The 5.9 kiloyear event was one of the most intense aridification events during the Holocene. It occurred around 3900 BCE (5,900 years BP), ending the Neolithic Subpluvial and probably initiated the most recent desiccation of the Sahara desert. Thus, it also triggered worldwide migration to river valleys, such as from central North Africa to the Nile valley, which eventually led to the emergence of the first complex, highly organised, state-level societies in the 4th millennium BCE.[1] It is associated with the last round of the Sahara pump theory.
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A model by Claussen et al. (1999) suggested rapid desertification associated with vegetation atmosphere interactions following a cooling event, Bond event 4.[2] Bond et al. (1997) identified a North Atlantic cooling episode 5,900 years ago from ice-rafted debris, as well as other such now called Bond events that indicate the existence of a quasiperiodic cycle of Atlantic cooling events, which occur approximately every 1470 years ± 500 years.[3] For some reason, all of the earlier of these arid events (including the 8.2 kiloyear event) were followed by recovery, as attested by the wealth of evidence of humid conditions in the Sahara between 10,000 and 6,000 BP.[4] However, it appears that the 5.9 kiloyear event was followed by a partial recovery at best, with accelerated desiccation in the millennium that followed. For example, Cremaschi (1998) describes evidence of rapid aridification in Tadrart Acacus of southwestern Libya, in the form of increased aeolian erosion, sand incursions and the collapse of the roofs of rock shelters.[5] The 5.9 kiloyear event was also recorded as a cold event in the Erhai Lake (China) sediments.[6]
In the Middle East the 5.9 kiloyear event led to the abrupt end of the Ubaid period.[7]
Historically the period of the 5.9 kiloyear event is associated with the increased violence noticed in both Egypt and throughout the Middle East, leading eventually to the Early Dynastic Period in both the First Dynasty of Egypt and Sumer. James DeMeo and Steve Taylor suggest that this period is associated with the rise of patriarchy, institutionalised warfare, social stratification, abuse of children, the development of the human ego, separation from the body, the rise of anthropomorphic gods and the concept of linear historic time.[8]