Sahara pump theory

Source: Wikipedia, the free encyclopedia.
Tassili
in the central Sahara

The Sahara pump theory is a hypothesis that explains how

mya), the Nile ceased to flow completely[clarification needed][2][3] and possibly flowed only temporarily in other periods[4] due to the geologic uplift (Nubian Swell
) of the Nile River region.

Mechanism

During periods of a wet or

Nile Valley and thence either southeast to the Ethiopian Highlands and Kenya or northeast across the Sinai into Asia. This separates populations of some of the species in areas with different climates, forcing them to adapt, possibly giving rise to allopatric speciation.[citation needed
]

Plio-Pleistocene

The

Homo and Macaca settled wide ranges.[6]

185,000–20,000 years ago

Between about 133 and 122 thousand years ago (kya), the southern parts of the Saharan-Arabian Desert experienced the start of the

anatomically modern humans
are dated from this period, but human occupation seems to end in the later arid period.

The Red Sea coastal route was extremely arid before 140 and after 115 kya. Slightly wetter conditions appear at 90–87 kya, but it still was just one tenth the rainfall around 125 kya. Speleothems are detected only in Even-Sid-2.[7]

In the southern

MIS 6), 110–90 (MIS 5.4–5.2), nor after 85 kya nor during most of the interglacial period (MIS 5.1), the glacial period and Holocene. This suggests that the southern Negev was arid to hyper-arid in these periods.[7]

The coastal route around the western Mediterranean may have been open at times during the last glacial; speleothems grew in Hol-Zakh and in Nagev Tzavoa Caves. Comparison of speleothem formation with calcite horizons suggests that the wet periods were limited to only tens or hundreds of years.[7]

From 60–30 kya there were extremely dry conditions in many parts of Africa.[8]

Last Glacial Maximum

An example of the Saharan pump has occurred after the

Inter-Tropical Convergence Zone (ITCZ) brings rain to the tropics, while dry descending air, at about 20 degrees north
, flows back to the equator and brings desert conditions to this region. This phase is associated with high rates of wind-blown mineral dust, found in marine cores that come from the north tropical Atlantic.

African humid period

Main article: African humid period

Around 12,500 BC, the amount of dust in the cores in the

Nile River deposited sediments in the delta also shows this period had a higher proportion of sediments coming from the Blue Nile, suggesting higher rainfall also in the Ethiopian Highlands. This was caused principally by a stronger monsoonal circulation throughout the sub-tropical regions, affecting India, Arabia and the Sahara.[citation needed] Lake Victoria only recently became the source of the White Nile and dried out almost completely around 15 kya.[10]

The sudden subsequent movement of the ITCZ southwards with a

El Niño-Southern Oscillation cycle, led to a rapid drying out of the Saharan and Arabian regions, which quickly became desert. This is linked to a marked decline in the scale of the Nile floods between 2700 and 2100 BC.[11] One theory proposed that humans accelerated the drying out period from 6,000–2,500 BC by pastoralists overgrazing available grassland.[12]

Human migration

Further information: Early human migrations

The Saharan pump has been used to date a number of waves of human migration from Africa, namely:[13][14][15]

  • hand axes
    , only as far as the Indian Subcontinent.
  • Middle Paleolithic: Homo heidelbergensis into the Middle East and Western Europe.
  • Upper Paleolithic:
    coastal migration
    " wave after 70,000 years ago)
  • Epipaleolithic:
    8.2 kiloyear event
  • Neolithic:
    5.9 kiloyear event
    : sometimes associated with certain population movements of the Neolithic period
  • Bronze Age Collapse and saw chariots appear in the Sahara.[16]

See also

References

  1. S2CID 186244151
    .
  2. ^ "Structural Controls Of The Egyptian Nile". Archived from the original on 2010-08-31. Retrieved 2009-06-27.
  3. ^ Lansbery, Leslie (2011). Geological and geomorphological evolution of the Egyptian Nile between Aswan and Kom Ombo: A remote sensing and field study approach (MS). Missouri University of Science and Technology.
  4. ISBN 978-1-4020-9725-6
    .
  5. ^ Walker, Stephen (8 October 2013). "Gilf Kebir". Orbit: Earth's Extraordinary Journey. Retrieved 20 December 2013.
  6. PMID 17868778
    .
  7. ^
    doi:10.1130/G23794A.1. Archived from the original
    (PDF) on 2011-07-21.
  8. PMID 16772383
    .
  9. ORNL Oak Ridge National Laboratory. Archived from the original
    on 2006-05-01.
  10. S2CID 42372016
    .
  11. ^ Burroughs, William J. (2007) "Climate Change in Prehistory: the end of the reign of chaos" (Cambridge University Press)
  12. ^ Boissoneault, Lorraine (2017-03-24). "What Really Turned the Sahara Desert From a Green Oasis Into a Wasteland?". Smithsonian. Retrieved 2017-08-15.
  13. ^ Stephen, Stokes. "Chronology, Adaptation and Environment of the Middle Palaeolithic in Northern Africa". Human Evolution, Cambridge University. Archived from the original on 2012-03-20. Retrieved 2013-01-15.
  14. ISBN 978-1682133194
    .
  15. ^ Harcourt, Alexander H. (2015) "Humankind: how biology and geography shape human diversity" (Pegasus Books)
  16. ^ Anderson, Helen (2016) "Chariots in Saharan Rock Art: an aesthetic and cognitive review" (Journal of Social Archaeology Vol 16 no. 3)
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