Mars, the fourth planet from the Sun is a dry and barren wasteland inhospitable
to life. This however is not Mars. This is the largest desert on Earth - Sahara. An
arid, desolate and mostly lifeless area that spans from the Red Sea in the east
to the Atlantic Ocean in the west, and from the Mediterranean Sea in the north
to the Sahel in the south. It covers more than 9 million square kilometres or 31%
of the continent of Africa. Putting this in relative terms the desert is as big
as the USA. Like any desert the Sahara has had a significant influence on life
within its borders but because of its size the deserts reach extends far
beyond. And some of these effects are even visible from space. Today most of
the Sahara is the devoid of life but this wasn't always the case.
Believe it or not the desert actually cycles between periods of humidity and
aridity every twenty thousand years. One of the main reasons for that is the
precession of the Earth's axis which in turn changes the location of the North
African monsoon. As the monsoon position shifts so does Sahara's rainfall and with
it the desert turns green. To no one's surprise the Sahara is currently going
through a dry period. It has been expanding during the last three thousand
years and continues to do so today through a process called desertification
As the desert grew it accumulated enough sand to cover the entire globe with a
layer 20 centimeters thick. Because of this vast amount of sand the Sahara can
generate huge dust storms. Such storms can be damaging to human health and can
have negative economic impact by eroding soils and damaging crops. Surprisingly
however they can also have beneficial effects through enriching ecosystems. Out
of all places in the world these are probably best observed in Central and
South American rainforests which receive most of their mineral nutrients through
the Sahara dust which is carried by air currents over the entire Atlantic Ocean
Looking at the size of the desert storms you might think that the Sahara consists
entirely of sand dunes but this is not the case. The dune fields some of which
rise to 180 meters in height only cover about 15% of the
surface. The rest consists of rocky plateaus, mountains and large Oasis
depressions. Sahara's highest point mount Koussi in Chad is a dormant volcano which
stands at three thousand four hundred and fifty meters and despite its
altitude receives little to no precipitation
Sahara's slowest point on the other hand Egypt's Qattara depression has somewhat
of a more interesting story. At a low point of 133 meters below sea level
there have been several proposals to flood the Qartara depression which lies
within close proximity to the Mediterranean Sea. It was argued that the
flooding of the depression could be used to generate power through a
hydroelectric turbine while rejuvenating the surrounding desert. However there are
concerns that flooding the area with seawater could lead to a hyper saline
lake which would not support a fish population or a salt pan which could
build up to tens of meters and eventually fill up the depression
Regardless of that people remain optimistic on the plan and it's not
difficult to understand why. Water is essential for life and nowhere is that
more evident than in the Sahara. The desert's spans through the territory of
eleven countries with a combined population of 300 million but less than
1% of that actually live in the desert. The areas with the highest concentration
of people are near sources of water which in turn is vital for agriculture
Growing crops elsewhere in the desert is nearly impossible and where vegetation
manages to survive it is very sparse. On top of that large regions of the desert
are hyper arid and often received no rain for years. Despite the lack of rain
however the Sahara still contains vast amounts of freshwater left over from its
humid period stored in large sedimentary aquifers deep beneath the surface. In
recent years people have found a way to tap into that water and this is the
result. These crop circles each about a
kilometer across are visible from space and symbolize the success of human
ingenuity in the harshest of conditions. The shape of the crop circles is a
result of an efficient center-pivot irrigation system which in this case
draws water from the Nubian aquifer which according to estimates contains
150,000 cubic kilometers of water. Despite that the solution is unlikely to
turn the whole Sahara into arable land. The problem with fossil water is that it
is a non-renewable resource and as such its increased usage would only result in
it's faster depletion this in turn would make life impossible for people who rely
on it for survival. If you'd like to know more about the Sahara or have any other
ideas for a future video please let me know in the comments below. Before we go
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