
Sahara Desert – Could you believe? The Sahara was once green - alinadragomir
https://www.matrixdisclosure.com/sahara-desert-green/
======
JPLeRouzic
A hypothesis called "The Saharan pump theory" explains how flora and fauna
have migrated through a physical link between Eurasia and Africa. This
hypothesis postulates that long periods of heavy rainfall for thousands of
years that have alternated with periods of drought in Africa, are associated
with a so-called "wet Sahara" phase, during which large lakes and rivers such
as mega-lake Chad, existed alternately with an immense desert, the Sahara. The
wet Sahara was probably a mosaic landscape of rivers, lakes, swamps,
woodlands, forest islands, wooded savannas and grasslands. Earth regions
higher than 45° of latitude where under a heavy shelf of ice. Mediterranean
sea was much lower than today.

The Middle Paleolithic was a period of African prehistory that began about
280,000 years BCE and ended approximately between 50,000 years and 25,000
years BCE.

Even during periods of drought, humans were most often able to follow the Nile
to cross the Sahara, as flora and fauna persisted on its banks. Migrations
between Eurasia and Africa were, however, interrupted when, during a desert
phase of 1.8 - 0.8 million years, the Nile at times stopped flowing completely
and at another period because of a geological uplift (movement of elevation)
of the Nile region.

This has resulted in changes in the flora and fauna in the region which have
made traveling at great distances very difficult. Evaporation exceeds
precipitation, water levels in lakes like Lake Chad, fall very low and rivers
become dry wadis. The once widespread flora and fauna must be retreated
northward into the Atlas Mountains and south into West and East Africa in the
Nile Valley and from there to South-East to the plateaus of Ethiopia and Kenya
or north-east to Asia via Sinai.

This separates the populations of the different species in zones with
different climates, thus requiring them to adapt either by migration or
speciation (evolution towards new species) or by exploiting different
resources.

The Saharan pump was invoked to explain three waves of human migrations
outside Africa, namely: Homo Erectus to Southeast Asia, perhaps twice, once as
far as China and India, once again to Pakistan. Homo heidelbergensis to the
Middle East and Western Europe. Homo Sapiens Sapiens towards the Middle East
and Western Europe, the so-called "out of Africa"

Between approximately 133 and 122 000 years BCE, the southern parts of the
Saharan desert had the beginning of the so-called "Abbassia Pluvial" period,
which is a very wet period with monsoon precipitation. This allowed the
Eurasian animals to travel to Africa and vice versa.

The Abbassia Pluvial period brought humid and fertile conditions to what is
today the Sahara desert, which then benefited from lush vegetation, fed by
lakes, swamps and river systems, many of which disappeared later in the drier
climate that followed the Abbassia Pluvial period. African wildlife, now
associated with the savannas, meadows and woods of the southern Sahara, had
penetrated all of North Africa during this period.

The Stone Age cultures, especially the Mousterian and Aterian have grown
significantly in Africa during the Abbassia Pluvial period. The transition to
more severe climatic conditions that accompanies the end of this humid period
may have encouraged the emigration of Homo Sapiens away from Africa.

The coastal road around the western Mediterranean was open during the last
glacial period and may have promoted exchanges. Wet periods were limited to
only tens or hundreds of years.

During the Pluvial Mousterian, the dried-up regions of North Africa became
again very humid, as during the rainy Abbassia period 50,000 years earlier.
There were lakes and even small inland seas (mega lake Chad), swamps and
hydrographic networks that no longer exist today. Where the Sahara Desert is
located today, there was the African wildlife typical of meadows and woods,
herbivores such as the gazelle, the giraffe or the ostrich, predators of the
lion to the jackal, hippopotamuses and crocodiles, As well as species that
have now disappeared, such as the Pleistocene camel.

The Mousterian Pluvial was caused by large-scale climatic changes during the
last glacial period. At about 50,000 BCE the Würm glaciation was well advanced
in the northern hemisphere. The ice caps in North America and Europe were
increasingly shifting the climatic zones favorable to human life to the
southern hemisphere. Temperate zones in Europe and North America were
transformed into arctic tundra, and rainfall strips typical of temperate zones
declined sharply at latitudes in North Africa.

Curiously, the same influences that created the Mousterian Pluvial also seem
to have made it disappear. At its maximum development, there are between 30
and 18,000 BCE, the Laurentide ice sheet covers not only an enormous
geographical area but reaches an altitude of 1750 meters. This creates a
specific meteorological system that affects the jet stream on the North
American continent. The jet stream splits into two entities, creating a new
climate over the northern hemisphere, which sets harsher conditions in several
regions of Central Asia and the Middle East, the end of the Mousterian Pluvial
and a Return to a more arid climate in North Africa.

Human settlements then move northwards. The late Paleolithic began in Egypt
about 30,000 BCE as evidenced by the skeleton of Nazlet Khater. The excavation
of the Nile exposed the first stone tools of that period.

Another example of climate change introduced by the Saharan pump occurred
after the last glacial maximum around 22,500 - 17,000 BCE. During the last
glacial maximum the Sahara desert was more extensive than it is today, with a
considerably weaker extent of tropical forests than today. During this period,
lower temperatures reduce the strength of Hadley's atmospheric cell, whereby
tropical climbing air brings rain in the tropics, while dry air descending to
about 20 degrees north latitude, Flows back to Ecuador and brings desert
conditions to this region. This phase is associated with high levels of wind-
borne mineral dust found in marine cores from the northern tropical Atlantic.

Around 12,500 BCE, begins a period of much more humid conditions in the
Sahara, bringing a savannah climate to the Sahara.

Analysis of Nile sediment deposited in the delta also shows that this period
had a higher proportion of sediments from the Blue Nile, suggesting higher
precipitation on the highlands of Ethiopia. This was mainly due to a stronger
monsoon activity in all tropical regions, affecting India, Arabia and the
Sahara.

The African wet period that took place between 12,800 and 3,500 years BCE, was
the last occurrence of a "Green Sahara". Climatic conditions in the Sahara
during the African wet season were dominated by a strong monsoon with heavy
rainfall. With the considerable increase in rainfall, vegetation in North
Africa is transformed into vast grasslands. The Sahel region to the south of
the Sahara becomes a savanna.

The African wet season was also characterized by a network of vast rivers in
the Sahara, large lakes, rivers and deltas. The four largest lakes were
Megachad Lake, Megafezzan Lake, Ahnet-Mouydir Lake and Lake Chotts. There were
large rivers in the area such as the Senegal River, the Nile River, the Sahabi
River and the Kufra River. These river and lake systems have provided
corridors that have enabled many animal species, including humans, to extend
their geographic range to the north, migrating across the Sahara.

A brutal climatic event occurred around 6,000 BCE. It is characterized by a
sudden drop in global temperatures that lasted several millennia. This sudden
cooling event may have been caused by the collapse of the Laurentide ice sheet
in northeastern North America, probably when the Ojibway and Agassiz glacial
lakes suddenly emptied into the North Atlantic Ocean. The melting pulse may
have altered the thermohaline circulation of the North Atlantic, reducing the
transport of heat from the tropics to the north of the Atlantic.

The sudden movement of the Hadley atmospheric cell towards the south causes
sudden cooling followed by slower warming, linked to changes with the El Niño
cycle, which leads to a rapid drying up of the Saharan and Arab regions.

