History * Africa * Science
What Made The Sahara Desert?
It used to be grassland with rivers, and full of life. What happened? Where did the water go?
Many creatures, including humans, used to roam the grassy planes that once covered the Sahara desert. They drank from and bathed in the many streams, rivers, and lakes.
Where there is now sand and bare rock, there was a lush green habitat more suitable for human existence about 5,000 years ago.
The Sahara was also once home to elephants, rhinoceros, giraffes, antelopes, hippopotamuses, and many other large animals that are not found in the desert.
We know the animals lived there because of ancient rock paintings, fossils, and archeological digs (among other things).
Today, extremely arid areas don’t receive rain for years, and most of the Sahara is mainly rocky stone plateaus dotted with sand dunes. It is visible from space as a bright golden patch across our otherwise blue-green globe. A smear that extends across Egypt and Arabia.
Mapping the Ancient Sahara Water
From the mid-twentieth century, there was speculation about a once-green Sahara because of the many rock paintings of animals and a lifestyle that didn’t make sense in today’s barren Sahara.
Why and how would ancient people have left the green parts of the continent to go to the desert and make rock art?
The big clue to the ancient past came from scanning the desert from above using technology that could penetrate the sand and create images of what was underneath.
The first Shuttle Imaging Radar (SIR-A) instrument, flown in November 1981, revealed three channels or dry river courses in the eastern Sahara of North Africa.
Subsequent imaging confirmed these and discovered more extensive ancient waterways that once flowed out into the Atlantic and the Mediterranean.
The extinct rivers explain many things:
- the fossils of animals that shouldn’t have been in an arid desert.
- the locations of oasises isolated amid the sand. They existed on the ancient river paths, and the occasional rainwater may still flow along these courses below the surface of the desert.
- the vast quantities of groundwater below the desert.
Confirming rivers used to run through the Sahara is one thing, but why were they once there, and where had they gone?
Sahara — the Scientific Explanation for Climate Change
Monsoon rains fall over a specific band of Africa — the green part!
David McGee et al., MIT researchers, analyzed dust deposits over the last 240,000 years — and concluded North Africa has swung between wet and dry climates.
When Earth is tilted to receive maximum summer sunlight, increased solar flux intensifies the region’s monsoon activity, making for a wetter, “greener” Sahara.
Today, the planet’s axis is at an angle that reduces the amount of incoming summer sunlight, so monsoon activity weakens, producing a drier climate in that region.
So, the change of angle of the titling Earth is a large part of the story.
I’m interested in the people who live in the Sahara, presumably they must have moved to the edge of the desert in every direction when it all got too dry.
The Historically Habitable Sahara
Investigations in the Ténéré of Niger have uncovered a fascinating history:
- It was beneath the sea c300 million years ago.
- Gadoufaoua is a major source of fossil dinosaurs.
- Gobero archeological burial site, which dates to c8,000 BCE.
The earliest graves at Gobero suggest there was plenty of food in the area at the time because the people were tall and remained in this area, beside the lake, for a long time with no signs of a nomad lifestyle.
The archeology at Gobero suggests dramatic climate change affected the people:
- 14,000–7700 BCE weakening monsoons and the aridification.
- 7700–6200 BCE a wet climate and evidence of a fisher-gatherer group known as the Kiffians.
- 6200 BCE — 5200 BCE dry and arid and uninhabitable.
- 5200 BCE to 2200 BCE second main occupation of Gobero by the Tenerians, a nomadic herding culture.
- 2500 BCE onwards Gobero becomes increasingly arid.
This, along with other evidence, such as the West African archeological site of the Tichitt people (in modern day Mauritania) points to a Sahara that was habitable just 5,000 years ago.
Fairly rapid climate change occurred in the area. However, the local conditions and timelines may vary somewhat in different parts of the vast Sahara.
In general, we can say:
- People occupied the Sahara region from around 9,000 years ago, possibly earlier.
- Around 6,000 years ago, the pastoral period started with animal herding.
- This time also saw the first stone circles, which predate Stonehenge.
- And more complex social structures.
- About 5,000 years ago, much of the Sahara had become as arid as today.
The people who lived in the area didn’t disappear, they adapted and/or moved to better lands. Some went toward the Nile, and others to the northern coastline.
They may have taken stories about their old lives with them and passed those stories on to their grandchildren.
The Garamantes are an example of people who adapted to survive in the arid lands.
They tapped into the plentiful ground water and built successful irrigation systems and large towns. The Roman historian Herodotus wrote about them in the 5th century BCE, and their Kingdom in the desert survived until the 7th century CE.
Pre-Historic Human-Driven Climate Change in Africa
Robert Korty and William Boos concluded the change in the Earth’s axis isn’t sufficient on its own to explain the African monsoon belt moved much further north at certain times in the past.
They studied the historical relationship between rainfall and patterns of air movement in the tropics. And they suggest the changes may be helped by a feedback loop involving vegetation.
As a result of his study of the transition from humid to dry Sahara between 8,000 and 4,500 years ago, archaeologist David Wright thinks desertification was helped by humans’ domesticated animals overgrazing the grasses.
The relationship of the pastoral period, grazing animals and even drought to the creation of the arid desert is by no means clear.
Dr Edward Armstrong et al have done further research on the changing Sahara climate over the past 800,000 years. Others have looked at the complicated relationship of the green lands, the edge of the desert, human impact, and the weather.
The greenery seems to recover in areas after prolonged droughts, the land doesn’t automatically become desert.
We can’t be sure what causes the tipping point to be breached, but desertification quickly accelerates after. And it occurred in the past in a repeating cycle related to the planet’s movements.
It’s difficult to imagine, but if nature is left to do its thing, thousands of years from now, the Sahara will be wet, lush, and green once again.
Please leave your comments on this or other thoughts about the history of Africa. Anything you would like particularly like to know about African history? It is fascinating.
