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Re: Scientists conclude asteroid, not volcanoes, wiped out dinosaurs

I looked at the articles. I don't have access to the actual report. Assuming the data they report backs their conclusions, they are saying that the Deccan Traps occurred over a much longer interval of time than the extinctions, which were very abrupt and correspond to the time of the asteroid impact.

I have several questions.

How do we know how abrupt were the extinctions? Were they really all that abrupt?

Were the Deccan trap eruptions like the Siberian traps, or were they just a series of super volcanoes?

I'm left vague on how much toxic gas was put out by either event.

If the extinctions really occurred very abruptly, within a few weeks of time, what caused this? Volcanic winter didn't cause that rapid a die off.

Also, don't flood basalt volcanoes put out iridium?

Dora Smith
Austin, TX

----- Original Message ----- From: "David Marjanovic" <david.marjanovic@gmx.at>
To: "DML" <dinosaur@usc.edu>
Sent: Saturday, March 06, 2010 5:17 AM
Subject: Re: Scientists conclude asteroid, not volcanoes, wiped out dinosaurs

It's extremely common in science that things turn out to be more complicated than we used to think, and then they turn out to be more complicated still. But this has a backlash -- it appears to be a widespread attitude that simple (or, rather, simple-looking!) explanations for anything must automatically be wrong. That non-sequitur has been a pet peeve of mine for... maybe 15 years now, and I'm only 27.

 I still don't understand why there has to be a single cause, and why
 the Deccan traps must have had no effect?

Because the main episode of Deccan eruptions _ended_ 100,000 years before the end of the Cretaceous, as did the global warming (by 3 to 5 °C) its CO2 outgassings had caused. This has been known since 2003:

Greg Ravizza is one of the 41 authors of the new paper.

 Why it has to be one or the other?

Because that's what the data say, in this case.

 The Siberian traps and CAMP seem to have had an impact.

Yes, but:

The Siberian traps are gihugrongous and set huge coal deposits on fire. That meant much more CO2 and CH4 outgassed than would have been possible otherwise. Despite several candidates, no suitable impact crater has yet been identified, while the stepwise temperature increase and C isotope ratio shift at the end of the Permian fit the volcanic scenario.

A similar fit appears to be present for the Triassic-Jurassic boundary, though there detailed research has only begun, and the CAMP doesn't seem to have been quite that big. It was, however, much bigger than the Deccan Traps.

(Unfortunately, the beginning of the Triassic is currently defined as the first occurrence of the conodont *Hindeodus parvus*. That was a non-event that happened quite some time after the extinction. The beginning of the Jurassic isn't defined yet, but the leading candidate is analogous. I hope they pick a carbon isotope excursion instead, as they did for the Paleocene-Eocene boundary.)