[meteorite-list] Antarctica vs. NWA masses

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:32 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86901B4EC40_at_US-Torrance.mail.saic.com>

John asked,

> Could the effects of glacial movements up against the mountains
> in Antarctica actually keep a larger percentage of heavier pieces
> buried deeper in the ice longer, while a larger number of smaller
> pieces would have surfaced first?

The exact answer depends on a lot of factors, including average
precipitation rate (currently extremely low -- Antarctica is a
desert), sublimation rates, terrestrial ages of falls, and meteorite
mass, density and friability. My guess is that the current meteorite
size distribution on the ice is not that far different from what has
fallen. Relatively recent large falls may still be buried, but
this should be a small fraction compared to the total accumulation
of material over such a long terrestrial lifetime.

There is still unavoidable human sampling factor, since larger
specimens can be spotted from greater distances than small ones,
but this factor is far less consequential in Antarctica than in
Northwest Africa, or most anywhere else for that matter. Perhaps
the more important factor is institutional sampling bias. With
Antarctica, everything gets classified; not so with NWA. As
others have already pointed out, NWA sampling bias skews the
statistics toward rarer types -- but I believe it also skews the
statistics toward larger specimens.

Bottom line is that the larger average mass of classified NWA
meteorites is not a reflection of fall statistics, nor is it
an indication of odd goings-on in Antarctica. It's simply a
case of institutional meteorite triage, perhaps coupled with
larger average finds in NWA due to more difficult search
surfaces.

Cheers,
Rob
Received on Mon 11 Aug 2003 12:57:38 AM PDT