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The Sahara Pump Theory explains how flora
Floristic province

A Phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phtyochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both regions overlap....
 and fauna left Africa
Africa

Africa is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km? including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area....
 to penetrate the Middle East
Middle East

File:GreaterMiddleEast1.pngThe Middle East is a region that spans southwestern Asia, western Asia, and northeastern Africa. It has no clear boundaries, often used as a synonym to Near East, in opposition to Far East....
 and beyond to Europe
Europe

Europe is, conventionally, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural , the Caspian Sea, and by the Caucasus Mountains to the southeast....
 and Asia
Asia

Asia is the world's largest and most populous continent. It covers 8.6% of the Earth's total surface area and, with over 4 billion people, it contains more than 60% of the world's current human population....
. African pluvial
Pluvial

In geology and climatology, a pluvial was an extended period of abundant rainfall lasting many thousands of years. The term is especially applied to such periods during the Pleistocene Epoch....
 periods are associated with a "wet Sahara
Sahara

The Sahara is the world's largest hot desert. At over 9,000,000 square kilometers , it covers most of Northern Africa, making it almost as large as the United States or the continent of Europe....
" phase during which larger lakes and more rivers exist.

One example of the Saharan pump has occurred since the Last Glacial Maximum
Last Glacial Maximum

The Last Glacial Maximum refers to the time of maximum extent of the ice sheets during the last glaciation , approximately 20,000 years ago. This extreme persisted for several thousand years....
 (LGM). During the Last Glacial Maximum the Sahara desert was more extensive than it is now because the extent of the tropical forests was greatly reduced.






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The Sahara Pump Theory explains how flora
Floristic province

A Phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phtyochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both regions overlap....
 and fauna left Africa
Africa

Africa is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km? including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area....
 to penetrate the Middle East
Middle East

File:GreaterMiddleEast1.pngThe Middle East is a region that spans southwestern Asia, western Asia, and northeastern Africa. It has no clear boundaries, often used as a synonym to Near East, in opposition to Far East....
 and beyond to Europe
Europe

Europe is, conventionally, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural , the Caspian Sea, and by the Caucasus Mountains to the southeast....
 and Asia
Asia

Asia is the world's largest and most populous continent. It covers 8.6% of the Earth's total surface area and, with over 4 billion people, it contains more than 60% of the world's current human population....
. African pluvial
Pluvial

In geology and climatology, a pluvial was an extended period of abundant rainfall lasting many thousands of years. The term is especially applied to such periods during the Pleistocene Epoch....
 periods are associated with a "wet Sahara
Sahara

The Sahara is the world's largest hot desert. At over 9,000,000 square kilometers , it covers most of Northern Africa, making it almost as large as the United States or the continent of Europe....
" phase during which larger lakes and more rivers exist.

One example of the Saharan pump has occurred since the Last Glacial Maximum
Last Glacial Maximum

The Last Glacial Maximum refers to the time of maximum extent of the ice sheets during the last glaciation , approximately 20,000 years ago. This extreme persisted for several thousand years....
 (LGM). During the Last Glacial Maximum the Sahara desert was more extensive than it is now because the extent of the tropical forests was greatly reduced. During this period, the lower temperatures reduced the strength of the Hadley Cell
Hadley cell

The Hadley cell is a circulation pattern that dominates the tropical atmosphere, with rising motion near the equator, poleward flow 10-15 kilometers above the surface, descending motion in the subtropics, and equatorward flow near the surface....
 whereby rising tropical air of the Inter-Tropical Convergence Zone (ITCZ) brings rain to the tropics, while dry descending air, at about [20th parallel north|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. Around 12,500 BC, the amount of dust in the cores in the Bølling
Bølling

B?lling can refer to:*B?lling lake, Denmark - a shallow lake in central Jutland, after which the following are named:*The B?lling Oscillation or Interstadial - a warm phase during the last phase of the Weichsel glaciation in Europe....
/Allerød
Allerød

Aller?d may refer to either of these:* Aller?d municipality, a town in Denmark** Aller?d station, a railway station in the Danish town* Aller?d Oscillation, a climatic period at the end of the last glaciation...
 phase suddenly plummets and shows a period of much wetter conditions in the Sahara, indicating a Dansgaard-Oeschger
Dansgaard-Oeschger event

Willi Dansgaard-Hans Oeschger events are rapid climate fluctuations that occurred 25 times during the last glacial period. Some scientists claim that the events occur quasi-periodically with a recurrence time being a multiple of 1,470 years, but this is debated....
 (DO) event (a sudden warming followed by a slower cooling of the climate). The moister Saharan conditions had begun about 12,500 BC, with the extension of the ITCZ northward in the northern hemisphere summer, bringing moist wet conditions and a savanna climate to the Sahara, which (apart from a short dry spell associated with the Younger Dryas
Younger Dryas

The Younger Dryas stadial, named after the alpine/tundra wildflower Dryas octopetala, and also referred to as the Big Freeze, was a brief cold climate period following the B?lling/Aller?d Oscillation interstadial at the end of the Pleistocene between approximately 12,800 to 11,500 years Before Present, and preceding the Boreal of t...
) peaked during the Holocene thermal maximum climatic phase at 4000 BC when mid-latitude temperatures seem to have been between 2 and 3 degrees warmer than in the recent past. Analysis of 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
Ethiopian Highlands

The Ethiopian Highlands are a rugged mass of mountains in Ethiopia, Eritrea , and northern Somalia in the Horn of Africa. The Ethiopian Highlands form the largest continuous area of its altitude in the whole continent, with little of its surface falling below 1500 m , while the summits reach heights of up to 4550 m ....
. This was caused principally by a stronger monsoonal
Monsoon

A monsoon is a seasonal prevailing wind that lasts for several months. The term was first used in English in India, Bangladesh, Pakistan, and neighboring countries to refer to the big seasonal winds blowing from the Indian Ocean and Arabian Sea in the southwest bringing heavy rainfall to the region....
 circulation throughout the sub-tropical regions, affecting India, Arabia and the Sahara. The sudden subsequent movement of the ITCZ southwards with a Heinrich event
Heinrich event

Heinrich events, first described by marine geologist Hartmut Heinrich, occurred during the Wisconsin glaciation period, or "ice age". During such events, armadas of icebergs broke off from glaciers and traversed the North Atlantic....
 (a sudden cooling followed by a slower warming), linked to changes with the El Niño-Southern Oscillation
El Niño-Southern Oscillation

El Ni?o-Southern Oscillation is a global coupled ocean-atmosphere phenomenon. The Pacific ocean signatures, El Ni?o and La Ni?a are important temperature fluctuations in surface waters of the tropical Pacific Ocean....
 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.

During these periods of a wet Sahara, the Sahara and Arabia become a savanna
Savanna

A savanna, or savannah, is a tropical, subtropical or temperate woodland ecosystem characterized by the trees being sufficiently small or widely spaced so that the Canopy does not close....
 grassland and African flora and fauna become common. During the following inter-pluvial arid period, the Sahara reverts to desert conditions usually as a result of the retreat of the West African Monsoon southwards. Evaporation exceeds precipitation, the level of water in lakes like Lake Chad
Lake Chad

Lake Chad is a historically large, shallow lake in Africa, whose size has varied greatly over the centuries. It is economically very important, providing water to more than 20 million people living in the four countries which surround it — Chad, Cameroon, Niger and Nigeria....
 falls, and rivers become dry wadi
Wadi

Wadi is the Arabic term traditionally referring to a valley; in some cases it may refer to a dry Stream bed that contains water only during times of heavy rain....
s. Flora and fauna previously widespread retreat northwards to the Atlas Mountains
Atlas Mountains

The Atlas Mountains are a mountain range across a northern stretch of Africa extending about 2,400 km through Morocco, Algeria, and Tunisia. The highest peak is Jbel Toubkal, with an elevation of in southwestern Morocco....
, southwards into West Africa
West Africa

West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the United Nations subregion of Western Africa includes the following 16 countries distributed over an area of approximately 5 million square km:...
, or eastwards into the Nile Valley and thence either south-east to the Ethiopian Highlands
Ethiopian Highlands

The Ethiopian Highlands are a rugged mass of mountains in Ethiopia, Eritrea , and northern Somalia in the Horn of Africa. The Ethiopian Highlands form the largest continuous area of its altitude in the whole continent, with little of its surface falling below 1500 m , while the summits reach heights of up to 4550 m ....
 and Kenya
Kenya

The Republic of Kenya is a country in East Africa. It is bordered by Ethiopia to the north, Somalia to the northeast, Tanzania to the south, Uganda to the west, and Sudan to the northwest, with the Indian Ocean running along the southeast border....
 or north-east across the Sinai into Asia
Asia

Asia is the world's largest and most populous continent. It covers 8.6% of the Earth's total surface area and, with over 4 billion people, it contains more than 60% of the world's current human population....
. This separates population
Population

File:Population density.pngIn biology, a population is the collection of inter-breeding organisms of a particular species; in sociology, a collection of human beings....
s of some of the species in areas with different climate
Climate

Climate encompasses the temperatures, humidity, atmospheric pressure, winds, rainfall, atmospheric particle count and numerous other Meteorology elements in a given region over long periods of time, as opposed to the term weather, which refers to current activity of these same elements....
s, forcing them to adapt
Adaptation

Adaptation is the process, which takes place under natural selection, whereby an organism becomes better suited to its habitat. Also, the term may refer to some characteristic which stands out as being especially significant in the organism's survival....
, possibly giving rise to allopatric speciation
Allopatric speciation

Allopatric and allopatry are terms from biogeography, referring to organisms whose ranges are entirely separate, so that they do not occur in any one place together....
.

The Saharan pump has been used to date four waves of human emigration from Africa, namely:

  • Homo erectus
    Homo Erectus

    Homo Erectus is a 2007 comedy film about cavemen that was written and directed by Adam Rifkin, and starring Giuseppe Andrews, Gary Busey, David Carradine, Ron Jeremy, Ali Larter, Hayes MacArthur, Adam Rifkin, and Talia Shire....
     (ssp. ergaster) into Southeast and East Asia
  • Homo heidelbergensis
    Homo heidelbergensis

    Homo heidelbergensis is an extinct species of the genus Homo which may be the direct ancestor of Homo neanderthalensis in Europe. The best evidence found for these hominins date between 600,000 and 400,000 years ago....
     into the Middle East and Western Europe
  • Homo sapiens sapiens "Out of Africa theory"
  • The spread of Afro-Asiatic languages.


See also

  • Abbassia Pluvial
    Abbassia Pluvial

    The Abbassia Pluvial was an extended wet and rainy period in the climate history of North Africa. It began c. 120,000 years before the present , lasted approximately 30,000 years, and ended c....
  • Mousterian Pluvial
    Mousterian Pluvial

    The Mousterian Pluvial was an extended wet and rainy period in the climate history of North Africa. It occurred during the Upper Paleolithic era, beginning around 50,000 years before the present , lasting 20,000 years, and ending around 30,000 ybp....
  • Neolithic Subpluvial
    Neolithic Subpluvial

    The Neolithic Subpluvial, sometimes called the Holocene Wet Phase, was an extended period of wet and rainy conditions in the climate history of northern Africa....