The Sahara, which means desert in Arabic, extends across North Africa. The Sahara is the largest non-polar desert in the world, with a surface area of over 9,000,000 km², equal to that of The the United States.
Although the Sahara is famous for its sand dunes, most of the surface is made up of hamada or rocky plateau. The stunning dune fields of the Sahara cover only about 15% of the entire desert surface and are found mainly in the north-central region. In the dune areas of Algeria and Libya, the thickness of the sand varies because the dunes can accumulate up to several hundred meters high, but then change as the sand shifts.
The desert expanse is dominated by rocky and barren expanses with arid hills and valleys.
What many don't know is that the Sahara was once a fertile area that supported thriving human communities. A core study has revealed that North Africa's ancient climate underwent rapid desertification and climate change that transformed the region from a humid, subtropical landscape to a desert in a matter of years. This occurred around 4200 BC. and we returned to the same desert conditions that dominated the area 13,000 years earlier.
As the climate began to change, the Sahara region became arid and vegetation died out. With nothing holding the ground, the action of the wind was able to remove all the fine sediments, until only sand and rock remained.
PROBABLE CAUSE
The transition from the mid-Holocene climate to the present one was determined by changes in the Earth's orbit and in the inclination of the Earth's axis. About 9,000 years ago, the Earth's tilt was 24.14 degrees, compared to 23.45 degrees today, and perihelion (the point in Earth's orbit closest to the Sun) occurred in late July, compared to early of January. At that time, the Northern Hemisphere received more summer sunlight, which amplified the African and Indian summer monsoon.
Changes in the Earth's orbit occurred gradually, while the evolution of North Africa's climate and vegetation was sudden. German researcher Claussen and his colleagues believe that various feedback mechanisms within Earth's climate system have amplified and modified the effects caused by orbital changes. By modeling the impact of climate, oceans and vegetation both separately and in various combinations, the researchers concluded that oceans played only a minor role in Sahara desertification.
MADE DIFFERENT
Wadi El Hitan (Valley of the Whales), Egypt, contains the fossil remains of an extinct suborder of whales. Evidently, the valley was part of a shallow marine basin 40-50 million years ago. Desertification has helped preserve and reveal an enormous amount of fossils.
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