# Re: Theories on the extinction of dinosaurs

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Larry Febo wrote:

> It seems that the size of the crater would be determined by both the mass of
> the object, and it`s speed. directly proportional to the mass, and
> proportional to the speed raised to the power of two.

It is proportional to these two factors, but not directly so. It's mostly a
function of total kinetic energy.  When an impactor is this energetic, even
zenith angle doesn't affect the size or shape of the crater very much.

> If they could
> (perhaps???) predict the size of the bolide from the amount of Iridium
> spread around (or some other method), then they would know the speed from
> the size of the crater. Seems better than trying to average the speed over
> that huge range of values (which translates into an even greater range of
> energy produced,  being the square of the velocity).

They try.  One of the problems is the difficulty in determining the size of the
crater.  Without a good size, it's hard to get a good energy estimate.
Quantifying from Iridium residuals is iffy, too.

> I personally would suspect a larger bolide, and much less speed. This way
> you get the appropriate sized crater, with less energy produced by the
> impact.

Your line of reasoning escapes me.  What physical interaction could lead to this
effect?   Also, we know that the impact velocity MUST be greater than 7.5
mi/sec.   Plus, an increase in size decreases the number of possible impactors
and the probability of an impact, while moving the velocity toward the extremes
of the bell curve reduces confidence in the estimate.  With no hard data, I'd
worry about the statistics if I weren't in the middle.  If you're going to
deliberately choose a low probability impactor, why not just go for a small
interstellar interloper at VERY high speed.  As long as we're guessing, I'd
rather think it was just a common local body doing it's everyday thing.

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