[meteorite-list] Experts Clash Over Demise of the Dinosaur
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Feb 2 13:39:36 2006
Experts clash over demise of the dinosaur
By Roger Highfield
The Daily Telegraph
February 2, 2006
The giant impact that shook the Earth
65 million years ago is still sending out shock waves, triggering a
scientific feud over whether the event really killed off the dinosaurs.
Efforts to identify what wiped out the great creatures have been
confused by evidence of massive volcanic activity in India at the same
time, and a fossil record that suggests the dinosaurs disappeared
gradually as the Earth's climate and geology changed over millions of years.
Now a bitter row has broken out on CCNet, a scholarly electronic
network, over a paper by Peter Schulte of the Universit?t
Erlangen-N?rnberg and colleagues in the journal Sedimentary Geology:
they conclude that two cores drilled in Brazos, Texas, provide new
support for the much-loved disaster movie scenario.
With Robert Speijer, Hartmut Mai and Agnes Kontny, Mr Schulte concludes
that the evidence is "unequivocal" that debris and "ejecta" sent out by
the impact coincides with the timing of the mass extinction.
Their work is the latest to back a remarkable hypothesis proposed in
1980 by the American father-and-son team Profs Luis and Walter Alvarez,
who came to a cataclysmic conclusion after studying a thin layer of
dirty sulphurous clay in Gubbio, Italy.
This clay marked what scientists call the K-T boundary, the junction
between rocks in which the fossils of dinosaurs are found, and those
above, in which dinosaur bones have been replaced by more modern creatures.
>From the chemistry of the clay, the Alvarezes deduced that there had
been a giant impact 65 million years ago, now called the Chicxulub impact.
The new paper, says the German team, "provides no evidence that
Chicxulub predated the K-P (K-T) boundary and allows for unequivocal
positioning of the K-P (K-T) boundary at the event deposit".
Not so, say detractors on CCNet. Prof Gerta Keller of Princeton
University accused the team of "ignoring scientific methods", making
claims with "no basis in fact" and "circular reasoning" by assuming a
K-T age for the Chicxulub impact when this age is in doubt and predates
the mass extinction.
Another detractor, from Utrecht University, denounced their "firm
conclusions claiming 'unequivocal' certainty".
Though common wisdom among many scientists favours an asteroid strike
ending the age of dinosaurs, one group of scientists remains doggedly
undecided about this vision of apocalypse: dinosaur experts.
Angela Milner, of the Natural History Museum, London, said yesterday:
"There is absolutely no consensus as to whether there was a sole cause
and what it was. The feud does not involve people who work on dinosaurs,
but sedimentologists and hard rock geologists."
The only thing that everyone can agree on is that the dinosaurs became
One problem is that the fossil record seems to show a gradual demise of
some dinosaurs, and of many other species, well before the actual impact.
For example, an obscure group of molluscs, called rudists, studied by
Peter Skelton at the Open University, slowly declined to only a few
species by 66 million years ago - a million years before the asteroid hit.
And there are other mass extinctions that seem free of devastating
impacts. The biggest happened about 250 million years ago, when 95 per
cent of life was extinguished. Vast flood basalts of exactly that age
are found in Siberia.
Many Earth scientists have come up with a different scenario for the
demise of the dinosaurs, blaming it on volcanic forces.
The issue matters to more than just academics. The demise of the
dinosaurs is of enduring interest to the public. And the world looks for
lessons from the past about the effects of global climate change or
asteroids striking Earth.
Received on Thu 02 Feb 2006 01:16:06 PM PST