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Cambridge Conference Digest - February 2, 1998

CAMBRIDGE CONFERENCE DIGEST, 02/02/98
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(1) RAMPINO'S NEW PAPER ON THE SHIVA HYPOTHESIS

(2) LOOKING AT ASTEROID 1620 GEOGRAPHER

(3) THE NUMBER DENSITY OF MAIN-BELT ASTEROIDS
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(1) RAMPINO'S NEW PAPER ON THE SHIVA HYPOTHESIS

From: Michael Rampino  wrote:
 
Benny:
 
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
 
===========================
(2) LOOKING AT ASTEROID 1620 GEOGRAPHER

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 
LETTERS-A JOURNAL OF ASTRONOMY AND SPACE ASTROPHYSICS, 1997, Vol.23, 
No.6, pp.758-767

*) UKRAINIAN ACADEMY OF SCIENCE, CRIMEAN ASTROPHYS OBSERV, P-O 
NAUCHNYI, UA-334413 CRIMEA,UKRAINE

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.

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(2) DID COSMIC IMPACT HIT EARLY CHINESE?

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

*) INSTITUE OF ATOMIC ENERGY, POB 275 96, BEIJING 102413, PEOPLES 
REPUBLIC OF CHINA

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 Inc.

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(3) THE NUMBER DENSITY OF MAIN-BELT ASTEROIDS

C.I. Lagerkvist and J.S.V. Lagerros: The number density of main-belt 
asteroids. ASTRONOMISCHE NACHRICHTEN, 1997, Vol.318, No.6, 
pp.391-393

ASTRONOMICAL OBSERVATORY, BOX 515, S-75120 UPPSALA, SWEDEN

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.

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