[meteorite-list] Re: hunting
From: meteorites_at_space.com <meteorites_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:40 2004
On Sun, 18 March 2001, Kelly Webb wrote:
> 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
> Kelly Webb
These are very good points, Kelly. I have read that much of what is now the hard baked Sahara was 10,000 years ago a lush green land supporting a wide variety of wildlife and flora. The question that should be investigated is how long does it take for a meteorite in say average conditions to survive and still be recognizable as meteorites? Also, many of the Sahara meteorites may have fallen during a time when the environment there was like the US Midwest, and maybe even before that. I think meteorites can survive longer than what was here-to-fore believe. Look at all the big finds that Nininger made in the semi-arid Midwest. It would be interesting to see what the terrestrial age dates come out on those. But then again I think that the terrestrial age date model is flawed, as there are at least one clearly recent fall-find that was dated at 13,000+ years (Lafayette, IN) But perhaps on a statistical average it might work.
Then, look at the meteorites that are being gathered at Gold Basin... They say that these are at least 20,000 years old, and look at their condition-- they are not too bad. (And I suspect that many of the so called "Gold Basin" meteorites are in fact many different falls)
Steve Schoner, AMS
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Received on Sun 18 Mar 2001 03:20:00 PM PST