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Re: Theories on the extinction of dinosaurs
On Sun, 21 Nov 1999 Dinogeorge@aol.com wrote:
> So by your definition there
> is zero evidence for >any< kind of cause for any mass extinction.
True. Therefore we ought to look closely at contemporary mechanisms,
mechanisms we do have evidence for.
> For that matter, we still have no proof of causes of >local< extinctions,
> just a bunch of speculation...
Okay. But we _do_ have tons of evidence for the operation of various
mechanisms and their effects on populations; such things as habitat
fragmentation, alien species' invasions, disease.
> Whole subject of extinction needs to be carefully rethought and redefined,
> including such concepts as cause and effect as inferred from coincidences in
> fossil record.
But glib assertions of asteroid-sufficiency suppress the pursuit of such
> Bad things happen all the time to animals, so you can expect
> lots of coincidences among such bad things everywhere in the fossil record.
> Most of the time these yield no mass extinctions; why not? On the other hand,
> when a mass extinction occurs at the same time as a documented asteroid
> impact that scatters itself all around the globe, why should we infer no
And when massive basalt flows gum up the atmosphere; continent-draining
deprives habitat; species invade...should we also infer no connection?
And basic problems remain with the premise of asteroid sufficiency.
Indeed, even the notion of mass extinction needs examination. I don't mean
its mechanisms but its very existence. Lillegraven and Eberle question
its relevancy among vertebrates of the Lance. They say there are only two
remarkable things revealed in their fossil collection: the disappearance
of dinosaurs and appearance of immigrant mammals. In other words, among
terrestrial vertebrates _there was no mass extinction_.
I read the study you mentioned. Here again it seems more opinion than
anything else as to whether dinosaur extinction should be tied to the
asteroid. Sheehan says words to the effect of: Such huge asteroids only
hit Earth once every 160 million years. The chances of this happening
just at the time of dinosaur extinction are very slim and the events are
therefore likely connected.
I beg to differ if this is supposed to be logic.
Firstly, as you say above, bad things are happening to animals all the
time. For example, if an asteroid hit today, future speculators might
blame our current mass extinctions on it. If it hit 3000 years ago, the
pyramids might appear to be a tribute to it. If 10,000 years(?) ago, it
caused the Ice Age. And so on.
Secondly, the appearance of a connection may be more an artifact of the
biased attention we give to dinosaurs (over other extinctions).
Something super-extraordinary must have caused it. That something, for
us, is an asteroid. But, for an alien observer, someone who sees cosmic
events all the time, they may not feel there is anything out of the
ordinary in an asteroid smoking a planet--it happens all the time. On the
other hand, they may feel that a truly extraordinary event is the rise of
badger-sized placental mammals. To the alien, this may be a
once-in-a-universe event. That dinosaurs disappeared just at _this_ time
might to them seem like a connection.
I don't see how you can distinguish between these points of view in any
meaningful/scientific way. I maintain the Earthling (you) and the alien
(me) both have valid points of view and that we must await more data to
actually confirm one or the other. I urge this more global view on you.