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|History of Chad|
The Neolithic Subpluvial, or the Holocene Wet Phase, was an extended period (from about 7500-7000 BCE to about 3500-3000 BCE) of wet and rainy conditions in the climate history of northern Africa. It was both preceded and followed by much drier periods.
The Neolithic Subpluvial was the most recent of a number of periods of "Wet Sahara" or "Green Sahara", during which the Sahara region was much moister and supported a richer biota and human population than the present-day desert.
The Neolithic Subpluvial began during the 7th millennium BCE and was strong for about 2,000 years; it waned over time and ended after the 5.9 kiloyear event (3900 BCE). Then the drier conditions that prevailed prior to the Neolithic Subpluvial returned; desertification advanced, and the Sahara Desert formed (or re-formed). Arid conditions have continued through to the present day.
During the Neolithic Subpluvial, large areas of North, Central, and East Africa had hydrographic profiles significantly different from later norms. Existing lakes had surfaces tens of meters higher than today, sometimes with alternative drainages: Lake Turkana, in present-day Kenya, drained into the Nile River basin.Lake Chad reached a maximum extent of some 400,000 square kilometers in surface area, larger than the modern Caspian Sea, with a surface level about 30 meters (100 feet) higher than its twentieth-century average. Some shallower lakes and river systems existed in the subpluvial era that later disappeared entirely, and are detectable today only via radar and satellite imagery.
The event is argued to have ended quickly in some places and more slowly in others. Local feedbacks between vegetation and the atmosphere may explain the variability in the records. However, the agents of initial devegetation are unknown since they seem to occur rapidly in some areas and slowly in others, out of phase with changing orbital precession.[clarification needed] The introduction of domesticated animals correlates in many places to a rapid change from grassland to scrubland vegetation, and it is hypothesized that Neolithic humans may have potentially played a role in stripping vegetation from the landscape, which induced cascading effects to the ecosystem and climate. For thousands of years, the Sahara ecosystem supported rich and varied flora and fauna, as well as large populations of pastoralists. Researchers in 2018 demonstrated through a climate-vegetation model that abundant biota persisted longer than expected in regions where ancient pastoral societies once flourished, concluding that pastoral environment management contributed to regional delays of up to 500 years in the advancement of the Sahara's desertification between 6000 and 7000 years ago.
North Africa enjoyed a fertile climate during the subpluvial era; what is now the Sahara supported a savanna type of ecosystem, with elephant, giraffe, and other grassland and woodland animals now typical of the Sahel region south of the desert, along with some now extinct megafauna such as Sivatherium and Pelorovis. Historian and Africanist Roland Oliver has described the scene as follows:
[In] the highlands of the central Sahara Desert beyond the Libyan Desert,... in the great massifs of the Tibesti and the Hoggar, the mountaintops, today bare rock, were covered at this period with forests of oak and walnut, lime, alder and elm. The lower slopes, together with those of the supporting bastions -- the Tassili and the Acacus to the north, Ennedi and Air to the south -- carried olive, juniper and Aleppo pine. In the valleys, perennially flowing rivers teemed with fish and were bordered by seed-bearing grasslands.
Clement and fertile conditions during the Neolithic Subpluvial supported increased human settlement of the Nile Valley in Egypt, as well as neolithic societies in Sudan and throughout the present-day Sahara. Cultures producing rock art (notably that at Tassili n'Ajjer in southeastern Algeria) flourished during this period.
The practical consequences of these changes took the form of increased abundance of fish, waterfowl, freshwater mollusks, rodents, hippopotamus and crocodiles. The riches of this increased aquatic biomass were exploited by humans with rafts, boats, weirs, traps, harpoons, nets, hooks, lines and sinkers. This "riparian" (river) way of life supported much larger communities than could that of typical hunting bands. These changes, along with the local development of pottery (whereby liquids could be both stored and heated) resulted in a "culinary revolution" consisting of soup, fish stew and porridge. The last mentioned implies the cooking of gathered cereals.
The classic account of the riparian lifestyle of this period comes from investigations in Sudan during World War II by British archeologist Anthony Arkell. Arkell's report described a Late Stone Age settlement on a sandbank of the Blue Nile which was then about 12 feet (3.7 m) higher than its present flood stage. The countryside was clearly savanna, not the present-day desert, as evidenced by the bones of the most common species found in the middens -- antelope, which require large expanses of seed-bearing grasses. These people probably lived mainly on fish, however, and Arkell concluded, based on the totality of the evidence, that rainfall at the time was at least three times that of today. The physical characteristics derived from skeletal remains suggested that these people were related to modern Nilotic peoples, such as the Nuer and Dinka. Subsequent radiocarbon dating firmly established Arkell's site to between 7000 and 5000 BCE. Based on common patterns at his site and at French-excavated sites already reported from Chad, Mali and Niger (e.g., bone harpoons and a characteristic "wavy line" pottery), Arkell inferred "a common fishing and hunting culture spread by negroid people right across Africa at about the latitude of Khartoum at a time when the climate was so different that it was not desert." The originators of the wavy line pottery are as yet unidentified.
In the 1960s, the archeologist Gabriel Camps investigated the remains of a hunting and fishing community dating from about 6700 BCE in southern Algeria. These pottery-making people (the "wavy line" motif again) were black African rather than Mediterranean in origin and (according to Camps) evidenced definite signs of deliberate cultivation of grain crops as opposed to simply the gathering of wild grains. Later studies at the site have shown the culture to be hunter-gatherers and not agriculturalists, as all the grains were morphologically wild, and the society was not sedentary.
Human remains were found by archaeologists in 2000 at a site known as Gobero in the Ténéré Desert of northeastern Niger. The Gobero finds represent a uniquely preserved record of human habitation and burials from what is now called the Kiffian (7700-6200 BCE) and the Tenerian (5200-2500 BCE) cultures.
Dotted wavy line pottery and fishing cultures have also been located in the Lake Turkana region in poorly dated contexts. By 3000 BCE, it does not appear that the Turkana Basin was populated with harpoon and dotted wavy line pottery users, but fishing remained an important part of peoples' diets into the late Holocene.
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