section_path: History/Emergence of civilization
section_name: Emergence of civilization
paragraph_text: Emergence of civilization
  
  The size of the Sahara has historically been extremely variable, with its area rapidly fluctuating and at times disappearing depending on global climatic conditions. At the end of the Ice ages, estimated to have been around 10,500 BCE, the Sahara had again become a green fertile valley, and its African populations returned from the interior and coastal highlands in sub-Saharan Africa, with rock art paintings depicting a fertile Sahara and large populations discovered in Tassili n'Ajjer dating back perhaps 10 millennia. However, the warming and drying climate meant that by 5000 BC, the Sahara region was becoming increasingly dry and hostile. Around 3500 BC, due to a tilt in the Earth's orbit, the Sahara experienced a period of rapid desertification. The population trekked out of the Sahara region towards the Nile Valley below the Second Cataract where they made permanent or semi-permanent settlements. A major climatic recession occurred, lessening the heavy and persistent rains in Central and Eastern Africa. Since this time, dry conditions have prevailed in Eastern Africa and, increasingly during the last 200 years, in Ethiopia.
  
  The domestication of cattle in Africa preceded agriculture and seems to have existed alongside hunter-gatherer cultures. It is speculated that by 6000 BC, cattle were domesticated in North Africa. In the Sahara-Nile complex, people domesticated many animals, including the donkey and a small screw-horned goat that was common from Algeria to Nubia. Between 10,000 and 9,000 BC, pottery was independently invented in the region of Mali in the savannah of West Africa. In the steppes and savannahs of the Sahara and Sahel in Northern West Africa, people possibly ancestral to modern Nilo-Saharan and Mandé cultures started to collect wild millet, around 8000 to 6000 BCE. Later, gourds, watermelons, castor beans, and cotton were also collected. Sorghum was first domesticated in Eastern Sudan around 4000 BC, in one of the earliest instances of agriculture in human history. Its cultivation would gradually spread across Africa, before spreading to India around 2000 BC.
  
  People around modern-day Mauritania started making pottery and built stone settlements (e.g., Tichitt, Oualata). Fishing, using bone-tipped harpoons, became a major activity in the numerous streams and lakes formed from the increased rains. In West Africa, the wet phase ushered in an expanding rainforest and wooded savanna from Senegal to Cameroon. Between 9,000 and 5,000 BC, Niger–Congo speakers domesticated the oil palm and raffia palm. Black-eyed peas and voandzeia (African groundnuts), were domesticated, followed by okra and kola nuts. Since most of the plants grew in the forest, the Niger–Congo speakers invented polished stone axes for clearing forest.
  
  Around 4000 BC, the Saharan climate started to become drier at an exceedingly fast pace. This climate change caused lakes and rivers to shrink significantly and caused increasing desertification. This, in turn, decreased the amount of land conducive to settlements and encouraged migrations of farming communities to the more tropical climate of West Africa. During the first millennium BC, a reduction in wild grain populations related to changing climate conditions facilitated the expansion of farming communities and the rapid adoption of rice cultivation around the Niger River.
  
  By the first millennium BC, ironworking had been introduced in Northern Africa. Around that time it also became established in parts of sub-Saharan Africa, either through independent invention there or diffusion from the north and vanished under unknown circumstances around 500 AD, having lasted approximately 2,000 years, and by 500 BC, metalworking began to become commonplace in West Africa. Ironworking was fully established by roughly 500 BC in many areas of East and West Africa, although other regions did not begin ironworking until the early centuries CE. Copper objects from Egypt, North Africa, Nubia, and Ethiopia dating from around 500 BC have been excavated in West Africa, suggesting that Trans-Saharan trade networks had been established by this date.