Friday, March 05, 2010

KT Extinction Jury Reviewed: Chicxulub Guilty

There is a lot of bluster out there about the recent paper in Science about the KT Extinction. An international panel of scientists went over the KT extinction data as presented by the Impactists and Vulcanists, those that favoured the Chicxulub Impact or the Deccan Traps as the killers for the end Cretaceous Extinction. That panel was made of 41 scientists and it was international in character. In the end, they stated that the KT Extinction was overwhelmingly backed with evidence that the Chicxulub Impact was what did the deed.

One of the very crucial arguments that the Vulcanists have been using is that the ecosystems of the Maastrichian had been under stress from the Deccan Traps. The panel found that for the 500k years prior to the end of the Cretaceous, the ecosystems of the world hadn't changed much. If the Vulcanists were right, there ought to have been a prolonged change that caused the ultimate collapse. There wasn't anything that was really major that took place. No gradual grind or collapse as the Deccans spewed their foulness into the world's atmosphere. As I noted before, dinosaur fossils have been found on the Indian subcontinent between the basalt layers from the Deccan Traps signifying that the DTs were not even capable of wiping out the local dino population, let alone the world's. However, this study confirms that and then some.

There are a handful of things that I was not aware of:

"There are also monster submarine landslides along the entire East Coast of the U.S. from the massive earthquake triggered by the impact," [Norris] said.
Very worth highlighting:

In some sites close to the impact, around the Gulf of Mexico and the Caribbean, there are two spherule-bearing layers, at times separated by sediment a few meters thick, and some of the recent controversy stems from this apparent duality. The lower layer consists of coarser particles including spherules and shocked minerals, and the upper layer consists of finer particles and has a higher iridium content.

"Reports of multiple horizons with elevated iridium concentrations fairly close to the Chicxulub crater have led to a lot of confusion, and suggestions of multiple impacts," said fellow author Greg Ravizza, a marine and environmental geologist at the University of Hawaii at Manoa. "A key point that cannot be ignored is that data from several sites far away from the Chicxulub crater provide no evidence of multiple large impacts. This observation lends very strong support to the careful stratigraphic synthesis in our paper demonstrating the very complex, and frequently disturbed, character of the sections closest to the Chicxulub crater."

The panel was able to discount previous studies that suggested that the Chicxulub impact occurred 300,000 years prior to the KT extinction. The researchers say that these studies had misinterpreted geological data that was gathered close to the Chicxulub impact site. This is because the rocks close to the impact zone underwent complex geological processes after the initial asteroid collision, which made it difficult to interpret the data correctly.

The number of links and bits are enormous. I really missed out yesterday by dealing with VCs rather than having time to blog about this. Look at Revisiting Chicxulub and Asteroid Killed Off the Dinosaurs. I'll add a link to the science abstract as soon as I can see it.

There's an awesome website using the google earth plug-in for the effects of the impact here.

Even so, I doubt that Dr Gerta Keller will concede defeat. :)


Unknown said...

The most interesting part for me is the separation of the sediments. With the impact markers, spherules and shocked minerals, meters below iridium, it's as though there was a time delay of high precipitation before the airborne material settled. I can imagine that for an aquatic hit. Muck up the sea wherein the heavy material precipitates fairly quick, leaving the finer materials, including actual asteroid materials, which would suffer the highest fragmentation, to settle later.

I find CT fascinating if for no other reason, to know what might mark the end of our reign.


Tor Bertin said...

When I graduated high school four years ago, my mom and I took a sort of 'scientific pilgrimage' to Chicxulub. One of the coolest moments of the trip (and seriously, possibly my life thus far) was visualizing the asteroid body crashing down on the distant horizon. Quite visceral.

Anonymous said...

I think one of the main reasons the vulcanist hypothesis gained so much traction is that during the last days of the dinosaurs, the only site that actually preserved what was going on in the terrestrial biota was Hell Creek (at least, the only one heavily studied). And there were some weird things going on in Hell Creek. One could say that it was due to a prolonged volcanic spurt, but one could also argue that the change in the local ecosystem that was going on back then, namely the inland seaway receeding and the climate shifting.

Anonymous said...

Science is not matter of polling. Scientific "panels" are somewheat suspicious. Why panel? Panel against whom? Keller? This is attempt to win scientific controversy using gross force. Sorry, i don't like it.

Will Baird said...

Panels are an attempt at reducing individual bias, anon. This isn't an attempt at bullying. Also, science is often a consensus activity.

This isn't the first time a panel for the KT extinction has been convened. They tried it during the early 90s and Keller, btw, participated. It was inconclusive for a lot of reasons. This is done about 17 years later and with more work done to review it.

You are aware of the Snowbird conferences, too, right?

The KT/KPg Extinction seems solved. There's little to no controversy left.

In fact, I'd bet in five to ten years, the PT Extinction will have reached this point. We're really close as is,'ll take more time just to be sure. A lot was learned from the whole KT study experience, so, other than a few unfortunate bits of grandstanding, the PT Extinction seems to have had less lashing out than between those in the KT studies.

The Triassic, Ordovician, and Devonian are where the action is at now.