Celebrating the age of the Earth

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Celebrating the age of the Earth
The Age of the Earth
Geological Society Special Publications
Society Book Editors
A. J. FLEET (CHIEF EDITOR)
P. DOYLE
F. J. GREGORY
J. S. GRIFFITHS
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J. P. TURNER
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GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO. 190
The Age of the Earth:
from 4004 BC to AD 2002
EDITED BY
C. L. E. LEWIS
History of Geology Group, Macclesfield, UK
&
S. J. KNELL
Department of Museum Studies, University of Leicester, UK
2001
Published by
The Geological Society
London
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Contents
Preface
vi
KNELL, S. J. & LEWIS, C. L. E. Celebrating the age of the Earth
FULLER, J. G. C. M. Before the hills in order stood: the beginning of the geology of time in
England
VACCARI, E. European views on terrestrial chronology from Descartes to the mideighteenth century
TAYLOR, K. L. Buffon, Desmarest and the ordering of geological events in epoques
RUDWICK, M. J. S. Jean-Andre de Luc and nature's chronology
TORRENS, H. S. Timeless order: William Smith (1769-1839) and the search for raw
materials 1800-1820
MORRELL, J. Genesis and geochronology: the case of John Phillips (1800-1874)
SHIPLEY, B. C. 'Had Lord Kelvin a right?': John Perry, natural selection and the age of the
Earth, 1894-1895
WYSE JACKSON, P. N. John Joly (1857-1933) and his determinations of the age of the
Earth
LEWIS, C. L. E. Arthur Holmes' vision of a geological timescale
YOCHELSON, E. L. & LEWIS, C. L. E. The age of the Earth in the United States (1891-1931):
from the geological viewpoint
BRUSH, S. G. Is the Earth too old? The impact of geochronology on cosmology, 1929-1952
KAMBER, B. S., MOORBATH, S. & WHITEHOUSE, M. J. The oldest rocks on Earth: time
constraints and geological controversies
DALRYMPLE, G. B. The age of the Earth in the twentieth century: a problem (mostly)
solved
HOFMANN, A. W. Lead isotopes and the age of the Earth - a geochemical accident
CALLOMON, J. H. Fossils as geological clocks
MANNING, A. Time, life and the Earth
STRINGER, C. B. Dating the origin of modern humans
REES, M. J. Understanding the beginning and the end
1
15
223
237
253
265
275
Index
285
25
39
51
61
85
91
107
121
139
157
177
205
Preface
CHERRY L. E. LEWIS & SIMON J. KNELL
This book is dedicated to the memory of John
Christopher Thackray (1948-1999), archivist at
the Natural History Museum (NHM) and Geological Society. It evolved from Celebrating the
Age of the Earth, the Geological Society's
William Smith Millennium Meeting, convened
in June 2000 by Cherry Lewis on behalf of the
History of Geology Group (HOGG), of which
Simon Knell was then a committee member.
John had been chairman of HOGG since its
foundation in 1992 and without him this project
would never have happened.
The idea began with a meeting between John
and Cherry, as she sought material for her
forthcoming book on Arthur Holmes.
Late in the sunny afternoon of 18th June 1998,
John Thackray and I were walking from the
Natural History Museum towards South Kensington tube, discussing possible topics for
future HOGG meetings. At that time John
was Chairman of HOGG and I was a new
member, of but a few months standing. It was
only the second time I had met him, but
already he had been immensely helpful in my
search for material relating to Holmes.
John had found a large number of Holmes'
letters in the NHM archives and I had spent
the day reading them, so I was full of all the
exciting things I had uncovered. 'What about a
meeting on Holmes and his contemporaries?'
I suggested, as we hovered on the pavement
waiting to cross the road. John looked doubtful, 'Would that be enough to fill a whole day?'
he asked, as we dodged the traffic, 'But we
could have one on the age of the Earth' he
continued, while we refuged on the island.
Instantly, standing in the middle of Thurloe
Street, we looked at each other and both knew
that this was 'it'. With the Millennium approaching The Age of the Earth seemed to
have a particular resonance. We threw a few
ideas around until we reached the station, but
I heard nothing more until I received this
email about two weeks later:
Dear Cherry,
we have just had a HOGG committee meeting,
and you will be alarmed to hear that your name
was mentioned. We were talking about what
meeting to have in the autumn of 1999 - the
end of the millennium ... [It was agreed] that
we should hold a one-day meeting on the history
of geochronology, age of the earth, geological
time scale, all that sort of thing ...
Then we had to think of a convenor.
All the committee coughed and looked at their
feet, until someone remembered that you are
working on AH and the age of the earth, and
might be just the perfect person. ... it is not a
huge amount of work.
Perhaps we could talk about it. Or perhaps you
wish you had never met us!
BWs,
John
How could Cherry refuse? Over the next few
months they exchanged frequent emails as it
became the main topic of much HOGG discussion. The idea grew: a one-day conference,
then two; a provisional line-up of British speakers soon became international; the end of 1999
became mid-2000, to give us more time to
organize it.
While Cherry organized speakers, John talked
to people behind the scenes: the Royal Society
liked the idea so much they suggested we apply
for sponsorship, while the Geological Society
elected it for the Millennium's William Smith
meeting. With funds pledged we could now invite
speakers from abroad, and to our delight the
Geological Society of America also promised to
sponsor two airfares. By the end of that year it
was all looking rather good, but it was then the
terrible shock came. John was seriously ill with
cancer. Incredibly, he lived only a few months
longer. He died on 6 May 1999 at the age of
fifty-one.
In the mid-1980s John had worked in the
Geological Museum where Simon also had an
office. John had been one of Simon's PhD
examiners and it was John who encouraged him
to join the HOGG committee. John really was
the lifeblood of that group but in remembering
him here we celebrate more than his breadth
of knowledge, professionalism and scholarship.
Unassuming, ever helpful, and with a wonderfully dry wit, John's most important quality was
PREFACE
the way he always put things into perspective.
With great affection we dedicate this book to
his memory.
We had a clear vision of what we wanted the
meeting to achieve, inspired by William Sollas
who in 1900, as President of Section C - Geology, had opened his address to the British Association for the Advancement of Science (BAAS)
in the following terms: The close of one century,
the dawn of another, may naturally suggest some
brief retrospective glance over the path along
which our science has advanced ... from which
we may gather hope of its future progress.'
Sollas' theme was the age of the Earth, then
perhaps the topic of interest to scientists from
many disciplines. And this was the point scientists from many disciplines. Not only did we
want to take a retrospective look at our science
over the last hundred years or so, but here was a
rare opportunity to involve people from a range
of scientific disciplines interested in the age of the
Earth as a topic, and geochronology as a tool geologists, biologists, archaeologists, astronomers and, of course, historians. In the early part
of the twentieth century it had been common
practice for scientists from the different BAAS
Sections to get together to share their knowledge
on subjects of interest to them all. Today it
rarely happens - we are all so 'specialized' - but
uniquely we had this chance.
Over two days (28 and 29 June 2000) the
audience was taken from Elizabethan 'mind
control' to the very cutting edge of work now
being done to date the Earth and its rocks. The
first day was largely given over to historians who
revealed the many ways in which the Earth's age
was first ignored and then grew to become one of
the most important scientific questions of all time.
The second day emerged from these historical
perspectives to that of scientists reflecting upon a
golden age of radiochemistry, as geochronological techniques were developed with which to
establish a geological time scale, and from which
all those used today have descended. The meeting
also included the William Smith lecture given by
Hugh Torrens, as well as contributions from other
distinguished individuals from a range of scientific disciplines, on how a knowledge of geology
Speakers and contributors to Celebrating the Age of the Earth, held at the Geological Society of London,
Burlington House, London, on 28 and 29 June 2000. Starting from the back row (row 4), left to right:
Row
Row
Row
Row
vii
4: John Calloman, Patrick Wyse Jackson, Ken Taylor, Martin Rudwick.
3: Martin Rees, Stephen Moorbath, John Fuller, Ezio Vaccari.
2: Aubrey Manning, Gerald Friedman, Chris Stringer, Joe Burchfield.
1: Richard Wilding, Stephen Brush, G. J. Wasserburg, Al Hofmann, Cherry Lewis.
viii
PREFACE
and geochronology contributes to, and overlaps
with, their subjects.
But this volume is not just a record of the
conference. There are a number of contributions
here that were not presented at the meeting and,
with time to reflect since the event, all papers
have been revised. As editors we certainly made
our authors work and in this regard we must
thank all the referees who contributed so much
to helping us. We would also like to thank the
publishing staff for their work in producing such
a splendid book; HOGG for sponsoring some of
the photos in the volume, as well as the Geological Society of London, the Royal Society
and the Geological Society of America for enabling us to Celebrate the Age of Earth in the first
place. John Thackray would have been proud
of us all.
It is recommended that reference to all or part of this book should be made in one of the following
ways:
LEWIS, C. L. E. & KNELL, S. J. (eds) 2001. The Age of the Earth: from 4004 BC to AD 2002. Geological
Society, London, Special Publications, 190.
MANNING, A. 2001. Time, life and the Earth. In: LEWIS, C. L. E. & KNELL, S. J. (eds) The Age of the
Earth: from 4004 BC to AD 2002. Geological Society, London, Special Publications, 190, 253-264.
Celebrating the age of the Earth
SIMON J. KNELL1 & CHERRY L. E. LEWIS2
1
Department of Museum Studies, 105 Princess Road East, Leicester LEI 7LG, UK
(email, [email protected])
2
History of Geology Group, 21 Fowler Street, Macclesfield, Cheshire SK10 2AN, UK
(email: [email protected])
Abstract: The age of the Earth has been a subject of intellectual interest for many centuries,
even millennia. Of the early estimates, Archbishop Ussher's famous calculation of 4004 BC
for the date of Creation represents one of the shortest time periods ever assigned to the
Earth's age, but by the seventeenth century many naturalists were sceptical of such
chronologies. In the eighteenth century it was Nature that provided the record for Hutton
and others.
But not all observers of geology enquired about time. Many, like William Smith, simply
earned a living from their practical knowledge of it, although his nephew, John Phillips, was
one of the first geologists to attempt a numerical age for the Earth from the depositional
rates of sediments. For more than fifty years variations of that method prevailed as
geology's main tool for dating the Earth, while the physicists constrained requirements for a
long timescale with ever more rigorous, and declining, estimates of a cooling Sun and Earth.
In 1896 the advent of radioactivity provided the means by which the Earth's age would at
last be accurately documented, although it took another sixty years. Since that time ever
more sophisticated chronological techniques have contributed to a search for the oldest
rocks, the start of life, and human evolution. In the attempt to identify those landmarks, and
others, we have greatly progressed our understanding about the processes that shape our
planet and the Universe, although in doing so we discover that the now-accepted age of the
Earth is but a 'geochemical accident' which remains a contentious issue.
Establishing the Earth's age and chronology has
been something of an intellectual baton passed
from one academic creed to another as each
seemed to offer new hope of solution or understanding. In the seventeenth century the Earth's
age was subject to the strictures of religious and
social orthodoxy. The product of Creation,
theological study offered one logical path to its
understanding, but also to its containment. This
pattern would repeat itself, as forces for an
expanded timescale repeatedly did battle with
those who thought the Earth relatively young,
This was never simply a conflict between 'progressive' science and a resistant society, but
rather a reflection of the path travelled by an
idea through a complexity of beliefs, dogmas,
theories, measurements and methodologies.
In the eighteenth century, Theories of the
Earth marshalled existing evidence, scientific
practice and analogy, to construct models for
the origin and development of the planet. At the
beginning of the nineteenth century, modern
geology emerged as a rigorous and empirical
field of study then centred on stratigraphy with
its implied notions of relative age. This, when
combined with the wide adoption of uniformitarianism, gave the sacience new and seemingly
rational ways to think about time. But the new
geologists were often reticent about discussing
time in terms of years. By the 1860s, however, the
subject added the great evolutionary debate to its
intellectual baggage as T. H. Huxley defended
Darwin's billion-year estimate for natural selection. Now both biologists and geologists joined
forces to demand a longer timescale which permitted the playing out of those evolutionary and
uniformitarian processes necessary to explain the
condition of the Earth.
However, the age of the Earth had acquired a
new interest group. Applying theoretical ideas
developed in the arly years of the century, a
number of respected physicists began to offer
hope of at last calculating the Earth's age in
years. But if their calculations were correct, then
those great underpinning theories of the natural
sciences could not be. With the discovery of
radioactivity in 1896, the future of the Earth's
age was firmly in the court of that emerging interdisciplinary subgroup, the geophysicists. In the
twentieth century these extended the timescale
From: LEWIS, C. L. E. & KNELL, S. J. (eds). The Age of the Earth: from 4004 BC to AD 2002. Geological Society, London, Special Publications, 190, 1-14. 0305-8719/01/$15.00 © The Geological Society of
London 2001.
S. J. KNELL & C. L. E. LEWIS
2
remarkably. With Einstein's general relativity
field equations, the topic was also returning to
cosmology, to explanations of the Earth's age in
the context of the age of the universe, to the realm
of astronomers.
What unifies these different approaches and
their practitioners is their extrapolation of time
from the study of process, whether that process
was observable or modelled by theory. Early
chronologers rigorously applied contemporary
historiographic methods to chart the 'progress'
of history. Later geologists would extrapolate
the time necessary for shaping the surface of the
Earth or for the deposition or erosion of observable strata. Biologists too envisaged a timedependent process of evolution. Physicists made
predictions and measurements from the physics
of heat and radioactive decay, and astronomers
deduced process from planetary construction
and arrangement. In the relative calm of the
early twenty-first century, in a field which has
seen centuries of deep controversy, we should
perhaps reflect upon the confidence our predecessors had in their age for the Earth. They
too thought they had 'got it right'.
Chronologies and theories
In one of his popular articles, Stephen Jay
Gould (1993, pp. 181-193) responded to James
Barr's (1985) definitive study of a great historical chronologer with a diatribe against previous
'Whiggish' interpretations of this early form of
scholarship. The historiography of science had
long rejected the notion of "progress', of the past
having been a succession of errors, but Gould
was here talking to scientists who necessarily
remained wedded to, and driven by, this concept of progress towards 'truth'. Though not
the first to do so, Barr saw chronologers not
as religious dogmatists but as rigorous scholars
working within the social and intellectual
constraints of their time. They were participating in the earliest of historiographic practices - the construction of a linear timeline of
events - which, in reconceived form, would later
underpin the great stratigraphic enterprise of the
nineteenth century.
Rees's early-nineteenth-century Cyclopaedia
separated 'sacred chronology' from other historical chronologies. Here chronology was 'one of
the eyes of history' and not simply the study
of ancient theological texts. Its potential sources
were many:
As its use is extensive, the difficulty of acquiring it is not inconsiderable. It derives necessary
assistance from astronomy and geography.
also from arithmetic, geometry, and trigonometry, both plain and spherical; and likewise from a studious and laboured application
of various sources of information, supplied
by the observation of eclipses, by the testimonies of credible authors, and by ancient
medals, coins, monuments and inscriptions
(Anon. 1819).
Chronologies were constructed as an analytical
tool so as to distinguish 'cause' and realize a
'chain of events' (Anon. 1837, p. 131). To achieve
this, their content was selective and thematic.
To discern the age of the Earth, the only 'credible authors' were those relating creation stories.
The Bible, or rather the texts from which it was
written, then became the primary historical
texts, key sources for the interpretation of
time. Historians generally point to Theophilus
of Antioch, of the second century AD. as perhaps
the first to use the Biblical record as a source
for the construction of a chronology. The art of
chronology, however, extended back long before
the Christian era, often deriving 'fabulous ages*
of hundreds of thousands of years for particular
civilizations (Anon. 1819, 1833, 1849). In the
sixth century BC Zoroaster, a religious teacher
who lived in Persia (now Iran), believed that the
world had been in existence for over 12000
years; the Roman writer Cicero relates that the
venerable priesthood of Chaldea in ancient
Babylonia held the belief that the Earth emerged
from chaos two million years ago, while the old
Brahmins of India regarded Time and the Earth
as eternal (Holmes 1913).
By the sixteenth century the Bible formed a
core resource for the writing of histories in
Europe. Of particular significance was the
interpretation of the Second Letter of Simon
Peter, which states 'One day is with the Lord as
a thousand years, and a thousand years as one
day' (2 Peter 3:8) (see also Dean 1981a; Oldroyd
1996a). It draws on Psalm 90 of the Old
Testament, "The human condition': 'Lord ...
To you, a thousand years are a single day*.
Chronologers read this literally, and made
each of the six days of creation equivalent to
1000 years. The Biblical motivation for discussing the Earth's limited age was to encourage the
living of 'saintly lives'. For here was not simply
the birth but also the death of the Earth, the
Judgement Day, which will 'come like a thief,
and then with a roar the sky will vanish, the
elements catch fire and fall apart, and the Earth
and all it contains will be burnt up* (2 Peter
3:10). If this were not enough to encourage
piety, Psalm 90 also pondered human mortality,
'over in a trice, and then we are gone.'
AGES OF THE EARTH
Fig. 1. Oil Painting of Archbishop James Ussher in
1658. Reproduced by kind permission of the governors
and guardians of Armagh Public Library.
Scholars and particularly the clergy - long an
intellectual elite - used these 6000 years as a
framework. The relative merits of the Hebrew
Massoretic text, the Samaritan Pentateuch and
Greek Septuagint were much debated, while
later studies of other civilizations revealed even
longer chronologies and other creation stories.
Given the range of sources and scope for
interpretation, it is no wonder that no definitive
chronology was produced.
Undoubtedly the most famous chronology
known to us today is that published in the seventeenth century by James Ussher (Fig. 1) but,
as Fuller (2001) shows, he was not alone nor was
he the most revered in his time (see also Anon.
1819, 1833). A brilliant scholar, Ussher had completed a draft whilst at Trinity College, Dublin,
in 1597. He was then only 16 years old. Barr
(1985) disentangled the complexity of Ussher's
work, of which his Creation date of 4004 BC is
best known. This curiously high-resolution date
is derived from traditional interpretations he
had inherited, which placed 4000 years between
the Creation and the coming of Christ, and an
adjustment to take account of evidence that
Herod (a contemporary of Christ) died in 4 BC.
However, only one-sixth of Ussher's chronology
was concerned with the Bible, the rest was a history of classical times. That we know of Ussher,
however, rather than one of the hundreds of
other chronologers, is simply an accident of history (for which, see Fuller 2001).
For one group of scholars it seemed the
answer might be found by undertaking comparative studies of published chronologies in
order to locate sources of error and correction.
William Hales' three-volume New Analysis of
Chronology (1809-1812) is an example which
3
became very familiar to early-nineteenth-century
British audiences, but he had predecessors and
contemporaries across Europe (Anon. 1837,
p. 133; Davies 1969, p. 13; Fuller 2001). From
his own studies Hales preferred a creation date
of 5411 BC. But by the time he published,
chronologies, however useful they were for the
construction of civil histories, were no longer
restricting views of the age of the Earth. Indeed
scholars had, for almost a century, taken the
debate beyond the religious confines of orthodoxy. Davies (1969, p. 16), for example, suggests
that scepticism of established chronologies
existed amongst seventeenth-century naturalists.
Though such views were rarely committed to
paper, he felt sure that the London coffee houses
must have been alive with such talk. The devout
John Ray (1627-1705), for instance, reflected
upon the oganic origin of fossils and considered
the implications for time of the depths of sediments and rates of denudation - a recurrent
theme in the centuries to come (Davies 1969,
p. 59; Dean 1981a, p. 444).
Despite the enforcement of religious orthodoxy by the state (Davies 1969, p. 11), freedom of
expression about the origins and history of the
Earth developed rapidly in the eighteenth century. In 1694, for example, Edmond Halley
considered the implications of a comet impact
on the Earth. He imagined an Earth repeatedly
reborn following chaotic destruction. It seemed
to support a view of an eternal Earth undergoing
periods of dissolution and recreation - a notion
then considered 'one of the most dangerous
of heresies' (Kubrin 1990, p. 65; Davies 1969,
p. 12). It was also a challenge to the British
establishment, much like that presented by theories of biological transmutation a century later
(Desmond 1989). Such ideas did not simply
undermine religious teaching but proclaimed as
a falsehood the natural social order into which
the established church and wider society were
divided. To counter such opinions of himself,
which were likely to affect his career prospects,
Halley then spent a good deal of his time
pursuing evidence for a finite age of the Earth.
For him, there were good socio-political reasons
for wanting to discover a particular answer
which reinforced accepted views (Kubrin 1990,
p. 65). Gould pondered one such of Halley's
observations (Gould 1993, pp. 168-180). Understanding that the salts in the world's oceans were
delivered to the sea via rivers, Halley suggested
that if the rate of contribution could be
calculated then here would be a measure for
the age of the Earth. It was an idea that was to
resurface in the late nineteenth century in the
hands of John Joly (Wyse Jackson 2001). What

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