[FPSPACE] Dinosaurs Demise by Chicxulub impact Challenged (Severely)

[Peter Pesavento]

>From the National Science Foundation website

 

http://www.nsf.gov/news/news_summ.jsp?cntn_id=114648
<http://www.nsf.gov/news/news_summ.jsp?cntn_id=114648&govDel=USNSF_51>
&govDel=USNSF_51

 

Press Release 09-076 
New Blow for Dinosaur-Killing Asteroid Theory

Impact didn't lead to mass extinction 65 million years ago, geologists find

April 27, 2009

The enduringly popular theory that the Chicxulub crater holds the clue to
the demise of the dinosaurs, along with some 65 percent of all species 65
million years ago, is challenged in a paper to be published in the Journal
of the Geological Society on April 27, 2009.

The crater, discovered in 1978 in northern Yucutan and measuring about 180
kilometers (112 miles) in diameter, records a massive extra-terrestrial
impact.

When spherules from the impact were found just below the Cretaceous-Tertiary
(K-T) boundary, it was quickly identified as the "smoking gun" responsible
for the mass extinction event that took place 65 million years ago.

It was this event which saw the demise of dinosaurs, along with countless
other plant and animal species.

However, a number of scientists have since disagreed with this
interpretation.

The newest research, led by Gerta Keller of Princeton University in New
Jersey, and Thierry Adatte of the University of Lausanne, Switzerland, uses
evidence from Mexico to suggest that the Chicxulub impact predates the K-T
boundary by as much as 300,000 years. 

"Keller and colleagues continue to amass detailed stratigraphic information
supporting new thinking about the Chicxulub impact, and the mass extinction
at the end of the Cretaceous," says H. Richard Lane, program director in the
National Science Foundation (NSF)'s Division of Earth Sciences, which funded
the research. "The two may not be linked after all."

>From El Penon and other localities in Mexico, says Keller, "we know that
between four and nine meters of sediments were deposited at about two to
three centimeters per thousand years after the impact. The mass extinction
level can be seen in the sediments above this interval."

Advocates of the Chicxulub impact theory suggest that the impact crater and
the mass extinction event only appear far apart in the sedimentary record
because of earthquake or tsunami disturbance that resulted from the impact
of the asteroid.

"The problem with the tsunami interpretation," says Keller, "is that this
sandstone complex was not deposited over hours or days by a tsunami.
Deposition occurred over a very long time period."

The study found that the sediments separating the two events were
characteristic of normal sedimentation, with burrows formed by creatures
colonizing the ocean floor, erosion and transportation of sediments, and no
evidence of structural disturbance.

The scientists also found evidence that the Chicxulub impact didn't have the
dramatic impact on species diversity that has been suggested.

At one site at El Penon, the researchers found 52 species present in
sediments below the impact spherule layer, and counted all 52 still present
in layers above the spherules.

"We found that not a single species went extinct as a result of the
Chicxulub impact," says Keller.

This conclusion should not come as too great a surprise, she says. None of
the other great mass extinctions are associated with an impact, and no other
large craters are known to have caused a significant extinction event.

Keller suggests that the massive volcanic eruptions at the Deccan Traps in
India may be responsible for the extinction, releasing huge amounts of dust
and gases that could have blocked out sunlight and brought about a
significant greenhouse effect.

-NSF-

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.friends-partners.org/pipermail/fpspace/attachments/20090430/7bcf6922/attachment.html