Wednesday, February 01, 2012

My Library: T. Rex and the Crater of Doom

No, this isn't a Harry Potter knock-off. The full title is "The story that waited 65 million years to be told -- how a giant impact killed the dinosaurs, and how the crater was discovered", by Walter Alvarez.

This is one of the books I spent ~$100 on in the museums of DC a few years back. Believe me, if I hadn't put a limit on myself, I would have come home with a few dozen pounds of books without any difficulty. Why did I pick this one out? Because the discovery of the crater and the confirmation of what killed the dinosaurs was pretty big news back when I was in middle/high school. And, frankly, who doesn't love dinosaurs? Dinosaurs are awesome.

Dr. Alvarez was one of those who spent more than a decade hammering out the science of the KT extinction, and this book is more than just a scientific explanation of the research, the theory, and its confirmation; it's also a personal tale. More than a decade? KT? 1) Yes. Science takes a very long time. You can find out in just one test that you've been wrong for years, while it can take years to prove that you're right. And even then, it could just be that you haven't been proven wrong yet. 2) KT stands for "Cretacious-Tertiary", the two geological periods in question. The Cretacious (spelled with a 'K' in German) was the end of the dinosaur age and the Tertiary is ours. There is a distinct dividing line between the two and a very clear mass-extinction event. Below the line you have an abundance of dinosaurs and plants and microbes of the Cretacious age. Above that line you have a world with much of its life, at all levels, wiped out.

There are several reasons why the impact theory was so difficult for Alvarez to espouse and prove. Proof is a difficult thing to come by for an event sixty-five million years in the past. If a comet or asteroid lands in the ocean, there's a very good chance that it will be erased by the forces of plate techtonics, for example. Erosion, subsidence, tectonics, all these things collude to hide and erase evidence. Also, for much of this, Alvarez and his collaborators were working blind, having to devise models and hypotheses with nothing to guide them. If there were an impact, what would the evidence for it be?

The other problem, advocating the hypothesis, was that geology had been dominated for a very long time by the doctrine of uniformitarianism. Geology was a popular pastime in the eighteenth and nineteenth centuries. Gentlemen (and one or two ladies) with a little time and a little hammer could venture out into the country and collect a few rocks or fossils and learn a bit about the world. However, absent radiometric dating and the like, they could only tell that some rocks were older than others (sedimentation and volcanism being somewhat understood, it was clear that the higher the layer of rock, the younger it was), but not their absolute ages. Thus early geology was fraught with argument from two different schools. One was a very Christian school, which advocated for a young Earth dominated by catastrophic processes like floods and earthquakes. They came up with some clever, albeit entirely incorrect, explanations and were known, among other names, as Catastrophists.

Eventually the Catastrophists were wiped out* by the other school of thought, the Aristotelian Uniformitarians, who believed the Earth to be much older and dominated by slow, gradual, relatively uniform processes. This school eventually won because, let's face it, the evidence was on their side. It gradually became clear that sedimentation and other geological processes were quite slow, and the layering of rock requires many eons. Also, there was a fairly popular theory developed in the middle of the 19th century by and English parson that explained the origin of the species by means of natural selection, which was evidently perfectly correct on its face and which also required vast eons of time to work its wonders.

Thus the uniformitarian view dominated geology, and still dominates it today. And this is good, because it's correct. The geological processes of the earth are quite slow because they involve the motion of rock and rock is not, by any measure, a hasty or intemperate medium. Geologists are and were of course aware of such things as earthquakes, tidal waves, and volcanic eruptions, but those are the end results of very slow processes, rather than sudden events in and of themselves. According to standard geological theory as of forty years ago, the extinction of the dinosaurs was a gradual event, the result of climactic shift over millions of years. This was apparently supported by the fossil record, as dinosaur fossils don't occur at the KT boundary. That fact has since been explained by statistics; fossils are very rare and in the event of a catastrophic extinction, you should expect a gap such as you would also find for a gradual extinction.

Alvarez and his collaborators (all named in the book) were not alone in advocating for occasional catastrophes. For example, geologists Pardee and Bretz spent decades arguing and proving that the scablands** of Washington state were formed by the sudden release of a glacial like when the glacier damming the lake melted; a literal flood. Not, perhaps, coincidentally, Bretz and Pardee were honored with the Penrose Medal (the highest award of the American Geological Society) in 1979, shortly before Alvarez began trying to explicate the mystery of the KT extinction.

They happened upon the idea of an extraterrestrial event almost by accident. In attempting to find out about the KT boundary, the question first asked by Alvarez was, "How long did it take to form?" and, on the suggestion of his father, he looked at iridium levels. Iridium is rare on earth, as it mostly sank to the core when the planet was still molten, however the countless bits of space dust that rain down on the planet every day shower us with small amounts of iridium all the time, so Alvarez looked to use it as a tool to determine the length of time for the boundary to form. The answer was wildly unanticipated (much higher levels of iridium than either a slow or fast deposition would indicate) and led them to the notion of a large impact.

The book documents many surprising successes, much satisfaction of a job well done, and a number of disappointing false leads. It concludes with the event that I remember from school, the discovery of the crater itself, buried under the Yucatan Peninsula of southern Mexico. Along the way it shows how years of dedicated work by many, many geologists around the world helped transform geology from a uniformitarian science to a uniformitarian science with occasional episodes of catastrophe.

The book is a bit basic for someone with a master's degree in science (me) but I think it covers all the necessary information well enough that anyone with a high school education should be able to follow it. It's also a fairly short read; I re-read it in order to write this (it had been a few years).

You know what the best part is? The science is still happening. Was the extinction event a single massive impact, or multiple? Did volcanism (the Deccan Traps) also play a part and how much? How long would an impact-winter last? Why did some species survive and not others? How exactly did the impact devastate the globe? Science is fun because there's always more answers.

Next: The Voyage of Argo by Appolonius of Rhodes

* Not entirely. Religious fundamentalists who like to stick their fingers in their ears and advocate, in the face of literal mountains of evidence, for a Young Earth, still believe things like the Grand Canyon were created in a very short period of time by a global flood.

** How evocative!
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