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http://www.catholic.org/green/story.php?id=50427
Why North Africa went from green to desert in ancient times – FAST
Scientists find sudden shift in Sahara climate in sediment cores.
Scientists studying North Africa’s ancient climate have learned that the region underwent swift desertification and climate shift transforming from a humid, subtropical landscape to desert sands within a matter of years.
About 13,000 years ago, the Sahara went from a dry desert like it is today, to a relatively wet region watered by monsoons. Between 8000 B.C. to 4200 B.C., the region enjoyed a tropical climate. Civilization took root in Egypt during this period.
At that time, many tropical animals are believed to have existed in the region as evidenced by period artwork and natural remains.
However, around 4200 B.C. the climate became suddenly dry once again. The causes of this prehistoric climate change have been traced to the planet’s axial tilt and a perihelion that occurred in July. This is distinct from modern climate change which may be caused by human activity and pollution.
Researchers have confirmed their conclusions with cores drilled from the bottom of the Atlantic Ocean where winds deposit massive amounts of Saharan dust each year. Scientists observed substantial increases in Saharan dust in layers dated between 6000 B.C. and 4200 B.C.
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DESERTIFICATION 