While modern humans think of the Sahara as a vast and forbidding desert, for a brief period in history, it was actually very pleasant. From around 10,000 BCE to 4,000 BCE, the Sahara was lush, green, and fertile, with a brief period of dryness from around 8,000 to 7,000 BCE. This period in the desert's history is sometimes known as the “Green Sahara” or “Green Period.”
Archaeologists have always been aware that the climate of the Sahara has changed radically throughout history. Mineral deposits in the desert indicated traces of lakes and rivers, for example, and remains of plant and animal life have also been found in the Sahara, indicating that the environment was once more hospitable. In 2000, a crew of archaeologists hunting for dinosaur bones stumbled across a graveyard in Niger, and realized that they had found traces of a civilization which had lived in the Green Sahara.
Several factors led to the formation of the Green Sahara. The Sahara has been a desert for a very long time, but around 10,000 BCE, the Earth's orbit wobbled slightly, causing a shift in weather patterns. The monsoons which drench Southern Africa today shifted up, pouring water onto the Sahara, where it formed bodies of water. Plants settled in, taking advantage of the moist environment, and they were followed by animals and humans who established lively civilizations. When weather patterns shifted again, the Sahara returned to a desert state briefly before greening once more. Around 4,000 BCE, the Sahara became a desert once more, and it is now rapidly expanding, due to a variety of factors.
Two separate human civilizations appear to have lived in the Green Sahara. The first lived from around 10,000 BCE to 8,000 BCE, during the first period of greening, and the second moved in during the second green period. When people lived in the Green Sahara, they left a number of legacies behind, such as hunting instruments, traces of textiles and artwork, and grave sites. Several grave sites carry high levels of pollen, suggesting that people were buried on beds of flowers.
Archaeologists continue to collect evidence about the Green Sahara and the people who live there, with much of this evidence coming from extremely isolated and severe areas of the desert. These finds illustrate how much the Earth's climate has changed, and how changes in climate can alter human civilization.