PLEASE NOTE:


*
Date sent:        Mon, 01 Sep 1997 14:42:17 -0400 (EDT)
From:             Benny J Peiser <B.J.PEISER@livjm.ac.uk
Subject:          BACK TO SQUARE ONE? DID DINOSAURS DISAPPEARED SLOWLY BEFORE THE K/T
         EVENT?
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

BACK TO SQUARE ONE? GRADUALISTS CLAIM THAT DINOSAURS DISAPPEARED
VERY SLOWLY - AND LONG BE THE K/T EVENT

Recent research papers contradict K/T Impact Hypothesis
 

B. Galbrun: Did the European dinosaurs disappear before the K-T
event? Magnetostratigraphic evidence. In: EARTH AND PLANETARY SCIENCE
LETTERS, 1997, Vol.148, No.3-4, pp.569-579

Debate on the non-catastrophic or catastrophic extinction of the
dinosaurs by an asteroid impact, K-T event, remains a controversy and
is mainly based on the interpretation of the sedimentary continental
sequences in the North American Western Interior. The global aspect
of this event needs to be tested in sedimentary record from all
continents where continuous terrestrial deposits through the
Cretaceous-Paleogene are well preserved. In the western Mediterranean
realm, recognition of the Cretaceous-Paleogene boundary is limited by
the lack of biostratigraphic data in the upper Cretaceous-lower
Tertiary continental sedimentary sequences. New magnetostratigraphic
results were obtained from the analysis of two sections in southern
France and compared to previous results in northern Spain. The last
occurrence of in situ dinosaurs eggshells, the only dinosaur remains
found, is located in Chron 30n (southeast France) or 31n (southwest
France and northern Spain). This last occurrence could demonstrate
that the extinction of the European dinosaurs occurred prior to the
Cretaceous-Paleogene boundary, and would therefore support the idea
of a gradual or stepwise extinction unlinked to the K-T event.

===================================================================
G. Keller, J.G. Lopez Oliva, W. Stinnesbeck, T. Adatte: Age,
stratigraphy, and deposition of near-K/T siliciclastic deposits in
Mexico: Relation to bolide impact? In: GEOLOGICAL SOCIETY OF AMERICA
BULLETIN, 1997, Vol.109, No.4, pp.410-428

Examination of 10 K/T boundary sections in northeastern and
east-central Mexico, and new data presented from 7 sections,
permit the following conclusions. (1) The globally recognized
K/T boundary and mass extinction in planktic foraminifera is
stratigraphically above, and separated by a thin marl layer of
Maastrichtian age, from the siliciclastic deposit that is commonly
interpreted as a short-term (hours to days) WT-impact-generated
tsunami deposit. A similar relationship between the WT boundary and
siliciclastic or breccia deposits is ob served at Brazos River in
Texas, Beloc in Haiti, and Poty Quarry in Brazil. (2) Stratigraphic
control indicates that deposition of the siliciclastic member
occurred sometime during the last 150 k.y. of the Maastrichtian, and
ended at least several thousand years prior to the K/T boundary. (3)
At least four discrete horizons of bioturbation have been observed
within the siliciclastic deposit that indicate episodic colonization
by invertebrates over an extended time period. (4) The glass- and
spherule-rich unit, which has been linked to the Haiti spherule
layer and the Chicxulub structure, is at the base of the
siliciclastic deposit and thus significantly predates the WT
boundary event. The stratigraphic separation of the K/T boundary and
siliciclastic deposits and the evidence of long-term deposition
between them, suggests the presence of two events: (1) a globally
recognized K/T boundary (impact) event marked by Ir anomaly and the
mass extinction, and (2) a Caribbean event (impact or volcanic and
probably linked to the Chicxulub structure) that predates the WT
boundary and is marked by glass and siliciclastic or breccia
deposits.

===============================================================
P. Bruns, H. Rakoczy, E. Pernicka, W.C. Dullo: Slow sedimentation and
Ir anomalies at the Cretaceous/Tertiary boundary. In: GEOLOGISCHE
RUNDSCHAU, 1997, Vol.86, No.1, pp.168-177

Iridium enrichments, at or close to the K/T boundary, are often cited
as evidence for impacts of cosmic bodies or volcanic events, or both,
that resulted in mass extinctions. A third possible explanation for
the high Ir concentrations, that the enrichments were caused by the
cosmic micrometeorite flux during times of slow sediment
accumulation, has generally been rejected. In this study we examine
the Ir/Au ratios and conclude that they may indicate enrichment of
siderophile elements by slow sedimentation. In addition, the concept
of slow sedimentation at the K/T boundary is consistent with many
aspects of the K/T boundary research such as the gradual decline of
the species before the major extinction level and recent reports of
faunal transitions from Cretaceous to Tertiary without sudden
extinctions, hiatuses or Ir anomalies.



*
Date sent:        Mon, 01 Sep 1997 12:07:11 -0400 (EDT)
From:             HUMBPEIS <B.J.PEISER@livjm.ac.uk
Subject:          Re: Great Chicago Fire
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

from: Mark Bailey <meb@star.arm.ac.uk

Re: Great Chicago Fire:

The suggestion made in the film `Target Earth', that the Great
Peshtigo Fire was started by a meteorite or bolide does not fit with
the evidence in both Father Pernin's (1874) account and that of Robert Wells
(1968) [Refs: P. Pernin 1971, `Wisconsin Stories: the Great Peshtigo Fire',
State Historical Society of Wisconsin; R. W. Wells 1968, `Embers of
October', reprinted 1995 Peshtigo Historical Society]. Wells, however, does
mention a report by Phineas Eames, one of the Birch Creek farmers, who
describes an event which closely resembles a bright fireball. This occurs
one hour after the devastating Peshtigo Fire, and so could not have been the
cause of the latter even if the fireball had touched ground.

Mark Bailey
Armagh Observatory
meb@star.arm.ac.uk



*
Date sent:        Mon, 01 Sep 1997 12:04:04 -0400 (EDT)
From:             HUMBPEIS <B.J.PEISER@livjm.ac.uk
Subject:          WHAT REALLY KILLED THE DINOSAURS?
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

WHAT REALLY KILLED THE DINOSAURS?

Ever since 1980, when Luis Alvarez and his colleagues published
their famous paper on the cosmic impact scenario which ought to
have killed off the dinosaurs 65 million years ago, the
controversy between gradualists and neo-catastrophists has
intensified (see in more detail William Glen, ed. The
Mass-Extinction Debates: How Science works in a Crisis (Stanford
University Press, 1994). This scientific battle is far from being
limited to different interpretations of the geological and fossil
records. Just like the controversy about Darwinism during the 19th
century had immense repercussions in practically all fields of
science, culture and politics, the new awareness of our
catastrophic past and life's vulnerable existence on a constantly
bombarded planet has significant implications on the newly
emerging worldview which is currently taking shape. Whilst the old
school of Darwinist gradualism stick to their core believe that
slow processes of "natural selection" and the subsequent "survival
of the fittest" lies at the heart of evolution and extinctions,
neo-catastrophists have revived the "biblical" idea of
extraterrestrial interventions and mass extinctions and produced
convincing astronomical and geological evidence for such
punctuations. It is hardly surprising that "the theory's biblical
overtones at first turned many scientists against it", as a recent
editorial in the NEW SCIENTIST (16 August 1997) emphasised. Let's
face it: the mass extinction debates have never been free of a
philosophical underpinning and religious bias. Because the idea
that cosmic impact catastrophes rather than gradual changes on
Earth might explain mass extinctions seemed too close to the
biblical worldview, many Darwinists have rejected and continue to
reject the proposal as such. According to their geocentric view,
internal causes alone (volcanism) triggered the gradual extinction
of the Dinosaurs, a lengthy process of many millions of years.
Curiously, the fact that a global impact catastrophe coincided
with the wipe-out of the dinosaurs at the K/T boundary, is somehow
regarded as a freak yet irrelevant coincidence.

As Fred Hoyle and Chandra Wickramisinghe have pointed out in their
latest book (Life on Mars?), the strong beliefs of many Darwinists
does often not falter despite the hardest material evidence. Just
like true believers, they are reluctant to take into
consideration new evidence or even to contemplate that they might
be wrong altogether. This unscientific dogmatism has lingered on
for more than 150 years, and there are no signs that it will be
overcome easily. After all, we are talking about belief-systems -
not hard science.

I have attached below a balanced review about the current state
of the ongoing controversy between the two schools of thought
which was published two weeks ago by the NEW SCIENTIST (16 August
1997). Further information about recent research on related
matters will be posted with a separate message.

The permission by the Editor of THE NEW SCIENTIST to post this
article for scholarly use on the cambridge-conference network is
greatfully acknowledged. The attached text may not be reproduced
or transmitted without prior permission of the copyright holder.

Benny J Peiser

P.S. It is rather curious to note that Bill Napier and Victor
Clube, two of Britain's most eminent catastrophists, are referred
to by the NEW SCIENTIST as "gradualists" - simply because both
have pointed out (even before Luis Alvarez entered the stage) that
cosmic catastrophes and cometary dust veil events can have
long-lasting ecological effects.

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

from: THE NEW SCIENTIST, 16 August 1997, pp. 23-27

WHAT REALLY KILLED THE DINOSAURS?

Was it the short, sharp shock of an asteroid? Or did a slow,
deadly cocktail of causes see them off? New Scientist sifts
through the evidence

ASK ANYONE you meet how the dinosaurs met their end 65 million years ago,
and they're likely to blame it all on an asteroid. And why not?  It's a
dramatic answer and the image of one huge blow obliterating those "terrible
lizards" at a stroke is almost irresistible. But could it have been that
simple? Was that really all it took to wipe out 65 per cent of Earth's
species?

The impact theory has had a firm grip on the headlines ever since
Luis Alvarez of the University of California, Berkeley, proposed
it back in 1980. And 11 years later, the discovery that the giant
Chicxulub crater off Mexico's Yucatan peninsula dated back to just
the right time gave the "catastrophists" a further boost.

But despite the success story, the catastrophists' viewpoint is far from
universally accepted. A group of scientists feel that it is flawed.
"Whatever wiped out the non~avian dinosaurs was a lot more complicated than
a single hammer blow from an asteroid," says Norman MacLeod of London's
Natural History Museum, who is one of the catastrophists' leading opponents.

For one thing, some scientists maintain that it is by no means
established that the impact coincides with the CretaceousTertiary
(K/T) boundary, which is when the dinosaurs became extinct.

What's more, when Alvarez first proposed the asteroid theory, his
principal piece of evidence was a global layer of iridium found exactly at
the K/T boundary. Iridium is rare on the Earth's surface, but more abundant
in space, making the impact of an asteroid a likely cause. Yet there are
alternative explanations, both cosmic and terrestrial, which MacLeod and
others in the "gradualist" school believe account equally well for the
iridium.

Their own view of the extinctions presents a picture of lengthy
decline before the dinosaurs' final coup de grace at the K/T
boundary. So the two camps are quite distinct: one adhering to a
vision of a quick and nasty end, the other to a slow and nasty
end. But both, in the end, have to rely on the main evidence in
the dinosaur debate - the fossil record. According to Peter
Sheehan of Wisconsin's Milwaukee Museum, himself firmly in the
catastrophists' camp: "The community is split right down the
middle. We all have the same data but we come to very different
conclusions."

It is not surprising. The fossil record is sparse, difficult to
interpret, and reveals an extraordinarily complex extinction
scenario at the end of the Cretaceous. Many groups of living
things besides the dinosaurs received their marching orders, while
others sailed through entirely unaffected. Bizarrely, the latter
group included amphibians such as frogs and salamanders, commonly
considered to be vulnerable to the slightest change in the
environment. But according to MacLeod, many dinosaur families had
been declining for millions of years before they all finally
vanished. Other creatures - for instance, two prominent groups of
mollusc-actually took a nose-dive more than a million years before
the boundary, he says.

The catastrophists beg to differ. Sheehan admits that the molluscs died
early, but argues that it had nothing to do with the eventual extinction of
the dinosaurs. "I see very little in the record that doesn't agree with a
catastrophic extinction," he argues. Dale Russell of North Carolina State
University agrees. Though he accepts that some dinosaur groups seem to
disappear in the last 2 million years of the Cretaceous, he believes this
was a local effect confined to continental North America, where a vast
inland sea was withdrawing at the same time.

Gerta Keller, a palaeontologist from Princeton University, is a
convinced gradualist, but she bases her theories not on dinosaur
bones, but on microfossils. Dinosaur remains are astonishingly
sparse - a mere 3000 fossils exist from a timespan of 150 million
years. But Keller's microfossils, the remains of tiny creatures
that also suffered from severe extinctions, are much more
abundant. She has found that the microfossils that suffered most
from the extinctions began to die out more than 100 000 years
before the K/T boundary.

The overall picture, then, is a muddy one. But what does emerge is that the
gradualist alternative to the impact theory - in all its flavours - has not
received nearly the same attention. No one doubts that the impact of a huge
asteroid would have been bad news for life on Earth. But for many such an
impact is not the cause of the majority of the extinctions, but a very
secondary event.

Choking dust

So, what of the primary event? There are both extraterrestrial and
terrestrial possibilities. Anthony Allen of Queen Mary and
Westfield College, University of London, and Shin Yabushita of
Kyoto University in Japan back an extraterrestrial candidate.
They argue that the Cretaceous extinctions came about when the
Solar System passed through the dense core of a giant molecular
cloud (GMC).

Stars like the Sun are born out of these massive clouds of cold
gas. Typically, a GMC will contain the mass of a million suns in
dust and molecular gas, mostly hydrogen. Yabushita and Allen say
it is inevitable that the Sun occasionally passes through the
fringes of such a cloud as it sails through the Galaxy.  Such an
encounter could take a million years because GMCs can be several
light years across.

While it passed through, dust from the cloud would accumulate in
the Earth's atmosphere, where it would reflect sunlight back into
space and severely cool the planet. Simultaneously, the GMC's
gravity would shake up the Sun's reservoir of comets, known as the
Oort cloud, which orbits far beyond Pluto. This would in turn send
more comets than usual towards the Sun, where they would pose a
threat to life on Earth. Such events may account for several of
the mass extinctions that have happened over time, believes Allen.

But choking dust and comet impacts make up only part of the
jigsaw. Allen and Yabushita claim the Cretaceous extinction event
was unique among all such encounters in that the Solar System
passed not through the outskirts of a GMC, but through its dense
core, exposing life to the threat of molecular hydrogen.

Usually, sunlight can ionise all the hydrogen within the Solar System.  But
if the solar neighbourhood were filled with the gas to a density of 100 000
molecules per cubic centimetre, the Sun could not ionise hydrogen as far as
the limits of the Earth's orbit. Crucially, say Allen and Yabushita, this is
the hydrogen density found in a typical GMC core.

So if the Sun passed through such a core, the Earth would spend
hundreds of thousands of years embedded in a cloud of neutral
hydrogen. This would threaten life on Earth, say the researchers,
because the hydrogen would mop up about a third of the oxygen in
the atmosphere.  The hydrogen would penetrate the atmosphere
because the planet's magnetic field, which shields us from ionised
gas, is no defence against neutral gas. And once the hydrogen was
in, lightning would cause it to mix with oxygen and so make water
(Monthly Notices of the Royal Astronomical Society, vol 238, p
146).

According to Allen and Yabushita, the amount of atmospheric oxygen
theoretically mopped up by this hydrogen matches the reduction in oxygen
found in air bubbles trapped in late-Cretaceous amber. Although such
measurements are controversial, with some researchers adamant they are not
pristine, Allen and Yabushita say the drop in oxygen is consistent across
all amber samples.

Deadly cloud

So, the chain of events set off by an encounter between the Solar System and
a GMC would explain why the extinctions took place gradually rather than all
at once, and also account for the Chicxulub crater-presumably the result of
a comet destabilised from the Oort cloud. It could even help to explain why
the Cretaceous extinctions were so selective. "We believe that the creatures
that were disadvantaged were the largest ones-the largest insects, largest
ammonites and largest dinosaurs," says Allen.  "The smaller species with
faster inspiration rates were less affected." Allen admits that such a
differential effect of reduced oxygen on organisms is unproven.
Nevertheless, he says that anecdotal evidence appears to support it.

Other gradualists do not believe that a killing mechanism as
elaborate as Allen and Yabushita's is needed. In the mid 1980s,
Victor Clube of the University of Oxford and Bill Napier of Armagh
Observatory in Northern Ireland pointed out that the lion's share
of cometary mass is to be found in relatively few giant comets,
measuring as much as 100 kilometres across. Meanwhile, working
independently of Clube and Napier, Fred Hoyle and Chandra
Wickramasinghe of the University of Wales College, Cardiff,
explored the effect that such a "super-comet" might have on the
Earth. Now the four have teamed up to present a comprehensive
picture.

They believe that "tidal" forces exerted by the Galaxy as a whole loosen
giant comets from the Oort cloud. Occasionally, such a body becomes trapped
in the inner Solar System, where the Sun sublimates it over many millennia,
causing it to dump large amounts of dust into interplanetary space. The dust
is swept up by the Earth during its orbit.

Eventually, the terrestrial atmosphere becomes clogged with enough
dust to drastically cool the planet. The process takes thousands
of years - a factor crucial to how organisms die off because the
oceans store only about a 10-year supply of sunlight. "Once this
supply is gone, there is no warmth left to stop the ice crystals
forming in the upper atmosphere," says Napier. "The presence of
the ice crystals mean that even when the dust is gone the climate
remains cool." MacLeod points out that there is no evidence of
glaciation at the end of the Cretaceous, but Napier counters that
a climate change as severe as an ice age isn't necessary to cause
a mass extinction. "Prolonged cooling, even without glaciation,
will be perfectly sufficient."

In Napier's scenario, major impacts occur in the dying days of the
supercomet when most of its ice has gone, at which point the rest of
it disintegrates into "cometary asteroids". Even so, these major
impacts are not the main killer: that privilege, Napier insists, belongs to
the dust. "By focusing on impacts, everyone has completely overlooked a much
more serious threat to Earth," he says. Napier's gradualist scenario could
even help to explain an enduring mystery: why extinctions and impact craters
seem to occur every 28 million years or so. Though many palaeontologists are
sceptical about whether this periodicity really exists, it is true that
every 30 million years the Oort cloud is subjected to maximum tidal stresses
for a period of a few million years because the Sun passes through the plane
of the Galaxy at those intervals.

Hellish acid rain

Extraterrestrial models are compelling solutions to the dinosaur
extinction dilemma. But MacLeod believes that an equally dramatic,
but home-grown, event precipitated the mass die-offs of the
Cretaceous: supervolcanism.

The Deccan Traps, a vast plateau in southern India, were created
over a few million years at the end of the Cretaceous when about a
million cubic kilometres of lava gushed onto the Earth's surface.
No eruption in recorded history was even a thousandth as big.
"Near Bombay, the flood basalt is still 2.4 kilometres thick,
after millions of years of erosion," says Dewey McLean of the
Virginia Polytechnic Institute and State University in Blacksburg,
who was the first to argue that supervolcanism caused the
extinctions back in 1979.

The eruption was undoubtedly severe. "The stress it imposed on the
environment would have been phenomenal," says Andrew Kerr of the
University of Leicester. "It beggars belief that the asteroid
impact people can ignore it."

A very similar outburst of supervolcanism, responsible for the
Siberian Traps, coincided with the biggest of all mass
extinctions, the Permian-Triassic extinction, which happened about
250 million years ago. "That involved perhaps as many as 95 per
cent of all species compared with 65 per dent at the K/T," says
Kerr. "And there is little evidence of an asteroid impact at the
time."

Sulphur dioxide unleashed by supervolcanism would have created hellish acid
rain, while an increase in carbon dioxide would have caused dramatic
greenhouse warming. It was this warning that McLean sees as the principal
culling mechanism. "It killed off embryos," he says.

MacLeod's mechanism, refined over the past few years, is not an
obvious one. When the air temperature rises, he says, adult
animals cool themselves by diverting blood to the surface of their
skin. This reduces the flow of blood to the oviducts and
uterus-the sites of fertilisation and of embryonic development.

This is important because uterine blood flow carries damaging heat away from
the region of the uterus and carries nutrien to the developing embryo. "In
cows, the embryo is killed if the oviduct temperture rises by a mere 1 to
1.5 degree C above the optimum during the first cleavage of the fertilised
egg-the day after insemination," says McLean. "Reduced blood flow within the
uterus while an embryo developing can also cause dwarfing an abnormalities
of the skeleton."

Large reptiles also control their blood temperature by varying the
blood flow between their core and skin. McLean says that, during
the rapid greenhouse warming caused by supervoleanism at the end
the Cretaceous, the process of shunting blood away from the

oviducts and toward the skin in female dinosaurs would have caused
their oviducts to heat above the optimum, killing or damaging an
embryos during the critical first cleavage "Times of rapid
greenhouse warming are especially hard on large animals," say
McLean. "Their small surface-to-volume ratios mean that they
retain excess blood heat, increasing the mortality rate of
embryos." So the supervolcanic hypothesis could perhaps explain
the selectivity of the extinctions as well as their gradual nature.

Geologists believe that a superhot blob of mantle rising from the
boundary between the Earth's core and mantle caused the Deccan
supervolcanism. Once this mantle plume reached the crust and spread out, its
tail provided a conduit allowing the tremendous heat of the Earth's core to
melt vast amounts of rock.

Such a mantle plume can explain the presence of a global layer of
iridium at the end of the Cretaceous. Iridium has an affinity for
iron and would have been concentrated in the Earth's iron core
when it formed. "A mantle plume would transport it back to the
surface," says McLean.

If the supervolcanism scenario is correct, the impact of an asteroid at
about the same time was simply a coincidence. In MacLeod's view, the Earth's
biosphere is subjected to a variety of different stresses such as volcanism
and impacts, all of which happen randomly in time.  "Occasionally, however,
such events come together," he says. "This happened at the end of the
Cretaceous, a period of profound environmental change when even the sea
level dropped by 100 metres."

Cretaceous cocktail

Napier has no objection to such a "multiple-whammy" scenario. "I
wouldn't want to ignore the effect of the Deccan Traps," he says.
"I'd be perfectly happy if the Cretaceous extinctions turned out
to have a cocktail of causes."

With so many possibilities, why has the asteroid theory become so
dominant? "It's simple and sensational and it was brilliantly
promoted by Alvarez, a Nobel laureate whose ideas demanded to be
taken seriously," says MacLeod. Proof of how effectively the idea
has been publicised was provided last November by an article about
Chicxulub in the Sunday Times. It ran under the headline "Dinosaur
death: mystery solved".

"When I read it, I couldn't believe it," says Kerr. "The story simply wasn't
true." And MacLeod adds: "I've heard it said that the only thing the impact
idea doesn't have is sex and the Royal family."

Competing with such an attractive idea leaves the gradualists with
an uphill struggle. And the fossil record is messy enough for the issue to
remain unresolved for some time. "I'm not going to change my mind and Norm
MacLeod is not going to change his," says Sheehan. Whatever it was that left
the dinosaurs in the lurch, we can only hope that it's not likely to recur
for a good while yet.



CCCMENU CCC for 1997

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