Date sent:        Mon, 02 Feb 1998 10:35:50 -0500 (EST)
From:             Benny J Peiser
Subject:          CC DIGEST 02/02/98
Priority:         NORMAL





Due to a computer problem which affected my university's e-mailbase
system on Friday, many list members apparently did not receive the CC
COMMENTS, 30/01/98. I will therefore tomorrow post last week's
comments by Duncan Steel, Clark Chapman and Bob Kobres (about the
problem of calculating impact probability and the implications for
NEO research and planetary defense) together with a number of
comments which I've received over the weekend. Should you wish to
contribute to this debate, please feel free to send any RELEVANT
arguments or suggestions. Can I re-assure list members that I will
limit this discussion to its essential arguments and main
differences. This should ensure that the CC-Network will continue to
focus on new scientific information and research findings rather than
on debating our individual belief systems.

Benny J Peiser

From: Michael Rampino wrote:


Here is a summary of the Shiva article:

The Shiva Hypothesis: Impacts, Mass Extinctions, and the Galaxy

Michael R. Rampino
NASA, Goddard Institute for Space Studies
New York, NY 10025
and New York University
New York, NY 10003

The discovery by Walter and Luis Alvarez and their colleagues at the
University of California at Berkeley of anomalous concentrations of
the rare element iridium in a thin clay layer at at the
Cretaceous/Tertiary (K/T) boundary in a rock outcrop near the town
of Gubbio, Italy, almost twenty years ago, triggered an upheaval in
the geological sciences. The intervening years have seen a
remarkable confirmation of the Alvarez group's hypothesis that the
unusual traces of iridium were the fingerprint of dust created by
the collision of a huge asteroid or comet with the Earth, and that
the occurrence of the tell-tale clay layer at the precise time that
the dinosaurs and some 75% of life on the planet disappeared was no
mere coincidence. This proposal culminated in the discovery of a
giant 65-million year old  impact crater in the Yucatan, widespread
evidence of massive tsunami in the Caribbean/Gulf of Mexico region
at the same time, and spectacular deposits derived from storms of
rock debris blasted out of the crater that were investigated during
recent Planetary Society expeditions to Belize in Central America.

The convergence of evidence for impact at the Cretaceous/Tertiary
(K/T) boundary has led to renewed interest in mass extinctions and a
recognition of their importance as a major driving force in the
evolution of life on Earth. The K/T mass extinction is but one of a

number of mass extinction events recorded in the fossil record, and
in fact was not the most severe. Could impacts be responsible for
the recurrent mass extinctions seen in the geologic record?  A few
years ago such a suggestion would have seemed far-fetched, but
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. The cyclic extinctions are followed
by explosive evolution of the surviving species that re-filled the
many life niches emptied by the global catastrophe, so we have named
this idea the "Shiva Hypothesis", after the Hindu deity of cyclic
destruction and renewal.

One of the most intriguing findings in the study of extinctions has
been that of a  possible cycle of these mass die offs.  Analyses of
the extinction record by Dave Raup and Jack Sepkoski revealed an
underlying cycle of about 26 million years in the mass extinctions
of the last 250 million years (the best-dated part of the record),
and recent work on an improved and better dated extinction data base
with Bruce Haggerty at NYU reveals that a cycle of 26 to 30 million
years persisted through the entire 540 million year record. Raup and
Sepkoski's original findings prompted Richard Stothers of NASA's
Goddard Institute for Space Studies and me, and independently Walter
Alvarez and Rich Muller at Berkeley, to analyze the record of impact
craters, and we detected a similar cycle in the occurrence of large
impacts on the Earth.  Furthermore, it seems that clusters of
craters of similar ages are closely correlated with the mass
extinction episodes. These results suggest that many impact events
on Earth were part of a periodic, most likely from showers of
comets, leading to periodic mass extinctions.

If a 26 or 30 million year periodicity in mass extinctions and
impacts is real, then it may be related to a known astronomical
cycle-the motion of the Solar System up-and-down through the plane
of the disk-shaped Milky Way Galaxy. Astrophysicists have determined
that the Solar System revolves around the center of the Galaxy about
once every 220 million years, and as it does so the Solar System
bobs up and down like a horse on a carrousel through the dense,
central portion of the galactic disk. In this cycle, the Sun and
planets pass through the dense region packed with stars and clouds
of interstellar gas and dust every 26 to 30 million years.
Stothers and I first suggested that passage of the Solar System
through the galactic plane could lead to gravitational disturbance
of some of the trillions of comets that orbit the Sun in the
so-called Oort Cloud, resulting in periodic showers of comets in the
inner Solar System. Recent work by astrophysicist John Matese and
colleagues at the University of Southwestern Louisiana has confirmed
that the pull of the combined mass of the material in the galactic
disk is sufficient to induce a hail of comets during our passage
though the central plane. Like Shiva, the Hindu Destroyer/Creator,
the cyclic impacts bring an end to one world, and allow the
beginning of a new one. With the Chicxulub impact 65 million years
ago, the Mesozoic world, populated by giant dinosaurs and flying
reptiles, gave way to the modern world of mammals and birds.

This cycle of doom has relevance to the present-day impact hazard,
as the Solar System passed through the Galaxy's central plane in the
last few million years, and by some accounts a barrage of comets
recently dislodged from the Oort Cloud should be approaching the
planets now. A few impact/extinction events may be out of phase with
the 30 million year galactic cycle, but it is expected that some
comet and asteroid impacts would occur independently of the periodic
perturbation of Oort Cloud comets.

These exciting new findings from astronomy, geology, and the
history of life point to a general theory relating mass extinctions,
and perhaps other geologic events, to the impacts of large comets
and asteroids on the Earth. In this view, mass extinctions of life
occur as discrete pulses, marked by abrupt mass mortality on land
and in the oceans, decimation of plant life, major environmental
perturbations shown by changes in carbon isotopes, and climatic
changes shown by oxygen-isotope shifts. The mass extinctions are
commonly followed by a period of rapid evolution of surviving
species, with newcomers filling the many niches abandoned en-masse
by the victims of global disaster.

In a growing number of cases, the times of mass extinction have
been found to be marked by evidence of great asteroid or comet
impacts, in the form of large, dated impact craters, and widespread
layers rich in iridium, shocked minerals, and glassy microtektites.
It may be that all of the major, and many of the minor, breaks in
the geologic record were caused by impacts of objects of various
sizes.  The underlying periodicity of about 30 million years that
seems to pervade the record of these events may well be related to
showers of comets from the Oort Cloud triggered as the Solar System
passes through the galactic plane. Thus the impact hypothesis of
mass extinctions, which began with study of a thin clay layer at
Gubbio, has grown in theoretical and observational support,
culminating in an important unifying concept in the earth sciences.

Michael R. Rampino
Earth & Environmental Science Program
New York University
100 Washington Square East
New York, NY 10003
(212) 998-3743 Office Phone
(212) 995-3820 Office Fax
(212) 242-0929 Home Phone
(212) 255-2739 Home Fax


V.V. Prokofeva*), L.G. Karachkina and V.P. Tarashchuk:
Investigations of oscillations in the brightness of Asteroid 1620
geographer during its approach to the Earth in 1994. ASTRONOMY
No.6, pp.758-767


Comprehensive investigations were conducted of Asteroid 1620
Geographer during its approach to the Earth in 1994. A frequency
analysis of fine photometric effects and oscillations in its
brightness was performed using data from a catalog of photometric
observations of asteroids. This analysis confirms the monolithic
nature of the very elongated body of the asteroid. In addition to
the known rotation period of the asteroid, periods of 0(d).8 and
2(d).8 are detected, as well as multiples of these periods. The
observed periodicity suggests that the first of these periods is
associated with free precession of the rotation axis of the
asteroid, while the second is due to forced precession with
precession angle 3 degrees +/- 1 degrees. The free precession could
have arisen either during the formation of the asteroid or during a
collision with another body. The presence of forced precession
and the fact that Geographer is associated with a meteor shower
is consistent with the possible existence of modest-sized
companions. Copyright 1998, Institute for Scientific Information Inc.


S.L. Guo*), W. Huang, X.H. Hao and B.L. Chen: Fission track dating
of ancient man site in Baise, China, and its significances in space
research, paleomagnetism and stratigraphy. RADIATION MEASUREMENTS,
1997, Vol.28, No.1-6 SISI, pp.565-570


A large number of artifacts (stone tools) have been discovered in
Baise (Bose), Guangxi, China in recent years. They show that ancient
man were living in the south of China during very ancient times.
During excavation, tektites were discovered in the same layer of
deposits as the stone tools. The structure of the layers of deposits
in this site was never disturbed, which is the evidence that the
stone tools were left behind by the ancient man at the time when the
tektites fell on the earth, which were slowly covered over by layers
of deposits. Fission track dating has been carried out on tektites.
The age of the tektites is 0.732 +/- 0.039 Ma, which is also the age
of the ancient man in Baise, Guangxi, China. The annealing degree of
spontaneous fission tracks in the tektite was investigated by
measuring track diameters. A correction of age for track fading
has been made by track diameter technique. According to current
understanding, tektites were formed by the impact of falling
asteroids or comets on the earth's surface. The dating shows that a
big impact occurred on the earth 0.732 Ma ago. The coincidence of
the age of the tektites with the age of geomagnetic polarity
reversal (similar to 0.73 Ma) from the Matuyama Epoch to the Brunhes
Epoch proposes a plausible explanation that the possible cause of
the geomagnetic polarity reversal is due to the big impact of space
objects falling onto the earth. The result of the dating also set up
a standard for inferring the ages of the deposits in South China as
well as in South-East Asia where laterite (red soil) deposits exist
in the entire region. Copyright 1998, Institute for Scientific Information


C.I. Lagerkvist and J.S.V. Lagerros: The number density of main-belt
asteroids. ASTRONOMISCHE NACHRICHTEN, 1997, Vol.318, No.6,


In this paper we have studied how the number density of asteroids
varies as a function of the mean distance from the sun.
Copyright 1998, Institute for Scientific Information Inc.


The Cambridge-Conference List is a scholarly electronic network
organised by Dr Benny J Peiser at Liverpool John Moores University,
United Kingdom. It is the aim of this international network to
disseminate the latest information and research findings related
to i) geological and historical neo-catastrophism, ii) NEO research
and the hazards to civilisation due to comets and asteroids, and
iii) the development of a planetary civilisation capable of
protecting itself against cosmic disasters. For further information
about this network and how to subscribe, please contact

Benny J Peiser .

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