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Re: impacts are cool!
> Or the math is off. The crater's only a couple hundred kilometers in
> diameter even by the largest estimates, which is a heckuva lot smaller
> than Mars.
A bullet can puch a hole in something quite a bit larger then its
diameter. The size of the crater and whatever global havoc the impact
causes is indicative of the kinetic energy released by the impact, not
just the size of the actual bolide. Kinetic enery equals mass times
velocity SQUARED; the speed of impact is more important in determining the
destrcutive potential of an impact then the size of the projectile.
As far as the crater being "smaller then Mars", not all of the energy
is directed into producing the crater; energy directed upward and outward
by the impact wouldn't contribute much to making the hole, but could
cause other effects; like vaporizing a whole lot of water. There are lots
of different ways to play around with the numbers, but they are all BIG
numbers. Nearly all impact scenarios predict a fairly impressive potential
for shaking things up all over the planet.
The fact that not all mass extinctions correlate in time with
impacts, and the fact that other known impacts are not demonstratively
tied to extinctions (or at least relatively smaller ones) certainly
suggests that an impact is not by itself enough to trigger a major mass
extinction; but it could certainly be an aggravating factor.