25 May 2007

When Worlds Collide

Ever since widespread consensus was reached last decade that a meteorite was at least partially responsible for the extinction of the dinosaurs (among other organisms) at the end of the Cretaceous, it's been en vogue to try to show that meteorite or comet collisions can be linked to all the major mass extinctions. I'm usually very skeptical of such studies, which are often highly speculative and smack more of self-promotion than of good science. That said, it's never worth shooting such hypotheses down without having first heard the evidence used to formulate them. With that in mind, I went to a talk last Friday given by two professors from the anthropology department here at Oregon. It was, in effect, a practice talk in advance of the official presentation of their findings this week at the Geological Society of America's meeting in Acapulco. The research group - which consists of 26 (!) members from representing many different fields - had come across several lines of evidence that seem to suggest that a small meteorite, or more likely a comet, smashed into Michigan 13,000 years ago. These lines of evidence included such things as an iridium spike and nannodiamonds, both of which are generally associated with some type of extraterrestrial impact. I was ready to be a skeptic, but I have to admit, their argument was very compelling. While the impact itself would have been relatively minor, the authors suggest that such an event in an area that was then covered by glaciers would shatter ice dams holding back massive glacial lakes, wreaking havoc on ocean circulation and, by extension, climate.
As anthropologists, the presenters I saw were most interested in how the impact might have affected North American paleoindian society. I was more interested in a topic they touched upon only briefly. For several years, one of the most contentious debates in paleontology has been the argument over whether humans are responsible for the extinction of large "Ice Age" mammals (megafauna). It's been a particularly vitriolic debate, with each side having its share of convincing arguments, bad science, and flat-out name-calling. This comet hypothesis will no doubt light an entirely new fire under a cauldron that's already been boiling for some time. As such, I have no doubt that the findings of this will be debated and subjected to several rigorous geological, anthropological, and paleontological test, and I for one look forward with great interest to seeing how well they hold up under scrutiny.

1 comment:

Hans said...

w00t! *raise the roof* Late Pleistocene Extinctions!

On very rare occasions, someone will suggest an impact in the Holocene was responsible, however the work you talk about is the first credible look at Pleistocene bolides as responsible for the extinctions (at least as far as I am aware).

The extinction is, of course, mediated by climate, and this view of climate caused extinctions is certainly not new. It is (in my estimation) one of the principle hypotheses behind the extinctions. So the real question, therefore, lies not in paleontology but in climatology. The novel hypothesis is not that climate caused the extinctions, but appears to be that an impact caused the Younger Dryas.