PLEASE NOTE:


*

CCNet, 24 September 1999
------------------------

     QUOTE OF THE DAY

     "Whoever God is, it is unlikely he or she makes comets in the same
      way as Professor Bill Zealey"
                  -- Sydney Morning Herald, 24 September 1999


(1) NO EVIDENCE FOR CLIMATE-PERTURBING COSMIC IMPACT AROUND
    4000 BP
    Doug Keenan <doug.keenan@virgin.net>

(2) THE 4000 BP EVENT: MORE QUESTIONS THAN ANSWERS
    Alastair Vaan <A.A.Vaan@soton.ac.uk>

(3) HOW TO CREATE YOUR OWN COMETARY SNOWBALL
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(4) THE DARK MATTER TELESCOPE
    Alain Maury <Alain.Maury@obs-azur.fr>

(5) URANUS' FUNNY SATELLITES
    Colin Keay <phcslk@cc.newcastle.edu.au>

(6) SURFACE OF MARS BLASTED BY SMALL METEORITES?
    Michael Paine <mpaine@tpgi.com.au>

(7) THE TRIASSIC-JURASSIC BOUNDAY FAUNAL MASS EXTINCTION
    J.C. McElwain et al., UNIVERSITY OF SHEFFIELD

(8) MASS EXTINCTION IN A DYNAMICAL SYSTEM OF EVOLUTION
     K. Tokita & A. Yasutomi, *) OSAKA UNIVERSITY

(9) THE GREAT REVOLUTIONS IN THE HISTORY OF LIFE
    A. Seilacher, TUBINGEN,GERMANY

(10) GLOBAL CATASTROPHES, MASS EXTINCTION & ULTRAVIOLET RADIATION
     C.S. Cockell, NASA,AMES RES CTR

(11) THE FUTURE OF THE FOSSIL RECORD
     D. Jablonski, UNIVERSITY OF CHICAGO

(12) GALACTIC YEARS & THE PERIODICITY OF GLOBAL CATASTROPHES
     S.G. Neruchev, ALL RUSSIAN GEOL EXPLORATION

(13) ON THE SYNCHRONEITY OF COSMIC IMPACT AND THE K/T MASS  
     EXTINCTION
     R.D. Norris et al. WOODS HOLE OCEANOG INST

===============
(1) NO EVIDENCE FOR CLIMATE-PERTURBING COSMIC IMPACT AROUND
    4000 BP

From Doug Keenan <doug.keenan@virgin.net>

Benny,

There is very strong evidence for a climatic upheaval c. 4000 BP. The
big question is "what caused the upheaval?" Many seem to believe that
the cause was a cosmic impact. I would prefer to not consider the
cause right now. Instead, I would like to consider a smaller,
related, question: is there evidence specifically for a
climate-perturbing cosmic impact c. 4000 BP? (Please note that this
is different from asking if a cosmic impact can explain the available
palaeodata.)  What follows reviews the evidence that I have seen
presented.

* The soil analysis of Courty [1998]. Courty reports the absence of
the materials usually associated with a cosmic impact: this is
evidence against such an impact. (M.-A. Courty [private comm.] has
agreed that a possible explanation for her data--which shows intense
burn--is an eruption whose ejecta contained oil/gas; no other
credible explanation has been suggested, as far as I know.)  Note too
that Courty took samples from a different context than Weiss et al.
[1993]; so it is not certain that Courty and Weiss et al. are
analysing the same soil.  Indeed, Courty claims that her soil
pre-dates Akkad, whereas Weiss et al. are clear that theirs is from
Akkad's terminus; as I understand it, however, the (relative) date
from Courty is unconfirmed by an archaeologist--so it could
conceivably be in error.

* Seismic disturbances in part of the Ancient Near East. The ANE has
four tectonic plate boundaries within it (and many volcanoes); the
Anatolian microplate would seem to be particularly susceptible to
disturbance. Earthquakes can thus easily occur in the ANE, without
cosmic impact.

* Widespread (global?) seismic disturbances.  Peiser [1998] presents
seven or eight palaeo-seismic events, in addition to those from the ANE.
His reference numbers are used here.

  [079]  The date is tentatively c. 2900 BC, by thermoluminescence
        (in Utah).
  [157] (i) Dates made in the 1960s--thus ranging over many
        centuries; the event was not an earthquake, but a gradual
        uplift (on E coast of N America). (ii) Date accuracy not
        reported; the event was a gradual subsidence (Veracruz, Gulf
        of Mexico).  As Peiser notes, these two events appear to be
        due to a gradual differential warping (of the N American
        plate).
  [162] The date is ~3400 (14C) BP, and almost certainly after
        1900 BC.
  [182] Large and at about the right time (in Fiji).
  [185] The date is almost certainly before 3750 BC.
  [213] The date is almost certainly after 1650 BC.
  [302] The date is roughly 2900 BC; the event was not an earthquake,
        but a gradual emergence.

(Note--refs 079 and 157 were unavailable to me; I have depended on Peiser.)
The above events do not constitute evidence for a cosmic impact c. 4000 BP.

* The apparent synchrony of (i) earthquakes in the ANE and (ii) the
onset of the climatic upheaval. As I understand it, no one has
proposed how a cosmic impact could force the observed climatic
anomalies. If, however, the ANE earthquakes were coeval with a
sufficiently-large eruption, then the climatic anomalies are
plausibly explainable [Keenan, 1999]. (This does not mean that an
eruption-with-earthquakes is the only plausible explanation, merely
that the evidence is not specifically for a cosmic impact.)

* Ancient texts. I propose that an ancient text be considered as
evidence for a cosmic impact only if either (i) it is supported by
scientific data or (ii) it gives some details that ancient people
would be unlikely to guess at. So far, no ancient texts have been
cited that meet this criterion.

* Craters reported by Schultz & Lianza [1992].  This is essentially
certain evidence specifically for a cosmic impact.  The date is very
roughly 5000 years ago (work is ongoing to make this more
accurate--P. H. Schultz, private comm., 1999-09-13).  The energy
release was ~350 Mtons TNT (roughly 20 times Tunguska) and the local
soil is loess, but the craters are <10 m deep, since the impact angle
was <15 deg from the horizontal. The meteorite was ~150 m in
diameter: the implied volume is minuscule (only 1% of what Mt. St.
Helens erupted in 1980). This and the impact angle imply that 
virtually all debris would have been placed on the ground or in the
troposphere--from where it would be quickly washed out. Hence effects
on the global climate would have been negligible.  It is not
plausible that the impact, which was in Argentina, would have caused
earthquakes in the ANE.

This obviously does not mean that there wasn't a climate-perturbing
cosmic impact c. 4000 BP.  I believe, though, that there is no
evidence available specifically for such an event.

Cheers,
Doug Keenan

References

Courty, M.-A. "The Soil Record of an Exceptional Event at 4000 B.P.
in the Middle East", Natural Catastrophes During Bronze Age
Civilisations (editors--Peiser, B. J., Palmer, T. & Bailey, M. E.)
93-108 (British Archaeological Reports [Archaeopress], Oxford, 1998).

Keenan, D. J. "The three-century climatic upheaval of c. 2000 BC, and
regional radiocarbon disparities", Los Alamos Archives:
Physics/9908052 (1999).  [Also available at 
http://freespace.virgin.net/doug.keenan .]

Peiser, B. J. "Comparative Analysis of Late Holocene Environmental
and Social Upheaval", Natural Catastrophes During Bronze Age
Civilisations (editors--Peiser, B. J., Palmer, T. & Bailey, M. E.)
117-139 (British Archaeological Reports [Archaeopress], Oxford,
1998).

Schultz, P. H. & Lianza, R. E. "Recent grazing impacts on the Earth
recorded in the Rio Cuarto crater field, Argentina", Nature 355:
234-237 (1992).

Weiss, H. & six others. "The Genesis and Collapse of Third Millennium
North Mesopotamian Civilization", Science 261: 995-1004 (1993).

===============
(2) THE 4000 BP EVENT: MORE QUESTIONS THAN ANSWERS

From Alastair Vaan <A.A.Vaan@soton.ac.uk>

Everybody seems desparate to find a cause for the event that must be
unusual and possibly exotic. It strikes me that we are suffering
similar problems to those faced not so many years ago with the Younger
Dryas, a story that only matured once a significant amount of proxy
data appeared. Despite the volume of data out there across this period,
synthesis is still a long way off and ideal records are lacking.

Proposing volcanic and impact theories is all very well, after all we
do have evidence of an igneous event of sorts at around the same time.
A couple of points though.

1. As far as the Akkad story goes, we have a tephra right before the
dust event which correlates well from the Tell Leilan site to the
Cullen and deMenocal Gulf of Oman core. One difficulty though - the
Gulf of Oman tephra lies anything up to 140 years prior to the dust
peak. There's a lag. Something that Courty (1998) is also aware of.

2. At the moment it could have been either or neither.. I note also that
Courty (1998) declines to make the distinction during the Syrian
studies and also that the entire picture is shrouded somewhat by
variations in the preservation of that tephra. We have absolutely no
handle on the magnitude of the impact/eruption which is very important
to implying it as an agent.

3. Importantly there is plenty of room for other mechanisms. Simple
autofluctuation as a response to declining insolation over the
Holocene, other oceanographic mechanisms, feedback involving vegetation
cover and others. All are still firmly in the ring (a volcano elsewhere
even...).
  
I read Keenan's paper with interest. I take it though that it won't go
through peer review? The NAO is certainly a factor in the interannual
variation of European climate, but much remains to be learned. The work
I have seen has had difficulties modelling even the near past and
palaeo-NAO work is in its infancy. The high NAO brings extra
precipitation to northern Europe, what then of the widespread
regressions in the majority of N. Europe's lakes? (Harrison et
al.(1993)

Other points include the fact that the event is not necessarily unique.
The Early-Mid Holocene transition has a similar trace in the
palaeo-record. Also there has been no clear separation made between
this Mid-Holocene break and the general Mid-Holocene transition from
the warmer Early/Mid Holocene (the end of the Atlantic period in the
Blytt-Sernander classification). Some palaeo-records point to a
distinct stepwise deterioration in climate across the 4-5KBP  period,
of which this event could easily be a part of.

We are of course hampered. As others have already pointed out, this
event is not necessarily easily found in our (apparently) most trusted
records(ice cores and dendroclimatology). Sub-global climate
fluctuations are always going to be difficult to elucidate by their
very nature. It will be some time before we know if it is a clealy
global thing. I know it's going to be another 6 months before I know
anything from my record (ODP leg 169S)...

I find a distinct irony in that the preservation of the igneous event
that might have lead to a widespread drought, is preserved in many
places by a cap of heavy rainwashed silt sealing it in :-)

Alastair Vaan

School of Ocean and Earth Science
University of Southampton
Southampton Oceanography Centre
European Way, Southampton, SO14 3ZH

Phone : +44 1703 595000 ext 26478
Fax : +44 1703 593059

===============
(3) HOW TO CREATE YOUR OWN COMETARY SNOWBALL

From Andrew Yee <ayee@nova.astro.utoronto.ca>

[http://www.smh.com.au/news/9909/24/national/national16.html]

Friday, September 24, 1999

Harvest of the heavens starts with a sludgeball on Earth
By JAMES WOODFORD, Science Writer

Whoever God is, it is unlikely he or she makes comets in the same way
as Professor Bill Zealey.

But Professor Zealey, the head of the Department of Engineering
Physics at the University of Wollongong, is almost certain that the
ingredients of the simulated comet cores he manufactures are the same
as the real thing.

By the time he has spent a $50,000 grant from the United States-based
Foundation for International Non-Governmental Development of Space,
he is almost certain he will be able to produce an object that feels,
looks and behaves like a chunk from the heart of a comet. The
foundation is a consortium of business leaders who believe that in
the next millennium, private industry will play a major role in space
exploration. Professor Zealey knows the ingredients of a number of
comets from studies of the light from the brilliant trails of gases
released by objects such as Halley's Comet.

He is most interested in copying dormant comets, known as "crypto
cometary asteroids", which are thought to make up about 30 per cent
of all near-Earth asteroids.

Real comets and asteroids formed over billions of years as tiny
particles collided and fused with each other.

Professor Zealey uses a $30, 10-year-old blender, dry ice, water ice
and four different recipes of minerals that are basically silicate
clays, mimicking the composition of real comets..

With the ingredients cooled to minus 80C, Professor Zealey is able to
get the "fluffiness" or porosity of a real comet -- they are thought
to be between 20 per cent and 60 per cent as dense as water ice.

In his quest for the perfect simulated comet, he and his students and
colleagues have trawled through literature from sources as diverse as
NASA and the ice studies of avalanche researchers.

"We are not forming a comet the same way as they form naturally but
we are trying to mimic what it looks like and feels like," he said.
"The general consensus now is that a comet is a fluffy, muddy
snowball. We think they're covered in a metre-thick layer that's like
asphalt."

At first, when Professor Zealey, whose early career included work on
the formation of stars, was approached to simulate cometary nuclei he
rejected the proposal as a joke.

That was until it was explained to him why such a research effort
could be worth billions of dollars.

It costs about $10,000 for every kilogram of payload lifted into
space and water will be crucial as a fuel -- hydrogen is easily
obtained from water in space -- and as a necessary requirement for
humans exploring the solar system.

Scientists already know of around 10 near-Earth objects at least a
kilometre in length that are probably dormant or extinct comets,
which contain billions of litres of frozen water.

In the next decade, as many as three missions are planned for
unmanned spacecraft to visit comets.

However, if water is ever to be retrieved from them, engineers will
have to construct drills and other equipment to harvest the ice. Such
a drill is likely to be fired like a harpoon through the crust of the
asteroid and into its core.

"This started out as fun but now it's very serious because of all the
commercial interest and the interest from the students," Professor
Zealey said.. "It's beginning to take on a life of its own."

Copyright 1999 Sydney Morning Herald

===============
(4) THE DARK MATTER TELESCOPE

From Alain Maury <Alain.Maury@obs-azur.fr>

Hello,

Just to mention this web site which has informations about an 8
meter, wide field telescope [http://www.dmtelescope.org].

There is a page which contains informations about detecting "all
significant near-Earth Asteroids". They have a web page on neo
detection. Reading it I get the feeling they are good cosmologists.
Their estimate of magnitude versus diameter does not seem right, and
they don't say what percentage of time might be attributed to NEO
searches, nor in what time frame they expect to find all significant
NEAs. They just quote : In a run of 3-4 clear nights the fast-slewing
telescope could be used to survey the entire visible sky (20,000
square degrees) to a limiting magnitude (10 sigma) of V=24 or
Ks=19. In a run of 3-4 clear nights the fast-slewing telescope could
be used to survey the entire visible sky (20,000 square degrees) to a
limiting magnitude (10 sigma) of V=24 or Ks=19.
http://www.dmtelescope.org/neo.html

I have added it for comparison on my NEO technical data page at
http://wwwrc.obs-azur.fr/schmidt/general/NEOsurvey.html

Alain

================
(5) URANUS' FUNNY SATELLITES

From Colin Keay <phcslk@cc.newcastle.edu.au>

Hi Benny...

Many thanks for your regular, interesting newsletter.

You sent this yesterday.....

>The three new candidate satellites were discovered in a search using
>the world-class wide-field imaging camera, known as CFH12K, which is
>a mosaic of CCD detectors covering a very large patch of sky
>(currently 35x28 arcmin, or roughly the area of the full moon). This
>instrument allowed the team to explore more than 90 percent of the
>region around Uranus in which satellite orbits are stable and to find
>these extremely faint objects, which are no more than 20 kilometers
>in diameter and orbit Uranus at a distance of 10 to 25 kilometers.

Yep! At a distance of 10 to 25 km the object would be indeed interesting.

Cheers, and keep up the good work.... Colin K

***************************************************************************
* Dr Colin Keay      :::::::     ~      ~   To  achieve  anything  really *
* Physics Dept     ~       :::::      ~      worthwhile in research it is *
* Newcastle Univ        ~       :::\ | /   ~  necessary to go against the *
* NSW, AUSTRALIA 2308 ~      ~     - o -       opinions of one's fellows. *
* phcslk@cc.Newcastle.edu.au       / | \  ~        "Where the Wind Blows" *
* www2.hunterlink.net.au/~ddcsk        ~       ~       ~    - Fred Hoyle  *

================
(6) SURFACE OF MARS BLASTED BY SMALL METEORITES?

From Michael Paine <mpaine@tpgi.com.au>

Dear Benny,

Explorezone has a report on an analysis of the geology of the Mars
Pathfinder landing site. The article concludes that the most likely
explanation for small crater-like depressions and cracks in many rocks
is meteorite impacts.

see http://explorezone.com/archives/99_09/23_mars_rocks.htm

"Prior to our observations most folks subscribed to atmospheric entry
models that stated that the smallest projectiles that could reach Mars
would make craters some 50 meters across," Horz said, adding that the
new study shows that more numerous small objects, capable of creating
craters as small as a few centimeters across, are possible... Impact
provides an efficient erosion process and explains the wide variety of
boulder and pebble-sized rocks that litter the surface."

Michael Paine
The Planetary Society Australian Volunteers

================
(7) THE TRIASSIC-JURASSIC BOUNDAY FAUNAL MASS EXTINCTION

J.C. McElwain*), D.J. Beerling, F.I. Woodward: Fossil plants and
global warming at the Triassic-Jurassic boundary. SCIENCE, 1999,
Vol.285, No.5432, pp.1386-1390

*) UNIVERSITY OF SHEFFIELD,DEPT ANIM & PLANT SCI,SHEFFIELD S10 2TN,S
   YORKSHIRE,ENGLAND

The Triassic-Jurassic boundary marks a major faunal mass extinction,
but records of accompanying environmental changes are limited.
Paleobotanical evidence indicates a fourfold increase in atmospheric
carbon dioxide concentration and suggests an associated 3 degrees to
4 degrees C 'greenhouse' warming across the boundary. These
environmental conditions are calculated to have raised leaf
temperatures above a highly conserved Lethal Limit, perhaps
contributing to the >95 percent species-level turnover of
Triassic-Jurassic megaflora. Copyright 1999, Institute for Scientific
Information Inc.

=============
(8) MASS EXTINCTION IN A DYNAMICAL SYSTEM OF EVOLUTION

K. Tokita*), A. Yasutomi: Mass extinction in a dynamical system of
evolution with variable dimension
      JN: PHYSICAL REVIEW E, 1999, Vol.60, No.1, pp.842-847

*) OSAKA UNIVERSITY,CONDENSED MATTER THEORY GRP,GRAD SCH
   SCI,TOYONAKA,OSAKA 5600043,JAPAN

Introducing the effect of extinction into the so-called replicator
equations in mathematical biology, we construct a general model where
the diversity of species, i.e., the dimension of the equation, is a
time-dependent variable. The system shows very different behavior
from the original replicator equation, and leads to mass extinction
when the system initially has high diversity. The present theory can
serve as a mathematical foundation for the paleontologic theory
for mass extinction. This extinction dynamics is a prototype of
dynamical systems where the variable dimension is inevitable.
Copyright 1999, Institute for Scientific Information Inc.

=============
(9) THE GREAT REVOLUTIONS IN THE HISTORY OF LIFE

A. Seilacher: Earth history seen as a long-term experiment: The great
revolutions in the development of life. ECLOGAE GEOLOGICAE HELVETIAE,
1999, Vol.92, No.1, pp.73-79

*) ENGELFRIEDSHALDE 25,D-72076 TUBINGEN,GERMANY

Evolution is a historical process and thereby unpredictable;
nevertheless the great revolutions in the history of life follow
similar patterns. Mass extinction, while being triggered by random
catastrophies, are preceded by greenhouse periods that favor the
evolution of extreme, and often bizarre, adaptations. Since
specialization always reduces tolerance, it is not surprising that
previously dominating groups of organisms were doomed in the face of
global ecological changes. Copyright 1999, Institute for Scientific
Information Inc.

============
(10) GLOBAL CATASTROPHES, MASS EXTINCTION & ULTRAVIOLET RADIATION

C.S. Cockell: Crises and extinction in the fossil record - a role for
ultraviolet radiation? PALEOBIOLOGY, 1999, Vol.25, No.2, pp.212-225

NASA,AMES RES CTR,MS 239-20,MOFFETT FIELD,CA,94035

A number of natural events can cause ozone depletion, including
asteroid and comet impacts, large-scale volcanism involving the
stratospheric injection of chlorine, and close cosmic events such as
supernovae. These events have previously been postulated to have been
sole or contributory causes of mass extinctions. Following such
events, UV-B radiation would have been elevated at the surface of the
earth. The possibilities for detecting elevated UV-B as a kill
mechanism in the fossil record are discussed. In the case of impact
events and large-scale volcanism, the taxa affected by increases in
UV-B radiation are likely to be similar to those affected by cooling
and by the initial drop in irradiance caused by stratospheric dust
injection. Thus UV-B may synergistically exacerbate the effects of
these other environmental changes and contribute to stress in the
biosphere, although UV-B alone Is unlikely to cause a mass
extinction. By the same token, however, this similarity in affected
taxa is likely to make delineating the involvement of UV-B radiation
in the fossil record more difficult. Cosmic events such as supernovae
may produce smaller extinction events, but ones that are 'cleaner' UV
catastrophes without the involvement of other environmental
changes. Copyright 1999, Institute for Scientific Information Inc.

=============
(11) THE FUTURE OF THE FOSSIL RECORD

D. Jablonski: The future of the fossil record. SCIENCE, 1999,
Vol.284, No.5423, pp.2114-2116

UNIVERSITY OF CHICAGO,DEPT GEOPHYS SCI,5734 S ELLIS AVE, CHICAGO, IL,
60637

The fossil record provides a powerful basis for analyzing the 
controlling factors and impact of biological evolution over a wide
range of temporal and spacial scales and in the context of an
evolving Earth. An increasingly interdisciplinary paleontology has
begun to formulate the next generation of questions, drawing on a
wealth of new data, and on methodological advances ranging from
high-resolution geochronology to simulation of morphological
evolution. Key issues related to evolutionary biology include the
biotic and physical factors that govern biodiversity dynamics, the
developmental and ecological basis for the nonrandom introduction of
evolutionary innovations in time and space, rules of biotic response
to environmental perturbations, and the dynamic feedbacks between
life and the Earth's surface processes. The sensitivity of
evolutionary processes to rates, magnitudes, and spatial scales of
change in the physical and biotic environment will be important in
all these areas. Copyright 1999, Institute for Scientific Information
Inc.

==========
(12) GALACTIC YEARS & THE PERIODICITY OF GLOBAL CATASTROPHES

S.G. Neruchev: Periodicity of global geologic and biologic events in
the Phanerozoic. GEOLOGIYA I GEOFIZIKA, 1999, Vol.40, No.4,
pp.493-511

ALL RUSSIAN GEOL EXPLORAT PETR RES INST,LITEINYI PR 39,ST
PETERSBURG 191104,RUSSIA

In the Phanerozoic 17 global events took place, which were
characterized by intense basaltic magmatism, active formation
of uranium deposits, accumulation of marine radioactive uraniferous
black shales, increase in the environment radioactivity, and, as a
result, mass extinction of old fauna and appearance of new species of
organisms. The greatest events (V-C, D-C, J-K) occurred every 216-217
Ma,  i.e., every galactic year. During this period, similar events
took place every ca. 30 Ma. The proposed periodic system includes
three large periods (galactic years) and seven series of similar
events. Copyright 1999, Institute for Scientific Information Inc.

============
(13) ON THE SYNCHRONEITY OF COSMIC IMPACT AND THE K/T MASS EXTINCTION

R.D. Norris*), B.T. Huber, J. Self Trail: Synchroneity of the K-T
oceanic mass extinction and meteorite impact: Blake Nose, western
North Atlantic. GEOLOGY, 1999, Vol.27, No.5, pp.419-422

*) WOODS HOLE OCEANOG INST,MS-23,WOODS HOLE,MA,02543

A 10-cm-thick layer of green spherules occurs precisely at the
biostratigraphic boundary between the Cretaceous and Paleogene (K-T
boundary) at Ocean Drilling Program Site 1049 (lat 30 degrees 08'N,
long 76 degrees 06'W), The spherulitic layer contains abundant rock
fragments (chalk, limestone, dolomite, chert, mica books, and schist)
as well as shocked quartz, abundant large Cretaceous planktic
foraminifera, and rounded clasts of clay as long as 4 mm interpreted
as altered tektite glass probably derived from the Chicxulub impact
structure, Most of the Cretaceous foraminifera present above the
spherule layer are not survivors since small specimens are
conspicuously rare compared to large individuals. Instead, the
Cretaceous taxa in Paleocene sediments are thought to be reworked.
The first Paleocene planktic foraminifera and calcareous
nannofossil species are recorded immediately above the spherule bed,
the upper part of which contains an iridium anomaly. Hence,
deposition of the impact ejecta exactly coincided with the
biostratigraphic K-T boundary and demonstrates that the impact event
was synchronous with the evolutionary turnover in the oceans. These
results are consistent with a reanalysis of the biostratigraphy of
the K-T boundary stratotype, which argues that shallow-marine K-T
boundary sections are not biostratigraphically more complete than
deep-sea K-T boundary sites. Copyright 1999, Institute for Scientific
Information Inc.

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