Re: Large animal extinctions: extinction-ex-astra
Fri, 12 Jul 1996 22:58:38 -0400
>This discussion seems to be centered around the merits of an ocean or land
>meteor impact. What if the meteor hit on the North Polar icecap? The ice is
>both deep and firm. The supposed meteor could blow away a mile or more of
>the ice and leave no crater. There would be no fires, nothing to burn. It
>would, though, melt a LOT of ice and possibly initiate the end of the ice
>age. How does this affect the discussion?
Actually, in most places the north polar ice cap is rather thin,
sometimes only a few meters thick, especially in the summer. There are
some places where the ice is as much as a kilometer thick, but overall
one would characterize the icecap thickness as highly variable, with an
average thickness that is significantly less than >1 mile.
I think that any reasonable size meteorite (as in extinction events)
would rather readily punch through most locations in the north polar cap.
The blast wave would easily devastate the ocean bed below, causing
recognizable characteristic ring-like structures. Interestingly, if you
consult you [National Geographic] map of the undersea Arctic Ocean, there
are what looks like to me to be some curious features on the ocean bed.
Of course, by now, the northern floating icecap, which is geologically
young, would have long-ago reformed and not show any scar.
Such a collision would have dramatic ecological effects.
However, when you consider the orbital dynamics of a collision, most
meteorites should impact the leading face of the earth as it orbits the
sun. As the vast majority of meteorites are found in solar orbits that
are in the ecliptic (+- 20 degrees), you would expect that most
collisions should occur in the middle latitudes. Of course, there are
still orbital trajectories which could give collisions at any point on
the earth's surface, but I think the chances of collision would decrease
significantly at the very high latitudes of the upper arctic. If such a
collision occured, the north polar area would just be a less likely place
to find it.
I think that data should rule in this case. Until we find supporting
evidence (for example, shocked rocks from core samples, wave debris
deposits, magnetic anomolies, local gravitational variations, tektite
debris fields, etc.), we simply cannot give this explanation very much
The extinction of large animals in the Americas coincided with the
arrival of Clovis man, a fierce hunter. Given the choice of two
explanations for the extinction events, man or a meteor into the icecap,
Occam's razor would suggest that man's influence is likely to be most
important. Other possible choices, such as other (more normal) causes of
dramatic climctic change causing the extinction events would also be a
more likely explanation, in my opinion, than meteorites.
(I understand how much fun speculation can be!)
"Truth, like beauty, is in the eye of the beholder."
> - Garak, "Deep Space Nine"