Re: Large animal extinctions - part 1

Dan Evens (
Wed, 10 Jul 1996 10:11:28 -0400

Wallace Neslund wrote:
> 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?

I think a meteor large enough to have caused any significant extinction would
still have cratered the rock etc. under the ice. Anyway, I'd expect you could
still go look for the remnants of the impact.

In many ways, it does not matter whether it is an ocean impact or a polar ice cap
impact. Meteors come in at 30 km/s or so, so they are in the ice for maybe 1/10th
second or less. It really makes very little difference whether it is ice or liquid.
The ice will use up a little more energy getting melted, but overall, that will
make not much difference. At 30km per second, you need something like 6 cubic
meters of rock to equal a megaton of tnt. If you had a meteor that was 10s of meters
in size when it impacts, you get one HELL of a big explosion no matter where it
hits. (That number is a vague recollection. It comes from the fact that a retrograde
orbit meteor has the cute feature of one cubic meter of rock giving you roughly the
equivalent of one megaton. Retrograde meteors come in at about 70km/s.)

In some ways a water/ice impact is worse than a ground impact. You get huge waves of
superheated steam rushing out. Anything in the near distance (100's of km? more?)
gets flash cooked.

I don't know enough about polar ice to know if 10K years is too long for ice features to
survive. The feature would certainly be gross enough for it to survive if it is possible.

The preceding are my opinions alone and have nothing
whatever to do with my employer. I don't even know what my
employer thinks. I'm not even real sure who the CEO is.
Dan Evens