It is indisputable that nothing in biology makes sense except in the light of evolution, but...

...nothing in evolution makes sense except in the light of Plate Tectonics.

28 August, 2009

Asteroid Smashteroid

Something MUST be at fault. Something HAD to have happened. After all, dinosaurs were one of the most successful groups of animals ever to have lived, weren't they (see Taxonomy, below). They were huge - they were powerful. They dominated the Mesozoic world. There has to be A reason they became extinct.

We are consoled by the tidy fable that the dinosaurs were wiped out by the equivalent of a massive train wreck one fine day 66 million years ago when a beastly great chunk of rock the size of small mountain range rammed the Earth amidships.

"What do you mean, fable?" you might well ask. "Didn't an asteroid slam into the Earth then?"

Yes it did. There is no question about that. Geologists even think we know the impact location (The Yucatan peninsula of Mexico.

The question is, is that what done in the dinos?  After nearly 30 years of wrangling over this one, it looks as though the few lonely, hold-out, mavericks (prime among them (us) Gerta Keller of Princeton Univ), are probably correct in their assertion that the bad bolide is not the sole reason for the mass extinction at the end of the Cretaceous Period, which saw the loss of dinosaurs amongst many other species (but few genera and no other order of taxa besides the dinosaurs). That a big rock from space proably caused some of the extinctions seen in the fossil record around that time is likely. BUT - the asteroid impact - the so-called smoking gun of dinosaur demise has been pretty positively dated to have occurred about 300,000 years before the onset of the MASS extinction. Species which were present in the Cretaceous but which are absent in the Paleogene - the criteria for demarcating the two periods - stubornly persisted AFTER the big crash, much to the chagrin of TV documentary producers who like a snap finsih.

There are alternative hypotheses about what it was that 'done the dinosaurs in'. But in the end, they were simply out-competed by other, non-dinosaurian populations, including their own evolutionary descendants, the birds (not all dinosaurs were big - many were chicken-sized and smaller).  Whether the selection event was protracted over hundreds of thousands of years, or precipitated by some catastrophe or other, the fact is that dinoasaurs were the only entire group (a taxonomic order) which failed to cross the Cenozoic threshold. All other taxa which could in any way be considered competitors of dinosaurs made it across that boundary and survive to this day.

So, with the more and more refined age dating, and the near-inescapable conclusion that the K-T bombshell occurred nearly half a million years before the actual K-T boundary, it seems that the consensus of scientists for two decades was wrong and lonely Gerta Keller and a handfull of others - who were derided as deniers of THE obvious answer - have been right all along. This is science of course, and theories are overturned in favor of data. W might still find something that proves Dr. Keller wrong, but such wouldn't necessarily make the asteroid hypothesis right - that's an "either-or" situation which is just as inappropriate here as it is in the evolution culture wars where creationists say, if evolution doesn't work, there can be only one other alternative - some god..

Now, where I have seen something similar to this before? Oh, I know... That's anpother post, though.
Post a Comment