, Idaho: 2,408 m deep.11. Strongest surface wind: 372 km/h (recorded in 1934).12. Greatest tides: Bay of Fundy, Nova Scotia: 16 m13. Biggest meteor crater: New Quebec, Canada: 3 km wide.

1. crust granite (continents)

basalt (oceans)

2. mantle peridotite (and denser forms)

3. outer core iron (liquid)

4. Inner core iron (solid)

Inside the Earth

The Earth's interior has a layered struc¬ture. The outermost layer is the crust;beneath this is the mantle; and in thecentre is the core. Temperatures andpressures inside the Earth are veryhigh at the core the temperature isthought to be about 3,500 degrees Cen¬tigrade and the pressure nearly 3,750tonnes per square centimetre.

The Crust: In relation to the Earth as a whole,the crust is as thin as a postage stamp stuckon a football. It consists of a thin skin of rock

which is less dense than the underlying man¬tle from which it has been derived by complexprocesses over many millions of years. Thereare two kinds of crust: continental crust,which makes up the continents, and oceaniccrust, which forms the ocean floors. Con¬tinental crust is lighter In weight and muchthicker than oceanic crust. It is also verymuch olderparts of the continental crustare over 3,500 million years old, whereasoceanic crust is nowhere more than 200 mil¬

lion years old.

The Mohoroviclc Discontinuity: The sharpboundary that marks the junction betweenthe crust and the mantle.

The Asthenosphere:Th\s Is a hotter, weaker,partly molten section of the top of the uppermantle with a consistency like thick porridge.It Is of great Importance because it enablesthe rigid plates of the crust above to moveabout.

The Upper Mantle: scientists believe that theupper mantle consists of dense, dark-col¬oured rocks, probably peridotite and perhapsalso dunite and ecloglte, composed of Ironand magnesium-rich silicate minerals. Frag¬ments of these rocks are found In volcanoes

fed by magma (molten rock) that originates Inthe mantle.

The Transition Zone: In this region, where theupper mantle grades into the lower mantle,higher pressures force the minerals tochange their structure.

The Lower Mantle: The minerals composingthe lower mantle are probably simple oxideswith very compact structures produced byhigh pressures.

The Core: Almost twice as dense as the man¬

tle, the core is probably composed of Ironwith some dissolved sulphur and silicon. TheEarth's magnetic field is generated In theouter core, which Is molten. The Inner core isthought to be solid.

On each planet an atmosphere beganto form when carbon dioxide and water

vapour were produced by volcanic activ¬ity (it may seem surprising, but one of themain things that emerges from the fieryfurnace of a volcano is water vapour).Although 87 degrees Centigrade is stillbelow the boiling point of water, thetemperature on Venus was already highenough for a great deal of water vapourfrom volcanic outgassing to stay in theatmosphere with carbon dioxide.

Both water vapour and carbon dioxideare very efficient at trapping infra-redradiation the process is called the"greenhouse effect". So less heat couldescape from the planet into space and as aresult its temperature quickly rose abovethe boiling point of water, and then stillhigher as still more water vapour joinedthe atmosphere. From then on, all pro¬duction of volcanic gases thickened theatmosphere and strengthened this green¬house effect. On Mars the opposite hap¬pened. Water may have flowed briefly onthe planet, but it soon froze. Venus is ahot desert; Mars is a cold desert. ButEarth is different.

On our planet the temperature washigh enough for liquid water to flow, butnot so high that water vapour could causea runaway greenhouse effect. Quite thereverse the warm waters of the youngoceans dissolved carbon dioxide out of

the air, leaving a much thinner atmos¬phere than on Venus, while white cloudsin the sky reflected away some of theincoming solar heat and let the planetcool. It is no coincidence, astronomers

believe, that the mass of all the carbondioxide in the atmosphere of Venus todayis roughly the same as the mass of carbondioxide locked up in carbonate rocks,such as limestone, laid down from theoceans around the Earth.

If our Sun had been a little warmer,

Earth too might have been a superhotdesert with a thick, carbon dioxide

atmosphere but if that were so, thenMars would be warm enough for water toflow and life to flourish. Or suppose theSun were a little cooler; our Earth mighthave ended up like Mars but Venuscould have become a pleasant planet ofoceans and cloudy blue skies. If you arenot fussy about exactly which planet yousettle on, the implication seems to be thatan Earth-like planet is an almost inevit¬able counterpart of every Sun-like star.

In the case of our Solar System, it justhappens to have been the third planet outfrom the Sun that was, by about 3,500million years ago, already in possessionof oceans of water, continents, a carbon

dioxide atmosphere and a comfortabletemperature. The scene was set for theemergence of life, and for life itself tobegin to change the environment of theplanet but that is another story.

8

What of the future? Our Sun has ex¬

isted in a more or less steady state for4,000 million years, keeping hot as itburns hydrogen fuel into helium in itsinterior. Eventually the supply of hyd¬rogen will be exhausted. When it is, theinner part of the Sun will collapse slightlyand become still hotter as helium is fused

by nuclear reactions into carbon. Thisgreater internal heat will cause the outer

layers of the Sun to expand and it willbecome a red giant star, engulfing theinner planets and burning them to cin¬ders. But there is no need to panic. OurSun is only halfway through its life-cycle,scarcely into middle-age, and "eventual¬ly", in this case, means not for another4,000 million years or more. The fate ofmankind lies in its own hands, not in thestars.

JOHN GRIBBIN, British astrophys,cist and sci¬ence writer, former member of the Science Poli¬

cy Research Unit of the University of Sussex,England, is physics consultant to the magazineNew Scientist. He has written many books onastronomy, geophysics and climatic change, aswell as two novels, and in 1974 he received the

United Kingdom's premier science-writingaward. His books on astrophysics include WhiteHoles (1977), Timewarps (1979), Genesis: TheOrigins of Man and the Universe (1981), andSpacewarps (1983).

Our place in the Solar SystemSun

A nuclear furnace that converts hydrogeninto helium, releasing an enormous amountof energy. Central star of the Solar System,making up 99 per cent of its mass. Meansurface temperature: 5,500 degrees Centi¬grade. Core temperature: 17 million degreesCentigrade. Diameter: 1.39 millionkilometres. Distance from Earth: 150 million

kilometres.

MercuryDense, probably partly metallic. May have athin atmosphere. Average midday temper¬ature: 350 degrees Centigrade. Diameter:4,840 kilometres. Distance from Sun: 57.9million kilometres.

Venus

Similar in composition to Earth. Shrouded ina dense atmosphere of carbon dioxide. Sur¬face temperature: 300 degrees Centigrade.Diameter: 12,104 kilometres. Distance fromSun: 108.2 million kilometres.

Earth

Silicate layers surround dense metallic core.Water, and an atmosphere of nitrogen andoxygen, support life. Surface temperature:Between 60 degrees Centigrade and -90degrees Centigrade. Diameter: 12,756kilometres. Distance from Sun: 150 million

kilometres.

Mars

Surface has Moon-like craters but also such

Earth-like features as canyons and volca¬noes. Atmosphere is carbon dioxide with alittle nitrogen and water. No evidence of life.Surface temperature: (?) 20 degrees Centig¬rade at Equator. Diameter: 6,760 kilometres.Distance from Sun: 227.9 million kilometres.

Asteroids

Small bodies revolving in paths betweenMars and Jupiter. Mostly less than onekilometre across. Mean distance from Sun:

414.4 million kilometres.

JupiterGiant frozen planet enveloped in a thickatmosphere of hydrogen and helium. Strongenergy source. Diameter: 142,700 kilometres.Distance from Sun: 778.3 million kilometres.

Saturn

Least dense of planets. Mainly hydrogen andhelium. Orbited by ice-covered fragments(rings). Diameter: 120,800 kilometres. Dis¬tance from Sun: 1,427 million kilometres.

Uranus

Probably ice with some solid ammonia, hyd¬rogen and helium. Owes its green appear¬ance to a methane-rich atmosphere. Di¬ameter: 47,600 kilometres. Distance fromSun: 2,869 million kilometres.

NeptuneProbably frozen methane, water and ammo¬nia. Diameter: 44,400 kilometres. Distancefrom Sun: 4,498 million kilometres.

Pluto

Most distant planet yet discovered. Composi¬tion unknown. Diameter: (?) 3,000 kilometres.Distance from Sun: 5,900 million kilometres.

The Moon

Its composition shows small but significantdifferences from that of Earth. Analysis ofMoon rocks reveals a far greater proportionof titanium, chromium and zirconium than is

found in the Earth's crust, suggesting thatthe Moon formed separately probably by anagglomeration of pre-existing solid particles.The surface is marked by countless cratersformed by falling meteorites. Bright areas(uplands) represent primeval crust. Darkareas are basins formed 3,600 million yearsago by impact and flooded by lava eruptions.

Meteorites

Stony and metallic debris, seared by heat,that falls to the Earth from outer space. Theyare probably fragments of colliding aster¬oids. They range in composition from Iron-magnesium silicate rock to nickel-iron. Theyhave a maximum age about the same as thatof the Earth.

A speck in space

The Earth and the Solar System are ex¬tremely small in relation to distances inspace. These are measured in light-years one light-year is the distance lighttravels in one year about 10 million mil¬lion kilometres.

The nearest of the 100,000 million stars in

our Galaxy is four light-years away, andthe Galaxy itself is 80,000 light-yearsacross. Yet it is only one of millions ofgalaxies in the Universe.The Solar System consists of the Sun andthe material revolving around it planets,moons, asteroids, comets, meteorites,

dust and gas. Most of this material circlesthe Sun in the same direction and in the

same plane.

o

©

Sun Mercury Venus Earth Mars Asteroids Jupiter Saturn Uranus Neptune Pluto

Wandering

ANYONE who has looked at a world map must have noticedhow snugly the coastlines of Africa and the Americascould be made to fit together, if the intervening ocean were

removed. Modern geophysics has established that all of theEarth's landmasses were indeed joined together in one super-continent, Pangaea, hundreds of millions of years ago, and thatthis supercontinent was broken apart, with the land massesdrifting to their present positions on the globe.

This idea took many years to become established. Specula¬tions about the fit of the continents go back to Francis Bacon(1561-1626), but the acknowledged "father" of the idea of con¬tinental drift was the German astronomer and meteorologistAlfred Wegener, who published the first comprehensive state¬ment of the theory in 1 91 2. Wegener thought that the continentsmight move through the thinner crust of the ocean floor, likeicebergs ploughing through the sea, and he gathered a wealth ofevidence showing how well the continents could be fittedtogether like some global jigsaw puzzle. But the idea of conti¬nents moving through the rocks of the sea floor did not seem

feasible, and found little favour until the 1 950s, when the develop¬ment of new geological techniques provided conclusive evidencethat the continents do move.

The key evidence came from magnetic studies of the oceanfloors. These showed that the crust of the Atlantic Ocean floor is

arranged symmetrically on either side of a great ridge of volcanicactivity which runs roughly down the centre of the ocean bed. Theinterpretation of this discovery is that new oceanic crust is beingcreated at the mid-ocean ridge, where it wells up through a crackin the Earth's crust and is pushing out on either side, steadilywidening the Atlantic.

Maps © Oxford University Press, Oxford

200 million years ago Present

135 million years ago In 50 million years' time

10

continentsOcean spreading ridge. Plates are separating; molten rock rises,adding new material to each plate.

In other parts of the world the reverse happens. The NorthPacific, for example, has no oceanic ridge, but there is a deeptrench running down the west of the ocean floor, next to theEurasian landmass. There the thin crust of the ocean floor isbeing pushed under the continent, back down into the mantlewhere It melts and is ultimately recycled. The net effect is thatthere is no change in the surface area of the Earthspreading inthe Atlantic and at other sites is balanced by contraction of thePacific. A piece of the Earth's crust that is bounded by spreadingridges and subduction zones is called a "plate", which gives theconcept of continental drift its modern name, "plate tectonics". Insome places, two pieces of crusttwo platesrub side by side,with no net creation or destruction of sea floor. This happenstoday along the notorious San Andreas fault in California.

The whole process of break-up and re-arrangement of thecontinents may have happened several times in the Earth's his¬tory, and is responsible for building mountain ranges, wherecontinents collide. India, moving northward into Eurasia, hasforced up the Himalayas, which are still growing. By contrast, theline of the Red Sea marks a new (by geological standards) crack inthe Earth's crust, a spreading ridge which is splitting Africa offfrom Arabia, and which may eventually cause this narrow sea toexpand into an ocean as large as the Atlantic is today.

Overwhelming evidence for the reality of continental drift, orplate tectonics, was collected during the 1 960s and 1 970s. But the"icing on the cake" has been provided only in the past few years.Using laser beams bounced off artificial satellites in orbit around

the Earth, it is now possible to measure directly the steadywidening of the Atlantic, calculated at a couple of centimetresevery year.

Ocean subduction zone. One plate underthrusts another. Theedge of one plate is pushed down into the mantle where it meltsand is recycled. Some of the molten rock rises to form an islandarc.

Collision zone. An underthrusting plate rams two continentstogether, forming a high mountain belt.

J

é

Transform fault. Two plates slide past one another with no addi¬tion or destruction of plate material.

Illustration © The Sunday Times with the Geological Museum, London

Eurasian Plate

continental crust

volcanoes

earthquake zone

subduction zone

. uncertain plate boundary

, movement of plate

" spreading ridge offset by transform faults

collision zone

11

Rocks around the clockThe concept of geological time

GEOLOGY is the science which

deals with the condition and the

structure of the Earth and the evi¬

dence afforded of ancient forms of life. It

includes the description of landforms, but itis much more concerned with the processesand forces responsible for the landscape wesee today.

These processes generally operate ex¬tremely slowly. Huge periods of time areinvolved in the crumpling of the Earth'scrust into mountain ranges, in the wearingdown of other mountains into plains, in theadvance and retreat of sheet ice and in the

relentless movement of vast sections of the

crust itself.

The concept of the enormity of geologicaltime is a relatively recent one in Westernthought. In AD 1656, James Ussher,Archbishop of Armagh in Northern Ire¬land, after careful study of the genealogiesrecorded in the Bible, calculated that the

Creation occurred at 8 pm on the 22nd ofOctober of the year 4004 BC, an estimate

which was widely accepted even as late asthe eighteenth century.

In 1785, however, the Scottish naturalist

James Hutton published his Theory of theEarth in which he suggested that the naturalprocesses such as mountain building anderosion were so slow that the Earth must

have been in existence for many millions ofyears. His views were generally discounteduntil the early 1830s, when another Scots¬man, the geologist Charles Lyell, gave themhis backing in his famous three-volumework The Principles of Geology, which laidthe foundations for evolutionary biology aswell as for an understanding of the develop¬ment of the Earth.

With the emergence of geology as a sci¬ence in its own right, people at last becameaware of the huge length of time naturetook to achieve the changes they recognizedas having occurred.

The Earth is a rocky planet and its his¬tory, virtually from its origin up to thepresent, can be elucidated from the study of

rocks exposed on its surface or attainable bydrilling.

Rocks can be grouped into three majorcategories: igneous rocks, formed from themolten material that rises from the Earth's

interior; metamorphic rocks, that havebeen transformed and crystallized by heatand pressure; and sedimentary rocks, whichhave a layered structure and are formedfrom fragments worn away from existingrocks and deposited elsewhere as sediment(see page 15).

Ancient igneous and metamorphic rocksprovide clues as to the origin and earlyhistory of the Earth's crust; younger de¬formed and igneous rock formations help usto understand how mountain chains were

formed; and sedimentary rocks, depositedin layers or strata over millions of years,provide the major evidence on which thestandard geological time-scale is based.

Sedimentary rocks contain fossils, the re¬mains of once-living organisms. Becauseliving things are continuously changing

4-71III ted

The land surface is shaped by erosionand deformation. Erosion by water,wind and ice wears away the rocks ofthe continental crust. Deformation

occurs where the crust is unstable,rocks fracture, shear, crush, fold or flowplastically.

Erosion Deformation

U-shaped valleys like this onein Alaska are formed by thegouging action of a glacier mov¬ing down a river valley. Themoving ice and the rocks it car¬ries abrade and carve out the

valley's steep sides.

Canyons are formed when uplift of theland increases the speed and cuttingpower of a river flowing through a plain.The most spectacular example is theGrand Canyon of the Colorado River, inplaces over 1.5 km deep (see colourpage 20).

Rift valleys, often calledGraben (the German for"trenches"), are the resultsof blocks of land sinking be¬tween parallel faults. TheEast African Rift Valley, theworld's largest, is nearly5,000 kilometres long.

12

through evolution, fossils found insedimentary rock provide the principalmeans of establishing the relative age ofrocks found in different geographical areas.In combination, therefore, stratigraphy(the study of the sequences of rock strata)and palaeontology (the study of fossils inrelation to the evolution of the Earth's

crust) might be described as the study of"history in layers".

With the development of radiometry inthe 1950s, it became possible for scientiststo supplement the relative age datingobtained from the fossil record with abso¬

lute age data (that is to say, age in years).The age in years of some types of rock canbe calculated from the amounts of radio¬

active elements and their decay products inthe minerals of which the rock is composed.Radioactive isotopes of uranium, potas¬sium and rubidium decay at known ratesinto stable isotopes of lead, argon andstrontium respectively. The decay productsbegin to accumulate in a mineral after it hascrystallized and cooled, thus, as it were,setting a "radioactive clock" running.

Just as "clock" time is divided into hours,

minutes and seconds, so geological time(see table page 14) is divided into Eras,Periods or Systems, and Epochs or Series.

The first era, known as the Precambrian,covers the span of time from the formationof the Earth's crust, about 4,600 million

years ago, until the time, about 570 millionyears ago, when, for the first time in thehistory of the Earth, evidence of variedforms of life preserved as fossil remainsbecomes plentiful. The Precambrian era,which some geologists also divide into twosub-divisions, the Archaeozoic and the Pro-terozoic, thus comprises nearly 90 per centof geological time.

Three eras span the period from the end

of Precambrian time to the present thePalaeozoic ("ancient life") era, from 570million to 225 million years ago, the Meso-zoic ("middle life") era, from 225 million to65 million years ago, and the Cenozoic"modern life") era, from 65 million yearsago to the present. Broadly speaking, in¬vertebrates and relatively simple verte¬brates, such as fish, amphibians and primi¬tive reptiles were in the ascendant duringthe Palaeozoic era, the Mesozoic era saw

the rise to domination of the larger reptiles,such as the dinosaur, and the Cenozoic, the

contemporary era, is the time of the domi¬nance of mammals.

The eras are divided into smaller units

called periods or systems. Most of them arenamed after geographical regions whererocks containing fossils characteristic oftheir segments of geological time have beenfound. Thus the Cambrian period is socalled after the ancient name for Wales and

the Permian period is named after theancient Russian kingdom of Permia.

Some periods are named, not after theirgeographical location, but after the physicalcharacteristics of their rocks. Thus the

name of the Cretaceous period is derivedfrom the Latin word for chalk, creta, while

the Triassic period is so named because, inGermany, rocks of this period are dividedinto three distinct layers consisting of redsandstones, limestone and shales.

In some cases, both types of nomencla¬ture are used for the same period by geolog¬ists in different parts of the world. Thus,two periods which North Americans call thePennsylvanian period and the Mississippianperiod (geographical names) are groupedtogether in Europe as the Carboniferousperiod (from the coal-bearing nature of itsstrata).

Periods are divided into epochs or series,

which are in turn sub-divided into ages or

stages, and at this point wide divergencesappear in the nomenclature used by geolog¬ists in different parts of the world.

This is basically because the relationshipbetween geological time and sequences ofrock strata has usually been modelled onnational or regional traditional thinking,and standards, terminology and classifica¬tion differ from country to country. Neitherthe names nor the dates shown, even on a

simplified table of geological time such asthat published on page 14, will be acceptedby all geologists.

The solution of many basic geologicalproblems would, therefore, be greatlyfacilitated if, through the adoption of com¬mon standards and terminology, data fromdifferent areas could be made intelligible to

geologists the world over. Achieving thisaim is one of the major aims of the Interna¬tional Geological Correlation Programme, aco-operative undertaking by the Interna¬tional Union of Geological Sciences andUnesco (see page 14).

Of particular importance are projectsaimed at progressively refining geologicaltime-scales. Geologists need accurate time-determination methods not only as a basisfor research on the evolution of the Earth's

crust, but also for identifying and assessingenergy and mineral resources.

An understanding of the natural pro¬cesses which have led to the accumulation

of mineral deposits or fossil fuels dependson the geologist's ability to understand thesequence of stages responsible for theformation of deposits and to make accuratecorrelations between sequences concernedwith the formation of similar deposits inwidely separated areas. To paraphrase theold saying: "Geological time is money".

Drawing © The Sunday Times, Geological Museum, London

Detachment, or décollement, is a common mechanismof folding in many lesser foothill ranges like the Jura(above). It occurs in flat sedimentary layers alongsiderising fold-mountains, in this case, the Alps. As theyoung fold-mountains rise, they push the sedimentarylayers sideways until they are detached from the under¬lying rocks and are rucked up like a carpet on a slipperyfloor. The "polish" or lubrication is a soft layer of rocksalt or clay underlying the sedimentary layers.

Overfolds form in fold-mountains when rucked-up rock

layers topple over. In Scotland, erosion has exposed theunderside of such a fold, a wide belt from Aberdeen toAntrim that is upside down.

Nappes are masses of rock that havebeen driven over younger rocks for longdistances until they cover them like acloth. The Matterhorn (above right) wascarved by glaciers out of a nappe ofpre-Alpine granite driven over Switzer¬land from the south.

13

Geological time scale

Era Period / System Epoch / Series Duration

millions of years

CENOZOIC

Quaternary Holocene 0.01

Pleistocene 2.5

Tertiary Pliocene 4.5

Miocene 19

Oligocène

Eocene

12

16

Palaeocene 11

MESOZOIC

Cretaceous

Names based on

geographical

location and

vary widely

71

Jurassic 54

Triassic 35

PALAEOZOIC

Permian 55

Carboniferous

Pennsylvanian

Mississippian

45

20

Devonian 50

Silurian 35

Ordovician 70

Cambrian 70

Proterozoic

or

AlgonkianPRFHAMRRIAN Not divided into periods 4030

Archaeozoic

or

Archaean

A geologist's hammer has been adopted as the "trademark"of the International Geological Correlation Programme(IGCP), a major scientific venture, jointly undertaken byUnesco and the International Union of Geological Sciences(IUGS), devoted to the study of the earth's crust and itsmineral and energy resources. The Programme involvessome 4,000 geologists In more than 110 countries, working onabout fifty research projects. It combines the advantages ofnon-governmental participation and guidance through Its sci¬entific partner, the IUGS, with the benefits of governmentalsupport through Unesco. Projects undertaken by the IGCPrange from study of geochronology to prospecting for eco¬nomic mineral deposits and processing of geological data.

14

A trilogyof rocks

Igneous rocks

Igneous rocks form from molten material(magma) that rises from the Earth's in¬terior. Magma that solidifies beforereaching the surface forms intrusive rockslike dolerite, gabbro and granite. Magmathat solidifies after reaching the surfaceforms volcanic rocks like basalt (the mostcommon), obsidian and pumice. As itcools and crystallizes, the magma's com¬position changes, producing hundreds ofdifferent types of igneous rock from re¬latively few types of mineral. Rapid cool¬ing may trap minerals formed at highertemperatures.

Metamorphic rocks

"4 Metamorphic rocks are rocks that havebeen transformed (metamorphosed) andcrystallized by heat and pressure. In thisprocess, the minerals of the original rockeither reform into larger crystals or reacttogether to form new minerals. The rocksproduced have a layered texture calledfoliation, familiar to us in slate. Meta-

morphism occurs in two types ofsituation: (i) around plumes of molten rockthat have risen in cool rock ("contact meta-morphism"); and (ii) in the interiors of fold-mountains where the heat flow is high, andbeneath ocean trenches where there are

high pressures ("regional metamor-phism"). Metamorphic rocks include slate,produced from clays at low temperaturesand pressures; schist and gneiss, formedat higher temperatures and pressures;and marble, formed from sandstone.

Sedimentary rocks

^ Sedimentary rocks have a layered struc¬ture. They contain all the world's oil andcoal and all its fossils. The first step in theirformation is the weathering of existingrock. The products are carried away asfragments or in solution and depositedelsewhere as layers of sediment. Theselayers, subjected to pressure or cementedtogether by other minerals, harden intosedimentary rock. There are three maintypes: (i) Fragmental. Made of pebbles(breccia, conglomerates), sand (grits,sandstones, siltstones), or mud (clays,mudstones, shales), (ii) Organic. Consist¬ing mainly of the fossil remains of plantsand animals (coal, fossil-bearing lime¬stones), (iii) Chemically formed by pre¬cipitation from salt water or hot springs(rock salt, gypsum, ironstone, some lime¬stones and siliceous cherts).

15

Drillinginto the unknown

by Yevgeni Kozlovski

1

THE structure of the Earth reflects the

long history of its evolution. By re¬constructing this history scientists

hope to find the key to such processes as theformation of the Earth's crust, volcanism,

and the upheavals, subsidences and foldingswhich led to the development, on theEarth's surface and in its sub-stratum, ofconditions which favoured the formation,accumulation and preservation of usefulminerals.

In the Soviet Union, study of the complexphysical and physico-chemical processeswhich take place within the Earth's hardcrust and the upper layers of the mantle isundertaken within the framework of a vast,integrated programme for the explorationof the "basement" of the country using

geological, geophysical and geochemicalmethods as well as deep and very deepdrilling.

The particularity of this programme isthat it focuses on the study of the Earth'scrust within the limits of the continental

zone where most of the planet's usefulminerals are concentrated. Geophysical ex¬plorations are being conducted along thesystem of profiles traversing the entire terri¬tory of the USSR, and deep and very deepdrilling is being undertaken at their pointsof intersection.

In this way it has been possible to explorethe Mohorovicic Discontinuity (the bound¬ary between the Earth's crust and the man¬tle) and to obtain new data on the structureand physical properties of the upper man-

16

tie, to identify zones where important frac¬tures occur in the Earth's crust and deter¬

mine their extent, and to pinpoint theboundaries and structure in depth of majortectonic elements which may be the site ofconcentrations of mineral ores, oil or gas.

At the heart of the programme is theexploration of the deep structure of thecontinental crust, on whose layers is im¬printed, as on the pages of a book, thewhole story of its formation. The first drill¬ing was made in the Kola Peninsula, on thefringe of the Baltic Shield, which is com¬posed of ancient crystalline rock datingback to Precambrian time. The Kola drill¬

ing has thrown some new light on the evolu¬tion and structure of the early continentalcrust of the Earth as a whole, since similar

formations are widely distributed in otherparts of the globe in India, North Amer¬ica, South Africa, Western Australia,Antarctica and Greenland. Very deep drill¬ing explorations being carried out in theUSA, Canada and the Federal Republic ofGermany are also contributing to our know¬ledge of the deep horizons of the Earth inareas potentially rich in mineral rawmaterials.

The direct observations made possible bythese drillings have provided the founda¬tions of the first factually-based model ofthe continental crust and have led to a

The Kola Peninsula in the far north of

the USSR Is the site of the first verydeep drilling made as part of an ambi¬tious programme aimed at exploring thedeep structure of the continental crustand seeking areas potentially rich inmineral, oil or gas deposits. Left, thedrilling rig and the accompanying build¬ings and workshops which house theindustrial and technical services. The

drilling rig is clad with corrugated ironsheeting to maintain a constant positivetemperature in this bleak Arctic environ¬ment.

Right, the new sophisticated and fullyautomated URALMACH 15000 drillingplant, which incorporates the very latesttechnology, is capable of drilling downto a depth of 15 kilometres. The derrickis 86 metres high and has a hoistingcapacity of 400 tons.

revision of earlier notions about the evolu¬

tion and structure of the Earth's depths.The Kola drillings have resulted in a

series of unexpected and very interestingdiscoveries.

One of our objectives was to borethrough the so-called granitic layer (theupper part of the consolidated crust) toreach a basaltic layer whose existence hadbeen deduced from geophysical data. Geo-physicists had observed sharp variations inthe speed of seismic waves at great depths,and, since these waves travel faster through

granite than through basalt, these varia¬tions were thought to indicate a transition inthe Earth's crust from a granitic to a basalticlayer. But this was no more than conjecturebecause, unlike the granitic layer, identifiedwith the Archaean granitoid gneiss which iswidely distributed over the surface of thecontinents, the basaltic layer does notemerge on the surface.

The Kola drilling was the first ever tobore through the line where the seismicwaves undergo a sharp change of speed. Butcontrary to expectations, no basaltic layer ^

17

^ was discovered. It became apparent that thevariations in the speed of diffusion of theseismic waves was related, not to a transi¬

tion from a granitic to a basaltic layer, but tothe decompaction of the rock which occursat great depths.

This phenomenon is due to the fact that,under the effect of the high pressure andtemperatures existing at great depths, wateris released from the crystalline network ofminerals and, because of the enclosed

space, exerts pressure on the rock, leadingto Assuring and consequently decompac¬tion. It turned out that the decompactedzone had subsisted over a long period.

The discovery of the phenomenon of"hydrogenous decompaction" not onlymakes it possible to explain the geologicalcharacter of certain boundary zones whichreflect seismic waves at great depths, thenature of hydrothermal fluids, and themechanism of tectonic deformations, it also

radically alters our ideas about the hydro-logical cycle in continental conditions andof the structure of the underground hydro¬sphere,

The drilling provided extremely interest¬ing information not only for geologists butalso for biologists. It was discovered that

. the deep horizons which had been thoughtto be "dead" since the beginning of timehad actively participated at some stage inthe biological processes which took place inthe depths of the Earth.

Isotopic carbon analysis revealed twosources of carbonic gas the first connectedwith the mantle and found mainly inArchaean rocks, the second of biogenicorigin and found predominantly in Protero¬zoic rock, in which petrified remains ofmicro-organisms (micro-fossils) estimatedto be thousands of millions of years old,were also found.

This was not an isolated discovery.Seventeen species of micro-organisms werefound, bearing witness to an extensive de¬velopment of biogenic processes on ourplanet in earliest times. Thus biological lifestarted on Earth much earlier than had

previously been estimated.Data supplied by direct measurement of

temperatures at great depths have obligedus to revise our concepts regarding presentand geohistorical variations of temperaturein the bowels of the Earth. It was previouslythought that in regions of slight tectonicactivity temperature rise in relation todepth increase was insignificant. However,although it was expected during the Koladrilling that the temperature at a depth often kilometres would be about 100 degreesCentigrade, it turned out in fact to bealmost double this estimate, at 180 degreesCentigrade. It was established that duringthe Proterozoic era the géothermie gradient(the temperature increase per 100 metres ofdepth) was five times higher than it is today.

Study of the thermic regime in the bowelsof the Earth also provided an answer to aquestion that has long preoccupied scien¬tists what is the contribution of the mantle

and of radioactive decay of elements inrocks to the overall heat flow in the interior

of the Earth? It was established that the

mantle was the chief source of ascendingheat.

Finally, the existence of underground wa¬ter inside the old crystalline massifs at prac¬tically all the levels reached was proved forthe first time. Inflows of highly mineralizedwater saturated with bromine, iodine andheavy metals were discovered, as well asgases circulating through the crystallinerocks in the zones of tectonic deformation.

At depths of 6.5 to 9.5 kilometres, zones oflow temperature hydrothermal mineraliza¬tion (copper, lead, zinc, nickel, silver), pre¬viously considered to be primarily near-surface formations, were discovered.

The large number of mineral associationsdiscovered in the rock strata traversed dur¬

ing the drilling confirms the possibility thatmineral deposits may be present in indus¬trially viable accumulations.

We were also led to revise our ideas

about the physical state and properties ofrocks at great depths. It emerged that rockfissures do not disappear as depth increases.

This journey towards the centre of theEarth the first to such a great depth (15kilometres) was made possible by the em¬ployment of radically new types of drillingtechnology and equipment. This vastundertaking necessitated the creation of aunique type of drilling installation theURALMACH 15000.

Drilling was effected by the open-shaft(untubed) method. This considerably im¬proved the quality and accuracy of geo¬physical measurements. The reconnaiss¬ance operations were conducted, not withsteel tubes, but with extra-strong heat-resis¬tant tubes made from specially-developedlight alloys capable of withstanding temper¬atures of 230 to 250 degrees Centigrade.The specially-designed, highly efficientrock-blasting and turbo-drills were pow¬ered by the energy of the drilling liquidpumped into the well. A completely newtype of apparatus was built to draw rocksamples from great depths intact and pre¬served in their original orientation.

The programme for the study of the sub¬terranean structure in depth provides forexploration throughout the territory of theSoviet Union. Drillings at very great depthare at present being conducted in the Trans-caucasus, the Urals, the Krivoi'-Rog Basinand the Muruntauski region of CentralAsia. A drilling is being set up in the Tiu-men district of Western Siberia.

The data provided by them will make itpossible, firstly, to assess the oil, gas andore-bearing potential of deep horizons and,secondly, to elucidate the essential ques¬tions relating to the tectonic evolution ofthe Earth in the light of the continental drifthypothesis. The programme provides forspecial experimental and theoretical studiesconcerning the elaboration of a generaltheory of the evolution and structure of theEarth's tectonosphere. The journey intothe Earth's past, undertaken by scientists todecipher its evolution, will continue.

YEVGENI KOZLOVSKI, of the Soviet Union, ishead of the interdepartmental council of theUSSR State Committee ofScience and Technol¬

ogy for the study of the deep layers of the Earthand for very deep drilling. Holder of the LeninPrize, he is the chief editor of a monograph ondeep drilling in the Kola Peninsula, and of theworld's first Encyclopaedia of Mining.

COLOUR PAGES

Opposite page

Top photo: (a) This pebble of volcanic ash,found near ¡sua in west Greenland, hasbeen shown to have an age of3,824 million(plus or minus 12 million) years and is theoldest known rock in the world. Other

rocks close to this age in the same area arethe Amitsoq Gneiss (b) and a banded ironformation (c), whilst the fourth rock (d) isan ancient Antarctic rock.

Bottom left: A stony meteorite from Bar-well, England. Meteorites have been datedback to about 4,600 million years.

Bottom right: A rock from the Moon. Theoldest rocks brought back from the Moonhave been dated at about 4,600 millionyears.

Photos © British Museum (Natural History) Geological Museum,London

Page 20

Above: One of the geological and scenicwonders of the Earth, the Grand Canyon isan immense gorge (in places over 1.5kilometres deep) cutby the Colorado Riverinto the high plateaux of northwest Arizo¬na, USA. Its rocks, including granite andschist some 4,000 million years old, con¬stitute a unique record of geologicalevents. Over 300 kilometres long, theCanyon is at some points more than 20kilometres wide.

Photo Alan Keler © Sygma, Paris

Below: Irazu, a volcano in the CordilleraCentral, Costa Rica, erupts in an inferno offlame and lava.

Photo Ernst Haas © Magnum, Paris

Page 21

Above: Gases, ash and incandescent,semi-solid lumps of lava are hurled up¬wards during a volcanic eruption.Photo Ernst Haas © Magnum, Paris

Below: The Hawaiian volcano Mauna Loa

during an eruption in 1984. Rising to 4, 169metres above sea level, Mauna Loa (mean¬ing "long mountain") has a dome 120kilometres long and 102kilometres wide. Ithas averaged one eruption every three anda half years since 1832.Photo Krafft © Explorer, Paris

18

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The restlessEarth

The uncertain art

of earthquake prediction

by EM. Fournier d'Albe

Colour page left

Above: Photo taken in 1965 shows the

boiling crater ofSurtsey, a volcanic islandformed off southern Iceland after a sub¬

marine eruption on 14 November 1963.(See picture story page 29.)Photo Ernst Haas © Magnum. Paris

Below: Air view of the church of the villageof San Juan and another edifice partiallyburled in lava flows from the eruption ofParicutin, in West Central Mexico. One ofthe Earth's youngest volcanoes, Paricutinbegan to erupt on 20 February 1943. Whenthe eruption ended in 1952, the peak was2,800 metres high.Photo Kraift © Explorer, Paris

IT is often said that one cannot claim to

understand a natural phenomenon un¬

less one can accurately predict itsoccurrence. If this is true, then the ability topredict earthquakes must be one of theprincipal goals of the science of seismology.

The scientist who ventures into this field,

however, incurs an unusual degree of per¬sonal and social responsibility. Prediction

of a potentially destructive earthquake mayhave serious disruptive effects on the socialand economic life of a community, whetheror not it eventually proves to be correct.Many lives were saved, for example, by thecorrect prediction of the Haicheng earth¬quake in China in 1975, but against thismust be set many cases of erroneous predic¬

tions which have not only damaged thereputations of the scientists concerned buthave also had considerable economic and

even political consequences.In the present state of knowledge it is not

possible to determine, by observation andcalculation, precisely where and when anearthquake will take place. This is because,in order to make a prediction with the re¬quired pinpoint accuracy, detailed informa¬tion is needed on the stress fields and the

mechanical properties of the Earth's crustover wide areas and down to depths ofseveral tens of kilometres. Even if it were to

become technically possible to obtain suchinformation, the cost of doing so wouldprobably remain prohibitive, and might in¬deed be greater than that of repairing thedamage caused by the earthquake itself.

The few successful predictions that havebeen made were based on the observation

of precursory phenomena of various kindsgenerated by the same deep-seated process

which leads to earthquakes yet not causallyrelated to the earthquakes themselves.Such phenomena might include suddenchanges in the level of minor seismic ac¬tivity, slight deformations of the Earth'ssurface, changes in magnetic or electrical

fields, unusual rise or fall of water levels in

wells, changes in the gravity field or abnor¬mal behaviourof animals. Howevernoneof

these precursory . phenomena has yetproved to be a reliable indicator of a forth¬coming earthquake. The methods so suc- ^

Thousands of lives were saved when

Chinese experts successfully predictedthe Haicheng earthquake of 1975 (seemap). Following a severe earthquake atXingtai, in 1966, scientists noted that theepicentres of subsequent tremors andshocks, including that of the earthquake inthe Bo Hai gulf in 1969, seemed to bemoving in a north-easterly direction to¬wards the heavilypopulated Liaoning Pro¬vince. By June 1974, scientists were pre¬dicting that there would be a major earth¬quake to the north of Bo Hai within one ortwo years. On 1 February 1975, a series ofminor tremors was correctly identified asthe foreshock heralding a major shock inthe area of the city ofHaicheng, and on thefollowing day more than a million peoplewere evacuated to temporary outdoorshelter. Early in the evening of 4 Februarythe main shock (magnitude 7.3) occurred.Although 90 per cent of the houses in thearea were damaged or destroyed, therewas very little loss of life.

©

23

^ cessfully employed at Haicheng failed topredict the terrible Tangshan earthquake inthe following year.

New data are constantly being accumu¬lated and there is hope that the accuracy ofpredictions will gradually improve,although they will of necessity remain prob¬abilistic in nature. They will not state, forinstance, that "an earthquake of magnitudeX will take place in area Y on a certaindate"; rather they will take the form of astatement on the probability of an earth¬quake of a certain magnitude occurring in agiven area during a specified period of time.

So much for the scientific side of the

problem. The next question is: What will bethe effects of the predicted earthquake, if itactually occurs? How many buildings willbe damaged or destroyed, and how manypeople will be killed, injured or renderedhomeless? Will telephone networks con¬tinue to function? Will streets be blocked bydebris?

In preparing to face an impending earth¬quake emergency, civil defence servicesneed answers to these questions. They needinformation on the expected strength of theseismic ground motion and on the vulner¬ability of buildings and urban lifelines tothis motion. They will need to prepare"scenarios" of the probable effects of thepredicted earthquake.

For this to be done, seismologists and

geologists have first to estimate what will bethe intensity of the ground motion causedby the expected earthquake and how thisintensity will vary from one part to anotherof the area round the earthquake focus.This they do on the basis of previous experi¬ence and of knowledge of the local charac¬teristics of the soil and sub-soil.

Then an inventory of buildings in the areahas to be compiled and an assessment madeof how each building is likely to react to theexpected ground motion, according to itsstructural type and to the materials of whichit is built. This is where the greatest difficul¬ty lies, since it is almost impossible to pre¬dict exactly how any individual building willbehave in an earthquake. The best one cando is to base the assessment on information

as to how similar buildings have behaved inrecent earthquakes elsewhere. Hence theimportance of carrying out detailed studiesof the damage caused each time an earth¬quake occurs. Already some extremelyvaluable information has come from the

studies made in Romania and Yugoslavia ofthe damage caused in those countries by theearthquakes of 1977 and 1979.

Clearly, all this work takes time andshould preferably not be left until an earth¬quake is impending. For this reason civildefence services in many earthquake-pronecountries are already collecting such in¬formation and preparing scenarios, so as to

be ready to deal more effectively with poss¬ible earthquake disasters, whether or notthey are predicted in advance.

Earthquake scenarios are invaluable notonly for planning the mobilization of rescueteams, medical and fire-fighting services,and the stockpiling of emergency suppliesof food and shelter against a possible earth¬quake, but also for planning the varioustemporary measures of protection that canbe taken in response to a prediction. Forinstance, inflammable or toxic substances

can be moved into safe storage, vulnerablesystems in chemical plants can be shut downfor a time, water levels in reservoirs can belowered and schools and theatres can be

temporarily closed. In the final stage of analert, people can be evacuated from theirhomes or places of work in vulnerablebuildings.

Such measures are costly and disruptiveof individual and social life. They may beresisted and cannot be prolonged for morethan a few days, and they will probably beabandoned after one or more false alarms.

They are therefore likely to be applied inresponse to an earthquake prediction onlyif the responsible authorities are convincedthat the prediction satisfies certain criteriaof accuracy and reliability.

As we have seen, scientific predictionsare likely to be expressed in terms of prob¬ability. Public authorities, on the other

The world's first seismometer

The first known instrument capable ofsensing earth motion was invented in AD132 by the Chinese philosopher ChangHeng. It consistedofa large bronze vessel,some two metres In diameter, around

which were spaced eight dragon headswith pivotingjaws In which were held eightballs. Inside the vessel was a pendulumwith eight arms each of which was con¬nected to one of the dragon heads. Whenan earthquake shock caused the pendu¬lum to vibrate, the arm connected to the

dragon head facing the direction of theshock caused its jaws to open allowing theball they held to fall into the open mouth ofone of the eight toads positioned aroundthe base of the vessel. The Instrument was

sensitive enough to detect an earthquakewhose epicentre was over 600 kilometresaway. It was not until 1856 that a seismo¬graph capable of recording the passage ofseismic waves and giving their amplitude,time ofonsetanddirection was installedat

the observatory at Vesuvius. Opposite

page, a modern reconstruction of ChangHeng's apparatus and, above left, Its modeof operation. Since the founding, In theearly 1960s, of the Worldwide Standar¬dized Seismograph Network (WWSSN),seismic observatories with standard

equipment and synchronized time-keep¬ing have been established virtuallythroughout the world. Map above showsdistribution of the WWSSNandassociated

observatories.

24

hand, have to make decisions on a "yes orno" basis. It is therefore of crucial import¬ance to develop an effective dialogue be¬tween scientists and public authorities. Thelatter need to acquire, through discussionswith the scientists, insight into the reason¬ing that leads to the formulation of predic¬tions in a particular form. For their part,scientists need to familiarize themselves

with the problems faced by public author¬ities, so that they will understand theresponses of the latter to predictions andthe reasons behind those responses.

It is essential that any earthquake predic¬tion that is communicated to the publicshould be accompanied by a verifiable esti¬mate of the probability of occurrence of thepredicted event within the specified limitsof time and space. If it is to be useful inpractice, the prediction must also meet thefollowing criteria:

(a) its lead time (the interval between theissue of the prediction and the expectedoccurrence of the event) should be longerthan the time required for putting intoeffect the appropriate protective measuresand for mobilizing the resources needed todeal with the emergency;(b) its time window (the duration of theperiod during which the event is predictedto occur) should be shorter than the max¬imum acceptable duration of protectivemeasures such as the evacuation of build

ings, the temporary closure of plants andthe mobilization of rescue services.

The above criteria are, of course, verydifficult to satisfy given the present state ofscientific knowledge, but experience hasshown that predictions that fail to meetthem can cause severe social and economic

disturbance without being of any great useto the community concerned. Earthquakeprediction is not only a scientific problembut one which concerns the community as awhole.

The development of techniques of earth¬quake-resistant design and constructionoffers the hope that in the course of timedeath and destruction in earthquakes willbecome a thing of the past. The phenomenaaccompanying some volcanic eruptions,however, are of such violence that there are

no means of protection against them. Theonly hope of survival lies in flight from thethreatened area. Accurate prediction oferuptions is therefore of vital importancefor the safety of people living on or nearactive volcanoes.

Fortunately, the problem of predictingeruptions is slightly less difficult than that ofpredicting earthquakes. This is because thepossible sites of volcanic eruptions areusually known. It is rare for an eruption tooccur anywhere but from an existing volca¬nic structure, although eruptions do some¬times occur at volcanoes that have been

dormant for so long that they are thought tobe extinct. By careful geological study it ispossible to identify and map the areasaround a volcano that have been affected in

the past by one or more of the destructive

phenomena that accompany eruptionsglowing avalanches, mudflows, lava flows,heavy ash falls, and so on.

A census can be made of the people wholive or work in these hazardous areas,together with an inventory of movableproperty and livestock. Evacuation routesto safe refuge zones can be identified andplans made for rapid evacuation in theevent of an eruption. Arrangements can beplanned for the emergency shelter andhousing of evacuees in the refuge zones. Ifworked out in detail beforehand, such planscan be instrumental in saving many liveswhen an eruption occurs.

As in the case of earthquakes, predic¬tions based on the observation of precur¬sory phenomena are necessarily expressedin terms of probabilities of eruption. Therewill always remain, therefore, the problemof making "yes or no" decisions in situationsof uncertainty. The risk of a possible catas¬trophe has to be weighed against the cer¬tainty of the inconvenience, hardship andcost of removing people from their homes,perhaps for periods as long as weeks ormonths.

Here again it is of crucial importance that ^

^ an effective dialogue be developed betweenscientists, civil authorities, the news media

and the public before any emergency arises.The threat of an imminent earthquake orvolcanic eruption is a great revealer of thestrengths and weaknesses of any com¬munity.

"Success stories" in dealing with suchthreats are still few, but they do demon¬strate that, if scientific predictions are pre¬cise and reliable, if the civil authorities are

prepared and have the means to takeappropriate protective action, and if thepublic is kept fully informed of the situationand of the action being taken to meet it, thelosses inflicted by these violent manifesta¬tions of nature can be reduced and may intime become a thing of the past.

E.M. FOURNIER D'ALBE, of the United King¬dom, is a specialist on earthquake risk man¬agement. Until 1979 he was head of Unesco'sDivision of Earth Sciences and was responsiblefor the initiation and development of the Organi¬zation's programme related to natural disastersand their prevention.

//Mechanism of earthquakes

Fault stuck after

last movement

Stress builds uprocks bend

like a bow

Focus

Earthquake! Rocksspring backand vibrate

When the Earth shakes

ALTHOUGH some minor earthquakeshave been triggered by human acti¬vities, such as underground nuc¬

lear testing and the construction of reser¬voirs and dams, the principal cause of allmajor earthquakes and most minor ones Isthe fracturing of rocks following the gra¬dual accumulation of stress during geolo¬gical processes.

The Earth's surface Is made up of aseries of plates (see page 10) and theseverest earthquakes tend to occur at theplate margins, where plates slide pasteach other as, for example, along the SanAndreas "fault" region of California. Dia¬gram above offers a simplified illustrationof the mechanism of an earthquake. Rockhas a certain elasticity and where adjacentareas of rock are subjected to the push/pull forces of plate movement stress gra¬dually accumulates. When the strain be

comes too great, the rock ruptures andtension is released as the rocks on either

side of the fault spring back violently. Thepoint at which the rupture originates iscalled the focus and the point on theEarth's surface directly above the focus iscalled the epicentre.

The energy released is emitted in waveswhich cause the ground to oscillate. It isthese seismic waves that are picked upand recorded by seismographs, instru¬ments which enable scientists to pinpointthe epicentre of an earthquake and to mea¬sure Its magnitude.

Two scales are commonly used to mea¬sure the size of an earthquake. The magni¬tude of an earthquakethe total amount ofenergy released or dissipatedis ex¬pressed In terms of the Richter Scale andis based on seismograph recordings ofthe amplitude of seismic waves. To cover

the huge size range of earthquakes, theRichter scale of magnitude is logarithmicrather than arithmetic, that is to say, thescale is so arranged that each increase inmagnitude of one unit represents a thirty-fold increase in earthquake size. Thus anearthquake of magnitude 8 on the Richterscale is 810,000 times as large as one ofmagnitude 4.

The intensity of an earthquake classifiesthe degree of shaking and is based oninspection of damage and on informationsupplied by people involved in the earth¬quake. The scale most commonly used iscalled the Modified Mercalli Intensity Scale(see below). Since this scale is based pure¬ly on observation of earthquake effects,the points on the scale are stated in Romannumerals, from I to XII, rather than in ordin¬

ary numbers, which might be interpretedas indicating some kind of measurement.

Modified Mercalli Intensity Scale

I Not felt by people.II Felt by people at rest on upper floors of buildings.

III Felt indoors; vibrations like a light truck passing outside. Hangingobjects swing.

IV Vibration like passing of heavy truck; windows, dishes and doors rattle.V Felt outdoors; sleepers wakened and liquids spilt.

VI Felt by all; many frightened and run outdoors; plaster and masonrycracked; furniture moved or overturned; windows, glassware anddishes broken.

VII Difficult to stand up; noticed by drivers of moving vehicles; plaster,loose bricks, tiles, etc. fall; large bells ring; waves on ponds.

VIII Difficult to steer vehicles; fall of stucco and some masonry walls; fall ofchimney stacks, towers, monuments; branches broken from trees;cracks to be seen in wet ground.

IX General panic; frame structures cracked and underground pipesbroken; conspicuous cracks in ground; sand craters.

X Most masonry and frame structures and foundations destroyed; se¬rious damage to dams and embankments; some bridges destroyed;large landslides.

XI Railway lines badly bent; underground pipes completely out of service.XII Damage nearly total; lines of sight and level distorted; objects thrown

up into the air.

26

Volcanoes

by Haroun Tazieff

VOLCANISM plays a fundamentalrole in the story of the Earth. Thecrust we live on, the water in

oceans, rivers and lakes and most of the

atmosphere we breathe are derived ulti¬mately from volcanic eruptions. Withoutvolcanism there would be no creation of

new oceanic crust through sea-floorspreading, no subduction (the draggingdown of older crust into the mantle where

it is melted and recycled), no orogenesis(mountain-building) and therefore noerosion and no sedimentation.

Without volcanism the Earth would

lack the colossal, continual flow of sul¬

phides, oxides, halogens, hydroxides ofall existing metals, emitted in the form ofgases at high temperature by fumaroles(volcanic vents) from the thousands ofactive craters, whether dormant or in

eruption, whether submarine or on land,scattered the length of the 100,000kilometres of the belts that mark the fron¬

tiers between the Earth's tectonic plates(see page 10) and the fractures occurringwithin those plates.

Without the contribution of submarine

fumaroles there would be no mineral sul¬

phide deposits; without fumaroles themarine environment, whose chemical

make-up made possible the emergence oflife and conditioned its evolution, would

not have existed; without fumaroles theEarth would have lacked the elements to

form the atmosphere whose compositionmade it possible for life forms emergingfrom the ocean to colonize the land and

then to evolve to give rise to humanbeings.

Like everyone else at that time, I wasunaware of all this when, in 1948, chance

brought me face to face for the first timewith the strange phenomenon of a volca¬nic eruption. Like all my fellow geologistsof that generation, especially my Euro¬pean colleagues, I had received from myteachers, among whom were some of in¬ternational renown, a course of instruc¬tion in which volcanism was barely men¬tioned, since, in their view, it representedno more than "a skin disease of the

planet".At all events, I knew practically no¬

thing at all about volcanism when, oneday in March 1948, to the north of LakeKivu in the Belgian Congo (now Zaire),

the first eruption I was privileged to seenot only opened the eyes of the naivegeologist I then was to the magnificenceof the spectacle but also to a phenomenonwhich, because of my lack of knowledge,raised more questions than it providedanswers.

In the forty or so years that have passedsince then, volcanology, moribund at theclose of the Second World War (barelysurviving in the United States and in NewZealand, but extinct everywhere else),gradually revived and finally, in parallelwith oceanography, came into full blos¬som. The new knowledge these two disci¬plines enabled us to garner soon revealedthe fundamental role played by volcan¬ism both in the phenomenon of sea-floorspreading and the genesis of life and itsevolution over the past 3,000 millionyears.

More than a third of a century spent inobserving eruptions from as close aspossible and in measuring everythingthere was to measure among otherthings energy flows (mainly thermal) andthe flow of matter (mainly in the form ofgases) has enabled me to establish that,rather than the liquid or lava phase, asmost people seem implicitly or explicitlyto imagine, it is the gaseous phase thatplays the active role in volcanism. Lava istotally passive and, without its eruptivegases, volcanism would simply not exist.Furthermore, eruptions always involvethe emission of gas, but not always oflava.

These considerations led me to the

conviction that, in order to understand

the mechanism of eruptions, it was essen¬tial to know the chemical compositionand thermodynamic evolution of theirgaseous phase. It would seem that thechemical composition of these gasesvaries from one kind of eruption toanother and from one type of magma toanother, but in our present state of know¬ledge it has not been possible to establisha correlation between the chemical varia¬

tions detected and the variations in activ¬

ity observed.

It must be admitted that, up to now,only an insignificant amount of data hasbeen acquired on the physico-chemicalcomposition of eruptive gases. By erup¬tive gases I mean those that have not been

subject to much cooling, oxidation by theair or hydration by groundwater, all ofwhich processes transform the gases to alesser or, more often, a greater extent.

Obviously, to measure the chemicaland physical properties of the eruptivegases before they degrade into fumarolegases, it is necessary to get close to thevents from which they are being emitted.This usually demands some physicaleffort and, at times, a certain amount of

courage. What too many volcanologistslack is not courage but a taste for muscu¬lar effort. Between the ages of twenty andthirty, some seem to possess it, but I havenoticed that, once they have attained acertain academic standing, they usuallyappear to lose it.

This would not be too serious were it

not for the fact that, in addition to the raw

data which will continue to be providedby the young and still enthusiastic volca¬nologists, a sine qua non of progress inthis field is experience of the actual eventof eruption, the complexity of which ismatched by its variability. This can onlybe acquired by direct observation of thephenomenon of eruption in all its succes¬sive forms.

The competence of the volcanologist inthis respect, like that of a physician, de¬pends both on proper knowledge of im¬portant publications and on experiencegained through the examination of a max¬imum number of subjects patients forthe doctor, volcanoes in eruption for thevolcanologist.

My first ten years of volcanologicalresearch in the field were devoted exclu¬

sively to seeking an explanation of thevarious aspects of the phenomenon oferuption. I soon became convinced thatthe maturation of dormant magma re¬sulted from the release of the gasesformerly dissolved within it. The chemic¬al properties, size and distribution of gasbubbles within the viscous mass, their

growth in size either by two or morebubbles joining up or by expansion dur¬ing their ascension through the magmaand of the magma itself, all these factorsplay their part in the maturation of themagma before the eruption and in itsevolution during the eruption itself.

Whether they can be measured ormerely observed, when correctly inter-

27

^ preted the parameters of an eruption en¬able us more or less to understand the

eruptive process and, consequently,sometimes to predict it.

This understanding enabled me, from1958 on, to answer accurately questionsput to me by the administrative or politic¬al authorities of a number of cities, pro¬vinces, even countries, where a volcano

appeared to pose a threat to public safety.Thus I found myself gradually movingfrom fundamental research to research

applied to the forecasting of possibleeruptions. Since 1981, when the FrenchGovernment decided to take an official

stand on the mitigation of catastrophicevents, my work in volcanology has beenlimited to this area.

Over nearly thirty years I have foundmyself in the position of having to answerquestions from the authorities in a dozenor so different countries. And if my re¬plies have not once been mistaken, this isbecause, like a good doctor, I have basedmy diagnosis on the information avail¬able interpreted in the light of my ex¬perience. Out of fifteen cases which Irecall, I was able to give nine reassuringreplies, to confirm the threat of dangerthree times and, on three occasions, was

obliged to admit that I did not know.Over this period, the questions put to

me were seldom in the form "Is there

going to be an eruption or not?" Usually Iwas asked whether there was or was not

any danger from an eruption actually tak¬ing place. While, under such circum¬stances, the latter question is clearly themost important, it is also the most diffi¬cult one to answer.

It is, in fact, relatively easy to predictan eruption when the volcano in question

is being properly watched over bygenuine experts with adequate equip¬ment. With the exception of eruptionsresulting from a build-up of steam press¬ure caused by overheating of under¬ground water beneath a blocked venthole eruptions which emit no magma orlava, but only steam, some fumarolegases and fragments of the rock blockingthe vent all volcanic eruptions are theresult of the ascent to the surface of the

globe of a certain volume of magma.This ascension of magma cannot occur

without some movement of the Earth's

crust in response to the pressure of themagma; either the crust stretches andbecomes deformed, or it fractures. Sur¬face deformations can be detected and

measured by such instruments as tilt-meters, extensometers and geodimeters.The opening of fractures, through whichmagma can infiltrate into the crust andrise to the surface, causes tremors which

can be recorded by seismometers.These geophysical observations and

measurements, which can give warning ofan eruption, often several months butsometimes only days or hours in advance(depending, among other things, on thedepth at which the magma is situatedbefore it begins its ascension), are sup¬plemented by other observations whichmay help the volcanologist in making aforecast. These include the temperature,composition and pressure of fumarolicgases, and changes in the magnetic fieldof the Earth's crust. All these indications

enable experienced volcanologists to de¬tect a coming eruption and to give a datefor its arrival, sometimes with very greatprecision.

Unfortunately, from the point of view

of saving lives, such predictions are oflittle importance. Magmatic eruptions,whether they be explosive or effusive,never start in disastrous fashion. The first

phase of an eruption is always (to myknowledge no exception to this rule hasever been observed) relatively moderate,allowing inhabitants time to leave thethreatened area.

Evacuation, the only way to protectpeople from major volcanic risk, is rarelynecessary, since it is quite exceptional foran eruption, after its initial phase, todeteriorate into a paroxysmal phase or tobecome even slightly more dangerous.Out of the average hundred eruptionsthat occur year after year throughout theworld, scarcely one will develop in thisway and so justify special precautions.

The major problem that faces the vol¬canologist is to forecast the evolution oferuption while it is taking place a taskinfinitely more difficult than predictingan imminent eruption. Once an eruptionhas begun, all the mechanical indica¬tions deformation or fracturing of thesurface connected with the rise of the

magma through the Earth's crust willhave disappeared and the flow of magmawill be "fluid", that is, it will no longerhave to fracture the rock in the depths orlift the flanks of the volcano to force its

way to the surface.Deprived of these two indicators that

are fundamental to the forecasting of acoming eruption (tremors and deforma¬tion of the surface), the volcanologist isobliged to establish his diagnosis on thebasis of his interpretation of the otherphysical and chemical indications men¬tioned above. Correlation of the various

factors involved and their interpretation ^

CONTINUED PAGE 31

Waves of destruction

At one o'clock in the afternoon of 26 August 1883 the first ofa series of increasingly violent explosions occurred on thevolcanic island of Krakatoa, in the Sunda Strait between Javaand Sumatra, Indonesia. An hour later, a black cloud of ashrose 27 kilometres into the air above the island.

The eruptions continued, reaching a climax with atremendous explosion at ten o'clock in the morning of thefollowing day which sent ash billowing 80 kilometres into theair and which was heard in Australia over 4,000 kilometres

away. All but a fragment of Krakatoa, the cone of a hugeunderwater volcano, disappeared beneath the waves.

On the neighbouring islands of Lang and Verlaten, volcanicash and debris lay 60 metres deep. Vivid sunsets caused byfine ash particles in the air were seen as far away as Europeand rafts of pumice (lava filled with gas bubbles) floated onthe surrounding ocean for many months.

Worse was to come; the collapse of the volcano triggered aseries of tsunamis, or seismic sea waves (often called tidalwaves, a misnomer since they have no connection withtides). The biggest wave, which attained a height of some 35metres, devastated some 300 towns and villages on theshores of Java and Sumatra, taking 36,000 lives.

Almost all tsunamis occur in the Pacific. They are causedby a sudden vertical movement of the sea bed resulting froma submarine volcanic eruption or an earthquake. Following a

disastrous tsunami in 1946, a warning system was estab¬lished covering the entire Pacific Ocean. Tsunami detectorsand seismic recording apparatus at seismic observatoriesaround the Pacific sound the alarm whenever a likely event isdetected. The information recorded is transmitted to the Hon¬

olulu Observatory which is responsible for assessing the riskand issuing warnings if this is considered necessary.

Sumatra

VKrakatoa o -

>. tth-ftll 4Rodriguu Island ' , \

"*"*** ¿Alte« Springt'-. art* ovtf which txplotlont wtrt httrd ..'

30004HTTi

28

Birth of an island

On 14 November 1963, a fiery eruption inthe Atlantic Ocean off the southern coast

of Iceland heralded the birth of a new

island. Named Surtsey, after Surtur, thefire god of Icelandic myth, the new islandrose from the water in a convulsion of

flame and steam. A weekafter the eruptionSurtsey had a surface area of 70 squaremetres and within three and a half yearshad grown to its present size of two and ahalf square kilometres with elevations ofup to 173 metres. When scientists visitedthe island after it had cooled, they wereastonished to find that plant life hadalreadyestablisheda footing. Constitutingas it does the first "virgin" ecosystemknown to man, Surtsey is now the siteof a long-term ecological research pro¬gramme.

29

Photo Jacques Huttin © Gamma, Paris

Cry havoc!

Although prediction of volcanic eruptionscan reduce orprevent loss of life, little canbe done to control damage to crops orproperty once an eruption is under way.The three major dangers arise from mud-flow, lava-flow and ash.

Over the last few centuries mud-flows

(sometimes known as lahars^ have provedto be the most dangerous, killing morepeople and destroying more property thanany other type of volcanic activity. Mud-flows often result from the rapidmelting ofice or snow on the slope of a volcano ormaybe due to heavy rain orsnow falls afteran eruption on new volcanic ash. Mud-flows have been known to attain speeds ofup to 70 kilometres an hourand to travelas

30

3fr

rar as Í80 kilometres. Left, the town ofArmero, Colombia, swallowed up by mudfollowing the eruption of the Nevado delRuiz volcano, in November 1985.

Thin lava-flows cool fairly quickly, butthicker flows may take years to cool com¬pletely. Various methods have beenattempted to check or divert lava-flows,including the use of water hoses to createa solid wall ofcooled lava andbombing thesides of a flow to split it into many smallerflows. Above left, lava-flow blocks a roadfollowing the eruption of La Fournaise vol¬cano on the French island of Réunion in

the Indian Ocean, on 18 March this year.Despite its name, volcanic ash is not the

product of burning; it consists of pulver

ized lava and fragments of rock throwninto the air by the sudden explosiveescape of volcanicgas. The eruption of theTambora volcano on the northern coast of

the island ofSumbawa, Indonesia, in 1815,which killed 50,000 ¡slanders, is estimatedto have had an explosive force equivalentto 16,000 megatons. The very fine ash fromsuch an eruption may travel huge dis¬tances andaffect weatherpatterns. Above,the village of Parentas, Indonesia, en¬veloped in volcanic ash following the erup¬tion, in 1982, of the Galunggung volcano.

CONTINUED FROM PAGE 28

^ is extremely difficult in view of our pre¬sent lack of sufficient research data and

experience in this field. And without cor¬relation to enable him to establish links of

cause and effect between what he has

been able to measure and observe, it isvirtually impossible for the volcanologistto establish a serious diagnosis.

Finally, I would like to remind readersof an article by me which appeared in theOctober 1967 issue of the Unesco

Courier. In it I drew the attention both of

politicians and of the inhabitants of the

regions involved to the great danger ofso-called "extinct" volcanoes. These vol¬

canoes are often, in fact, only dormant,which implies that they will one day be¬come active again. This is a risk whichshould be taken seriously and construc¬tion should be avoided within the dangerzone surrounding such volcanoes.

The extent of the danger zone will de¬pend on the nature of the volcanic activity(whether it is effusive or explosive), thesize and altitude of the volcano con¬

cerned, and even the climate of the re¬

gion in which it is situated.

The importance of climate and altitudewas demonstrated in dramatic fashion on

13 November 1985 with the eruption ofthe Nevado del Ruiz volcano in Col¬

ombia. Had it not been for the height ofthe volcano and the climate of the region,which made possible the formation of athick icecap on its summit, the upsurge oflava at a temperature of 1,000 degreesCentigrade would not have provoked themelting of hundreds of thousands of cubicmetres of ice and the formation of "la-

hars", those terrible torrents of volcanic

mud which swallowed up the town ofArmero, claiming the lives of 23,000victims.

What I wrote almost twenty years agoabout the danger represented by Vesu¬vius (Italy) or the Campi Flegrei (thePhlegraean Fields, Naples, Italy), MountFuji (Japan) or Mount Rainier (USA),remains true today, as witness what hap¬pened at Mount St. Helens, a close neigh¬bour of Mount Rainier, and at Helgafellin Iceland. The authorities of countries

within whose borders potentially danger¬ous volcanoes are situated those

thought to be extinct as well as thoseknown to be active, such as Merapi (In¬donesia) or Etna (Italy), Sakurajima(Japan), Vulcano (Italy) or Pichincha(Ecuador), to name but a few shouldtake advantage of the "days of peace" toconsider the problems that will arise andprepare' the action they will take whenthese sleeping giants reawaken.

HAROUN TAZIEFF, eminent French volcanolo¬gist, was formerly Director of Research at theCentre National de la Recherche Scientifique.Until recently Secretary of State for the Preven¬tion of Major Disasters, he is the author of manybooks and studies on volcanology. He has alsoproduced a number of films and documentariesincluding Les Rendez-vous du Diable (The De¬vil's Rendezvous, 1958) which achieved world¬wide acclaim.

31

Quaternary. Large mammals like mastodons (A), sabre-tooth cats (B), and bluewhales (C) are at first dominant. For the last million years, ice intermittently coversmost of the northern hemisphere. Some animals migrate; some, like woollyrhinoceroses (D), adapt to the cold. Early man (E), using stone tools and making fire,is succeeded by modern man.

mTertiary. Mammals evolve rapidly, producing such specialized types as the lemurPlesiadapis (A), ancestor of the primates, five-toed Phenacodus (B) and hornedTitanotherium (C). Birds evolve, including giant flightless forms like Diatryma (D).Fish, reptiles and invertebrates now resemble those of today; for example, the sandshark (E) has hardly changed.

Cretaceous. On land, flowering plants like magnolia (A) appear. In the sea, modernbony fishes evolve alongside sea-urchins (B) and bivalve molluscs (C). At the end ofthe period, giant dinosaurs, like Stegosaurus (D), and large flying pterodactyls (E)suddenly die out. New types of small mammal, such as the shrew-like Phascolother-ium (F), evolve.

Jurassic. The sea shelters brachiopods, cephalods called ammonites (A), belem-nites (B) and fossil oysters such as Gryphaea (C). There are bony fishes, sharks andtwo groups of marine reptiles: ichthyosaurs (D) and plesiosaurs. Great dinosaurs likeBrontosaurus (E) share the land with small mammals. Archaeopteryx (F), the ances¬tral bird, takes wing.

Triassic. Such mammal-like reptiles as Cynognathus (A), ancestors of the mammals,are succeeded by small animals, dinosaur-ancestors like Omothosuchus (B). Club-mosses, horsetails and seed ferns become rarer; they are replaced by cycads,ginkgoes (C) and conifers. In the sea, new invertebrate groups evolve. Sea-lilies (D)and reef-building corals are numerous.

Permian. Mammal-like reptiles like Dimetrodon (A) rule the land. Large amphibiansare scarce. In the sea, cephalods (B), two-valved molluscs (C) and primitive bony fish(D) continue to thrive; corals and sea-urchins grow scarcer, and most of the sharks dieout. A forest of seed ferns covers the southern land mass. More varied plant lifeflourishes in the north.

°Y'.MM

Carboniferous. The amphibians (A) become a large and important group; theyeventually give rise to the reptiles, the first full-time land vertebrates. Conifers and treeferns (B) evolve, and dragonflies (C) and other insects appear. Sharks (D) dominatethe sea. In shallow water, brachiopods (E), corals (F), cephalopods, sponges andsea-lilies are common.

-

II

Devonian. Armoured fish (A) and bony and scaly fish (B) flourish in fresh water.Sharks and spiny fish colonize the sea. Brachiopods (C) and molluscs called cephalo¬pods (D) continue to evolve; trilobites grow scarce and graptolites die out. On land,simple vascular plants (E) are followed by clubmosses, horsetails and ferns. The firstamphibians evolve from scaly fish.

Silurian. The land is conquered, first by colonies of seedless vascular plants and laterby scorpion-like arthropods. In fresh water, small fish and large eurypterids orwater-scorpions abound. The sea ¡s teeming with invertebrates, especially trilobites(A), crinoids or sea-lilies (B), corals (C), horny-coated eurypterids (D), brachiopods (E)and graptolites (F).

Ordovician. Shelly invertebrates flourish, especially trilobites (A), brachiopods (B),cephalopods (C) and gastropods or sea-snails (D). Corals, two-valved molluscs andbranchy or mossy colonies of bryozoans appear. Graptolites (E, F), some looking likehard spider webs, spread. In fresh water the first fish (known only from scalefragments) evolve.

Cambrian. At the dawn of this period a number of animal groups develop shells andhard parts of calcite and horn. These include trilobites (A, B), brachiopods (C, D),sponges (E) and crustaceans. The trilobites, so called from their three-lobed bodies,evolve into a large and varied group of crawlers and swimmers that dominates the seafor the next 100 million years.

U

Precambrian. During this period, which goes back to the beginning of geological time,complex organic compounds evolve from simple inorganic chemical substances.Bacteria (A, B) and algae (C, D) appear early in the period. By its close, soft-bodiedmarine and freshwater animals like worms (E, F), jellyfish and sponges have evolved. Oil

32

Life from spaceDoes life on Earth have its origins in comets?

by Chandra Wickramasinghe

Since 1962, astronomers Professor Chandra Wickrama¬singhe and Sir Fred Hoyle have been studying the nature ofinterstellar dust and have concluded that terrestrial life had

its origins in the gas and dust clouds of space. Life, theybelieve, in direct contradiction to Darwinian theory, wasderived from and continues to be driven by sources outsidethe Earth (see the Unesco Courier, May 1982). Although theirconclusions are strongly contested by other scientists, initialappraisal of data obtained from the study of Halley's cometappears to lend support to at least some aspects of theirviewpoint.

COMETS are inextricably linked withthe history of the Earth. Cometarybodies, as well as debris from them

in the form of fine dust particles, have beencolliding with the Earth from the very ear¬liest days of its existence as a planet some4,600 million years ago. It is now clear thatvolatile materials from comets, includingwater, contributed in significant measure tothe primordial oceans and atmosphere.

Cometary impacts and the acquisition ofcometary material did not, however, stop indistant geological time. As recently as 1908,a comet, or part of a comet, collided withthe Earth in the Tunguska Valley of Siberia,exploding at a height of 8.5 kilometres inthe atmosphere and devastating hundredsof square kilometres of taiga forest.

The entire Solar System today is sur¬rounded by a spherical halo of somethousands of millions of comets located at a

distance of about a tenth of a light-year (alight-year is the distance light travels in ayear about 10 million million kilometres).Passing stars cause cometary objects fromthis halo to become deflected into orbits

that bring them to the inner regions of theSolar System at the rate of about one or twoa year. The Earth is well and truly entwinedwithin these orbits so material shed from

these comets must be reaching us quiteplentifully. This material becomes trappedin the Earth's upper atmosphere, addingsteadily to the store of terrestrial volatilematerials. Fluctuations must occur in the

rate of in-fall of cometary debris over longperiods of geological time. It is now widelybelieved that significant increases in thisrate would trigger the onset of episodes of

global glaciations (ice ages) such as areknown to have occurred.

A typical comet, such as Halley's comet,has a mass of some 100,000 million tons and

a direct hit from such an object would havedramatic consequences for our planet. For¬tunately, such collisions are exceedinglyrare, occurring at intervals averaging about300 million years, coinciding approximatelywith the time intervals between successive

bursts in the evolution of terrestrial life.

Smaller comets are more numerous and

could collide more frequently.This much is more or less agreed upon by

most scientists. A less popular view, advo¬cated by the British astronomer Sir FredHoyle and myself, is that comets were alsoresponsible for the importation of organicmolecules that contributed to the origin oflife on our planet. We have further sug¬gested that the Earth continues to receiveready-formed living structures such as bac¬teria and viruses even at the present time.

From 1975 onwards, we have accumu¬

lated evidence to support our view thatorganic dust grains, including organic po¬lymers (large chains of carbon-based orga¬nic molecules), exist on a vast cosmic scale.These dust grains populate the clouds of gasthat exist between stars and give rise to thevisual effect of dark patches and striations

(1) The adjective "organic" is often commonly used tomean "living", in the sense that a plant, a tree or a humanbeing is "living"; chemists employ it in a restricted sense todescribe compounds containing carbon combined withhydrogen. All living things contain carbon and hydrogenand thus are organic, but not all things that containcarbon and hydrogen are living. "Biological" means "ofor relating to life or living things".

seen against the diffuse light of the MilkyWay. In 1981, through a combination oflaboratory studies, mathematical computa¬tions and astronomical observation, we ar¬rived at the conclusion that the bulk of

cosmic dust was not merely organic butdistinctly biological in character ^.

In a series of publications we have pre¬sented arguments to support the theory thatlife on Earth had its origins in comets andthat evolution is controlled by the con¬tinuing input ofcometary material. Becausethe injection of comets from the outer SolarSystem is sporadic, this input of cometarymaterial is not expected to be uniform andregular in time, and so the effect on evolu¬tion will also be sporadic. This sporadiccharacteristic clearly shows up in the fossilrecord which traces the evolution of terrest¬

rial life.

A dramatic example is provided by theextinction of the dinosaurs 65 million yearsago. It has recently been argued by manyscientists that this event was caused by acomet which shrouded the Earth in a halo of

fine particles. These particles acted like asmog that darkened the skies for decadesand caused withering of plankton and plantsand the demise of all large creatures that fedon plants.

Sir Fred Hoyle and I believe that such apurely physical cause is unlikely in view ofthe fact that the extinction of the dinosaurs

also coincided with an extinction of a largefraction of the genera of all plants, animalsand micro-organisms and the emergence ofseveral brand new orders of living forms.We identify this extinction/speciation eventof 65 million years ago with a genetic stormthat resulted from an exceptionally largenew crop of comets that were injected intothe inner regions of the Solar System.

The first clear-cut detections of organicmolecules hydrogen cyanide (HCN) andmethyl cyanide (CH3CN) came fromobservations of comet Kohoutek, in 1973

and 1974. But cometary theories cameunder very much closer scrutiny in Marchthis year when, as the culminating point ofthe International Halley Watch, the Euro¬pean space satellite Giotto penetrated towithin a few hundred kilometres of the

nucleus of Halley's comet (see the UnescoCourier, March 1986).

The payload of Giotto included a variety

33

^ of scientific experiments and a videocamera that was intended to send back col¬

our pictures of the comet's nucleus. Earlierin March, the Soviet space satellite Vega 2successfully accomplished a similar mission.Pictures of the comet's nucleus, taken byVega 2 from a distance of several thousandkilometres, showed tentative indications

that it may be split into at least two frag¬ments. Giotto might have been able to settlethis matter but for an unfortunate hitch in

communications that occurred seconds be¬

fore the moment of closest approach. In theevent, the best pictures we have is of thenucleus surrounded by a peanut-shapedshroud of obscuring dust.

What is to be learned from the first

appraisals of the data sent back by the va¬rious missions to comet Halley?

Our organic theory of comets predictsthat cometary nuclei must develop a highlyporous mesh-like surface layer of polymericparticles. Evaporation of material on alarge scale can only occur from places on thesurface where this surface layer becomesabraded or broken. A consequence is thatcometary nuclei must have exceedinglyblack, non-reflective surfaces, a propertywe predicted only weeks before the Giottoencounter.

The Giotto pictures showed a few placeswhere the nucleus could be seen through"holes" in the dust halo, and the surface

showed up as amazingly black Giotto in¬vestigators described it as being "blackerthan the blackest coal". This was indeed a

triumph for the organic model.

More triumphs were to follow. Giotto'sparticle impact analyser was equipped todetermine the chemical make-up of thecometary dust particles by measuring thedistribution of the masses of atoms within

them. J. Kissel, the principal investigatoron this experiment, reported on 17 Marchthat analysis of one per cent of the total datarecord indicated that the dust was made up .of the elements carbon, oxygen, nitrogenand hydrogen with very much smalleramounts of other chemical elements. Two

logical possibilities follow from this data.These atoms can exist in the form of volatile

ices such as water, carbon dioxide and

ammonia together with simple hydrocar¬bons such as methane, or they could occurin the form of highly stable organicpolymers. Since, in other experiments, thetemperature of these particles was mea¬sured at 125 degrees Celsius, well above theboiling points of ices and simple hydrocar¬bons, it follows that the cometary particlescould only be made of organic polymers.

Both Vega 2 and Giotto experiments indi¬cated that hydrogen atoms, hydroxyl radic¬als and water molecules were also released

quite liberally from the comet. However,the amounts of these substances were not

inconsistent with the water associated with

living cells (60 per cent by volume of suchcells is water). Significantly there was noevidence whatever for a halo of icy particlesaround the nucleus which is predicted bythe widely accepted "dirty snowball" com¬etary theory first propounded by US astro¬nomer Fred Whipple.

On the morning of 30 June 1908, a hugeaerial explosion with an energy equivalentto that of 10 to 15 megatons of TNT devas¬tated some 2,000 square kilometres ofpine forest (left) near the Tunguska RiverIn central Siberia. The explosion Isthought to have been caused by a comet,ora fragment ofa comet, colliding with theEarth. An object such as this would havedisintegrated in the Earth's atmospherecreating a fireball and a powerful blastwave but no crater.

Scarcely two weeks after the Giotto ren¬dezvous an important observation of thecomet in the infra-red region of the spec¬trum was made by astronomers DayalWickramasinghe and David Allen, usingthe 154-inch Anglo-Australian telescope atSiding Springs, New South Wales. Theydiscovered remarkably strong signals due toemission from heated organic dust over thewavelength range from 2 to 4 micrometres.Basic structures of organic molecules in¬volving linkages between carbon and hyd¬rogen atoms (CH bonds) absorb and emitradiation at wavelengths near 3.4 mic¬rometres; for any assembly of complexorganic molecules such as bacterium thisabsorption band is in general very broadand takes on a highly distinctive profile.The most remarkable fact that emerged wasthat the profile of this emission from Hal¬ley's comet matched precisely the be¬haviour of a dried-out bacterium as mea¬

sured in the laboratory.

Although a full appraisal of the recentobservations of comet Halley cannot yet beoffered, it is already clear that a few quiteremarkable facts have emerged. The cometis clearly not an inorganic dirty snowball asmost astronomers had previously held. It isorganic. Within a mammoth chunk of orga¬nic matter, some 8 kilometres long and 4kilometres wide, a large proportion of wa¬ter molecules and traces of other materials

are also trapped. Whether one likes it ornot, the organic material of the cometoccurs predominantly in the form of parti¬cles whose absorption properties, sizes anddensities are identical to the predictions of abacterial model.

Interpreted in the most conservativepossible way, the latest discoveries indicateat the very least that comets could haveprovided the raw materials, the organicbuilding blocks from which life emerged onthe Earth. More realistically, in my view,the data point in a decisive way to life in theform of bacteria and viruses being con¬tained in comets and brought by them to theEarth.

NALIN CHANDRA WICKRAMASINGHE is pro¬fessor of applied matriematics and astronomy atUniversity College, Cardiff, Wales, and Directorof the Institute of Fundamental Studies, SriLanka. In 1962, while at Cambridge University,Professor Wickramasinghe, who is ofSri Lankanorigin, was awarded the Powell Prize for Englishpoetry. His views on the space origins of terrest¬rial life are fully developed in two books, SpaceTravellers: the Bringers of Life and Evolutionfrom Space, of which he is the co-author with SirFred Hoyle.

34

The hand of man

by Stephen Boyden and Malcolm Hadley

THE human species evolved late, verylate, in the history of our planet; butduring man's short time on Earth,

his hand has wrought pervasive change inair, water and soils, in other livingcreatures, in the whole tightly connectedsystem of interacting parts of which theenvironment consists and this in but the

last instant of geological time.The history of man's changing rela¬

tionship with his habitat in terms of boththe impact of human society on the naturalenvironment and the conditions of life of

human beings can, at the risk of over¬simplification, be divided into four distinctbut overlapping ecological phases: thePrimeval Phase, the Early Farming Phase,the Early Urban Phase and, finally, theModern Industrial Phase.

During the Primeval Phase sometimesalso called the pre-domestic or hunter-gatherer phase human populations prob¬ably differed little from those of otheromnivorous mammals in the extent and na¬

ture of their interaction with the ecosystemsof which they were a part. As hunter-gatherers they had their natural place in thefood cycle, deriving their energy, in chemi¬cal form, from natural foodstuffs of animal

and plant origin. They in turn provided foodfor other predators and their remains werereturned to the soil through the processes ofdecomposition. The amount of energy usedby an early hominid group in its naturalhabitat would have been more or less

equivalent to the energy value of the food¬stuffs consumed by members of the group.In short, our ancestors fitted into their en¬

vironment in much the same way as anyother animal species.

Then, probably about half a million yearsago, in the volcanic lands of the East Afri¬can rift valleys, man began to use fire,deliberately and regularly, both for protec¬tion and as a means of obtaining and cook¬ing food. Fire was used to drive game out ofthe undergrowth and to attract animals tothe fresh herbaceous growth that sprang upon ground cleared by fire.

This was a highly significant developmentwith considerable ecological impact. Forestand grass fires became much more frequentevents, bringing about important changes inthe plant cover of certain areas of theEarth's surface. Suddenly, human societieswere using considerably more energy thanpreviously, since the flow of "somatic"energy (the energy that flows through thebodies of human beings for metabolism,physical work and growth) was now sup¬plemented by "extra-somatic" energy(energy such as that derived from fuel,which does not flow through living orga¬nisms).

The use of fire thus brought about aqualitative change in the relationship be¬tween the human species and its environ¬ment. The ecological consequences wererestricted to the destructive effects of fire

itself, and the chemical products of thecombustion of wood (mainly carbon diox

ide) were easily absorbed into the system asa whole with negligible repercussions.Nevertheless, the use of fire is an early andclear example of man's potential as a modi¬fier of the environment. Man had alreadybecome a significant ecological force, andhuman groups no longer fitted into theirlocal ecosystems in quite the same way asother animals.

In addition to fire, the most significantecological effect of man on the environmentduring the primeval phase was probably thespread of the human species itself. Manappears to have roamed the open Africansavannah until about one million years ago,when he fanned out into a great variety ofother habitatsarid steppes, high altitudegrasslands (in Ethiopia) and forest grass¬lands. Following these initial excursions,man ventured further out into a wide rangeof different climatic and ecological settingsin all five continents of the world. ^

Rock painting dating from about 2000 BC,from the Rusape area of Zimbabwe. Theway of life represented is that of LateStone Age hunters. Bushmen were stillmaking paintings like this in the 19th cen¬tury, but some of the surviving examplesmayhave been the workofsouthern Bantupeoples.

35

Engraving by the Swiss artist Aloys Fell-mann (1855-1892) depicts men at work in atypical 19th-century factory at a time whenthe industrial revolution was gatheringmomentum in Europe.

The Early Farming Phase began , in someregions of the world, about 12,000 yearsago. With the domestication of animals andplants, for the first time in the story of theEarth, a living creature came, quite con¬sciously and deliberately, to manipulate thebiological processes of nature for his ownpurposes.

As domestication spread and farmingtechniques advanced, the total impact ofhuman society on the environment in- .creased significantly. The face of the Earthwas beginning to be changed by the hand ofman, to the extent that, in the northern

hemisphere, vast areas of forest land dis¬appeared, to be replaced in some instancesby farming land and in others by less lux¬uriant and more open vegetation. In somecases, man's agricultural activities triggeredmassive erosion. In eastern Fiji, for exam¬ple, where man arrived some 3,000 yearsago, at least 50 centimetres of soil was lost ina period of 150 years, from between 1,900and 1,750 years ago.

Among other important implications offarming practices was the introduction ofmonoculture food crops, on which manypopulations came to be almost entirely de¬pendent for sustenance. This developmentclearly had some practical advantages, butit also involved serious risk, since, if themonoculture crop failed for any reason,then widespread starvation was virtuallyinevitable.

One further consequence of mankind'sdeliberate manipulation of biotic processesis worthy of mention. Selective breeding ofanimals and cultivation of plants for desir¬able qualities relating to food productionbrought into existence a range of forms oflife which would otherwise never have seen

the light of day.Fire, of course, remained in use during

this second ecological phase and it came toplay an important role in the manufactureof metal implements. With the invention ofsuch devices as watermills, windmills and

sailing ships, extra-somatic energy came tobe used for performing work of various

kinds. Compared with what was to happenlater, however, the ecological impact ofthese machines was relatively slight, beingrestricted mainly to the role that shipsplayed in the migratory movements of thehuman species, the geographical spread oftechnologies and the re-distribution ofsome animal and plant species.

Human groups became much less no¬madic than in the primeval phase, althoughthe length of time they remained in one

. place depended to some extent on the kindof farming they practised. The new lifestylehad significant consequences for the inter¬relationships between human populationsand microbial and other parasites andpathogens. In some areas, for example,malaria and schistosomiasis became impor¬tant causes of ill-health and death, partlycounteracting the reduced mortality result¬ing from the protection which the new livingconditions gave against some of the hazardsof life experienced in the primeval phase.

Despite all the changes that agricultureproduced, the early farming phase sharedtwo important ecological characteristicswith the primeval phase which are not fea¬tures of modern societies. First, the rate ofuse of extra-somatic energy (mainly fire)paralleled the rate of increase in the humanpopulation. Second, man's activities did notinterfere significantly with the naturalbiogeochemical cycles of the biosphere,such as the carbon, nitrogen and phosphor¬us cycles.

The Early Urban Phase started about5,000 years ago, with the establishment ofthe first cities in Mesopotamia and, not longafter, in China and India. These early citiesushered in the third ecological phase ofhuman existence, which was marked by aseries of fundamental changes affecting theorganization of human society and the lifeexperience of its members. Some, but notall, of these changes have persisted andremain features of many urban settlementsin the modern world.

The most obvious changes were simplythe huge increase in the number of people

gathered together in one place and the factthat the majority of their inhabitants werenot directly involved in such subsistenceactivities as farming, fishing and hunting.The urban populations were supported byfood surpluses produced by nearby farmerswho lived and worked beyond the city walls.

Because many urban populations came torely for their sustenance on a single staplefood, such as rice, maize, a cereal grain orpotatoes, there was a narrowing of therange of foods consumed by individuals.Specific deficiency diseases, including rick¬ets, scurvy, beri-beri and pellagra, werecommon in different parts of the world.There was a constant threat and repeatedoccurrence of famine, since urban popula¬tions did not have a wide range of alterna¬tive sources of food to turn to when one

supply failed.Increased population density had a

marked effect on the interrelations between

human populations and potential parasiticor pathogenic organisms. Pestilence be¬came one of the major facts of life. Typhus,cholera, typhoid, the plague, smallpox,malaria, infant diarrhoea and many otherinfectious diseases were a constant cause of

fear and alarm and were among the maincauses of death.

One of the most significant biosocial de¬velopments which accompanied early urba¬nization was the advent of job specializa¬tion. Some degree of specialization existedin the early farming and even in the hunter-gatherer societies, but, apart from the sex-based division of labour, most people werejacks-of-all-trades. It was during the earlyurban phase that specialization really cameinto its own.

Part of the ecological importance of thisdevelopment lies in the fact that, for thefirst time in human history, different groupswithin a single society experienced quitedifferent conditions of life. Job specializa¬tion led in turn to a reinforcement of the

tendency of human societies to establishhierarchies. Instead of being relativelyspontaneous, transient and dependentupon the nature of the task in hand, thehierarchical structure of society becamemuch more rigid, more extreme and morepermanent. It frequently came to be deter¬mined by heredity rather than by commonconsent based on ability and personality.

Urbanization also introduced entirelynew concepts of ownership. In primevaltimes, an individual "owned" only thosepossessions he had made himself and nomore than could be easily carried when hemoved from one camp site to another. Inthe early farming phase, animals, crops andstored grain became the objects of own¬ership, but, at least in the early stages, thiswas usually communal ownership. In earlycities, individual and family ownership be-

36

Highway intersection at Villefranche, nearLyon, France a typical construction ofour modern, energy-hungry, industrialsociety.

came very important and has remained soever since in many parts of the world.

As in the preceding phases, the naturalbiogeochemical cycles were still intact, andthe rate of energy use by society still par¬alleled changes in population size. The bio¬sphere as a whole and most of the eco¬systems to which human populations be¬longed were, despite some short-term fluc¬tuations, still essentially in a state of dyna¬mic equilibrium. The existence of cities didnot, of course, mean an end to self-suffi¬

cient subsistence agricultural societies,which indeed continue to exist in some

areas of the world today.Until very late in this period, few cities

contained many more than 100,000 inhabi¬tants. One notable exception was Rome,which, around the time of Jesus Christ, hada population of about one million.However, although cities have until veryrecently contained only a very small percen¬tage of the total human population, theyhave had an ecological impact out of allproportion to the number of people living inthem.

The Modern Industrial or TechnologicalPhase began with the so-called industrialrevolution. This industrial transition, as we

prefer to call it, started in Europe and inNorth America some 150 to 200 years agoand is still taking place in many parts of theworld. Though it began only seven or eightgenerations ago, this phase has had an im¬pact on the Earth and its workings quitedisproportionate to its duration. Its ecolo¬gical characteristics are not shared with anyof the preceding phases of human existence.This is most strikingly illustrated by thepresent situation regarding population,energy and the biogeochemical cycles.

While the early farming and early urbanstages provided protection from some of thecauses of death that characterized the

primeval stage, they were associated withnew causes of mortality in the form of mal¬nutrition and pestilence. In the modern in¬dustrial phase, greatly improved knowledgeof the nutritional requirements of our spe¬cies, and new practices in public health andmedicine, including the pharmaceutical re¬volution, have resulted in a remarkablechange in population dynamics. As a conse¬quence, the human population is nowdoubling at the rate of once every thirty-fiveto forty years, in contrast to the overall rateof once in 1 ,500 years during the early farm¬ing and early urban phases.

Another outstanding feature of the mod¬ern industrial phase, and one which deter¬mines many of its other characteristics, hasbeen the massive introduction of machines

and manufacturing processes powered byextra-somatic energy. The chief sources ofthis energy have been the fossil fuels, begin¬ning with coal, but with petroleum products

and natural gas now more important. Insome places, hydroelectric power makes asignificant contribution and nuclear poweris rapidly coming to the fore. In highlyindustrialized countries like the United

States, the amount of power used on a percapita basis is now thirty times greater thanit was prior to the industrial transition.

Thus, unlike the situation in the earlierphases, the rate of increase in energy use inthe modern industrial phase no longermatches the rate of increase in population,and the ratio of extra-somatic energy usedby society is continually increasing. Global¬ly, the amount of energy flowing throughhuman society is doubling about twice asfast as the population.

In many areas the natural biogeochemic¬al cycles are no longer intact. Interferencewith the carbon and phosphorus cycles, forexample, may well give rise to very seriousecological problems in the future. In thecase of the nitrogen cycle, vast amounts ofnitrogenous waste products of human com¬munities, which in previous eras were re¬turned to the soil, are now lost to rivers and

oceans, and industrial processes are dis¬charging substantial quantities of nitrogenoxide into the atmosphere.

A significant change of a qualitative na¬ture has been the synthesis, often in verylarge amounts, of thousands of new chemi¬cal compounds, many of which have potenteffects in biotic systems. Vast quantities ofthese synthetic chemical substances arefinding their way into the oceans, the soiland the atmosphere and, of course, intoliving organisms.

Complexity and unpredictability are twoother characteristics of the present phase ofhuman existence. Modern technology andthe economic web of interdependence ofcountries are making problems of land useand resource management much more com¬plex than they were even a generation ago.Machines are now available, for example,for clearing large areas of forest in a veryshort space of time. With modern com¬munications technology, a decision taken

now in a financial centre in a temperatezone can lead to the felling, within a week,of a tropical forest tree 10,000 kilometresaway which has taken one hundred years togrow.

If certain widely accepted predictionsabout future increases in the level of energyuse turn out to be correct, by the year 2050mankind will be using about as much energyas is used by all other animals and plants puttogether. One does not have to be a special¬ist to see that this kind of growth in energyuse, and the concomitant increase in the useof resources and the outpouring of wastes,cannot go on indefinitely.

Opinions differ as to how much longerthe biosphere is likely to be able to toleratethe ever-increasing load which human soci¬ety is placing on it. There are some whobelieve that mankind is incapable of bring¬ing under control the accelerating processeswhich threaten the collapse of the biosphereand civilization and that the collapse of thesystem will be total and will involve theextinction of the human species. Others aremore optimistic, believing that man, withhis great ingenuity, will succeed in reachinga new ecological equilibrium before it is toolate.

STEPHEN BOYDEN, ofAustralia, is a specialistat the Centre for Resource and Environment

Studies, Australian National University, Canber¬ra, and leader of the integrative research studyon the ecology of Hong Kong undertaken withinthe framework of Unesco's Man and the Bio¬

sphere (MAB) Programme. The theme of thisarticle is treated in greater depth in a book to bepublished later this year.

MALCOLM HADLEY is a staff member of Un¬

esco's Division of Ecological Sciences. A zoolo¬gist, he is responsible for the co-ordination ofactivities in the humid tropics within Unesco'sMan and the Biosphere (MAB) Programme.

37

1986: Year of Peace/ 7

Over 400 representatives of 1 1 5 interna¬tional non-governmental organizationsand 71 national organizations from 36countries attended "Together forPeace", a Conference held in Geneva

from 20 to 24 January 1986 to mark theInternational Year of Peace. Topics dis¬cussed at the Conference, held underthe auspices of the Board of the Confer¬ence of Non-Governmental Organiza¬tions in Consultative Status with the

Economic and Social Council of the Un¬

ited Nations, included questions of dis¬armament, development, social prog¬ress, justice, human rights, satisfactionof basic human needs, and preparationof societies for life in peace. At the endof the Conference, the following appealwas adopted by acclamation.

We appeal to all people of the world to join in acommon pursuit of peace.

With just a decade and a half for this centuryto come to a close, we are convinced of the

duty and obligation of all people to makeconcerted efforts to usher in a world of peaceas the new century opens. We are convincedthat it can be done, that the present danger¬ous trends in world affairs can be stopped andreversed. We see signs of hope in the newspirit of dialogue and openness among lead¬ers of nations and in the determination of the

people to attain peace.We do not have to recount the threats to

peace. The race towards nuclear catastropheis keeping up its momentum. As if the earthand the oceans can no longer bear the weightof weapons outer space is explored for sta¬tioning of arms. Hundreds are killed every dayby non-nuclear weapons. Hunger takes itsdaily toll of thousands. Millions are deprived ofbasic human needs and fundamental human

rights. Millions still groan under dominationand exploitation. Apartheid continues, de¬nying justice, destroying people and destabi¬lizing nations.

We appeal therefore to work together for aworld of peace, not where war is merelyabsent, not where human survival is just pos¬sible, but where justice prevails and humandignity is upheld.

We reiterate that the nuclear arms race

constitutes the greatest threat to peace andsurvival. Our appeal therefore assumes aspecial urgency in this regard. ...

As we pledge to work together for disarma¬ment we appeal to all to join in and supportefforts for an immediate end to all nuclear

weapon tests, a comprehensive test bantreaty, the prevention of an arms race in outerspace, elimination of chemical weapons andall other weapons of mass destruction, andsubstantial reduction in conventional

weaponry. We believe that it is possible toimplement a systematic and credible pro¬gramme for the elimination of nuclearweapons by the end of the century.

We believe that peace is inextricably inter¬linked with development and social progressand that its foundation is justice. Deprivationand disparity are threats to peace. We there¬fore call for a strategic development initiativefor a new international economic order that

ensures just economic relations between andwithin nations. We further appeal for genuinerespect of the rights of people to decide theirown destiny, their rights to self-determinationand interdependent development, non-in¬terference in their internal affairs, in conditions

of security and social progress.We emphasize that the exercise of human

rights and freedoms is an essential element of

peace. Violations of them are a major cause ofarmed conflicts. The fuller the rights that everyperson enjoys in society, the more stable thatsociety will be; the fullerthe implementation ofhuman rights globally, the more stable inter¬national relations will be. ...

We recognize that peace is an essentialrequirement for the satisfaction of basic hu¬man needs such as food, shelter, health, edu¬cation, labour and environment. As we com¬

mend recent co-operative actions across con¬tinents to meet emergency needs for food, weappeal for more systematic and concertedattempts to prevent death by starvation andfor the adoption of long-term policies national¬ly and internationally to ensure food for all.

We call for joint actions to promote substan¬tial reduction of military expenditures with aview to rectifying the current distortion in theuse of resources. We agree that every gunthat is made, every warship launched, everyrocket fired, signifies in the final sense a theftfrom those who hunger and are not fed, thosewho are cold and are not clothed.

Recognizing the importance of preparationof societies for life in peace we call for a neworientation in education, science, culture, reli¬

gion and mass media towards peace-making.The resources available in these areas can

be more constructively utilized for peace. ...Nations must seek peace together. We can

only create a common future if we can copewith the common crisis we face and build

peace on the basis of the concept of commonsecurity. We appeal for a greater commitmentto international co-operation for which the uni¬versal instrument is the United Nations. We

pledge our continued support to the UnitedNations and its agencies. ...

We realize that the odds are tremendous.

But we are confident that the determination of

the people to achieve peace will prevail. Wehave optimism and hope because we aretogether for peace. It is in that spirit that werenew our commitment to peace and inviteyou all, all peoples of the world, to join in thechallenging tasks ahead.

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38 IMPRIME EN FRANCE (Printed in France) - Dépôt légal : C 1 - Juillet 1986 -PHOTOCOMPOSITION : Ateliers de l'UNESCO - PHOTOGRAVURE-IMPRESSION : MAURY-IMPRIMEUR S.A., Z.l. route d'Ëtampes, 45330 MALESHERBES.

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