PLEASE NOTE:
*
Date sent: Tue, 09 Dec
1997 09:17:26 -0500 (EST)
From:
Benny J Peiser <B.J.PEISER@livjm.ac.uk
Subject:
Re: CC Digest, 9/12/97
To:
cambridge-conference@livjm.ac.uk
Priority: NORMAL
CAMBRIDGE-CONFERENCE DIGEST, 9 December 1997
(1) COMETS AND DISASTER IN THE BRONZE AGE
(2) GLOBAL WARMING: BOTH SIDES OF THE ARGUMENT COULD BE WRONG
=======================================================================
From: BRITISH ARCHAEOLOGY, Journal of the Council for British
Archaeology, December 1997
COMETS AND DISASTER IN THE BRONZE AGE
Cometary impact is gaining ground as an explanation of the
collapse
of civilisations, writes Benny Peiser
At some time around 2300 BC, give or take a century or two, a
large
number of the major civilisations of the world collapsed,
simultaneously it seems. The Akkadian Empire in Mesopotamia, the
Old
Kingdom in Egypt, the Early Bronze Age civilisation in Israel,
Anatolia and Greece, as well as the Indus Valley civilisation in
India, the Hilmand civilisation in Afghanistan and the Hongshan
Culture in China - the first urban civilisations in the world -
all
fell into ruin at more or less the same time. Why?
A thousand years later, at around 1200 BC, many of the
civilisations
of the same regions again collapsed at about the same time. This
time, disaster overtook the Myceneans of Greece, the Hittites of
Anatolia, the Egyptian New Kingdom, Late Bronze Age Israel, and
the
Shang Dynasty of China.
The reasons for these widespread and apparently simultaneous
disasters - which coincided also with changes of cultures and
societies elsewhere, such as in Britain - have long been a
fascinating mystery. Traditional explanations include warfare,
famine, and more recently 'system collapse', but the apparent
absence
of direct archaeological or written evidence for causes, as
opposed
to the effects, has led many archaeologists and historians into a
resigned assumption that no definite explanation can possibly be
found.
Some decades ago, the hunt for clues passed largely into the
hands of
natural scientists. Concentrating on the earlier set of Bronze
Age
collapses, researchers began to find a range of evidence that
suggested that natural causes rather than human actions, may have
been initially responsible. There began to be talk of climate
change,
volcanic activity, and earthquakes - and some of this material
has
now found its way into standard historical accounts of the
period.
Agreement, however, there has never been. Some researchers
favoured
one type of natural cause, others favoured another, and the
problem
remained that no single explanation appeared to account for all
the
evidence.
Over the past 15 years or so, however, a new type of 'natural
disaster' has
been much discussed and is beginning to be regarded, by many
scholars, as
the most probable single explanation for widespread and
simultaneous
cultural collapse, but not only in the Bronze Age but at another
times as
well. The new theory has been advanced largely by astronomers,
and remains
almost completely unknown amongst archaeologists (a few notable
exceptions
include the dendrochronologist Prof Mike Baillie of Queen's
University,
Belfast, and Dr Euan MacKie at Glasgow University). The new idea
is that
these massive cultural disasters were caused by the impact of
comets or
other types of cosmic debris on the Earth.
The hunt for natural causes for these human disasters began
when the
Frenchman Claude Schaeffer, one of the leading archaeologists of
his
time, published his book 'Stratigraphie Comparee et Chronologie
L'Asie
Occidentale' in 1948. Schaeffer analysed and compared the
destruction layers
of more than 40 archaeological sites in the Near and Middle East,
from Troy
to Tepe Hissar on the Caspian Sea and from the Levant to
Mesopotamia. He was
the first scholar to detect that all had been totally destroyed
several
times in the Early, Middle and Late Bronze Age, apparently
simultaneously.
Since the damage was far too excessive and did not show signs of
military or
human involvement, he argued that repeated earthquakes might have
been
responsible for these events.
At the time he published, Schaeffer was not taken seriously by
the
world of archaeology. Since then, however, natural scientists
have
found widespread and unambiguous evidence for abrupt climate
change,
sudden sea level changes, catastrophic inundations, widespread
seismic activity and evidence for massive volcanic activity at
several periods since the last Ice Age, but particularly at
around
2200BC, give or take 200 years. Areas such as the Sahara, or
around
the Dead Sea, were once farmed but became deserts. Tree rings
show
disastrous growth conditions at c 2350BC, while sediment cores
from
lakes and rivers in Europe and Africa show a catastrophic drop in
water levels at this time. In Mesopotamia, vast areas of land
appear
to have been devastated, inundated, or totally burned.
Scholars who, following Schaeffer, favour earthquakes as the
principal cause
of civilisation collapse argue that the world can expect vast
earthquakes
every 1000 - 2000 years, leading to widespread abandonment of
sites; while
scholars who prefer climate change as the principal cause argue
that severe
droughts caused agriculture to fail and that societies inexorably
fell apart
as a result.
Yet what was the cause of these earthquakes, eruptions, tidal
waves,
fire-blasts and climate changes? By the late 1970s, British
astronomers Victor Clube and Bill Napier of Oxford University had
begun to investigate cometary impact as the ultimate cause. Then
in
1980, the Nobel prizewinning physicist Luis Alvarez and his
colleagues published their famous paper in 'Science' that argued
that a
cosmic impact had led to the extinction of the dinosaurs.. He
showed that
large amounts of the element iridium present in geological layers
dating
from about 65 million BC had a cosmic origin.
Alvarez's paper had immense influence and stimulated further
research
by such British astronomers as Clube and Napier, Prof Mark Bailey
of
the Armagh Observatory, Duncan Steel of Spaceguard Australia, and
Britain's best known astronomer Sir Fred Hoyle. All now support
the
theory of cometary impact and loosely form what is now known as
the
British School of Coherent Catastrophism.
These scholars envisage trains of cometary debris which
repeatedly
encounter the Earth. We know that tiny particles of cosmic
material
penetrate the atmosphere every day, but their impact is
insignificant.
Occasionally, however, cosmic debris measuring between one and
several
hundred metres in diametre strike the Earth and these can have
catastrophic
effects on our ecological system, through multimegaton explosions
of
fireballs which destroy natural and cultural features on the
surface of the
Earth by means of tidal-wave floods (if the debris lands in the
sea), fire
blasts and seismic damage.
Depending on their physical properties, asteroids or comets
that
punctuate the atmosphere can either strike the Earth's surface
and
leave an impact crater, such as the well-known Barringer Crater
in
Arizona caused by an asteroid made of iron some 50,000 years ago.
At
least ten impact craters around the world dating from after the
last
Ice Age, and no fewer than seven of these date from around the
3rd
millennium BC - the date of the widespread Early Bronze Age
collapses
- although none occurred in the Near East.
Alternatively, comets and asteroids can explode in the air. A
recent
example - known as the Tunguska Event - occurred in 1908 over
Siberia, when
a bolide made of stone exploded about 5km above ground and
completely
devastated an area of some 2,000 km' through fireball blasts. The
cosmic
body, although thought to have measured only 60 m across, had an
impact
energy of about 20 to 40 megaton, up to three times as great as
the Arizona
example (about 15 megaton), and was equivalent to the explosion
of about
2,000 Hiroshima-size nuclear bombs - even though there was no
actual
physical impact on the Earth. (The object that destroyed the
dinosaurs, by
contrast, is thought to have had a diametre of about 10km.) A
smaller
cometary blast occurred over the Brazilian rainforest in 1930.
In addition to the physical impact of comets, the British
astronomers
point to occasional massive influx of cosmic dust high above the
stratosphere which can cause a dramatic drop of global
temperature,
leading to the suspension of agriculture; and also the massive
influx
of cosmic chemicals (associated with dust) with, as yet,
incalculable
biochemical potentials but which may be harmful to DNA and can
trigger
evolutionary mutations.
Until recently, the astronomical mainstream was highly
critical of
Clube and Napier's giant comet hypothesis. However, the crash of
comet
Shoemaker-Levy 9 on Jupiter in 1994 has led to a change in
attitudes. The
comet, watched by the world's observatories, was seen split into
20 pieces
and slam into different parts of the planet over a period of
several days. A
similar impact on Earth would have been devastating.
According to current knowledge, Tunguska-like impacts occur
every 100
years or so. It is, therefore, not farfetched to hypothesise that
a
super-Tunguska may occur every 2000, 3000 or 5000 years and would
be
capable of triggering ecological crises on a continental or even
global scale. In the past, skeptics have demanded the evidence of
a
crater before they would accept an argument of cosmic impact, but
it
is now become understood that no crater is necessary for
disastrous
consequences to ensue. The difficulty this leaves scholarship,
however, is
that in a Tunguska Event no direct evidence is left behind. It
may be
impossible to prove that one ever took place in the distant past.
The extent to which past cometary impacts were responsible for
civilisation collapse, cultural change, even the development of
religion, must remain a hypothesis. But in view of the
astronomical,
geological and archaeological evidence, this 'giant comet'
hypothesis
should no longer be dismissed by archaeologists out of hand.
Dr Benny J Peiser is a historian and anthropologist at
Liverpool John
Moores University
Further reading:
Bailey, M. E., Palmer, T. & Peiser, B. J. [eds.] 1998,
Natural
Catastrophes during Bronze Age Civilisations: Archaeological,
Geological, Astronomical and Cultural Perspectives (Oxford:
British
Archaeological Reports, in preparation)
=======================================================================
(2)
GLOBAL WARMING: BOTH SIDES OF THE ARGUMENT COULD BE WRONG
From: Jonathan Shanklin <jdsh@mail.nerc-bas.ac.uk
Benny,
A few points on the subject.
The concensus view on global warming is that from the IPCC:
The balance of
evidence suggests that increased greenhouse gases are having an
effect.
There is the possibility that the IPCC is wrong, but they could
be wrong in
either direction. Vociferous minorities are just that and they
exist on both
sides of the debate. They do little to enhance the public view of
science.
Some parts of the world have definitely warmed. The Antarctic
Peninsula is a
case in point where the mean annual temperature has risen by 2.5
deg C over
the past 50 years. We think that this is a regional effect, but
only on the
basis that global climate models don't suggest that the area is
unduly
sensitive to global warming. The effect can be seen in decaying
ice-shelves
and increased vegetation (albeit in one form of grass). Regional
changes
should not be used to validate or invalidate global changes
unless there are
very good scientific reasons for doing so.
The view of GLOSS is that global sea level has risen 10 - 25
cm in the past
century. These are objective measurements made on an
international basis.
I think it is worth pointing out that NASA satellites failed
to detect the
ozone hole, although it was there in the data once they looked
for it. It
must be realised that almost by definition satellites use cutting
edge
technology which is very difficult to use for detecting long term
changes.
Each new sensor tends to be different and makes measurements in a
different
way. Satellites are very good for getting a global view of what
is going on
'now'.
It is true that the majority of climatologists do not consider
solar
variation as a factor in their models. This does not invalidate
the
models or the predictions, but it does make interpreting past
climate
and predicting future climate more uncertain.
Finally it does not really matter whether the predictions of
global
warming are right or wrong. What is undeniable is that we are
using up
resources, which have a finite lifetime, in a wastefull and
thoughtless
fashion. This is what needs to change.
Jon Shanklin
j.shanklin@bas.ac.uk
British Antarctic Survey, Cambridge, England
http://www.nbs.ac.uk/public/icd/jds