Thursday, December 07, 2006

Debating Chixulub

A theory is better than its explanation ~ H. P. Woodward

Sixty-five million years ago, the dinosaurs shuffled off this mortal coil, and it's generally agreed on what dispatched them. The creatures appear to have been in decline, most likely due to climatic changes, possibly aggravated by huge lava eruptions that formed the Deccan Traps. Then, as if things weren't bad enough, a meteor came crashing down and finished them off.

Now, one version of the meteor's effects is that the entire planet caught fire, burning all the vegetation and all the dinosaurs who didn't have asbestos feathers, followed by a long-term winter caused by all the debris thrown into the air, which killed off all the vegetation (again) which caused the remaining dinosaurs to starve to death. This is the “dumb version” model. I've written before about this extreme description and how silly it is.

A more reasonable explanation is that the dinosaurs, as said were in decline. A meteor whacks the planet, causing huge amounts of damage on the continent where it impacted. It further throws tons of debris into the air, probably generating a prolonged period of cold which would have depleted the vegetation stocks. This would have probably caused the remaining herbivores to bite the dust. With the plant-eaters gone, the meat-eaters would have been very hard up for food and would undoubtedly gone to that big Cretaceous Park in the sky.

Of course, it would be nice if there was a crater to find that dated to around the time of the dinosaurs' demise, but we've got a reasonably big planet which is geologically active and has around 75% of its surface hidden under water. Not finding a crater would not mean that there was no meteor. Even without the hole in the ground, it's clear some sort of intervention from outer space occurred, because in the geological record at the point at which the dinosaur fossils disappear (known as the K-T boundary), there is a thin, dark, iridium-rich layer, and iridium is not common on Earth. It's most likely source would be from a significant meteor impact.

Despite the odds, a few years ago a crater was found off the Yucatan peninsula that was created 65 million years ago. The crater, dubbed Chixulub, was formed by a huge rock and would have readily accounted for the iridium layer. Bingo, say the scientists. The “smoking gun” has been found.

Initially, theorists laid the bulk of the blame for the mass extinction on the Chixulub event. As time has gone on, the other factors mentioned above have been recognized as precursors that would have made an impact event all the more devastating to the dinosaurs. Generally with few exceptions, paleontologists seem to have accepted the scenario of climate change (probably influenced by the Deccan eruptions) punctuated by the Chixulub impact as ringing down the dinosaur epoch.

Then along comes Gerta Keller from Princeton. The article I mentioned above was partly inspired by a program on the Science Channel (I think it was) that was pushing Ms. Keller's theory, which, to cut to the chase, is that Chixulub was not the cause of the extinction event. After generating a fair amount of misinformation, the program revealed that Ms. Keller thought another meteor was responsible. Well, she's mulled it over a bit, and now she's decided that there were a number of meteors of which Chixulub was only the first, according to this. In addition, the Deccan traps played a part, and the actual killer meteor may have landed where the traps were.

Thus, since last spring, when she was on TV, she's added more meteors, but she still has as her main goal the discrediting of Chixulub as the cause. In fact, that seems to be the only reason for her research. It was what she set out to prove, and by golly, she found evidence, at least in her mind, that proves it. Unfortunately for Ms. Keller, others have evidence that says otherwise.

In the TV program, in my opinion, most of her “proofs” were reasonably refuted, so I was a bit surprised to see her releasing a paper so long after the original report of her theory. However, she evidently did some reworking and gathered additional data. Now someone else has gathered even more data.

A study lead by Ken MacLeod of the University of Missouri, Columbia, investigated more core samples, this time along the northeast coast of South America. You can read the article for the details, but, basically, they indicate no evidence of another impact beyond that of Chixulub.

Ms. Keller reacted by saying that the core samples must have been “rearranged” or have sections “missing.” She describes the results as “rather hyper-inflated.” In other words, her basic response is, “Is not! Is not!”

Essentially, that was her response to criticisms of her theory on the TV program, where she said those who disagreed simply had too much investment in the Chixulub theory to let it go. Rather than respond to the criticisms, she merely dismisses them as professional churlishness.
Which is pretty lame.

I can't say categorically that she's wrong because I don't have the expertise to evaluate the evidence myself. I will say that every refutation of her theory I've seen makes sense. Ms. Keller's responses sound weak by comparison. Much of the basis of her theory lies in analyzing sediments that were thrown up by the impact of the Chixulub meteor, which are a hodgepodge of layers folded up and over one another. And, frankly, it seems that she approached those sediments with the idea of discrediting existing theories, not with the attitude of investigating with an open mind.

Ms. Keller may be on to something, but I am always suspicious of grandiose announcements “disproving” accepted theories. The goal of science is discovery, not disproving things. Einstein did not set out to disprove Newton's view of gravity, rather he expanded on it. Darwin did not set out to disprove Biblical creation; he sought to understand how we and the other creatures of the planet got to be the way we are. In investigating the universe around us, scientists often replace old theories aside; it's what scientific investigation is all about. But setting out to invalidate a theory isn't impartial investigation. It's almost like trimming jigsaw puzzle pieces to fit where you want.

You'll still get a picture; it just won't make much sense.

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