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Admin
Apr
29
Image Credit: Dawn Endico
Conventional wisdom tells us that the dinosaurs went extinct as a result of a massive asteroid strike about 65 million years ago, which created the Chicxulub crater in the Northern Yucatan peninsula. The asteroid, with its estimated 10km diameter, caused an environmental catastrophe that wiped out the dinosaurs, and a good deal of other life as well. Of course the problem with conventional wisdom is that it’s not always right. There never really was a handy northwest passage, and the world didn’t turn out to be flat.
The meteor impact may suffer from a similar problem (the problem of being wrong, that is). A new study lead by Gerta Keller (Princeton) and Thierry Adatte (U of Lausanne) suggests that the Chicxulub impact preceded the KT boundary by about 300,000 years. They found no decrease in diversity immediately after the impact line, suggesting that the extinction was caused by something else, like the Deccan Traps volcanic eruptions.
This is pretty interesting stuff. Most theories these days regard the Chicxulub impact as the “straw that broke the camel’s back,” the event that triggered the KT extinction. Many groups, including the dinosaurs, were in fairly serious decline long before KT, a decline usually attributed to the effects of increased volcanic activity (less sunlight, greenhouse effect, etc). If the Chicxulub impact is to be removed from the equation, a reevaluation of volcanism and other factors would seem to be in order.
But the real problem here is that the asteroid impact hypothesis seems to have become conventional wisdom, when from a scientific standpoint, it was never really anything more than one of several plausible options. If there are any geology types lurking around here, I’d love to hear your opinions. What does this new study mean for you? Feel free to comment.
You wrote: “Many groups, including the dinosaurs, were in fairly serious decline long before KT, “.
During the Late Cretaceous? The Latest Cretaceous? The Latest Maastricthian?
References, please?
During the Maastricthian.
I was probably a little generous in writing what you quoted, because there is a fair bit of debate over the strength of the evidence for the decline. In geological terms, the decline was rapid regardless of whether it occured before or at the KT boundary.
The main evidence for a gradual extinction comes from North America, especially the Hell’s Creek formation in Montana.
Here are the sources I used:
A general overview of the theories:
http://www.ucmp.berkeley.edu/diapsids/extinctheory.html
A couple pages dealing with the gradul decline issue:
http://palaeo.gly.bris.ac.uk/communication/Belton/evid.html
http://palaeo.gly.bris.ac.uk/communication/Belton/intro.html
A page dealing with the Deccan traps volcanism:
http://filebox.vt.edu/artsci/geology/mclean/Dinosaur_Volcano_Extinction/pages/studentv.html
If you have further information or a different opinion on this stuff, feel free to speak up!
Can the fossil record of the geological column be really broken down in to “slices” so fine that you can prove that, say 250 000 years or 275 000 years after the impact there still was the pre-extinction variety of species around?
Ah, that question didn’t make sense, I’m afraid, (once again I tried to wreste with the English language and it got out from under me and banged me on the head). Maybe someone can still understand it and can tell me I’m pathetically ignorant of geology matters.
The question made sense to me! The answer is that I don’t know, but the people who did this study seem to think so.
Here is a quote from the Sciencedaily article:
“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.’”
and also:
“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.”
Full ScienceDaily link:
http://www.sciencedaily.com/releases/2009/04/090427010803.htm
While the debate is far from easy to follow, one has to realize that lots of uncritical data flow around. Those websites mentioned, for instance, ‘nicely’ leave out the only really thorough statistical valid study of the way the dinosaurs died out, done by Peter Sheehan.
http://www.dinodata.org/index.php?option=com_content&task=view&id=685&Itemid=25
or other interesting stories when you plug in “sheehan dinosaur extinction” in Google
Most of the rest of ‘gradual decline’ of dinosaurs is hearsay, and “common wisdom” on the part of vertebrate paleontologists, who are caring a great deal about restoring fossils, but not much about statistics.