[meteorite-list] Re: hunting

From: Kelly Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:40 2004
Message-ID: <3AB48539.97D14342_at_bhil.com>

colin wade wrote:
"Here's one for Kelly to work out .... typical distance run per hash
~6km, 2.2m width 90% probability of detection , 1m either side say 50% ,
total area searched 3 X 400 X6k m^2 , 7.2km^2, length run 2400km"

Dear Colin,
    Assuming that higher fall rate I personally believe in, 7.2 square
kilometers would receive one piece of a fall every 1000 to 1200 years
(instead of the 3000 to 4000 years the MORP rate would predict).
    Since this is a desert environment, a stone would persist for a long
time if undisturbed and not transported. The Moroccan stones (NWA's)
seem to have ages of 5000 to 40,000 years, for example. So, Qatar could
have an average of 3 to 8 stones every square kilometer (depending on
which rate of fall you use) if they have accumulated for 40,000 years.
    I'll chicken out on two points, though. Statistics is, well,
statistical; it assumes the distribution of meteorites is random, but of
course in reality, they fragment and fall in clusters (the strewn
fields). If your 7.2 square kilometers was the ellipse of a strewn
field, it could have 20 stones on it (or 200 or 2000). So, where you
find one, you should look for others.
    The other chicken-out point is geological change. Has Qatar been a
desert environment for 40,000 years? As recently as 10,000 to 12,000
years ago, most of what is now the Sahara was a well-watered grassland
with scattered forest patches and lakes, supporting a rich game
population, which in turn supported a happy population of
hunter-gatherers. Even 2000 years ago, North Africa was a breadbasket
for the Romans. How much wheat do they grow in Libya today?
    There was at least one British archeologist (Bibby) who thought that
Bahrain was the location of Dilmun, the unidentified seat of a
mercantile empire that traded with Sumer and the Harappan cities of the
Indus valley 6000 to 8000 years ago. If so, it's hard to imagine that it
was then the same hard baked brick of a land that it is today. Ur was a
much nicer neighborhood back then, too, as I hear tell...
    Sorry, but this is a sore point with me. I know I can't convince my
Illinois farm neighbors that if they had lived here 12,000 years ago,
their house would have a half-mile thick stab of ice for a roof, but it
annoys me that even archeologists seem to ignore the geology of their
own digs. There's a famous cluster of them working the Illinois River
valley down to the 12,000-year+ level (that's one really deep hole!)
where, they insist, humans suddenly appear culturally full-blown, which
they interpret to mean they have dated the first arrival of humans.
    I can't seem to get across to them that all they have dated is the
sudden appearance of the Illinois River! Before glaciation, all the
midwest US rivers, even the mighty Mississippi, didn't exist; the entire
central US drained slowly and sluggishly to the north by now vanished
rivers which emptied into Hudson Bay and the Arctic Ocean. When the ice
melted, the land rebounded, and now everything runs south like crazy.
    So, I'd have to ask, how long do we know Qatar has been an arid
environment?

Kelly Webb
Received on Sun 18 Mar 2001 04:51:54 AM PST