[meteorite-list] Meteorite-Greenhouse Gases Combo Linked to Mass Extinction

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Oct 25 13:57:46 2006
Message-ID: <200610251757.KAA17055_at_zagami.jpl.nasa.gov>

http://www.zeenews.com/znnew/articles.asp?aid=331416&ssid=26&sid=ENV

Meteorite-greenhouse gases combo linked to Mass Extinction
zeenews.com
October 25, 2006

Washington: So what triggered the mass extinction of the
dinosaurs some 65 million years ago? Was it a giant meteor impact or a
volcanic activity? Neither of the two, according to a latest study by
plant fossil expert Nan Arens of Hobart and William Smith Colleges in
New York.

According to her, it was not a single activity like a meteor impact or a
volcanic eruption but something known as the press/pulse theory of mass
extinctions that brought about the end of great lizards.

According to the press/pulse theory, "the worst die-offs happen when
some sort of interminable, multi-generational pressure on life is
combined with a few powerful blows". She believes some species might
already have been vulnerable when the triggering event occurred.

To test the idea, she and her undergraduate student Ian West compiled a
large database of marine organisms and their extinctions through
geological time.

They divided the last 488 million years into four groups: Suspected
meteor impacts (pulses), gigantic volcanic flood basalt eruptions
(presses), periods with neither presses nor pulses, and times when press
and pulse coincided, and compared average extinction rates in each of
these groups.

Flood basalt eruptions are considered "presses" because they release
vast amounts of greenhouse gases into the atmosphere and can change the
Earth's climate.

The researchers found similar extinction rates when a pulse or press
occurred by itself, and when neither effect was occurring.

"However, when an impact occurred during a time of volcanic flood - that
produced higher extinction rates," Discovery News quoted Arens as saying.

"The goal of our work was to come up with a unifying theory of mass
extinctions. We also wanted to make the theory applicable to the rapid
extinctions now being seen as a result of accelerating climate change
(press) and the ongoing destruction of wild habitats by human activities
worldwide (pulse)," said West.

Gerta Keller of Princeton University said the study had "essentially put
in a more eloquent way what other palaeontologists had been saying for
many years".

"Namely that the impact-kill hypothesis is all wrong. Impacts alone
could not have been the killing mechanism for the K-T or any of the
other major mass extinctions. I'm very happy they have done the analysis
based on the literature and come up with the same conclusions that
palaeontologists have been preaching all along," said Keller.

Arens is presenting her work on October 25 at the annual meeting of the
Geological Society of America in Philadelphia.
Received on Wed 25 Oct 2006 01:57:43 PM PDT