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*

CCNet DIGEST 25 May 1998
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(1) COSMIC DISASTERS AND EARLY BRONZE AGE COLLAPSE
    BBC News, 25 May 1998 
    http://news.bbc.co.uk/hi/english/sci/tech/newsid_100000/100101.stm

(2) EXPERTS SAY ASTEROID DANGER IS REAL
    The Associated Press, 22 May 1998

(3) COMETS PUMMELED EARTH 36 MILLION YEARS AGO
    The Planetary Society

(4) A FREQUENTLY ASKED QUESTION ON THE NEO THREAT
    Victor D. Noto <vnn2@phoenixat.com>

(5) DUSTY DEBRIS AROUND NEARBY STARS
    W.S. Holland et al., JOINT ASTRONOMY CENTRE

(6) PALAEOENVIRONMENTAL CHANGES ACROSS THE K/T BOUNDARY
    J. Roger et al., UNIVERSITY OF PARIS

===============
(1) COSMIC DISASTERS AND EARLY BRONZE AGE COLLAPSE

From the BBC   
http://news.bbc.co.uk/hi/english/sci/tech/newsid_100000/100101.stm

CLUES TO BRONZE AGE COMET STRIKE

Evidence is growing that a huge comet smashed into the Earth about
4,000 years ago.

Scientists are pointing to studies of tree-rings in Ireland which have
revealed that about 2,354-2,345 BC there was an abrupt change to a
colder climate.

They have also highlighted discoveries by archaeologists in
northern Syria of a catastrophic environmental event at about the
same time. This is also about the time that Bronze Age civilisations
collapsed.

Firework displays of meteors

Dr Bill Napier, an astronomer at Armagh Observatory, and Dr Victor
Clube, from Oxford and Armagh universities, say the evidence points
to a comet hitting the Earth, and have called for more research.
Writing in Frontiers, the magazine of the Particle Physics and Astronomy
Research Council, Dr Napier suggests that the Comet Encke, first
observed in 1786, might be a remnant of the object along with its
associated stream of meteors, called the Taurids.

This giant mother-comet is thought to have been disintegrating as
recently as 5,000 years ago.

At this time, and for some millennia afterwards, the night sky would
have
been lit up by a bright light caused by dust particles, cometary
fragments, and firework displays of meteor storms.

The scientists highlight ancient civilisations' preoccupation with the
sky. Cosmic icons were widespread Dr Napier wrote: "People have
assumed that this was driven by the need for a calendar for both
agricultural and ritual purposes. "However, this explanation does not
account for the doom-laden nature of much cosmic iconography and early
sky-centred cosmic religions associated with these societies."

Icons apparently depicting comets were widespread among early
civilisations. The new evidence also ties in with ancient prophecies,
including the Book of Revelations in the Bible, which appears to
describe
cataclysmic events involving objects falling from the sky.

Dr Napier said the ancient swastika, a symbol of great antiquity
stretching back to at least 1400 BC and found from China through India
to the New World, may also be a cometary image.

Comets are giant dirty snowballs in space, made of ice and dust. Unlike
asteroids, which are rocky, there is no known upper limit to their size,
and the largest can measure several hundred kilometres across.

Every 100,000 years or so one of these rare, giant objects enters an
orbit that crosses the path of the Earth.

Copyright 1998 BBC

=====================
(2) EXPERTS SAY ASTEROID DANGER IS REAL

From The Associated Press, 22 May 1998

By PAUL RECER

WASHINGTON (AP) - A mile-wide asteroid could smash the Earth, causing
widespread death and destruction, and ``we wouldn't even know it was
coming,'' an expert told a congressional panel Thursday.

Such an asteroid, striking the planet at thousands of miles an hour,
would ``threaten the future of modern civilization'' by darkening the
sky for a year, causing widespread starvation by destroying food crops
and directly or indirectly killing millions of people, said Clark R.
Chapman, an asteroid expert with the Southwest Research Institute in San
Antonio.

Testifying at a hearing of the House Science Committee's panel on space
and aeronautics, Chapman said a mile-wide asteroid would gouge a crater
bigger than Washington, D.C., and deeper than 20 Washington Monuments
piled on top of each other.

Chapman said the chances of such an asteroid striking the Earth next
year are one in a few hundred thousand, but this ``is more likely to
happen than that the next poker hand you are dealt will be a royal
flush.'' The odds for a such a poker hand are about 649,000 to one, he
said.

A person's lifetime chances of being killed by an asteroid, of any size,
are about one in 20,000, said Chapman. He noted the odds of being killed
by an asteroid are about the same as the risk of dying in a passenger
aircraft crash, but more likely than being killed by a tornado or a
flood.

The scientist said that an asteroid much smaller than a mile wide
exploded over Tunguska, Siberia, in 1908 and the shock wave flattened
trees across an area larger than New York City. Such a burst over a
major city, he said, could kill millions instantly.

Chapman and other experts said that the Earth's only protection from
such a space bombardment is to search the skies, find asteroids apt to
hit the Earth and then rocket out bombs that would divert the space
rocks away from the planet.

With a 10-year warning, ``we could probably save ourselves,'' said
Chapman. ``At the very least, we could evacuate ground-zero and save up
food supplies to weather a global environmental catastrophe.''

But he said that little effort is being put out to find
Earth-threatening asteroids and only about 10 percent of an expected
2,000 near-Earth objects have been identified and tracked.

Rep. Dana Rohrabacher, R-Calif., the committee chairman, pressed Chapman
on his statement that a killer asteroid could hit without warning.

``Yes,'' said Chapman. ``A mile-wide asteroid could hit tomorrow and we
wouldn't even know it was coming.''

Rohrabacher said that a committee led by the late asteroid expert Eugene
Shoemaker recommended five years ago that the National Aeronautics and
Space Administration start a systematic effort to search out, identify
and plot all asteroids that pose a threat to the Earth. The report said
the effort would cost about $5 million a year, but the congressman said
the space agency has done little to follow up on that recommendation.

Also, he said, an Air Force asteroid mission was canceled last year
after President Clinton used his line-item veto against the project.

In response, Carl Pilcher, NASA's science director for solar system
exploration, told the panel that his agency a year ago recognized it was
not spending enough to complete a comprehensive survey of
earth-threatening asteroids. Pilcher said, however, that NASA has six
missions either planned or under way to explore, land on and sample
asteroids. He said this work is essential for science to understand how
best to divert threatening asteroids.

Copyright 1998 The Associated Press.

====================
(3) COMETS PUMMELED EARTH 36 MILLION YEARS AGO

From The Planetary Society
http://www.planetary.org

Posthumous Paper by Astronomer Gene Shoemaker Details Evidence of
Cataclysmic Comet Shower

Geochemical evidence from a rock quarry in northern Italy indicates that
a shower of comets hit Earth about 36 million years ago.

The findings not only account for the huge craters at Popagai in Siberia
and at Chesapeake Bay in Maryland, but posit that they were but a tiny
fraction of the comets active during a period of two or three million
years during the late Eocene period. The work provides indirect evidence
that a gravitational perturbation of the Oort comet cloud outside the
orbit of Pluto was responsible for sending a wave of comets swarming
toward the center of the solar system.

Shoemaker's Legacy of Discovery

In a paper published today [22 May 1998] in the journal Science, a group
from the California Institute of Technology, the United States
Geological Survey Flagstaff office, and the Coldigioco Geological
Observatory in Italy, report their evidence of a very large increase in
the amount of extraterrestrial dust hitting Earth in the late Eocene
period. The writers include the husband-and-wife team of Gene and
Carolyn Shoemaker, well known for their work detecting comets and
asteroids. Gene Shoemaker died in a car crash last year while this
research was in progress.

According to lead author Ken Farley, a geochemist at Caltech, the
contribution of Shoemaker was especially crucial in the breakthrough.
"Basically, Gene saw my earlier work and recognized it as a new way to
test an important question: Are large impact craters on Earth produced
by collisions with comets or asteroids?" Farley says.

"He suggested we study a quarry near Massignano, Italy, where sea-floor
deposits record debris related to the large impact events 36 million
years ago. He said that if there had been a comet shower, the technique
I've been working on might show it clearly in these sediments."

Carolyn Shoemaker said that she and her husband went to Italy last year
to perform field work in support of the paper.

Tracking an Ancient Disaster

In geologic samples, the researchers detected a helium isotope known as
3He, which is rare on Earth but common in extraterrestrial materials.
This isotope is abundant in the Sun, and some of it is ejected from
the Sun as solar wind throughout the solar system. The helium is easily
picked up and carried along by extraterrestrial objects such as
asteroids and comets and their associated dust particles.

Thus, arrival of extraterrestrial matter on Earth's surface can be
detected by measuring its associated 3He. And even this material is
unlikely to include large objects like asteroids and comets. Because
these heavy, solid objects fall into the atmosphere with a high
velocity, they melt or vaporize, giving their helium up to the
atmosphere. This 3He never falls below very high altitudes, and soon
reenters space.

But tiny particles entering the atmosphere are another story. These
particles can pass through the atmosphere at low temperatures, and so
retain helium. These particles accumulate on the sea floor, and sea
floor sediments provide an archive of these particles going back
hundreds of millions of years. 

Elevated levels of 3He would suggest an unusually dusty inner solar
system, possibly because of a flurry of active comets. Such an elevated
abundance of comets might arise when a passing star or other gravity
anomaly kicks a huge number of comets from the Oort cloud into
elliptical, sun-approaching orbits.

Discovery in Italy

When Farley took Shoemaker's suggestion and traveled to the Italian
quarry, he discovered that there was indeed an elevated flux of
3He-laced materials in a sedimentary layer some 50 feet beneath the
surface. Because this region of Italy was submerged in water until about
10 million years ago, the comet impacts and microscopic debris had
accumulated on the ocean bed, and this debris was preserved because
dying organisms had cooperatively covered the debris over the eons.

The depth of the sedimentary layer suggested to the researchers that the
3He had been deposited about 36 million years ago. This corresponds to
the dating of the craters at Popagai and Chesapeake Bay.

More precisely, the 3He measurements show enhanced solar system
dustiness associated with the impacts 36 million years ago, but with the
dustiness beginning 0.5 million years before the impacts and continuing
for about 1.5 million years after. The conclusion is that there were a
large number of Earth-crossing comets and much dust from their tails for
a period of about 2.5 million years.

In addition to Gene and Carolyn Shoemaker and Ken Farley, the paper was
cowritten by Alessandro Montanari, who holds joint appointments at the
Coldigioco Geological Observatory in Apiro, Italy, and the School of
Mines in Paris.

(C) 1998 The Planetary Society

==================
(4) A FREQUENTLY ASKED QUESTION ON THE NEO THREAT

From Victor D. Noto <vnn2@phoenixat.com>

Hi Benny:

One question which comes up in every conversation with people just being
introduced to the NEO's threat is this and it may be that intuitively
they know there may be no answer.

"How long can we expect to wait till the next catastrophic impact?" or
"When do you expect we will be hit by a big asteroid (Comet)?

Implicit in the question is the size is over 1/2 km which would be
catastrophic for the whole globe but as you know a ocean impact of less
size (~200 meters) may be catastrophic for a good portion of the coastal
populations of the world causing millions of deaths and trillions in
damage and ~ 50 meter rock over the tristate area of NYC would kill
millions of people and cause great stress to the economies of the world.

The short answer I usually give but I am not very satisfied with the
response is "You can expect an impact anytime from right now to millions
of years perhaps into the future."  Although this answer may be
technically correct it tell the listener we really do not know the
answer so why worry.

It's the old lesson that you can not get people excited about events
that have low probability even if they have very catastrophic
consequences (like being hit by lightning). And yet people all over this
country got excited this past week about a Powerball lottery game with
millions in prize money where the odd were 1 in 80 million to win.
Perhaps it is easy to think about what they would do with all that money
than what to do if faced with an "extinction level event". Go figure.

The question is how does an impact flux which adheres to the poissonian
process (one in which events occur randomly in time and is not
predictive) can your answer convey some excitement and urgency to the
listener. I think what the questioner is asking is when will the next
impact take place - like 30 years from now on 2028 at 3pm in the
afternoon a 2 km impacter will hit Southern California. So if you say a
50 m rock's mean time between impact is 100 years people want to know if
that means 100 from 1908 so we will be hit on 2008 with a 50 m rock.

You and I know that the process of randomness does not lend itself to
this kind of prediction. In fact two tunguska-like events can occur
within weeks or centuries of each other. Taken over the 100's of
thousands of years you can deduce that the mean of the event is about 1
every 100 years or so but you can never still predict the event with any
degree of certainty nor even say if the event is overdue. Ultimately
therein lay the problem to arouse even the people who appear to
be aware of the problem and perhaps this is the secret of why the XF11
incident was so effective.

I canvased some people I work with and who saw the movie Deep Impact,
about whether the movie Deep Impact left anyone with a feeling of
urgency at addressing the problem of a asteroid or comet threat. To a
man none feel moved in that direction. Most feel it was not a serious
threat or it is something that no one could do anything about like the
weather. The movie is good in that it did make people think of the
prospect of the threat but it still is a long way from arousing people
to action.

Personally I think that all you can do is continue to hit the subject
hard at the academic level to educate the masses and eventually larger
numbers will be sufficiently aware to take action.

What say your readers in answer to this frequently asked question?

Victor Noto - Kissimmee, Florida USA
Email: vnn2@phoenixat.com
http://www.phoenixat.com/~vnn2/BIGROCK.htm

================
(5) DUSTY DEBRIS AROUND NEARBY STARS

W.S. Holland*), J.S. Greaves, B. Zuckerman, R.A. Webb, C. McCarthy,
I.M. Coulson, D.M. Walther, W.R.F. Dent, W.K. Gear, I. Robson:
Submillimetre images of dusty debris around nearby stars. NATURE, 1998,
Vol.392, No.6678, pp.788-791

*) JOINT ASTRONOMY CENTRE, 660 N AOHOKU PL, HILO, HI, 96720

Indirect detections of massive - presumably Jupiter-like - planets
orbiting nearby Sun-like stars have recently been reported(1,2). Rocky,
Earth-like planets are much more difficult to detect, but clues to their
possible existence can nevertheless be obtained from observations of the
circumstellar debris disks of dust from which they form. The presence of
such disks has been inferred(3) from excess far-infrared emission but,
with the exception of beta Pictoris(4), it has proved difficult to image
these structures directly as starlight dominates the faint Light
scattered by the dust(5). A more promising approach is to attempt to
image the thermal emission from the dust grains at submillimetre
avelengths(6,7). Here we present images of such emission around
omalhaut, beta Pictoris and Vega. For each star, dust emission is
detected from regions comparable in size to the Sun's Kuiper belt of
comets. The total dust mass surrounding each star is only a few lunar
masses, so any Earth-like planets present must already have formed. The
presence of the central cavity, approximately the size of Neptune's
orbit, that we detect in the emission from Fomalhaut may indeed be the
signature of such planets. Copyright 1998, Institute for Scientific
Information Inc.

=====================
(6) PALAEOENVIRONMENTAL CHANGES ACROSS THE K/T BOUNDARY

J. Roger, C. Bourdillon*), P. Razin, L. LeCallonnec, M. Renard,
M.P. Aubry, J. Philip, J.P. Platel, R. Wyns, M. Bonnemaison:
Palaeoenvironmental and biotic changes across the Cretaceous/Tertiary
boundary in the Oman Mountains (in French). BULLETIN DE LA SOCIETE
GEOLOGIQUE DE FRANCE, 1998, Vol.169, No.2, pp.255-270

*) UNIVERSITY OF PARIS 06, DEPARTMENT OF GEOLOGY,F-75252 PARIS 05,FRANCE

Two new sites, revealing a record of the events at the K/T boundary,
have been recently discovered in the Oman Mountains at the eastern end
of the Arabian plate. In the Buraymi Basin, located at the northwestern
flank of the chain, the K/T boundary is intersected by a basinal facies
uccession, whilst in the Sur area, the transition is illustrated within
a confined carbonate platform sequence. This period exhibits important
palaeoenvironmental and biotic changes which originated from the
conjunction of multiple factors. These came together over differing
intervals of time, i.e., long period of time, short time scale and
instantaneous event. At the scale of the long period of time (4 Ma)
stretching from late Maastrichtian to the Danian (P1c), the Oman
Mountains recorded profound modifications in terms of their
palaeogeographic context, undoubtedly linked to plate reorganisation.
This was initially shown by the emersion of the rudist platforms and the
flooding of the margins in the late, but not terminal, Maastrichtian.
This first tectonic event introduced an hemipelagic and a turbiditic
sedimentation. As a consequence, this episode created, at the southern
limb of the chain, the confined Murka sub-basin characterised by a
carbonate platform sedimentation. Because the transition terminal
Maastrichtian-earliest Danian correspond to a period of tectonic
quiescence, the sedimentation persisted through the K/T boundary without
any notable modification. A second tectonic episode in the Danian
P1b/P1c interval, accentuated the flooding of the plate margins where
basin deposits were accumulating. The renewal of planktic foraminifera
took place in stages suggesting a gradation of palaeoecological
conditions spread over a short time scale (1 to 2 Ma). This gradation is
marked by the succession of three waves of extinction which took place
from the late Maastrichtian to the KIT boundary. Diversity of the
benthic foraminifera then increased progressively from subzone P1b
onwards, showing the re-establishment of the ecosystem in P1c. The
iridium anomaly detected at the WT boundary at both sites would tend to
reinforce the hypothesis of a meteorite impact. the effects of which
would have added to these events that unfolded over a longer rime scale.
Copyright 1998, Institute for Scientific Information Inc.

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