PLEASE NOTE:
*
CCNet DIGEST, 18 August 1999
----------------------------
COMETS MAY HAVE CAUSED EARTH'S GREAT EMPIRES TO FALL
From Phil Burns <pib@nwu.edu>
A number of U. S. papers on Tuesday carried an article written by
Robert S. Boyd of Knight Ridder's Washington Bureau entitled
"Comets
may have caused Earth's great empires to fall." You can read
the
article at
http://www.kentuckyconnect.com:80/heraldleader/news/081799/nationaldocs/17catastrophe.htm
http://www7.mercurycenter.com:80/premium/nation/docs/disaster17.htm
among other places.
The dates of the environmental downturns suggested as possibly
attributable to accretion events will be familiar to most
everyone
on this list: 3200 B.C., 2300 B.C., 1628 B.C., 1159 B.C., and
530-540
A.D.
Curiously the article quotes David Keys on the mid-530s event but
doesn't mention that he believes a large volcanic eruption of a
proto-Krakatoa, and not an impact event, was the cause. Other
quotes
come from Mike Baillie, Mike Rampino, Donald Yeomans, and Robert
Shoch.
-- Phil "Pib" Burns
Northwestern University, Evanston, IL. USA
pib@nwu.edu
http://www.pibburns.com/
================
EARTH BATTERED THROUGH HISTORY BY COMETS
Published Tuesday, August 17, 1999, in the San Jose Mercury News
http://www7.mercurycenter.com:80/premium/nation/docs/disaster17.htm
Earth battered through history by comets
Researchers say impacts caused global crises, mass extinctions
BY ROBERT S. BOYD
Mercury News Washington Bureau
"My name is Ozymandias, king of kings,
Look on my works, ye mighty, and despair.
Nothing beside remains. Round the decay
Of that colossal wreck, boundless and bare,
The lone and level sands stretch far away."
-- Percy Bysshe Shelley
WASHINGTON -- Recent scientific discoveries are shedding new
light on
why great empires such as Egypt, Babylon and Rome fell apart,
giving
way to the periodic "dark ages" that punctuate human
history.
At least five times during the last 6,000 years, major
environmental
calamities undermined civilizations around the world. Some
researchers
say these disasters appear to be linked to collisions with comets
or
fragments of comets like the one that broke apart and smashed
spectacularly into Jupiter five years ago this summer.
The impacts, yielding many megatons of explosive energy, produced
vast
clouds of smoke and dust that circled the globe for years,
dimming the
sun, driving down temperatures and sowing hunger, disease and
death.
Warning for future
The discoveries are changing the way scientists and historians
look at
the past -- and offer a warning about what might happen to our
planet
in centuries to come.
The last such global crisis occurred between AD 530 and 540 -- at
the
beginning of the Dark Ages in Europe -- when Earth was pummeled
by a
swarm of cosmic debris.
In a forthcoming book, "Catastrophe, the Day the Sun Went
Out," British
historian David Keys describes a two-year-long winter that began
in AD
535. Trees from California to Ireland to Siberia stopped growing.
Crops
failed. Plague and famine decimated Italy, China and the Middle
East.
Keys quotes the writings of a sixth-century Syrian bishop, John
of
Ephesus: "The sun became dark. . . . Each day it shone for
about four
hours and still this light was only a feeble shadow." A
contemporary
Italian historian, Flavius Cassiodorus, wrote: "We marvel to
see no
shadows of our bodies at noon. We have summer without heat."
And a
contemporary Chinese chronicler reported, "Yellow dust
rained like
snow."
Researchers say similar environmental calamities occurred around
3200
B.C., 2300 B.C., 1628 B.C. and 1159 B.C. Each led to the collapse
of
urban societies in widely scattered portions of the globe.
Destructive as they were, the natural disasters that have plagued
Earth
since the dawn of human civilization are but popguns compared
with the
truly titanic catastrophes of prehistoric eras.
Learning from fossils
There have been at least five of these monster events, each of
which
wiped out most of the creatures living at the time, the fossil
record
shows.
The best known was a six-mile-wide meteor that smashed into what
is now
the Gulf of Mexico 65 million years ago. The collision wreathed
the
planet in clouds of dust, poisoned the atmosphere and drove the
dinosaurs, then rulers of the Earth, into extinction. Traces of
the
enormous crater, at least 100 miles across, created by the impact
were
found in 1990.
Even that wasn't the biggest blow the Earth has suffered. The
mother of
all extinctions, which wiped out 90 percent of living species,
happened
about 245 million years ago. Paleontologists say other mass
extinctions
occurred about 214 million, 360 million and 440 million years
ago.
Although the evidence is debated, a growing number of researchers
contend that most, if not all, of these ecological disasters are
connected to bombardments from space.
"Recent evidence is converging on the conclusion that mass
extinctions
coincided with comet or asteroid impacts, and that periodic comet
showers, triggered by the solar system's motions through the
Milky Way
galaxy, may provide a general theory to explain impact-related
mass
extinctions," said Michael Rampino, a geologist at New York
University.
"After an impact, the dense dust cloud that is created by
the impact
spreads through the atmosphere, cuts out sunlight," Rampino
said. "This
stops photosynthesis and causes the climate to get cold and dark,
leading to the mass extinction of large numbers of
organisms."
These disasters, while terrible for their victims, opened the way
for
the survivors to flourish, diversify and -- for humans -- take
over the
world.
"We mammals may owe our pre-eminent position atop the
Earth's food
chain to a collision some 65 million years ago that wiped out
most of
our competition, including the dinosaurs," said Donald
Yeomans, a NASA
astronomer who tracks comets and asteroids.
These discoveries are lending weight to a revised theory of
evolution.
Instead of proceeding gradually by a series of tiny changes, as
Charles
Darwin proposed 140 years ago, life developed in a series of
starts and
stops, biologists now believe. They call it "punctuated
evolution,"
periods of slow development interrupted by wholesale extinctions
and
recoveries.
"It may take millions of years, but as the new organisms
fill all the
new niches that were emptied out, a whole new biosphere is
created,"
Rampino explained.
Evidence supporting this catastrophic theory of evolution is
accumulating from many sources:
- Studies of oak and pine tree rings in Europe and North America
provide a year-by-year chronology of good times and bad dating
back
5,000 years. Extremely narrow growth rings are testimony to
environmental setbacks that coincide with human catastrophes.
- Ice cores recently pulled out of glaciers in Greenland and
Antarctica
preserve a record of environmental changes over the last 400,000
years.
- Deep ocean drilling and surveys on land have detected more than
150
impact craters -- like the mile-wide Meteor Crater in Arizona --
demonstrating that Earth has been the target of frequent
bombardment
from space. Three or four craters are discovered each year, and
many
more are thought to be buried underground or in the sea.
Quiet period now
NASA and the Air Force are searching for comets and asteroids
that
might be on a collision course with our planet. Fortunately,
nothing of
a dangerous size -- arbitrarily defined as more than a kilometer
(0.6
miles) in diameter -- has been spotted heading our way for at
least a
century. But astronomers say a major impact is inevitable.
"Earth is currently enjoying a quiescent period," said
Robert Shoch, a
Boston University geologist. "But around 2200 AD, it is
likely (sic!)
that a new flow of comet fragments will enter Earth-crossing
orbits and
pose a real threat to our planet.
Obviously, the bigger the object and the faster it travels, the
more
damage it causes. A direct hit is not required; simply passing
through
one of the streams of cosmic rubble littering the inner solar
system
can have unpleasant consequences.
The civilization-shattering events of the historic era "must
have been
near misses, because if we had been hit by a full-blown comet in
the
past 10,000 years or so, we wouldn't be here today," said
Mike Baillie,
a British archaeologist who studies tree rings.
Copyright 1999, San Jose Mercury News
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ANTARCTIC FUNDING INITIATIVE
From Jon Shanklin <j.shanklin@bas.ac.uk>
British Antarctic Survey, Cambridge, England
http://www.nbs.ac.uk/public/icd/jds
UK University contributors may be interested in the BAS Antarctic
Funding
Initiative. The next round is coming up shortly:
Dear Colleagues,
This is to advise you that the Announcement of Opportunity for
the
second round of AFI has just been launched. The deadline
for receipt
of Outline Bids will be Friday 20th August 1999, with the
Planning
Meeting at Fitzwilliam College, Cambridge on Tuesday 14
September.
Further details can be found on the AFI web site:
http://www.nerc-bas.ac.uk/public/afi/index.htm
where you can also download
the header form for your Application.
Please note that this round introduces a new mechanism, the
Collaboration Gearing Scheme, to support collaborative work with
BAS,
where staff from the external institution require no additional
funding
for salaries, grants or direct science costs.
David Peel
[AFI Co-ordinator]
During the BAS Q3 re-organisation I made a outline proposal for
study,
which was deemed interesting, though I didn't follow it up with a
formal proposal. The outline included the following points:
Key global question(s) addressed (300 words maximum):
1. Our climate is controlled by the sun, and the sun is a
variable
star. How does this variation show itself in the climatic
record? Do
energetic solar events influence the weather or ozone layer?
2. The shape of the earth's orbit changes due to
gravitational
perturbation from other planets. These changes are linked to
climatic
change through Milankovitch forcing, but may also influence the
amount
of extra-terrestrial dust collected by the earth and hence the
earth's
albedo. Which is the key forcing and how will it change in the
future?
3. Our planet suffered severe impact bombardment shortly after
its
formation and the bombardment continues to this day at a greatly
reduced level. Impacts have altered the course of evolution
on our
planet, perhaps most notably following that associated with the
demise
of the dinosaurs. There is some evidence that impacts
within the last
few thousand years have influenced the course of history and that
our
civilisation may end with an impact. What evidence for
these impacts
is there in the Antarctic and what predictions can be made for
the
future?
4. The discovery of a Martian meteorite in Antarctica showed
supposed
evidence for life. What form might such life take and did
it influence
the origin of life on earth? How much terrestrial
contamination is
present in supposedly pristine samples?
Method of delivery identifying BAS special contribution (200
words
maximum):
1. BAS ice-core studies can be used to discover the
variation with
time of the flux of extra-terrestrial material entering the
earth=s
atmosphere. They can also be used as at present to investigate
past
climates.
2. There is evidence for a relatively recent impact event
in the
Bellingshausen Sea. BAS geophysical studies can be used to
investigate
its size and effects. Remote sensing techniques could be used to
assess
if there other Antarctic impact craters.
3. Investigation of KT boundary sequences in BAT.
4. Study deep Antarctic rock samples collected using
>sterile=
techniques for terrestrial biota.
5. Are solar activity indices reflected in BAS weather or
ozone data?
6. Reconnaissance flights to blue ice areas could include
prospecting
for meteorites on an opportunistic basis. Well over half
the world=s
meteorites have been found in Antarctica.
7. US DoD satellites occasionally image major bolides
events. BAS
could attempt opportunistic recovery of samples.
Etc.
Jon Shanklin
j.shanklin@bas.ac.uk
British Antarctic Survey, Cambridge, England
http://www.nbs.ac.uk/public/icd/jds