05 August 2008

Uncommon Commentary #17: Asteroid Asininity

The reason for the dinosaurs' extinction is not known and probably never will be; the explanation most in vogue nowadays, however, is the one that I consider the least plausible of all, viz., that our prehistoric friends died out because an asteroid or meteoroid (not "meteor" or "meteorite") or comet or something struck Earth. Many scientists have a disagreeable penchant for speaking on matters of conjecture as if all the facts were known (at least to them), and this habit is never more irritating than when they and others behave as if the cosmic-collision conceit had won universal acceptance. Proponents never address what I consider to be the obvious objection (to this and to most other alleged causes of "mass extinction"): Why would this putative cataclysm have caused the extinction of all archosaurs (dinosaurs and their reptilian relatives) except for the crocodilian lineage, along with toothed birds and the nautilus-like ammonoids, but not of the many species that survived into our time, the Cainozoic Era?
Some concrete evidence has actually been put forth in favor of the supposition that I'm doubting, although, notably, the supposition came first. This evidence is that "The PT Boundry [sic] contains large amounts of iridium--unnatural to the usual earth composition…" (http://periodic.lanl.gov/elements/77.html) This inadequate statement refers to 1) the Permian-Triassic Boundary, which marks the onset of the archosaur-dominated Mesozoic Era, and 2) an element often found in asteroids. Since the demise of the dinosaurs took place at the end of the Mesozoic, it had nothing to do with the event suggested by that unusual abundance of iridium, but perhaps it resulted from the same sort of occurrence (even though no similar discovery has been made concerning the strata laid down when the dinosaurs went extinct, which happened 65 million years ago, give or take a few weeks). Such speculation does not, however, answer the question that I've raised as to how this catastrophe could have been selective. A disaster that poisoned the atmosphere, for instance, would have effected the disappearance of air-breathing animals, but not of fish and other creatures that extract oxygen from the water; it's inconceivable that any kind of condition would leave the crocodylians unscathed but lead to the perishing of their closest relations. There may be key information that I am missing, but, if so, defenders of the theory are at fault for not providing it. Really the whole issue is a bogus one, since, after all, extinction is normal, and survival for many millions of years is not; that's why the term "living fossil" applies to an exception to this rule. Too many scientists, unfortunately, suffer from an intellectual hubris that won't permit them to concede that there's anything they don't know. Tempting as it might be to declare that iridium has solved the mystery, it's hard to avoid concluding that the asteroid-impact is a palæontological deus ex machina, serving not to quash ignorance but to disguise it.