[ExI] New Blow For Dinosaur-Killing Asteroid Theory
dan_ust at yahoo.com
Wed Apr 29 15:28:21 UTC 2009
--- On Tue, 4/28/09, John K Clark <jonkc at bellsouth.net> wrote:
>> the Chicxulub impact predates
>> the K-T boundary by as much as 300,000
> So the largest impact in at least 100 million years and
> probably MUCH longer
> happened at just about the same time (300,000 years is a
> mere trifle even if
> true) as a HUGE mass extinction and it's all just a big
I'm not so sure. I'm not aware of the resolution involved here. If it's precise enough to be certain, then, IMO, it would seriously call into question that the Chicxulub impact caused the extinction event.
> You are in a massive thunderstorm and see your friend
> struck by lightning,
> you run to him and see he is dead. Maybe the lightning
> didn't kill him,
> maybe he had a stroke a tenth of a second before and was
> already dead
> when the lightning hit him. Well maybe, but probably not.
I think that analogy doesn't fit the case well. Let me try one better. It's more like you find a bunch of skeletons -- human and other animals -- in a valley. The skeletons are decades old. You're not sure what killed them. Then you find evidence that there was a forest fire there. You think the forest fire was around the same time, but let's say you can't date it to the specific year or month at this time. Let's say you know if happened sometime in the 1920s and the bodies seem to date back to 1926. Do you know if the fire caused the deaths?
> Having said that I must also say I find it odd that the
> huge volcanic Deccan
> Traps in India occurred at just about the same time as the
> impact and the
> extinction. Everything seemed to be going wrong at the same
> time; but if it
> didn't we wouldn't be here.
That's kind of what I thought reading Archibald's book years ago, but it really depends on whether an impactor of that size can cause the kind of (postulated episodic?) mantle upwelling. Also, regarding the Deccan Traps, there's seems to be some evidence the Triassic-Jurassic extinction event -- one much smaller than the K/T one, it appears -- was caused by volcanism, specifically the whatever formed the Central Atlantic Magmatic Province. There's much debate on this, but it could show that massive volcanism sans an impactor not only happens but can cause mass depletions or mass extinctions.
Ditto for the end Permian event, but the evidence seems, to me, even more sketchy there.* My guess is: Come back in twenty years and a lot of what's considered the majority view on all these extinctions will be heavily revised.
* A recent and decent (IMO) lay summary of this is _Extinction: How Life on Earth Nearly Ended 250 Million Years Ago_ by Douglas H. Erwin. A sad shortcoming of this book, though, is he hardly talks about the organisms themselves.
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