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."