PLEASE NOTE:
*
Date sent: Fri, 04 Apr 1997 12:57:01 -0500 (EST)
From: HUMBPEIS <B.J.PEISER@livjm.ac.uk>
Subject: NO MASS EXTINCTION?
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
"LITTLE EVIDENCE FOR A CATASTROPHIC MASS EXTINCTION"?
Have you ever wondered how the 'giant comet' hypothesis
of Bronze Age collapses could be accurately tested?
Obviously, the debate about and the scientific tests on
the K/T boundary event and the mass extinction of the
dinosaurs could give us at least some faint clues.
Instead of looking for iridium layers or massive impact
craters, however, one would expect to find clear evidence
for widespread and simultaneous pattern of
site destructions which cannot be explained according
to any alternative physical scenario. Yet, the K/T
boundary debate also demonstrates just how strong the
opposition to neo-catastrophism in some parts of the
scientific community still is.
If, as was initially claimed by Luis Alvarez and his
team, a catastrophic mass extinction occurred at the end
of the Cretaceous period, the smoking gun (i.e. iridium,
layer & massive impact crater) and the dead body (i.e.
extinct species) had to be detected. Since both pieces of
evidence have been discovered over the last 15 years, the
comic origin of the K/T boundary catastrophe is now
widely accepted.
However, as William Glen has pointed out in one of the
best books on the K/T controversy [W. Glenn, ed. THE MASS
EXTINCTION DEBATES: HOW SCIENCE WORKS IN A CRISIS,
Stanford University Press, 1994): An impact's
instantaneous global effects fly in the face of
gradualism, geology's (and archaeology's) philosophical
paradigm.
In view of this 150-year old dogma, it is not that
surprising that a number of palaeontologists still doubt
whether a mass extinction occurred at the end of the
Cretaceous - regardless of the growing evidence. In fact,
some gradulists even question whether any mass extinction
ever happened.
The following article from the NEW SCIENTIST (5 April
1997, p. 19) summarises the latest attempt to saveguard
the almost extinct belief of nineteenth century
"gradualism". However, if even the K/T boundary event
is
still that controversial, the advocates of "coherent
catastrophism" might just as well brace themselves for
similar criticism and reactions. But then, I guess, it is
excatly these intellectual contests for scientific
truth and progress which make research and debate such an
enjoyable activity.
Benny J Peiser
P.S. Perhaps I should remind the sport enthusiasts among
the non-UK list members that another and equally exciting
contest, the 150the Grand National in Liverpool
(Aintree), will take place tomorrow. Mud-loving Suny Bay
seems to be a fair bet - that is, if it rains tomorrow.
In the unlikely event of glorious sunshine, you might be
wiser to put your money on Avro Anson.
-------------------------------------------------------
The New Scientist, 5 April 1997, p. 19
DID SEA-LEVEL FALL KILL THE DINOSAURS?
Changes in the earthly environment may have played a much
bigger part in killing the dinosaurs 65 million years ago
than exotic visitors like asteroids, claims a new
report.
British researchers studying the fossil record of
extinction at the end of the Cretaceous period - when
the dinosaurs and many other species disappeared - now
suggest that most died out gradually as falling sea
levels and volcanic eruptions took their toll. Most
palaeontologists believe that the mass extinction was the
result of a dramatic change in climate caused by an
steroid crashing into what is now Mexico.
The team, led by Norman MacLeod of the Natural History
Museum in London, looked at changes in the populations of
a wide range of plants and animals at the end of the
Cretaceous. MacLeod says their results show that a few
groups of species showed no change. Others declined
gradually, he says, and only single-celled marine life
showed a sudden decline at the time of the asteroid
impact. There is "little evidence for a catastrophic mass
extinction," he says.
Instead, he says, the species died out due to several
environmental changes. Most extinctions were caused by a
drop of 100 metres in sea level, and when volcanic
eruptions in India threw debris into the atmosphere. The
impact in Mexico, he says, merely killed off a few
stagglers. The team's 28-page report appears in the
latest issue of the JOURNAL OF THE GEOLOGICAL SOCIETY
(vol 153, p. 265).
Few impact advocates seem swayed by the claims, however.
According to the London team, ammonites - hard-shelled
cousins of the squid and chambered nautilus - declined
for 11 million years before finally vanishing. But
Charles Marshall of the University of California at Los
Angeles says there is clear evidence that the impact
killed half of to three-quarters of ammonite species that
lived along the French and Spanish coast towards the end
of the Cretaceous.
Proponents of the impact theory admit that some
extinctions came before the asteroid. But dinosaur
specialist David Fastovsky of the University of Rhode
Island says that "there is absolutely no evidence" that
dinosaur diversity dropped drastically before the impact.
Fastovsky suggests that MacLeod failed to take into
account the limitations of the fossil record. The only
good records of dinosaurs in the last 10 million years of
the Cretaceous, he says, come from western North America
in the final two million years of this period. Others
were not preserved, reducing the apparent diversity.
Jeff Hecht, Boston