Intriguing Question

Maybe they're to busy on the Gobi and there abouts, digging up Dinosaur fossils! Maybe you and I should get some financing to get the natives to recognize and search for meteorites!!
10-15 years from now they too will be search out! Don't forget the Kalahari. It's perkin right now!! Jerry Flaherty

Hi Peter, List,

This question also puzzled me some time until I learned that deserts in Mongolia are rarely sand deserts but rather grass filled steppes or a kind of bush where it is not easy to spot dark meteorites. I learned that from a meteorite hunter who had an (unsuccessful) try some years ago. This is of course probably not valid all throughout that country.

I also guess not all areas were explored (roads are quasi inexistant in most parts).

And, yes, it seems permission from Chinese is needed, possibly also an "expertized" official guide....?

This possibly does not explain all but the grass-like steppe is certainly a reason.

Happy New Year again to all (from Portugal, where I spend some time in Lisbon university and where I may devote some rare free hours in...looking for meteorites...(dealers ? collectors ? exhibits ?))

Happy hunting,

Zelimir

Hola Peter, All,
I know individual aspect of your questions have been addressed, but
I'd like to as well...

>I know the Sahara desert is about a galgillion square miles.
Then there are the deserts in Calif., South America, the Antarctic continent
and God only knows where else. Why don't I see any meteorites from the
Gobi desert, or maybe the Mongolia desert.

Well, yeah, it's big.  But the main reason that there are more
meteorites found in the Sahara than elsewhere is because there are
more people looking.  There are just as many martian and lunar
meteorites elsewhere, but they tend to be harder to recognize due to
harder hunting terrain (similar rocks, etc) - and because there are
probably twenty or so meteorite hunters in the southwest who get out
into the wilderness with some frequency - probably a few more, since
Franconia became popular.  Compared to the undefined number of hunters
who have been scouring the Sahara for the past decade, well, it's just
not much of a comparison.
Same goes for South America, though Antarctica has seen a good deal of
thorough hunting, as results would suggest.

>And then there is little dinky Roosevelt Co, NM at just 2,455 sq
miles and it has a
staggering
109 meteorites, which comes to one for every 22.5 sq miles. What gives?

This is due to, as has been said, the hunting of Skip Wilson, who has
spent years in the area, hunting blowout after blowout with remarkable
success.  A good bit of hunting land paired with his diligence has
turned up pretty spectacular results...
That said, the density of meteorites that actually exist on the land
should be, at the very least, several per square mile; yes, many have
been found, but there are still countless more waiting to be
discovered.

>They are of a wide variety of classifications, so it can't be turning
every piece in
for classification. I can't speak for anyone else, but I find this
very puzzling.

I don't see why he couldn't be turning every stone in for
classification; data gathered suggest that smaller falls would be more
common than larger ones, and this would mean that the majority of
falls would consist of small, individual stones.

I also don't know how many of his finds have been paired with one
another, but I have the feeling that if he has been concentrating on
individual areas (as opposed to moving on whenever he finds a
meteorite), it would stand to reason that he has found at least a few
paired meteorites, whether or not they are listed as such in the
catalogue.

Regards,
Jason

Hi Jasoon, Peter and the List,

Some thoughts on why the Sahara is so productive:

Another significant factor is the climate over the
past several thousand years. The sahara and parts of
the American southwest have been dry for a long time,
this increases the terrestrial recognizability time of
any meteorites that are there. The sahara has another
interesting and significant factor having to do with
the sand dunes; slowly moving dunes provide a soft
landing and a protective environment as meteorites are
covered by a slow moving dune. Later (sometimes much
later) meteorites are uncovered in great shape with
significant terrestrial age.

Another factor is economic; most of us in the US that
hunt meteorites do so on weekends and vacation time.
Our motivation is to get out in nature and do a bit of
'big science'. Many of the hunters in the sahara are
subsistance hunting, many are truely professional full
time hunters. I get in 25 days of meteorite hunting
tops per year, the locals in the sahara get in well
above 100 days per year in many cases. They have in
many cases spent their lives in the desert. I have
only spent a total of 10 or 12 weeks in the areas
where I hunt. They are better at seeing the odd rock.

A few American hunters that are retired and in good
health likely pass the 100 days per year in the field
hunting mark. I hope to be one of them in 12 or 13
years:)

Pat

Hi, All,

> The [S]ahara and parts of the American southwest
> have been dry for a long time...

The American SW, yes. The Sahara, no. It's desertification
began in the eastern Sahara about 14,000 years ago and
worked its way slowly west. Cyrene on the Egyptian-Libyan
border was a flourishing Greek city-state 2700 to 2200 years
ago, then dried up and blew away.

Western North Africa was the "breadbasket" of the Roman
Empire and was still producing agricultural surpluses for
Rome as late as 400 CE. Agriculture was practiced more than
200 miles further inland from the North African shore than
is possible today.

During the most recent glaciation, the Sahara was a bountiful
land with a substantial Neolithic population. Some 8000 to
10,000 years ago, most of the interior Sahara was grassy
plains with scattered forests, lakes and rivers. The present
progressive desertification of the Sahara is irreversible because
of runaway sand generation The Sahara will be a desert now
for millions of years to come, most likely.

Sterling K. Webb

Pat, Sterling, others,

moving or resting sand is not conserving meteorites but is one of the major threats to the preservation of meteorites. Most if not all meteorite aggregation fields in the Sahara have one thing in common: they are free of sand. In fact they are shielded against the sandflow by ridges or mountain chains, e.g. the Djebel al Aswad is bordering the east of the Dar Al Ghani.

These natural barriers that prevent the sand from entering certain areas are commonly situated in the east or northeast of the aggregation field. And the winds on the African continent tend to blow from the northeast during the whole year since at least ten thousand years.

The surface horizons of the meteorite concentration areas such as the HAH and the DAG are mostly composed of pebbles and top soil and are free of quartz sand.

Terrestrial lifetimes of meteorites decrease as soon as quartz sand is involved due to the quick mechanical abrasion.

It is true that meteorites found in aggregation areas in the Sahara were sedimented and protected by soils from wheathering before the recent wind erosion uncovered them. This process started about 12 - 10,000 years ago and continues until present. But these sediments that are being eroded today were not composed of quartz sand.

There is a good paper on the mechanisms responsible for meteorite concentration in the dense aggregation areas by Schlueter et al. :

J. Schlüter et al. (2002) The Dar al Gani meteorite field, Meteoritics & Planetary Science 37, 1079-1093.

I fully second Sterling's post on this subject but take the liberty to add, that desertification in the Sahara may not be such an irreversible process as suggested.

A single acacia growing on a hammadah or on an erg-surface accumulates soil in a radius of 25 - 40 meters. This soil layer can reach up to 1 m height during the lifetime of the plant. A climate change involving a noticeable growth of humidity, triggerd by a change of e.g. ocean currents, would soon lead to the spreading of Savannah vegetation into the Saharan voids.

Cheers
Svend