Elsevier Encyclopedia of Geology

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Figure 17 Plate reconstructions for South-east Asia–Australasia at 35 Ma (Early Oligocene) and 25 Ma (End Oligocene). (Repro-

duced with permission from Hall R (2002) Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-

based reconstructions and animations.

Journal of Asian Earth Sciences 20: 353–434.)

ASIA/South-East 191

Figure 18 Plate reconstructions for South-east Asia–Australasia at 15 Ma (Middle Miocene) and 5 Ma (End Miocene). (Reproduced

with permission from Hall R (2002) Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based

reconstructions and animations. Journal of Asian Earth Sciences 20: 353–434.)

192 ASIA/South-East

Figure 19 Reconstructions of East and South-east Asia for the last 30 Ma, showing the variation in the distributions of deep sea,

shallow sea, land, and mountains.

ASIA/South-East 193

Tin deposits During the twentieth century, 70% of

the tin mined in the world came from the South-east

Asian tin belt. The tin mainly occurs as cassiterite ore

in Late Cenozoic alluvial placer deposits that form

part of the 400 km wide South-east Asian tin belt,

which extends 2800 km from Burma and Thailand

through Peninsular Malaysia to the Indonesian tin

islands of Bangka and Belitung (Figure 21). Historic-

ally, these deposits have been extremely important to

the economic development of Malaysia and South-

east Asia, and, altogether, 9.6 million tonnes of tin

(54% of the world’s total tin production) has come

from this tin belt. The tin deposits of the region are

associated with the major granite/granitoid bodies of

South-east Asia and formed during the emplacement

of these intrusive igneous bodies, which were produced

by major plate-tectonic processes as the continental

blocks of the region converged and collided with each

other. The South-east Asian granites form three major

north–south belts or provinces: a Western Granitoid

Province of Cretaceous–Cenozoic (149–22 Ma) age, a

Central Granitoid Province of mainly Late Triassic and

Early Jurassic (230–184 Ma) age, and an Eastern Gran-

itoid Province of Permian, Triassic, and Early Jurassic

(257–197 Ma) age (Figure 14). The Eastern Province

was formed by subduction on the western margins

of the Indochina and East Malaya terranes during

convergence with the Sibumasu terrane. When these

two continental terranes collided, the Central Pro-

vince granites were generated. The younger Western

Province granites were principally formed when the

West Burma terrane collided with Sibumasu and by

subsequent subduction processes. The Main Range

and Eastern Belt granites of Peninsular Malaysia form

parts of the Central and Eastern Granitoid Provinces,

respectively. The tin mineralization occurred within the

granites themselves and more especially in the country

rocks that immediately surrounded them. Subsequent

to mineralization, the granites and the country rocks

into which they were intruded were uplifted and

eroded, and the tin ore was deposited and concentrated

in river alluvium.

Figure 20 Oil- and gas-bearing Cenozoic sedimentary basins and major fault zones of South-east Asia.

194 ASIA/South-East

In addition to placer tin deposits there are also a

wide variety of primary tin deposits. However, only

two major primary tin fields have led to significant

deep-mine production: the Sungei Lembing Mine

near Kuantan, Pahang, Peninsular Malaysia, and

Kelapa Kampit on Billiton Island. The lodes of these

mines are developed in contact-metamorphosed Car-

boniferous–Permian argillaceous sedimentary and

andesitic tuffaceous rocks within aureoles around

high-level Permian–Triassic granitoids.

Mississippi Valley-type epigenetic deposits Strati-

form deposits of predominantly galena and sphaler-

ite are most commonly hosted in shallow-marine

carbonate-dominated sequences on the rims of large

sedimentary basins where changes in salinity caused

deposition. The continental regions of South-east

Asia, with their extensive Palaeozoic carbonate

platforms, are suited to Mississippi Valley-type epi-

genetic deposits, and some have been identified. One

of the best-known deposits in the region, now con-

sidered to be of this type, is at the Bawdwin lead–zinc

mine north-north-east of Rangoon, Myanmar. Mining

here can be traced back to 1412.

Iron ore deposits Iron ore deposits are widespread

in the region, but significant production has been

restricted to three areas: South-east China (Hainan,

Kwangtung, Fukien), the Malay Peninsula, and the

Philippines. The deposits are predominantly of con-

tact pyrometasomatic type and are associated with

plutons emplaced at a wide range of depths. Peninsular

Malaysia was a major producer of iron ore, with pro-

duction reaching 7 million tonnes in 1964. However,

all major deposits have now been worked out.

Coal and lignite deposits South-east Asian coal de-

posits are almost entirely confined to deposits of sub-

bituminous and lignitic coal in relatively small Tertiary

terrestrial basins. There are minor occurrences of

Figure 21 Distribution of the principal mineral deposits of South-east Asia.

ASIA/South-East 195

bituminous coal and anthracite in Palaeozoic and

Mesozoic formations of the older Sundaland contin-

ental core of the region, but these are generally un-

economic except for deposits of Triassic anthracite

mined in northern Vietnam.

Diamonds, sapphires, and other gems Alluvial dia-

monds with no obvious sources (‘headless placers’)

are found in several areas of South-east Asia, includ-

ing Myanmar, southern Thailand (Phuket), Sumatra,

and Kalimantan (Figure 8). These deposits occur in

relatively young geological terranes, in contrast to

the Archaean or Proterozoic terranes that host most

primary diamond deposits and their associated

alluvial workings.

Significant quantities of diamond have been re-

coveredfromtwoareasinMyanmar:Momeikinthe

northern part of the country and Theindaw in the south-

ern part. The Momeik diamonds are recovered during

mining of gemstone gravels; the Theindaw and Phuket

diamonds are by-products of tin dredging. These sites,

and those in Sumatra, lie within the Sibumasu terrane,

which was detached from north-western Australia in

Palaeozoic times and drifted northwards to become

part of South-east Asia. The Myanmar–Thailand dia-

monds may be derived either from lamproitic intrusives

within this terrane or secondarily from Permian glacial–

marine sediments. The Kalimantan diamonds lie in

another terrane, with a different origin, and, like eastern

Australian diamonds, they may be directly or indirectly

related to subduction processes.

Sapphire, ruby, zircon, and spinel gemstones

and jade are worked at a number of localities in

South-east Asia from alluvial and eluvial gravels de-

rived from nearby outcrops of extensive Pliocene–

Pleistocene high-alkali basalt fields. The basalts are

usually basinite and nephelinite. The main centres for

the mining of these gemstones are at Pailin, Bokeo,

and Rovieng in Cambodia, Chanthaburi, Trat, and

Kancharaburi in Thailand, south of Haikou on

Hainan Island, in the Mogok and Lonkin areas of

Myanmar, and in Taiwan. Most of the South-east

Asian rubies come from the Trat area of Thailand,

which supplies 70% of the world’s production. Ruby,

sapphire, and spinel are mined in the Mogok area of

Myanmar from placers and eluvial deposits derived

from marbles and calc-silicate migmatites associated

with alaskite (Mogok Gneiss). Jadeite is mined in

the Lonkin area of Myanmar, which is the world’s

foremost source of high-grade jadeite.

Further Reading

Fraser AJ, Matthews SJ, and Murphy RW (eds.) (1997)

Petroleum Geology of Southeast Asia. Special Publica-

tion 126. London: Geological Society.

Hall R and Blundell D (eds.) (1996) Tectonic Evolution of

Southeast Asia. Special Publication 106. London: Geo-

logical Society.

Hall R and Holloway JD (eds.) (1998) Biogeography and

Geological Evolution of South-East Asia. Amsterdam:

Backhuys Publishers.

Hamilton W (1979) Tectonics of the Indonesian Region.

USGS Professional Paper 1078. Washington: US Geo-

logical Survey.

Hutchison CS (1989) Geological Evolution of South-East

Asia. Oxford: Clarendon Press.

Hutchison CS (1996) South-East Asian Oil, Gas, Coal and

Mineral Deposits. Oxford: Clarendon Press.

Meng LK (ed.) The Petroleum Geology and Resources of

Malaysia. Kuala Lumpur. Petronal. P.

Metcalfe I (1988) Origin and assembly of South-east Asian

continental terranes. In: Audley-Charles MG and Hallam

A (eds.) Gondwana and Tethys, pp. 101–118. Special

Publication 37. London and Oxford: Geological Society

and Oxford University Press.

Metcalfe I (ed.) (1994) Gondwana dispersion and Asian

accretion Special Issue of Journal of Southeast Asian

Earth Sciences 9: 303–461.

Metcalfe I (ed.) (1999) Gondwana Dispersion and Asian

Accretion. IGCP 321 Final Results Volume. Rotterdam:

A A Balkema.

Metcalfe I and Allen MB (eds.) (2000) Suture zones of East

and Southeast Asia Special Issue of Journal of Asian

Earth Sciences 18: 635–808.

Metcalfe I, Smith JMB, Morwood M, and Davidson I (eds.)

(2001) Faunal and floral migrations and evolution in SE

Asia–Australasia Lisse: A A Balkema.

Shi GR and Metcalfe I (eds.) (2002) Permian of Southeast

Asia. Special Issue of Journal of Asian Earth Sciences, 20:

549–774.

ASTEROIDS

See SOLAR SYSTEM: Asteroids, Comets and Space Dust

196 ASIA/South-East

ATMOSPHERE EVOLUTION

S J Mojzsis, University of Colorado, Boulder, CO, USA

Introduction

Earth is unique among the planets of the Solar System

in having sustained conditions of temperature and

pressure that permit stable liquid water at the surface

for more than 4 Ga. The long-term stability of liquid

water is fundamental to the origin and propagation

of life, and Earth is exceptional among the known

planets in having a biosphere. Abundant free oxygen

accumulated in the atmosphere as a metabolic waste

product of oxygenic photosynthesis; the high free-

oxygen content contrasts markedly with the atmos-

pheres of the neighbouring planets of the inner Solar

System (Table 1). This globally oxidative condi-

tion was at first deleterious to microbial life, but led

to the emergence of aerobic metabolisms, sexual

reproduction, and multicellularity.

Appreciating how the current physical and chemical

state of the atmosphere came to be requires knowledge

of the initial conditions. The elemental ingredients that

go into making a habitable world are ultimately de-

rived from cosmologic nucleosynthesis – the formation

of primarily hydrogen (

H) and helium (

He), with

minor amounts of

He, and

Li, at the Big Bang

approximately 13  1 Ga ago. All the other naturally

occurring elements in the periodic table were created by

stellar nucleosynthetic and supernova reactions. These

events contributed gas and dust to the interstellar

medium, and a cloud of such supernova ashes collapsed

to form the solar nebula and, ultimately, the Sun and

planets about 4.56 Ga ago (see Solar System: The Sun).

Origin of a Habitable World

Solar System and Planetary Formation: Relevance

to Atmospheric Evolution

Following Big Bang nucleosynthesis, local concentra-

tions of gas collapsed to form the first galaxies and

the nebulae and stars that comprise them. Gravity

binds these immense structures together, and it is the

gravitational collapse when stars form that creates

the pressures needed to initiate thermonuclear fusion

reactions, which convert four

H nuclei to one

nucleus and release energy. This energy provides an

outward force that counters the inward gravitational

collapse. Although seemingly violent and cata-

strophic in our Earth-bound (solid–liquid–gas) view

of matter in the universe, such systems are remark-

ably stable and are sustained over many millions of

years throughout the lifetime of a star on the main

sequence. In smaller stars, such as the Sun, luminosity

changes over the stellar lifetime, beginning with a

short (less than 100 Ma) early phase of variable

brightness, which lasts until the so-called main se-

quence of hydrogen fusion commences (Figure 1).

Time in the main sequence is long for a star such as

the Sun, of the order of 8 Ga, but it eventually draws

to a close when much of the hydrogen fuel is ex-

hausted. At that stage, the star expands and enters a

Table 1 Atmospheric constituents of the inner planets

Earth Venus Mars



78.084% 3.5% 2.7%

20.946% tr. 0.13%

O <4% 30 ppm 0.03%

Ar 9340 ppm 70 ppm 1.6%

350 ppm 96.5% 95.32%

Ne 18.18 ppm 7 ppm 2.5 ppm

He 5.24 ppm 12 ppm nd

1.7 ppm nd nd

Kr 1.14 ppm 25 ppb 0.3 ppm

0.55 ppm nd nd

O 320 ppb nd ?

CO 125 ppb 17–45 ppm 0.08%

Xe 87 ppb 1.9 ppb 0.08 ppm

10–100 ppb nd >0.04 ppm

HCl 1 ppb 0.6 ppm nd

20–90 ppt 25–150 ppm nd

S 30–100 ppt 3 ppm nd



Abundance values are given for dry air. Abbreviations: tr.,

trace; ppm, 10

6

1

; ppb, 10

9

1

; ppt, 10

12

1

; nd, not

detected.

Figure 1 Secular changes in solar luminosity with time. Solar

luminosity is expressed as fraction of current solar luminosity.

ATMOSPHERE EVOLUTION 197

red giant phase, when helium is consumed to synthe-

size the isotopes

C and

O (via

Be). This is a rapid

process in comparison to the length of time spent in

the main sequence. When helium becomes depleted,

the star collapses from a red giant into a white dwarf,

which is dominantly composed of oxygen and

carbon. Some of these stellar objects can continue to

accrete mass from companion stars and become in-

creasingly unstable, resulting in what are termed

type-I supernovae. In the absence of a massive stellar

companion, white dwarf stars slowly cool and darken

over eons. The solar nebula of approximately 4.6 Ga

ago was derived from the violent remains of perhaps

several supernovae. There is evidence that more than

one event occurred around the time of the collapse of

the solar nebula, injecting it with short-lived nuclides

such as

244

Pu,

Fe, and

Al, which were important

heat-producing elements in the larger differentiated

asteroids and proto-planets. During nebular collapse,

the central region of the disk concentrated hydrogen

and helium and eventually formed the Sun. The Sun

entered its main sequence about 50 Ma after the initi-

ation of cloud collapse. Solar radius and luminosity

increased steadily as hydrogen was converted to

helium; this is because, as the average density of the

Sun increased, the rate of hydrogen fusion also in-

creased.

For stars greater than ten times the solar mass,

hydrogen fusion proceeds at higher temperatures and

pressures. In such stars, time in the main sequence

may be brief, as short as 10 Ma, before they enter the

red giant phase. Since these stars burn hotter and at

higher pressures, fusion of helium continues beyond

Ctoyield

Ne and

Mg, as well as beyond

Oto

create

Si, and, finally,

Fe. Iron has the greatest

binding energy per nucleon (Figure 2) and represents

the limit of the energy-yielding thermonuclear-fusion

products. When even this elemental fuel becomes ex-

hausted, a super-massive star will rapidly collapse and

can explode as a type-II supernova, one of the most

exergonic events in the universe. Such an event was re-

cently observed as SN 1987A, a supernova approxi-

mately 150 000 light-years distant, which proceeded

with fusion beyond

Fe to create gold, lead, isotopes

of thorium (

232

Th) and uranium (

235

238

U), and tran-

suranic elements up to

244

Pu and beyond. Super-

nova events randomly fertilize the galaxy with heavy

nuclides, including the unstable radioactive heat-

producing elements (potassium, uranium, and thor-

ium) that are responsible for keeping planetary

interiors warm and dynamic over geological time-

scales. It is estimated that about 50% of all interstellar

dust is created in supernova explosions. Cosmic dust is

the crucial raw material in the creation of a habitable

world.

Formation of the Earth: Primary Atmosphere

A rapid accretion by asteroid-like bodies (termed ‘plan-

etesimals’) formed the planets of the Solar System (see

Earth Structure and Origins). A volatile envelope –

captured from nebular gases and perhaps containing

significant amounts of hydrogen, helium, methane, and

ammonia – would have already started to accumulate

when the growing proto-Earth reached a critical mass

Figure 2 Binding-energy curve of the nuclides.

198 ATMOSPHERE EVOLUTION

of 10–15% of its present value. Whatever this primary

atmosphere was, intense solar wind from the young

Sun and later energetic impacts, culminating in the

Moon-forming event, would have led to significant

gas loss. Evidence for this can be seen in the con-

centrations of the noble gases (helium, neon, argon,

krypton, xenon). Abundances of these chemically un-

reactive gases in Earth’s atmosphere are far less than

their solar or cosmic equivalents (Figure 3). This could

be due to either solar wind or impact-induced erosion

of planetary atmospheres (or both).

Formation of the Moon: Loss of the

Primary Atmosphere

Evidence from a combination of lunar samples,

meteoritics, interplanetary probes, isotopic studies,

and physical models shows that the accretionary

phase of the planets was intense and short-lived,

lasting for less than 100 Ma after the initial collapse

of the solar nebula. Under conditions of intense early

bombardment, the conversion of the kinetic energy of

millions of impacting planetesimals to thermal energy

would have heated the proto-Earth to melting, fur-

ther facilitating differentiation into core, mantle,

crust, and atmosphere (see Earth: Mantle; Crust).

Sometime between 4.5 Ga and 4.45 Ga an object

the mass of Mars entered an Earth-crossing orbit.

The consequences of this event were profound. The

giant impact hypothesis envisages total Earth melting,

blow-out of the tattered remnants of primary atmos-

phere captured during accretion, and devolatilization

of the material that coalesced to form the Moon (see

Solar System: Moon).

Abatement and Cooling

As planetary accretion slowed, heat rapidly radiated

from the surface into space, and the Earth’s surface

rapidly cooled, forming a solid chill crust. Outgassing

due to the internal differentiation of the planet into

core and mantle resulted in the formation of a dense

atmosphere, probably composed of carbon dioxide,

steam, and other gases. Condensation of oceans

onto the primordial surface could then have occ-

urred as a consequence of either intrinsic water from

planetary outgassing or later contributions from

comets and meteorites. Comets and meteorites are

primitive undifferentiated objects rich in volatiles and

reduced organic compounds – attractive procreative

ingredients for the origin of life. Some postulate that

all the water on the Earth’s surface could have been

delivered from comets without the need for outgass-

ing of water vapour from the mantle. However, if

the

H composition of the three comets meas-

ured so far is typical of these objects, the oceans could

not have been produced solely by cometary water

(Figure 4). To explain the data whilst still accepting

the cometary origin of the hydrosphere, terrestrial

water requires an additional component with a

Hmuchlessthanthatofaverageseawater.The

weight of present evidence suggests that the likeliest

source of this water is intrinsic planetary outgassing.

However, it could be that prebiotic reactions on the early

Earth leading to the origin of life required a significant

contribution from comets, and several models predict

that these contributions could have been large.

Liquid water, a source of energy, and organic raw

materials are presumed to be necessary to initiate bio-

logical processes. Depending on the compositions of

the earliest retained (secondary) atmosphere and hy-

drosphere, prebiotic molecules could have been syn-

thesized in the atmosphere, formed at hydrothermal

vents, or delivered by comets. The oceans were an

early feature of the Earth. The oldest known rocks of

sedimentary origin are >3.8 Ga ferruginous quartzites

and banded iron formations from southern West

Greenland and unequivocally support the presence

of surface seas at that time. Rare zircons from the

Jack Hills region of Western Australia are as old as

4.38 Ga and contain oxygen isotopic compositions

that are consistent with the presence of substantial

liquid water at or near the Earth’s surface and inter-

acting with the crust within 150 Ma of the origin of

the Moon.

Figure 3 Noble-gas abundances on Earth in comparison with

cosmic abundances (adapted with permission from D. Hunten

et al.inMeteorites and the Early Solar System, eds. John F. Kerridge

and Mildred Shapley Matthews. ß 1988 The Arizona Board of

Regents).

ATMOSPHERE EVOLUTION 199

Origin of the Secondary Atmosphere

Following the loss of the primary planetary atmosphere

as a result of the energetic solar wind, bombard-

ments, and the Moon-forming event, the secondary

atmosphere began to accumulate. The large masses

of the Earth (5.97  10

g) and Venus (4.87  10

and their planetary inventories of heat-producing

elements allow the long-term persistence of high geo-

thermal gradients and associated volcanism. In the

case of the Earth, plate tectonics is possible in part

because of a steep geothermal gradient that allows

for the ultimate recycling of sediments and volatiles.

On smaller bodies, such as the asteroids, the Moon,

Mercury, and the icy moons of the outer planets,

geothermal gradients are shallow; these bodies cooled

quickly and early in Solar System history and are

effectively cold dead worlds. Mars is an intermediate

case between the warmer Earth and Venus and ‘dead’

worlds such as Mercury and the Moon. Comparisons

of terrestrial volcanic-gas compositions with the at-

mospheres of the neighbouring planets show broad

similarities (Tables 1 and 2). Water appears to have

been lost on Venus due to thermal escape and was

trapped in the crust of Mars by weathering and cold

temperatures.

There is a growing consensus that the early (sec-

ondary) atmosphere of Earth was dominated by car-

bon dioxide, nitrogen, and water vapour, with minor

components of noble gases, hydrogen, methane, and

sulphurous compounds. To explain the early presence

of liquid water when solar output was considerably

less than today (Figure 1), it is necessary to assume

that a dense carbon dioxide greenhouse atmosphere

(possibly including methane) increased insolation on

the early Earth. Such an atmosphere must have had a

partial pressure of carbon dioxide (pCO

) of at least

1 bar (and probably more) to keep the planet from

freezing over (see Solar System: Asteroids, Comets

and Space Dust; Meteorites; Mercury; Venus; Mars;

Jupiter, Saturn and Their Moons; Neptune, Pluto and

Uranus).

Weathering and hydrothermal reactions of crustal

materials immediately commenced once the atmos-

phere and hydrosphere were established. Hydrother-

mal vents would have been ubiquitous on the early

Earth, and it is estimated that the total volume of

Earth’s oceans could have cycled through the crust in

less than 1 Ma. Carbon dioxide and water (as car-

bonic acid) react with silicate minerals to add carbon-

ate and silica to the oceans, as represented in the Urey

equation:

þ H

O þ CaSiO

¼ H

þ SiO

þ Ca

2þ

Figure 4 Hydrogen isotopic composition of various Solar System objects (adapted from A. Drouart et al. 1999).

Table 2 Terrestrial volcanic-gas compositions

St Helens Etna Kilauea



91.58 53.69 78.7

0.269 0.57 1.065

0.913 20.00 3.17

CO 0.0013 0.42 0.0584

0.073 24.85 11.5

S 0.137 0.22 3.21

OCS 2  10

5

nd 0.0054

0.0003 0.21 1.89

SO nd 0.03 nd

HCl 0.089 nd 0.167

HF nd nd 0.20



Values are given in volume % (¼mol %); nd, not detected.

200 ATMOSPHERE EVOLUTION

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