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Constant Change Although its has an extremely hot and dry climate today, the Sahara has undergone many changes over the last few thousand years. Some 10,000 years ago, the Sahara wasn’t a desert. Parts of the Saharan region were covered with grass and low bushes. T ese areas were full of plants, animals, and even people. T e Sahara began to go through the process of desertifi cation—or drying up—about 4,000 years ago. Why the change? Scientists think the Sahara


dried up due to a gradual, natural change in Earth’s orbit around the sun. T e change altered the pattern of sunshine on Earth. Changes in Earth’s tilt also caused changes in weather patterns. Before the change, the northern hemisphere received more hours of summer sunlight each day. T is intensifi ed heavy summer rains, called monsoons. Aſt er the change, there were fewer hours


of light, fewer monsoons, and less rain. Plants died. Rivers and streams dried up. Scientists think some parts of the Sahara may have dried up quickly and others more slowly.


Pools of Life Not all parts of the Sahara are dry, however. Water can be found at an oasis. An oasis is a lush, green area surrounded by desert. Most are formed from underground rivers or other water sources below ground. Rock layers under the surface trap and channel water in pockets and along fault lines. Water can bubble to the surface naturally or can be brought up by man-made wells. In the middle of a hot desert, the sight


of an oasis can be welcoming. Timia Oasis, in northern Niger, exists in one of the most hostile terrains on Earth. Its water comes from deep within the Aïr Mountains. A pool of water fl anked by palm trees opens


up to a rich network of lush gardens. Oranges and pomegranates hang from branches. T e wide, spreading leaves of date palms and citrus trees create a cool canopy for herbs and garden vegetables. T is beautiful oasis is tended by the Tuareg people. Oases provide habitat for animals and


people. But only two percent of the Sahara is covered by oases.


An oasis formed in this extinct volcanic crater deep in the Sahara.


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