Sahara Desert, Libya
The area the Sahara occupies today has not always been a desert but, like all the Earth, has undergone marked climatic changes. In the late Ordovician period (more than 400 million years ago) it was even covered with ice.
It was later partly invaded by the sea. During the Mesozoic era (between 200 and 65 million years ago) it was watered by great rivers, and dotted with lakes and marshes.
Thirty-five million years ago the formation of the Rift Valley, a geological feature that stretches from Syria to Mozambique, caused considerable climatic and environmental change to the Saharan region. This marked the end of the dense, uniform mantle of forest that covered virtually the whole of the African continent. The formation of mountains created a barrier that blocked the circulation of moisture-laden air coming from the sea. Thus two very different environments came into being: the primitive tropical forest gave way to savannah near the Rift Valley, but survived further west, along the great rivers.
Archaeological finds show the presence of humans in the Sahara more than 10,000 years ago. Rock paintings in the Akakus region and in the Messak plateau in Libya bear witness to a past time when the Sahara was home to forests, rivers, and animals. Satellite surveys have brought to light evidence of this past, identifying rivers and lakes that vanished thousands of years ago.
The Sahara region experienced a wide range of non-desert conditions, which lasted for a relatively long period of time; and until recently, in geological terms, the fate of the people who lived there was inextricably linked with climatic conditions.
These conditions began to change drastically when the last ice age ended in Europe (between about 20,000 and 12,000 years ago), and north Africa began to Desert is a natural feature of the earth. Deserts of different sizes and with differing features have appeared and disappeared over the various geological eras. The most striking example of this slow but iecome arid. A brief humid phase followed (between about 9,000 and 7,000 years ago), and then gradually there came a further period of increasingly arid conditions, lasting until the present day. From about 5500 BC, in a few centuries, the Sahara was transformed from grassland to desert.
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image: : A view of the Akakus desert and the Messak massif in the Libyan Sahara.
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image: Sand dunes in the Akakus desert. Thousands of years ago this region
was covered with forest, and inhabited by humans and animals.
was covered with forest, and inhabited by humans and animals.
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image: This Landsat image of the Messak plateau clearly shows the traces
of river systems that once brought water, and life, to these regions.
of river systems that once brought water, and life, to these regions.
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