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Re: Bernd: Meteor May Not Have Destroyed Dinosaurs Afterall?

>It has always been my understanding that the debris from a major impact
>would plume into the upper atmosphere.  My gut feeling is that the rising
>vapor from any boiling oceans, while possibly rising higher than normal
rain
>formation, would not make it up as high as the existing, spreading, dust
>blanket.  Therefore, the dust could not be 'rained out' as it would exist
at
>a higher level than any recycling effects water vapor might have.
>
>Best Regards,
>Julia


I think this amounts to another popular misconception Julia. Ask yourself
just what, exactly, is keeping the dust up there, in the upper reaches of
the atmosphere?

In the lower atmosphere large dust particles quickly settle, while smaller
dust particles rise and fall many times due to air currents. In the upper
atmosphere, where the air is thinner and air movement is more directional
(i.e. less chaotic), only the smallest of particles remain suspended - the
rest fall under the influence of gravity to the weather-forming layers. To
suggest that particles stay in the upper atmosphere for many years, as
someone put it, doesn't tie in with atmospheric physics as I understand it,
and would appear to suggest that the dust defies gravity!

Another point to bear in mind is that, post-impact, the atmosphere would be
very turbulent with considerable mixing of the various layers. The
atmosphere would tend to quickly settle into a state of equilibrium, largely
gravity-driven. That would make it more likely for atmospheric particles to
be filtered out.

When the idea of a K-T impact was first suggested some scientists (mainly
astronomers) assumed a period of post-impact freezing would occur due to
large quantities of dust in the atmosphere blocking out the sunlight. That
would help to explain the extinction quite nicely and it has become quite a
popular scenario. But subsequent research does not seem to favour any
extended cold period (e.g. the Denver research). Much of what has been
written about the effects of giant impacts amounts to little more than
guesswork by people venturing outside their own areas of expertise.

Regards,

Phil Bagnall
www.ticetboo.demon.co.uk



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