Elsevier Encyclopedia of Geology

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switching positions (Figure 5). Such reversals may

occur over periods of a few hundred thousand years,

but there have been longer periods without reversal of

around 10 Ma. The intensity of the dipole field varies,

being particularly strong during long stable periods

and weakening just before reversal. The position of

the north magnetic pole, first located by James Clark

Ross in 1831 in the Boothia Peninsula, north-east

Canada, shows secular displacement and is at present

accelerating northwards towards Siberia (Figures 6A

and 6B). The magnetic field is believed to be due to

convection in the liquid outer core (Figure 7)(see

Magnetostratigraphy).

Ozone Layer

There is a layer of ozone (O

), a blue-green poisonous

gas, in the stratosphere at an altitude of between 15

and 40 km (Figure 8). This is important because it

absorbs the carcinogenic part of the solar spectrum

(ultraviolet B). It is produced by photochemical

reactions, and its concentration displays natural vari-

ations, being more abundant at the poles and less so in

equatorial regions, though it is created at the equator

and destroyed at the poles, where the concentration

shows seasonal variation. Chlorofluorocarbon com-

pounds, used as refrigerants and aerosol sprays, are

believed to threaten the ozone layer; stratospheric jet

planes would also do so, but relatively few are in use.

Plate Tectonic Movement and

Mantle Convection

Space exploration has revealed no other body

(planet, satellite, or asteroid) with evidence of lateral

plate-tectonic displacement attributable to mantle

convection, with accompanying ridge eruptivity,

spreading away from ridges, subduction at plate

margins, and continental collision (Figure 9). The

upper mantle, though solid, is capable of very slow

thermal convection over the vast periods of geo-

logical time. Mantle convection and plate tectonics

probably did not operate in the Archaean and earliest

Proterozoic (before 2000 Ma), though some minor

shuffling of numerous small plates may have oc-

curred. There is evidence that it operated through

most of the Proterozoic and Phanerozoic, and the

Earth’s surface at present consists of relatively few

Table 2 Volumes, masses, and densities of the various concentric shells of the Earth (from C M R Fowler (2000) Earth Structure. In:

Hancock PL and Skinner BJ (eds.)

Oxford Companion to the Earth, pp. 276–280. Oxford: Oxford University Press)

Depth (km)

Volume

(10

)

Volume

(% of total)

Mass

(10

kg)

Mass

(% of total)

Density

(10

kg m

3

)

Crust 0–Moho 10 0.9 28 0.5 2.60–2.90

Upper mantle Moho–670 297 27.4 1064 17.8 3.35–3.99

Lower mantle 670–2891 600 55.4 2940 49.2 4.38–5.56

Outer core 2891–5150 169 15.6 1841 30.8 9.90–12.16

Inner core 5150–6371 8 0.7 102 1.7 12.76–13.8

Whole Earth 1083 100 5975 100



The Moho is 25–35 km deep under the continents and 6–7 km deep under the oceans.

Figure 5 Magnetic-polarity divisions of geological time (chrons,

subchrons, transitional zones, and excursions) (reproduced from

Harland WB, Armstrong RL, Cox AV,

et al. (1990) A Geologic

Timescale 1989

. Cambridge: Cambridge University Press).

424 EARTH STRUCTURE AND ORIGINS

plates, some of them immense (for example the one

includes India, the Indian Ocean, Australia, and the

Tasman Sea) (Figure 10). That plate movement has

occurred and is occurring cannot be seriously doubted,

though attempts at instrumental measurements have

Figure 7 The magnetic field of the Earth is due to convection in

the outer core, for which the configuration is not determined (re-

produced from D Ravat (2000) Magnetic field, origin of the Earth’s

internal field. In: Hancock PL and Skinner BJ (eds.)

Oxford Compan-

ion to the Earth

, pp. 630–631. Oxford: Oxford University Press).

Figure 8 The configuration of the ozone layer (reproduced

from F Drake (2000) Ozone-layer chemistry. In: Hancock PL and

Skinner BJ Oxford Companion to the Earth, pp. 772–773. Oxford:

Oxford University Press).

Figure 6 (A) The movement of the north magnetic pole since

James Clark Ross located it in 1831. (B) The accelerating move-

ment of the pole at the present time, which could herald a rever-

sal (reproduced from McCall GJH (2003) Pole up the pole.

Geoscientist 13: 9, with the permission of the Geological Society

Publishing House).

EARTH STRUCTURE AND ORIGINS 425

yielded conflicting results and suggested differences in

movements at margins and within plates. There are

conflicting opinions as to whether convection operates

down into the lower mantle (the more orthodox view)

or only above the 670 km boundary, which forms a

barrier. The latter view (‘closed upper-mantle circula-

tion’) is held by D L Anderson and W B Hamilton and

considers the reality or otherwise of deep plumes, rising

from the base of the mantle. Plumes were originally

invoked to explain chains of seamounts and/or islands

such as the Emperor Seamount and Hawaiian Islands

in the Pacific Ocean, where the ages of the individual

islands become progressively younger towards the

south-east. Oceanic lithosphere is hypothesized to

move over a static hotspot. Sceptics believe that the

670 km barrier cannot be penetrated by a rising plume

(see Mantle Plumes and Hot Spots). There is also no

agreement on the mechanism of plate movement.

Ridge push, subducting-slab pull, and a combination

of both have all been favoured, as has a mechanism of

gravity gliding. The plate movement must start with

spreading away from the ridge before subduction

begins to operate (no slab yet to pull), so slab pull can

never provide the entire answer. It seems fair to say

that, whereas the plate-tectonics paradigm must rea-

sonably be accepted as fact, the mechanism remains

unexplained, and mathematical calculations do not

really explain how the forces needed to move the plates

are derived (see Plate Tectonics).

Geochronological Comparisons –

Earth and Other Solar System Bodies

It is early days yet in Space exploration, so, whereas

we can derive a very detailed and accurate chron-

ology for our own planet, based on the radioactive

decay of isotopes, palaeontology, palaeomagnetism

etc., we have very little chronological information

about other bodies. There is no palaeontological

data for other bodies (there may have been no life

there). We have isotope-based data for the Moon, but

there is really no geochronological data from there

for the last 3000 Ma or so. Palaeomagnetism cannot

be applied to bodies other than the Earth. There is a

set of dates for the formation of the rocks comprising

the SNC meteorites (shergottites, Nakhlites and chas-

signites), which are supposed to have come from

Mars, and these have contributed to a Martian geo-

chronology (which may yet prove to be wildly incor-

rect). Isotopic dates of around 4500 Ma for the

formation of the asteroids have been derived from

chondritic meteorites, and slightly younger dates,

recording a slightly later melting process in the aster-

oidal parent bodies, have been derived for achondritic

meteorites (see Solar System: Meteorites). For Venus

and Mercury we have no yardsticks at all, although

surmises have been made from the radar-derived

images of Venus. Mercury resembles the Moon in its

surface cratering and appears, like the Moon, to be a

‘dead’ multicratered body with no or negligible erup-

tivity since the deduced bombardment that formed

the craters (see Solar System: Mercury; Venus). Se-

quential relationships without any benchmarks have

been derived from the superposition orders of crater

populations and volcanic structures. The comparison

diagram (Figure 11) utilizes the very limited evidence

from outside the Earth to make this comparison.

Figure 9 The widely accepted configuration of plate movement

away from a mid-ocean ridge and down subduction zones be-

neath continents (reproduced from Van Andel TJ (1994)

New Views

on an Old Planet

, 2nd edn. Cambridge: Cambridge University

Press, with permission from the author and publisher).

Figure 10 The tectonic plates of the Earth, Ar ¼ Arabia; Phil ¼

Philippines (reproduced from Van Andel TJ (1994)

New Views on

an Old Planet

, 2nd edn. Cambridge: Cambridge University Press,

with permission from the author and publisher).

426 EARTH STRUCTURE AND ORIGINS

The Origin of the Earth

The Earth was formed from the nebula that produced

the Solar System. It is almost universally accepted

that the Sun, the planets and their satellites, the aster-

oids, and the comets of the Oort ‘cloud’ grew from a

cloud of gas and dust that contracted under its own

gravity. The cloud of gas and dust had some degree of

rotation (Figure 12) and, as the centre contracted, the

angular momentum forced the remains into a flat-

tened disk, in the plume perpendicular to the axis of

rotation of the proto-Sun. This was apparently a very

rapid process, perhaps taking place over 10 000 years.

The dust particles accreted heterogeneously to pro-

duce lumps that formed planetesmals, the first small

solid bodies, and cooling occurred.

We can estimate the composition of the original

nebula from the solar abundances of elements, ob-

tained spectrographically, and analysis of primit-

ive meteorites (e.g. carbonaceous chondrites) (see

Solar System: Meteorites); however, these are only

estimates, and a second method is based on an assu-

mption that may not be entirely accurate. Radioactiv-

ity-based dating methods (relying on the decay of

radiogenic isotopes), as applied to terrestrial igneous

rocks, allow us to date the condensation to 4500 Ma

ago (the so-called ‘age of the Earth’), and it is believed

that condensation was rapid, taking about 100 000

years.

Accretion of the Earth and the other planets may

have been slow and heterogeneous or rapid and homo-

geneous. Which of these two models is correct re-

mains uncertain, but the first model, if correct, could

have produced a layered mantle (see Earth: Mantle).

After condensation and accretion, the Earth

evolved rapidly into a planet with most of its present

properties. This could have taken no more than 500

Ma and was probably effected more rapidly: the

oldest known minerals are zoned zircons from the

Mount Narryer gneiss terrain, Western Australia,

which give spot SHRIMP ages of 4400 Ma and are

believed to have been formed by partial melting of pre-

existing granitic crust (see Minerals: Zircons). This

evidence indicates that there was solid rock at the

Earth’s surface astonishingly soon after condensation

and accretion.

The oldest actual rock dated is a component of the

Acasta Gneiss in the Slave Province of Canada, which

has an age of 4000 Ma. Despite the existence of the

Mount Narryer minerals, there is no other really

significant evidence from geology of the Earth per-

taining to the 500 Ma prior to the formation of the

Acasta Gneiss, and this is called the ‘Hadean Eon’,

Figure 11 A comparison between the eons and eras of the geological column and sequences of events that have been deduced for

the other inner planets, the Moon and satellites of the outer planets on the basis of the very limited evidence available from Space and

meteoritical research (modified from G J H McCall (2000) Age and early evolution of the Earth and Solar System. In: Hancock PL and

Skinner BJ (eds.)

Oxford Companion to the Earth, pp. 8–11. Oxford: Oxford University Press).

EARTH STRUCTURE AND ORIGINS 427

Figure 12 The development of the Earth as a planet in the Solar System from the nebula.

428 EARTH STRUCTURE AND ORIGINS

geology’s dark ages. We do know something of this

period from the Moon – the lunar rocks brought back

by Apollo and Lunik date from this period – and it is

reasonable to invoke a bombardment of the Earth,

like the Moon, during this period. However, there is

no trace of this in the geological record of the Earth.

The lack of evidence of ejecta from the Moon in Space

means that it is difficult to attribute all the heavy early

cratering of the Moon to bombardment by impacting

objects from Space (see Solar System: Meteorites).

Nevertheless, the early Earth must have swept up

asteroids, comets, and any other debris in its path

for a few million years after it attained its present size.

The Earth, after accretion, must have heated up

internally and melted in order to separate, gravita-

tionally, the core (part liquid and part solid), mantle,

and crust. This heating would have been caused by

the radioactive decay of elements and by gravitational

energy – the latter as the dust, or dust and planetes-

mals, condensed and accreted into a ball. It has also

been suggested that heat could have been produced by

impacts on the surface, though much of this heat

would have dissipated into Space. The heavy elem-

ents, mainly iron, would have gravitated to the core,

and the lighter silicate material would have ended

up in the mantle and crust. A primitive and highly

mobile surface layer, perhaps a magma ocean, would

have initiated the crust, and from this small-scale

proto-continents separated. More ‘way-out’ models

for the formation of the crust invoke early impacts,

the subsidence of large impact-generated basins in

the basaltic proto-crust, and partial melting of the

basalt to form the proto-continents. The early proto-

continents were certainly small, and the extent of the

continents increased until around 3200 Ma, when

the Kaapvaal (South Africa) and Pilbara (Western

Australia) cratons were formed.

The very lightest volatile elements would have sep-

arated at the same time to form the proto-ocean and

proto-atmosphere. This volatile component would

have had a bulk composition of 10–20% water

and contents of other volatiles in line with those of

carbonaceous chondrite meteorites, according to the

chondritic Earth model. The first atmosphere was

almost certainly reducing rather than oxygenating.

Our present oxygen-containing atmosphere was

derived later, though how much later is debatable,

and relates, in its origin, to the onset of biological

activity. How and when life originated is still a mys-

tery – there are models that suggest that it originated

within the early developing Earth, but there are also

models that suggest that it arrived on the planet from

comets or primitive meteorites (see Origin of Life).

Further Reading

Anderson DL (1999) A theory of the Earth: Hutton,

Humpty Dumpty and Holmes. In: Craig GY and Hull

JH (eds.) James Hutton: Present and Future, pp. 13–35.

Special Publication 150. London: Geological Society.

Edwards K and Rosen B (2000) From the Beginning.

London: Natural History Museum.

Hamilton WB (2002) The closed upper mantle circulation in

plate tectonics. In: Plate Boundary Zones, pp. 359–410.

Geodynamics Series 30. American Geophysical Union.

Hancock PL and Skinner BJ (2000) Oxford Companion to

the Earth. Oxford: Oxford University Press.

Harland WB, Armstrong RL, Cox AV, et al. (1990)

A Geologic Timescale 1989. Cambridge: Cambridge

University Press.

Holmes A (1965) Principles of Geology, revised edn.

London and Edinburgh: Nelson.

McCall GJH (2000) Age and early evolution of the Earth

and Solar System. In: Hancock PL and Skinner BJ (eds.)

Oxford Companion to the Earth, pp. 8–11. Oxford:

Oxford University Press.

McCall GJH (2003) Pole up the pole. Geoscientist 13: 9.

Price NJ (2001) Major Impacts and Plate Tectonics.

London and New York: Routledge.

Rothery DA (1992) Satellites of the Outer Planets. Oxford:

Clarendon.

Van Andel TJ (1994) New Views on an Old Planet, 2nd edn.

Cambridge: Cambridge University Press.

Vita-Finzi C (2002) Monitoring the Earth. Harpenden:

Terra.

Wilde SA, Valley JW, Peck WH, and Graham CM (2001)

Evidence for the early growth of continents and oceans

from <4 Ga detrital zircons. AGSO – Geoscience

Australia Record 2002/3: 6–8.

EARTH STRUCTURE AND ORIGINS 429

EARTH SYSTEM SCIENCE

R C Selley, Imperial College London, London, UK

Introduction

What on Earth is Earth System Science?

Earth system science is founded on the precept that

the Earth is a dynamic system that is essentially closed

materially, but open with respect to energy. This

statement needs to be qualified by noting that the

Earth continues to accrete matter from space in the

form of meteorites, asteroids, and comets. Incoming

energy is principally derived from solar radiation at a

rate that may fluctuate with time. Earth processes in

the lithosphere, the biosphere, and the atmosphere

are linked, with a change in one impacting on one

or more of the others. Earth system science has

grown out of an appreciation of the need to integrate

geology with other scientific disciplines, not only to

understand the planet on which we live, but also most

particularly to predict its future in general and

climate change in particular. Earth system science

requires a holistic approach to education in which

students learn geoscience, bioscience, climatic sci-

ence, astroscience, and space science synchronously

and seamlessly.

The Genesis of Earth System Science

In the fourteenth century Richard de Bury (Bishop

of Durham 1333–45) divided all research into

‘Geologia’ (geology), the study of earthly things, and

‘Theologia’ (theology), the study of heavenly things.

Masons, miners, and engineers were the first investi-

gators of rocks. The Church taught them that the

Earth was an inert mass of rock formed in 7 days.

Subsequently natural philosophers pondered the

meaning of fossiliferous strata and how it was that

they were intruded by crystalline rocks and truncated

by unconformities. Gradually it dawned on these nat-

ural philosophers that the rocks were not formed in

an instant, but resulted from processes, many of

which could be observed on the modern surface of

the Earth. This was formulated in Hutton’s principle

of uniformitarianism, (see Famous Geologists: Hut-

ton) and was epitomized in the dictum that ‘the

present is the key to the past.’

As Lyell (see Famous Geologists: Lyell) wrote in his

Principles of Geology in 1834:

The entire mass of stratified deposits in the Earth’s crust

is at once the monument and measure of the denudation

which has taken place.

By the beginning of the twentieth century it was

realized that the history of the Earth could be inter-

preted in terms of cycles. Davies (1850–1934) recog-

nized the landscape cycle, commencing with uplift,

followed by youthful, mature, and senile landforms,

followed by rejuvenation. Stratigraphers recognized

cycles of weathering (see Weathering), erosion, trans-

portation, deposition, and diagenesis. Sedimentologists

discovered that all sedimentation is cyclic, although

some is more cyclic than others. The hydrologic cycle

was revealed, in which water fell as rain on land,

flowed into rivers, was discharged into the world’s

oceans, evaporated and reprecipitated. Geochemists

identified the cycles of carbon (see Carbon Cycle)and

other key elements, such as nitrogen, oxygen, and

sulphur.

Agassiz (1807–73) (see Famous Geologists: Agas-

siz) was the first geologist to establish the existence of

ancient glaciation. Subsequently evidence accumu-

lated for past climatic cycles of alternating ‘green-

house’ and ‘icehouse’ phases, as they became

picturesquely termed.

Thus cyclicity was revealed in rocks, water, and

air – or the lithosphere, the hydrosphere, and the

atmosphere. The extent to which these cycles inter-

related with one another was little understood. Initially

palaeontologists took the view that the evolution of

the biosphere responded to external changes, and

had little inter-reaction with them. Subsequently it

was realized that this is far from the case. The stroma-

tolitic limestones (see Fossil Plants: Calcareous Algae)

of the Late Precambrian, some 3400 My BP, are a

dramatic example (Figure 1). These limestones are the

relicts of primitive algae and cyanobacteria. They are

found worldwide in Late Precambrian and Phanerozoic

strata, and form today in tidal-flat environments.

Stromatolitic limestones provide the earliest case

preserved in the stratigraphical record of the inter-

action of organic and inorganic processes to form

rock. Their creators, the first abundant photosynthe-

sizers, took carbon dioxide from the atmosphere, re-

placed it to some degree with oxygen, extracted

calcium from sea water, and precipitated the vast

limestone rock formations that are preserved all over

the world to this day (see Atmosphere Evolution).

Analysis of ice cores from modern polar regions

shows a strong positive correlation between carbon

430 EARTH SYSTEM SCIENCE

dioxide concentrations in the atmosphere and tem-

perature. It is reasonable to assume such linkage in

the past, and that the precipitation of stromatolitic

and other limestones may be one of several causes of

global cooling. In the history of the Earth extensive

episodes of limestone formation have been followed

by global cooling several times. The Late Precam-

brian stromatolitic limestones demonstrate the link-

age between biosphere, lithosphere, and atmosphere,

and provide a good starting point to examine what is

now called Earth system science.

Biogeochemical Cycles

The appreciation of the interplay of atmosphere,

biosphere, and hydrosphere, demonstrated by stro-

matolites, coupled with the realization that many

Earth processes are cyclic, has lead to the concept

of the biogeochemical cycle. This term is applied to

the flux of material in and out of the lithosphere,

hydrosphere, biosphere, pedosphere, and atmosphere

(which collectively constitute the geosphere), and

the chemical and physical changes that occur there-

in. The material Earth, or geosphere, is a closed dy-

namic system, within which there is a constant

recycling of its components. It is not, however, a

closed system with respect to energy, because this

constantly reaches the Earth in the form of solar

radiation (Figure 2).

A variation in solar energy will impact on the dy-

namics of biogeochemical cycles. As a generalization,

an increase in solar radiation may result in global

warming, and a decrease may result in global cooling.

The situation is more complex than this, however,

because of the interconnected nature of the cycles or

systems.

Some Definitions Defined

Biogeochemical cycles are described and modelled

in terms of reservoirs, material, fluxes, sources,

sinks, and budgets. The reservoir is the amount of

material in a given Earth system, such as oxygen in

the atmosphere, or water in the ocean. The flux is the

amount of material moved from one reservoir to

another – for example, the amount of water lost

from the ocean to the atmosphere by evaporation.

The source is the flux of material into a reservoir,

and the sink is the amount of material removed

from it. The budget is the balance sheet of the

amount of material lost or gained in a system. If

source and flux are in equilibrium, such that the

amount of material in the reservoir is constant, it is

in a steady state. A system of two or more reservoirs,

in which material is transferred cyclically without an

external flux, is termed closed. Commonly Earth

systems are interconnected or coupled: a variation in

the flux of one affects the dynamics of the other

(Figure 3).

Awareness that the geosphere consists of a multi-

tude of coupled systems, where a variation in the flux

of one will have a ‘knock-on’ effect on others, poses

the question ‘why is not the Earth in a permanent

state of dynamic chaos?’ Why, for example, does the

Earth’s climate alternate between glacial and intergla-

cial episodes, without fluctuating wildly all the time?

The answer lies in feedback, a concept familiar to

physiologists and engineers. For example, the tem-

perature of the human body remains constant, thanks

to the feedback effect of the hypothalamus, and the

temperature of a house remains constant owing to

regulation of the central heating system by a thermo-

stat. A feedback is when a process in one system

causes changes in another one that in turn influences

the first system. A positive feedback accelerates

the original process; a negative feedback retards it.

A positive feedback may be illustrated by considering

the effect of increasing the CO

content of the atmos-

phere (by burning fossil fuels, by volcanic eruption,

or whatever). This greenhouse gas will result in an

increase in temperature, which will result in evapor-

ation increasing from the oceans to the atmosphere

and an increase in water vapour, another greenhouse

gas, which will accelerate the increase in tempera-

ture. Negative feedbacks are rarer than positive feed-

backs in the geosphere, but include heat transfer

towards the poles and the cooling effect of volcanic

ash clouds.

Figure 1 A bedding surface showing the characteristic collo-

form brassicamorphic structure of a stromatolitic limestone. Late

Precambrian, Ella Island, East Greenland. Extensive Late Precam-

brian stromatolitic limestones provide early evidence of the inter-

relationship between the biosphere, the hydrosphere, and the

atmosphere. Earth system science is all about these interrelation-

ships.Formodernexample

see Minerals:Carbonates Figure 2G.

EARTH SYSTEM SCIENCE 431

Earth System Science and the

‘Gaia’ Hypothesis

Since the 1970s James Lovelock developed the Gaia

hypothesis, named after the ancient Greek goddess of

the Earth (See Gaia). As originally conceived the

‘Gaia’ concept envisages the Earth as a super-organ-

ism that operates to regulate its own environment,

principally temperature, to keep it habitable for the

biosphere. Lovelock has never argued that the bio-

sphere consciously anticipates environmental change,

but only that it automatically responds to it. None-

theless some sections of the public have construed it

that way, and in the popular mind Gaia gained a

quasi-mystical connotation, enhanced by its name.

The great value of the Gaia hypothesis is that it

presents the interdependence of the constituents of

the geosphere in a media-friendly way. Earth system

science also involves a holistic approach to the geo-

sphere, but without the ‘ghost in the machine’. None-

theless Amazon, the internet book shop, still classifies

books on Earth system science under ‘Religion and

Spirituality > New Age > Earth-Based Religions >

Gaia’.

Impact of Earth System Science

on Geology

When the dust of history has settled over the present

period it may be argued that Earth system science has

had as large an effect on geology as did plate tectonics

some 40 years previously (See History of Geology

Since 1962). Its import may be wider still however.

This is because Earth system science is an important

Figure 2 Overview of the cyclic processes on Earth. The placements of the geological and geographical features are not meant to

represent their true positions on the Earth, but to provide an overview of some of the Earth systems. Reproduced with permission from

Jacobson MC, Charlson RJ, and Rodhe H (2000) Introduction: Biogeochemical cycles as fundamental constructs for studying Earth

system science and global change. In: Jacobson MC, Charlson RJ, Rodhe H, and Orians H. (eds.)

Earth System Science, pp. 3–13. San

Diego: Academic Press.

432 EARTH SYSTEM SCIENCE

tool in the study of climate change, a topic of great

current concern. In particular it focuses attention on

how anthropomorphic activities, such as the combus-

tion of fossil fuels and deforestation, may have fed

back into atmospheric systems, and hence affected

global climate (see Palaeoclimates).

Moving from the practical to the theoretical, Earth

system science has brought about a decline in the

reductionist approach to science in general and to

geology in particular. (Reductionism is the process

of knowing more and more about less and less.)

In its infancy geology was advanced by natural

philosophers (the term ‘scientist’ was not popularized

until 1858 by Huxley) who were polymaths. It was

relatively easy to be a polymath in the nineteenth

century, because the pool of scientific knowledge

was limited. As the pool of knowledge expanded

into a lake, then a sea, and finally an ocean, scientists

have had to focus their attention on progressively

smaller and smaller areas of knowledge, thus losing

sight of the wood for the trees. Distinct disciplines of

chemistry, physics, life science, and geology have

evolved, all with their own specialized subsets. Earth

system science, by taking a holistic view of the Earth,

has had a beneficial effect on the development of

interdisciplinary scientific research. Concomitant

with this, however, has been a decline in the training

of geologists who can identify rocks, minerals, and

fossils, and map their distribution over the Earth.

Geology has become disseminated into Earth science.

University Geology Departments have metamorph-

osed into Departments of Earth Science, coupled

with geography, environmental science, etc. These

departments no longer produce graduates with

focused geological knowledge, but Earth scientists

who are Jacks-of-all-trades and masters of none.

Figure 3 The cyclic processes and fluxes between major reservoirs on the Earth. Reproduced with permission from Jacobson MC,

Charlson RJ, and Rodhe H (2000) Introduction: Biogeochemical cycles as fundamental constructs for studying Earth system science and

global change. In: Jacobson MC, Charlson RJ, Rodhe H, and Orians H. (eds.) Earth System Science, pp. 3–13. San Diego: Academic Press.

EARTH SYSTEM SCIENCE 433

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