[meteorite-list] Cold hunting?

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:54 2004
Message-ID: <3F611ADE.BB3F6C52_at_bhil.com>

Hi, Rob,

    Actually, I seem to recall that Phil Bland at the Natural History
Museum in London (formerly called The British Museum and always will be
in my head) did a study doing terrestial age-dating all the meteorites
from several given areas, just to get the age distribution and a figure
on how long meteorites survive in a surface location and to get a handle
on the fall rate.
    Somewhere in the Meteorite List archives there's a summary article
on it...
    As I recall, he came up with a terrestial fall rate about 2 to 2-1/2
times the MORP rate, survival times of 40,000 to 50,000 years in deserts
like the Sahara, and very short survival times for chondrites in squishy
Britain. About what you'd expect, in other words.
    Part of his figure of a fall rate only 2-1/2 times the MORP rate in
his study is the assumption that the Sahara has always been as dry as it
is now. The wetter the Sahara actually was, the greater the fall rate
would have to be to produce the existing survivor stones.
    I scrounged around and found a great deal of substantial geological
research done in the Sahara before World War II, when there was much
freer access to the area.
    First, there are extensive surface traces of former waterways and
full riverene drainage systems still visible, enough so that fairly good
maps of the "old" wet Sahara can be drawn.
    Then, there has been considerable research on the "buried" rivers of
the Sahara, where the water still flows, but hundreds of feet under the
surface. These buried rivers connect existing oasises and the pattern of
their interconnection can be determined by a comparison of the dozens of
species of fish that are found only in the buried rivers!
    Now, that must have been interesting research, going fishing in the
Sahara! Amazingly, it turns out that the buried rivers of the Sahara are
(or were) apparently connected to or with similiar buried rivers in the
Middle East and northern East Africa in geologically recent time. (None
of the fish are blind fish as you find in cave ecosystems.)
    Then, there's the neolithic art (12,000 to 16,000 years old) in the
depths of the Sahara, showing hunting scenes with a plentitude of game
animals that are now only found many hundreds of miles south of the
Sahara.
    I was going to send all these references to Dr. Bland but I got lazy
(or stayed lazy) and never did it. Anyway, the point being that more
rocks have to fall on a wet Sahara to produce the existing age
distribution than on an eternally dry Sahara. About twice as many, a
fall rate of 4 to 5 times the MORP rate, because the Sahara wasn't ever
soaking wet. It was sort of like Nebraska, but without the winters.
    I wonder if there isn't some way of factoring out the "finder's
percentage" and deriving not just a minimum fall rate but the actual
fall rate from such an area collection?


Sterling K. Webb
--------------------------------------------------------
"Matson, Robert" wrote:

> Yes -- the MORP study rate is definitely too low. If there's
> a researcher out there that would be interested in terrestrial
> age-dating a representative sampling of my finds, we could
> place a nice lower bound on the annual fall rate.
>
>
>
> --Rob
>
>
Received on Thu 11 Sep 2003 09:01:18 PM PDT