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Quartz
12-03-2006, 12:12 PM
It's widely (but not wholly) accepted that the dinosaurs were wiped out by a massive meteorite impact at Chicxulub. But around the same time we have the Deccan Traps and the birth of the Atlantic. Did the Chicxulub meteorite cause these?

Polycarp
12-03-2006, 12:43 PM
The Atlantic Ocean began to form with the rifting of Pangaea (or, to be more specific, of Laurasia, as Gondwanaland was already separating) about 200 million years ago. In other words, the Atlantic was beginning to form or in existence for the majority of the time the dinosaurs were flourishing. While particular new developments in its formation may have contributed to the decline of the dinosaurs, it is definitely not reasonable to identify a geomorphic action around 130 million years old at the time as a significant cause.

The Deccan Traps appear to have been caused by the passage of India in its voyage north to collide with Asia across a hot spot off the coast of Madagascar. This was deep-mantle upwelling, of the same sort that today has caused the Hawaiian Islands. There seems no plausible connection between it and Chicxulub other than their being synchronic events (over a geological time frame).

However, though the popular press, with its fondness for dramatic disaster scenarios, would have us believe that scholars are united behind the concept that "the Chicxulub impact killed off the dinosaurs," in point of fact there is still a great deal of healthy debate on the relative impacts of the Chicxulub impact, the Deccan upwelling, evident climatic change at about the same time that may or may not be caused by either or both the other changes....

In short, the answer to your question is "No" -- and the fact of the matter is that Chicxulub is a "smoking gun" in one of those classic "with a twist" murder mysteries in which it may well turn out that Mr. Boddy died of a heart attack when confronted by an intruder with a gun, and his habit of inhaling lava fumes contributed to his death. ;)

Polycarp
12-03-2006, 12:54 PM
Just to add one other small variant on this, there's pretty strong evidence that the dinosaurs died off at "almost precisely" the time of the Chicxulub impact -- the K-T boundary is fairly clear across most of the available strata from that period. But "almost precisely" here means "within the order of a million years" -- hardly simultaneous to anyone but a geologist or cosmologist! And if if's demonstrated that dinosaurs were in decline (a question itself hotly debated) prior to the K-T event, then you might have a "false cause" scenario:

Consider the following hypothetical series of events: Another Indian Ocean earthquake, a big one, creates a tsunami substantially stronger than the Boxing Day event. It impacts westernmost Java squarely, and wipes out a lot of wildlife -- including the few surviving Javan rhinoceroses (R. sondaicus). Now, they're a protected species, formerly much more widespread (as their distant cousins the Sumatran rhinoceros remain). But what has threatened them is the spread of humans, the infamous "rhinoceros horn" medicine superstition, the decline of habitat, etc. It would be grossly in error from any reasonable ecological sense, though technically true, to say that they were driven extinct by tsunamis.

The Scrivener
12-03-2006, 12:57 PM
Did anybody else read this thread title and wonder if it had anything to do with old record labels (Atlantic, Decca... with Chicxulub being perhaps a Latin or world music label) and their shady business practices? :o

Polycarp
12-03-2006, 01:37 PM
Did anybody else read this thread title and wonder if it had anything to do with old record labels (Atlantic, Decca... with Chicxulub being perhaps a Latin or world music label) and their shady business practices? :o

You think shady business practices on the part of record labels may have had some relationship to the extinction of Marc Bolan's group (http://en.wikipedia.org/wiki/T._Rex_(band))?

Exapno Mapcase
12-03-2006, 05:07 PM
This is a timely question. A new study puts additional weight on the meteorite-being-the-sole-cause side:

New evidence that meteorite killed the dinosaurs, MU researcher finds (http://www.stltoday.com/stltoday/news/stories.nsf/sciencemedicine/story/309881DECE8825D78625723600175A80?OpenDocument)
It took just a single meteorite impact to do in the dinosaurs, according to a University of Missouri at Columbia geologist.

A growing body of evidence shows that a massive meteorite, crashing into Mexico's Yucatán Peninsula, triggered the mass extinctions of 65 million years ago.

But some geologists have debated the exact timing of the impact, saying it doesn't quite line up with the extinctions. They suggest other events — additional impacts, lava flows or climate change — could be to blame. Or maybe the stress of Earth's gravitational field ripped a large asteroid into several smaller ones that hit all at once, much as the comet Shoemaker-Levy 9 broke into 21 pieces before it hit Jupiter in 1994.

Yet new rock samples taken from deep sea sediments support the theory that a single impact at Mexico's Chicxulub crater was all it took, says MU paleontologist Ken MacLeod. His study is in press with the Geological Society of America Bulletin.

Note that the article does what Polycarp says the popular press doesn't do: present several sides of the argument. I don't agree with him that popular science articles are all that one-sided in general. I think that they've backed off considerably from the early days after the notion first became widely accepted.

The Scrivener
12-03-2006, 08:11 PM
You think shady business practices on the part of record labels may have had some relationship to the extinction of Marc Bolan's group?

No, but you should hear the paleontologists argue over the demise of Dinosaur Jr....

Meurglys
12-04-2006, 07:54 AM
Some scientists believe they have discovered an immense impact crater under the ice in Antarctica which, they postulate, may be the site of the impact that caused the Permian Extinction event.
Apparently, also they think that certain lava outflows in Siberia (which was directly opposite their crater at the time due to Continental Drift) may be a direct result of the impact.

No idea if the Deccan Flats area was opposite Chicxulub when it struck...

No exact cite; it's in an article in the current New Scientist (http://www.newscientist.com/home.ns) magazine I was browsing through.

Polycarp
12-04-2006, 08:56 AM
This is a timely question. A new study puts additional weight on the meteorite-being-the-sole-cause side:

New evidence that meteorite killed the dinosaurs, MU researcher finds (http://www.stltoday.com/stltoday/news/stories.nsf/sciencemedicine/story/309881DECE8825D78625723600175A80?OpenDocument)


Note that the article does what Polycarp says the popular press doesn't do: present several sides of the argument. I don't agree with him that popular science articles are all that one-sided in general. I think that they've backed off considerably from the early days after the notion first became widely accepted.

This is truly helpful.

And, lest I be misunderstood, I was not reconstructing the Myth of the Monolithic Media here. Rather, I intended my comment to say that typically newspaper and popular-magazine journalism tends to find hypotheses of disaster scenarios far more newsworthy than hypotheses of gradualistic, multivariant-cause effects. Tell me as a newspaper reporter that woolly mammoths died off from a global pandemic of elephant worms, it's a much better story than that they died off from a combination of a half dozen causes including a decline of mid-latitude taiga as the ice retreated. And certainly newspapers that have had the sense to assign reporters interested in science to tackle science stories (e.g., NY Times, Raleigh N&O, Seattle P-I among others) will try to do balanced coverage of differing views among reputable scientists.

The fact that the Siberian and Deccan Traps respectively are closely associated temporally with the two most famous (largest?) mass extinctions tends to suggest some connection. Perhaps it takes the combination of massive Traps-style areal-flow vulcanism and asteroid impact to trigger a really serious MX event.

Which, of course, makes me wonder what anomalistic events (vulcanism, impacts, etc.) are associated with the lesser MX events -- post-Devonian, post-Triassic, Eocene, etc. As well as what if anything was immediately ante-Cambrian (or perhaps ante-Vendian) that qualifies along these lines.

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