CCNet DIGEST, 18 August 1999
COMETS MAY HAVE CAUSED EARTH'S GREAT EMPIRES TO FALL
From Phil Burns <firstname.lastname@example.org>
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
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
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
EARTH BATTERED THROUGH HISTORY BY COMETS
Published Tuesday, August 17, 1999, in the San Jose Mercury News
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
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
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
"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
"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,"
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 <firstname.lastname@example.org>
British Antarctic Survey, Cambridge, England
UK University contributors may be interested in the BAS Antarctic Funding
Initiative. The next round is coming up shortly:
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.
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
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
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
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.
British Antarctic Survey, Cambridge, England
CCCMENU CCC for 1999
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