PLEASE NOTE:


*

Date sent: Thu, 17 Jul 1997 11:03:40 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: Re: IS THE SKY FALLING?
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

IS THE SKY FALLING?

In the following extracts from the recently published article "IS THE
SKY FALLING?", [see SKEPTICAL INQUIRER, May/June 1997],
David Morrison describes the sceptical position among American
astrophysicists regarding historical catastrophism and the problem of
detecting the rate and extent of past impact events as well as
assessing the current and future impact hazards.

I believe that the debate between advocates of what David calls the
"standard paradigm" of neo-catastrophism and those who support the
alternative paradigm of "coherent catastrophism" is far too important
to be ignored or simply left to astronomical speculations. Quite the
opposite, these contrasting theories are in need of rigorous testing
and thorough research in order to shed further light on our cosmic
environment. The implications of this 'cosmic' debate for all fields
of social and intellectual discourse are far-reaching. I therefore
hope that David's healthy scepticism will help to stimulate (rather
than block) further debate and research so that we can eventually
"sort out who is right and who is wrong." It goes without saying that
it is vital for human civilisation not just to understand our cosmic
environment much better but also to intervene and take action in
order to be prepared in case of any future cosmic threat.

Benny J Peiser

I wish to thank the David Morrison, The Skeptical Inquirer and their
publisher, the Committee for the Scientific Investigation of Claims of
the Paranormal (CSICOP), for their permission to circulate extracts
of David's paper on this network. For further information, please
contact David Morrison <dmorrison@mail.arc.nasa.gov> or:

The Skeptical Inquirer: The Magazine for Science and Reason
944 Deer Dr. NE
Albuquerque, NM 87122
505-828-1990 Fax: 505-828-2080
e-mail: kenfrazier@compuserve.com
also kcfrazi@sandia.gov
Skeptical Inquirer/CSICOP Web Site: http://www.csicop.org

---------------------------------------------------------------------

Extracts from: IS THE SKY FALLING?
Skeptical Inquirer, May/June 1997

By David Morrison

As the millennium approaches, the media are playing up asteroid and
comet impacts. Ten popular-level books were published in 1995 and
1996 dealing with the dangers of cosmic impacts, and now we are
seeing a spate of television and movie productions, both factual and
fictional, that describe the impact threat. It is easy to dismiss all
this as media hype and millennial madness, but it would be a mistake
to do so. While some books and films may be motivated by a desire to
milk public credulity for a quick buck, most are serious efforts to
inform the public about a real danger that is recognized by the
scientific community. [...]

There is a considerable divergence among scientists in how such
issues are framed and discussed, and an even wider disparity on the
way these issues are presented to the public.

Let us begin with what I call the "standard paradigm" -- that of
random impacts on Earth by small comets and asteroids. This is the
consensus view of most scientists, and it is reflected in two NASA
reports to the U.S. Congress, the Spaceguard Survey Report of 1992
and the follow-up report in 1995 inspired by public interest in the
collision of Shoemaker-Levy 9 with Jupiter. As the principal author
of the Spaceguard Survey Report and a member of the follow-up working
group (chaired by Gene Shoemaker), I identify with this consensus
position.

The standard paradigm uses the cratering history of the Moon and
other evidence to deduce the average historical rate of impacts on
Earth by objects of different sizes or impact energies. It then
assesses the destructive potential of impacts of different energies
on Earth today in terms of probable casualties, noting in particular
the existence of a threshold at about one million megatons of energy
(corresponding to a two-kilometer asteroid) at which the global
climate is severely affected and everyone is at risk, independent of
proximity to the impact. One conclusion of such studies is that the
statistical risk is greatest for impacts near the global threshold,
amounting to an average risk of death for each individual on Earth of
nearly one in a million per year, comparable to the risk of other
more frequent (but less catastrophic) events such as earthquakes,
severe storms, and volcanic eruptions. It is also noted that, unlike
other natural disasters, impacts can be avoided entirely by
deflecting an incoming object, if several years warning time is
available.

Although most people agree that the greatest risk is posed by objects
two kilometers or larger in diameter, others focus their attention on
smaller impactors, especially those in the 200- to 500-meter range.
When impacts of this size occur in the ocean, they produce tsunamis
capable of inundating large stretches of coastline. Although the
average risk for inhabitants of the planet is less from tsunamis than
from the global catastrophes caused by larger impacts, the risk for
persons living on shorelines may be greater. This fact, together with
the higher frequency of smaller impacts, leads some to argue that we
need a defense system against any object larger than 200 meters
diameter.

A major divergence of opinion concerns what our response to the
impact threat should be. Most of the scientists involved in such
assessments conclude that there is a significant risk and that
governments should take some action (especially in searching for
potential impactors), but that it is premature to build any defense
systems in the absence of a specific identified threat. Others, the
best known being Edward Teller (the father of the H-bomb), argue
strongly for a more aggressive approach to asteroid defense. They
would initiate experiments, eventually to include nuclear
explosives, designed to learn more about how to deflect or destroy
asteroids and comets. Some even advocate construction of a standing
nuclear defense system to deal with the smaller impactors, for which
the warning time might be short. But at least, they assert, we should
start now to develop the technology for such a system.

These arguments concerning the magnitude of the threat and the most
appropriate response make good TV and newspaper copy. They can lead
to serious analyses of the various threats that we face on Earth and
of the role of governments in dealing with potential disasters, both
natural and human. All fit within the standard paradigm. But there is
another viewpoint, held by a handful of British neo-catastrophists,
that challenges this position.

The British Neo-Catastrophist School

The alternative viewpoint is advocated in its extreme form by
astronomers Victor Clube and Bill Napier, who interpret historical
records as indicating that Earth has been subject to extreme
battering from space within the past few millennia. In their popular
books The Cosmic Serpent and The Cosmic Winter, they take the
position that the emergence of astrology in the western
Mediterranean, the association of gods with planets in many ancient
cultures, the widespread fear of comets and belief in angels, and
many other aspects of our cultural and religious history are a
reflection of massive bombardment of the planet a few thousand years
ago. They further conclude that more recent historical events,
including the collapse of the Roman Empire, the Dark Ages, and even
the English Civil War, are related to climate changes induced by
exceptional deposition of cosmic dust in Earth's atmosphere.. Although
their historical analysis is suspiciously similar to that of Immanuel
Velikovsky, Clube and Napier adamantly reject the association,
arguing that unlike Velikovsky they root their explanations in sound
physical and astronomical principles.

Supporting Clube and Napier are British astronomers Duncan Steel and
Mark Bailey, who have concluded that the solar system is currently
experiencing the aftermath of the break-up of a giant comet some
millennia in the past. Our planet still intersects debris from this
comet in what they call the Taurid complex of dust, small comets, and
asteroids. They term this theory coherent catastrophism. Steel and
Bailey estimate that the present lull in impacts will end in about a
thousand years, when our orbit again crosses the denser parts of the
Taurid complex, at which time the impact risk will rise by at least a
factor of a hundred. All of these neo-catastrophists argue that
urgent action is required to prevent the collapse of civilization
under the next cosmic onslaught.

Most of us find these neo-catastrophist arguments difficult to
swallow. Putting aside the issue of the Velikovskian interpretation
of history and legend, the impact rate is still constrained by the
cratering history of the Moon, which reflects the long-term average.
If there are huge "spikes" in the frequency of impacts, produced by
the break-up of giant comets, they must be compensated by much lower
flux rates between peaks. Yet Clube, Steel, and their colleagues
simultaneously assert that the consensus group underestimates the
current impact rate, and that a big spike is coming. You can't have
it both ways. If they are correct that almost all impacts occur
during the spikes, then the present danger must be very low, and we
have centuries to prepare to deal with the next peak. But they don't
see it that way, and neither do the authors of several of the recent
books.

Impact Science and Pseudoscience

While I believe that the British neo-catastrophists are wrong about
the threat to Earth, their work is science, not pseudoscience. They
are making their case to other scientists, and time will sort out who
is right and who is wrong. They do, however, sometimes attract the
attention of fringe elements. For example, the Society for
Interdisciplinary Studies (SIS), a British group that espouses a
skeptical philosophy but includes many defenders of Velikovskian
ideas, is sponsoring a conference that features Clube and focuses on
evidence for cosmic catastrophes in the ancient world.

Every week I receive two or three inquiries from the public asking if
some story they have read or heard about an imminent world-shattering
impact is correct. These stories are not confined to the supermarket
tabloids but have apparently attracted a following on the World Wide
Web. Some people ask about a comet called Wormwood, with obvious
reference to the apocalyptic vision in Revelation 8:10-11, when "the
third angel sounded, and there fell a great star from heaven, burning
as it were a lamp. . . . And the name of the star is called
Wormwood."

Then there is Comet Hale-Bopp. In November 1996 the press gave
general coverage to a wild claim that this comet was accompanied by a
spaceship and was headed toward an impact with Earth. (See Alan Hale,
"Hale-Bopp Comet Madness," SI, March/April 1997.) The story
apparently started when an amateur astronomer photographed the comet
near a moderately bright star. In a curious logical progression he
assumed the star was a spacecraft, that the spacecraft was at the
same distance as the comet, and that the over-exposed stellar image
represented the angular diameter of the craft, which would make it
comparable in size to the giant planet Saturn. Others embellished the
story by concluding that the spacecraft was traveling in the same
orbit with the comet and that the trajectory was about to shift
toward Earth. The mystery to me is why this fantasy was given serious
media attention, even on a slow news day. I fear that we may see more
of this sort of thing as the public becomes more aware of the threat
of impacts. [..]

On the positive side, the impact issue is proving to be an excellent
vehicle for communicating some interesting aspects of contemporary
science to the public. The topic, bringing together astronomy,
environmental threats, and dinosaurs, is a natural. It focuses on the
way historical science works (how can we figure out what really made
the dinosaurs go extinct?), on the fragility of the environment (how
can one small impact have global consequences?), on the nature of
evolution (why were the mammals who succeeded the dinosaurs so
different from them?), and on the nature of probability (if big
impacts take place only once every million years, why worry now?).
There is great potential here to teach good science as well as
stimulate a useful public policy debate. Let's hope these lofty
goals are achieved in practice.



*

Date sent: Thu, 17 Jul 1997 10:29:54 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: Environmental Damage Caused By Meteor Crater Impact
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL

ENVIRONMENTAL PERTURBATIONS CAUSED BY RECENT IMPACT EVENTS

Over the last two decades, only two impact events and their
catastrophic effects on evolution, ecology and geomorphology have been
thoroughly researched: The K/T boundary impact which caused the
Chicxulub Crater in Mexico's Yucatan Peninsula c. 65 million years ago
and the aerial impact over the Tunguska river in Siberia in 1908. Now,
David A. Kring, an American researcher, has calculated the likely
environmental damage caused by the impactor which created Barringer
Crater come 50.000 years ago.

It should be emphasised that there are a number of important factors
which determine the magnitude and energy yield of such impacts and
their environmental effects. The c. 25 meter d impactor which caused
the impressive hypervelocity crater in Arizona (~1.2 kilometers in
diameter) was an i r o n bolide. On the other hand, the bolide which
impacted the atmosphere over Siberia 90 years ago was of a stony nature
- some 60 to 100 meters across. The Barringer impactor "only" yielded
an impact energy of ~5-15 megatons, whereas the Tunguska blast yielded
almost twice, perhaps up to three times as much energy (~15-40
megatons). In other words, a relatively small iron bolide which
penetrates the protective shield of the earth's atmosphere can create
an impressive impact crater whereas a much bigger stony bolide might
never hit the Earth's surface. Due to their catastrophic detonation
above ground - or in the oceans - they often leave no obvious
fingerprints behind.

Yet, "for every impact producing a crater like the one on the Arizona
desert, there must have been about 70 which have left no trace (...) a
few dozen sporadic impacts in the tens of megatons, and a few in the
100 to 1,000 megaton range, must have occurred within the pst 5,000
years" (Clube & Napier 1990, 246).

In fact, the rate of the recent impact craters (> 50.000 years) does
not appear to be random. Rather than impacting more or less randomly in
time over the last 50,000 years, recent impactors appear to have
created impact craters at particular peaks: Three impact craters have
been dated to c. 50,000ka BP (Barringer, Arizona d = 1.2km; Lonar,
India d = 1.8km; and Odessa, Texas d = 0.2km). Even more interesting to
prehistorians and Bronze Age specialists is the fact that at least five
recent impact craters have been dated by Gene Shoemaker and RAF Grieve
to ~5000/4000 years BP (Boxhole, Australia; Campo del Cielo, Argentina;
Henbury, Australia; Kaalijarvi, Estonia; Rio Cuarto, Argentina) i.e.
coinciding with the climate catastrophe and the collapse of urban
civilisations at the end of the Early Bronze Age. Although the exact
datings of these and other impact craters might not be entirely
accurate, the observable pattern of impact producing periods in the
more recent history of mankind gives rise to important questions.

The paper by David Kring, therefore, opens the way to research on
the nature and extent of the more recent impact events and their
environmental and cultural effects on human and societal evolution.

Benny J Peiser
-----------------------------------------------------------------------

from: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

University of Arizona News Services

----------------------------------------------------------------------------
From: Jeff Harrison, UA News Services, 520-621-1877,
jeffh@u.arizona.edu
----------------------------------------------------------------------------

July 15, 1997

Environmental damage caused by Meteor Crater impact

Fifty thousand years ago, a rock half the size of a football field in
diameter struck the flat plain of the southern Colorado Plateau near
what is now Winslow, Ariz. In an article published Monday, July 14, in
the journal Meteoritics and Planetary Science, David A. Kring estimates
that the blast from the meteorite impact sent a shock wave with 2,000
mile per hour winds that destroyed virtually every living thing in its
path for at least 3 km.

In 1992, Kring, a research scientist at the Lunar and Planetary
Laboratory at The University of Arizona in Tucson, and LPL colleague
William V. Boynton, published evidence confirming that the 65
million-year-old Chicxulub Crater in Mexico's Yucatan Peninsula was
produced by the impact of an asteroid or comet.

"One of the things we realized when we studied the extinction of
dinosaurs, is that impact cratering affects the environment either of
the local region where the impact occurred, or in the case of the
Yucatan event, the entire world. So, what we're beginning to do is look
at other impact events and assess what the environmental damages were,"
said Kring.

Meteor Crater may be the best preserved impact crater in the world. As
such, it provides geologists with a ready-made field laboratory for
studying impact sites. Among scientists, says Kring, Meteor Crater is
as important geologically as the Grand Canyon.

At the time of the impact, northern Arizona was much different, with
flowing streams and lush grasslands and forests. Using scaling
relationships determined from nuclear explosions, Kring says that the
meteorite that struck Arizona created a shock wave that radiated over
the landscape, creating an air blast with hurricane force winds as far
as 40 km (about 24 miles).

Vegetation would have been completely destroyed for up to 1,500 square
km, and damaged over an additional 600 square km. Large animals as far
away as 4 km would have been killed outright. Those as far as 24 km
away might have sustained crippling injuries. Geologically, the force
of the meteorite lifted the land around it, creating a visible rise in
the plateau that hides the crater. Still, no extinctions were likely to
have happened, and within several years, new plants and animals would
have colonized the blast area within several years.

"We think the impact would have affected plants and animals as far away
as Winslow, but probably the blast would not have reached Flagstaff
(about 40 miles to the west).

Compared to Chicxulub, Meteor Crater is small potatoes. The object that
struck the Yucatan was about 6 miles in diameter and had repercussions
both life forms and weather around the world. A number of reputable
scientists think it may have either wiped out the dinosaurs, or at
least set in motion the conditions that led to their demise. Objects
the size necessary to create Meteor Crater fall on Earth every 1,600 to
2,000 years, mostly falling into the oceans. Those striking land have a
frequency of about every 6,000 years. Kring says this and future
studies may help scientists understand the interactions between impact
events and the surrounding vegetation and animal life.

"What we want to find is the threshold at which extinctions occur, both
globally and locally" says Kring. "We know that Chicxulub had global
ramifications. Somewhere between that event and the Meteor Crater
event we probably crossed the threshold that drives extinctions."



CCCMENU CCC for 1997

The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of

The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of Georgia or the University System of Georgia.