[meteorite-list] Past Climate of the Shara Desert was "Cold hunting?"

From: Paul <lenticulina1_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:54 2004
Message-ID: <20030912133133.82002.qmail_at_web21413.mail.yahoo.com>

On Thu, 11 Sep 2003 20:01:18 -0500
In the thread "Cold hunting?"
Sterling K. Webb, stated:

>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.

Actually, there has been a significant
amount of recent research. This and
earlier research is summarized on a few
web pages and available on-line.

The best of them are:

1. AFRICA DURING THE LAST 150,000 YEARS
by Jonathan Adams at;

http://members.cox.net/quaternary/nercAFRICA.html
http://www.esd.ornl.gov/projects/qen/nercAFRICA.html

In that web page, Dr. Adams stated:

"SAHARA
(dates in Guo et al are given in 14C years
ago on the left, approximate calibrated of
'real' dates are given on the right)

Moist 9,500-8,200 14C ya (10,400-9,100 ya)
Slight drying 8,200-8,000 14C ya (9,100-8,900 ya)
Moist 8,000-7,000 14C ya (8,900-7,900 ya)
Moderately dry 7,000-5,700 14C ya (7,900-6,500 ya)
Moist 5,700-4,000 14C ya (6,500-4,500 ya)
Very dry - as dry as at present - 4,000-3,800
        14C ya (4,500-4,100 ya)
Slightly moister than present 3,800-3,500
        14C ya (4,100-3,700 ya)
After 3,500 14C ya (3,700 ya). Remaining about
        as dry as at present"

Guo Z., Petit-Maire N. & Kroepelin S. (2000).
Holocene non-orbital climatic events in
present-day arid areas of northern Africa
and China. Global and Planetary Change.
vol.26 pp.97-103.

Also, there is:

Claussen, M., Brovkin, V., Ganopolski, A., 2002,
Africa: Greening of the Sahara. In: Steffen, W.,
Jager, J., Carson, D.J., Bradshaw, C., eds.,
pp. 125-128,Challenges of a Changing Earth. P
roceedings of the Global Change Open Science
Conference, Amsterdam, the Netherlands, 10-13
July 2001, SpringerVerlag, Berlin, New York.

http://www.pik-potsdam.de/~claussen/papers/claussen+al_africa-hotspot_igbp_02.pdf

"Sahara's Abrupt Desertification Started By
Changes In Earth's Orbit, Accelerated By
Atmospheric And Vegetation Feedbacks" at:

http://www.sciencedaily.com/releases/1999/07/990712080500.htm

Yours,

Paul
Baton Rouge, LA

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Received on Fri 12 Sep 2003 09:31:33 AM PDT