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In the heart of the Sahara Desert, along the western edge of the Aïr Massif (air mah-SEEF), there is an archaeological site, known as Gobero, that dates back to the very dawn of the Holocene, 11,700 years ago.
There are skeletons under the sands of Gobero – skeletons in what may be the desert’s first cemetery. Their bones are long, so the people who lived at Gobero must have been unusually tall – maybe even unusually healthy.
How could that be?
Gobero is in one of the driest places on Earth. In many years, not one drop of water falls there. It’s more than 600 kilometers from the nearest river or lake, and 1,500 kilometers from the Mediterranean Sea.
How could anyone find enough water – or food – to live there, let alone to thrive there, so many years ago?
Well, there’s a clue in the teeth that still cling to the skeletons at Gobero. It turns out that the teeth are full of isotopes – a variant of an atom – that must have come from fish.
There’s more. Scattered about the site are harpoons and fishhooks, delicately carved from bone. Ancient pollen, trapped in sediment, once belonged to reeds that must have grown in water.
The sand sinks as you walk from Gobero, down into a shallow depression over 10 kilometers long. Dig a little, and you’ll find other skeletons in that depression – skeletons of giant fish, and hippopotamuses, and crocodiles.
So, there’s our answer.
At the dawn of the Holocene, the Sahara was green – a vast and fertile savannah, crisscrossed by rivers that drained into lakes. The people at Gobero thrived because they had settled next to one of those lakes, and there were few better places on Earth to live.
But the Green Sahara’s days were numbered. The sand was coming.
For people across the drying Sahara, there would be two options: escape, or die.
Welcome to the fifteenth episode of The Climate Chronicles, the fourth of our third season, “Into the Holocene.”
The Sahara is world’s largest hot desert, covering over nine million square kilometers. It’s about as big as China and the United States, combined, and it covers nearly a third of Africa.
It’s so dry that some of its regions haven’t recorded anymeaningful rain in decades.
If there’s any environment on Earth that seems truly permanent, maybe even timeless, it’s the Sahara.
But today’s desert is only about 4,000 years old. There are towns and cities on Earth – Jericho, for example, and Damascus – that are almost three times older than the Sahara.
It’s a mind-bending truth. And in this episode, we’ll break it down. We’ll explore what I consider to be the most important climatic shift of the Holocene: the creation of today’s Sahara desert.
And we’ll follow the climate refugees who, in escaping the expanding desert, may have helped establish one of the great societies in human history.
Not far from the remains of Gobero, and in many other places across the Sahara desert, the trunks of petrified trees recall a very different time in the history of the region – and the Earth.
The trees date to the Cretaceous, the last and longest period in the Mesozoic Era, when dinosaurs roamed the Earth. It was in the early Cretaceous, about 140 million years ago, that Africa split from South America. By the late Cretaceous, around 66 million years ago, it was sliding into its present location.
During the 80 million years of the Cretaceous, our planet was, for the most part, much hotter and wetter than it is today. Sea levels were so much higher that waters cut right through the Sahara – and across today’s North America.
Enormous forests and wetlands covered those parts of the Sahara that hadn’t been flooded. Spinosaurus, one of the largest predators in Earth’s history, prowled through swamps and snagged gigantic fish. Carcharodontosaurus – a carnivore as big as T-rex – hunted the Paralititan, a 130,000-pound titanosaur, along tropical rivers.
The period’s rains washed over the Sahara, draining silicon dioxide – which is common in rocks – down into sandy floodplains. There, the silica entered into trees, slowly turning them into stone.
And the stone survives. Across Algeria, Egypt, Libya, Morocco, and Niger, sand swirls over petrified tree trunks.
Now, in the early Holocene, the people of the Green Sahara chiseled into these trunks. They chipped away the stone that had been wood, then carved it into arrowheads, axes, and knives. Tools for fishing, or for bringing down big animals in wetlands and woodlands.
The toolmakers and weaponsmiths forged a connection across 66 million years, between two periods when the Sahara was full of life and water.
But between those periods, the Sahara was often dry.
You see, in a way, after it began to approach its present location, the Sahara wanted to be dry. There are many reasons, but one stands out: the current location of the African tectonic plate.
Now, every scrap of land on Earth once belonged to a single, giant continent: Pangea. Early in the reign of the dinosaurs, about 200 million years ago, that continent began to come apart.
The reason was maybe the biggest catastrophe in the history of life on this planet: a vast upwelling of magma – millions of cubic kilometers – oozing from fissures over thousands of years.
It was volcanism on an unimaginable scale, something that almost seems like it should happen on Venus, not Earth. It choked our atmosphere with carbon dioxide, acidified the oceans, and drove some 80% of all species into extinction.
Pangea’s fragmentation recreated a smaller supercontinent that had actually existed before its formation – Gondwana. Both South America and Africa were part of Gondwana. But during the Cretaceous, they too began to come apart.
Gondwana had been well south of the equator. Now, newly freed Africa began to migrate north. By about 90 million years ago, in the twilight of the dinosaurs, the Sahara began to inch into one of two enormous dry zones – or, in other words, aridity belts – that circle the globe.
And that was when its lush, tropical rainforests began to dry out for the very first time. There was no flipping of a switch. The Sahara didn’t become a desert overnight. But very slowly, rainforests eased into drier savanna landscapes.
Now, the world’s aridity belts lie on opposite sides of the equator, or more accurately, between about 20 and 30 degrees north and south. Today, the northern belt encompasses the Sahara, the Arabian Desert, the Syrian Desert, the Thar Desert (in India and Pakistan), the Kyzylkum and Karakum Deserts (in Kazakhstan, Uzbekistan, and Turkmenistan), the Gobi Desert in China, and the Sonoran, Chihuahuan, Mojave, and Baja California Deserts in the United States and Mexico.
The southern belt includes the Atacama Desert in Chile and Peru, the Namib Desert in Namibia, the Kalahari Desert (in Botswana, Namibia, and South Africa) and the Great Victoria and Great Sandy Deserts (in Australia).
That’s a lot of deserts! And the reason they all exist in about the same zone – the same belt – is beautifully simple.
You may remember that, in episode 12, we mentioned the thermal equator. It’s where sunlight has the most direct path to Earth’s surface, and where the Sun is therefore exactly overhead at noon.
It’s the belt around the Earth where solar heating is strongest. And it doesn’t quite line up with the actual equator, because the zone of maximum solar heating responds to things like land warming up more quickly than water, or – as we’ve seen – one hemisphere cooling versus another, or changes in ocean currents. The thermal equator therefore meanders and moves across the Earth.
Anyway, in this zone of maximum heating, there’s a ton of hot air, and hot air rises. When the air rises, it cools down, and that releases moisture as rain.
This is the engine that drives the intertropical convergence zone, or ITCZ, the world-straddling rain belt that has come up a few times now in The Climate Chronicles. The ITCZ is super important because it moves as the thermal equator moves, and its movement brings rain to some regions, but drought to others.
Its movement, in other words, can bring life or death on a continental scale.
Now, after the hot air rises at the thermal equator, it moves poleward. As it does, it radiates heat into space. So, as it moves higher in the atmosphere and further north or south, it gets cold, dense, and – having lost its moisture – dry. Being cold and dense, it falls back to Earth’s surface. It packs together more and more as it descends – and that heats it up again.
Being warm, it has the capacity to hold more moisture than cold air. But when it begins to descend, it’s still dry. This turns it into a sponge that soaks up all the moisture it can get on the surface. As it absorbs that moisture, it sweeps across land – or water – towards the thermal equator, where it came from. It does this for one very simple reason: when hot air rises at the thermal equator, the air pressure goes down. It creates a kind of vacuum effect, as air rushes in to fill the void. And the vacuum pulls the descending air back towards it.
This dynamic happens on both the northern and southern sides of the thermal equator. Each loop of air, arcing from the thermal equator, is called a cell, more specifically a Hadley Cell, after George Hadley, an eighteenth-century lawyer and amateur meteorologist. That was not so uncommon in those days. Elites had their day job, and then some were revolutionary scientists on the side.
Hadley wanted to know what caused the trade winds, the persistent winds that blow east to west around the equator.
These winds powered worldwide shipping in the age of sail. They were essential to the emerging global economy of the eighteenth century, and Hadley therefore wanted to know how they worked. He proposed an explanation: giant loops of air, bending up from the thermal equator, pushed east to west by Earth’s rotation. He was right, of course, and we now have a term for his two loops, or cells: the Hadley Circulation.
Now, the twin cells of the Hadley Circulation explain the two aridity belts we mentioned a few minutes ago. It’s that sponge action where the air loops back down towards the surface. The air dries out land – like the Sahara Desert.
So, when northern Africa reached its current spot, the Sahara began to dry out. But drying out and turning into the world’s biggest hot desert are two very different things. And continental drift – the movement of tectonic plates – didn’t dry the Sahara only by pushing Africa into the aridity belts created by the Hadley Circulation.
The northern movement of the continent also shrank the ocean that had separated it from Eurasia. Winds flowing off this ocean, known as the Tethys, once brought moisture into the Sahara. But over millions of years, the Tethys was squeezed into a sea, which we call the Mediterranean, that didn’t provide as much humid air. The death of the Tethys reshaped the circulation of the atmosphere, rerouting rains away from the Sahara.
Plate tectonics dried out the Sahara in another way. By about 25 million years ago, the movement of Africa began to lift up the Atlas Mountains, along the Sahara’s northwestern perimeter. At roughly the same time, a giant magma plume, welling up from Earth’s mantle, created the Ethiopian and East African highlands to the east.
The mountains scraped moisture out of the air before it flowed into the Sahara. That’s because, as air rises over high land, it expands and cools. In colder air, water molecules move more slowly and can no longer stay separate. They clump together to form clouds and rain. The rain falls on the side of the mountains that faces the flow of the air – or in other words, the wind. The other side, bordering the Sahara, is dry. And the winds that sweep off the mountains and blow into the Sahara are also dry.
There was one more way that the movement of Earth’s tectonic plates dried out the Sahara – and this one was indirect.
The Indian plate also broke free of Gondwana, and it too crashed into Eurasia – about 45 million years ago. Remember, it was that collision that began to cool down the Earth, by lifting up the Himalayas and scraping carbon dioxide out of the atmosphere.
Not long after, Antarctica – yet another former part of Gondwana – followed Africa by splitting from South America. Africa had moved north, but Antarctica drifted south until a current of polar water began to flow around it, isolating it from the rest of the Earth.
By around 34 million years ago, the position of Antarctica and the current together allowed ice sheets to form on the new continent – when the concentration of carbon dioxide in the atmosphere, and in turn the temperature of the Earth, fell below a critical threshold. The expanding ice sheets then further cooled the Earth.
And this was critical for the Sahara, because the flow of moisture into Northern Africa also depends on the temperature of surrounding surface water. When the sea surface is warm, it evaporates more easily. Water vapor in the air blows into the Sahara, bringing rain. The opposite is true when the sea surface is cold.
So, when the Earth really began to cool down, about 34 million years ago, the Sahara wanted to be dry. And the colder Earth got, the drier it wanted to be.
Earth was rarely as cold as it was about 20,000 years ago, during the Last Glacial Maximum. That was why the Sahara had never been as dry. Rain in the desert was even rarer than it is now. Rivers that had once wound their way across northern Africa had become “seasonal, then ephemeral,” until finally, they “dried up,” as the geographer Martin Williams puts it.
Grasses and trees that once fixed soil in place died out on a vast scale. And as the soil dried out, it began to move. Eventually, it piled up in immense dunes, swirling some 800 kilometers south of their present range.
The trade winds were much stronger during the Last Glacial Maximum than they are today. Part of the reason is that, with ice sheets covering huge stretches of the Earth, the difference between temperatures at the thermal equator, and temperatures further north and south, was so much greater than it is now. This big difference between temperatures created huge differences in air pressure, and those differences supercharged the trade winds.
The strong winds blew enormous quantities of dust off of the Sahara – and other, growing deserts. This is why the world of the Pleistocene glacial periods was not only much colder and drier than our world, but also much, much dustier.
During the Last Glacial Maximum, maybe the chilliest and driest glacial of them all, the atmosphere filled up with perhaps four times more dust than it holds today. In some places – the Atlantic Ocean west of the Sahara, for example, where the wind had swept across northern Africa – the amount of dust in the atmosphere could reach 20 times its modern value.
Dust in the atmosphere can make for spectacular sunrises and sunsets. I bet the Earth of the Pleistocene glacials was a beautiful place, with gloriously vivid evening and morning skies above the ice sheets – even if it was a much more dangerous world to live on.
Anyway, dust blowing off the Sahara gives us some of our best evidence for the climate of the region. Some of the dust ended up in the ocean, and eventually made its way down to the seafloor, where it ended up in sediments. By drilling down into the ocean floor, we can extract cores lined with layers created by the accumulation of sediments over time. The concentration of Saharan dust in those layers gives us an indirect measurement – a proxy – for the dryness of the Sahara. The more dust in a layer, the drier the Sahara probably was when the layer was formed.
Sediment cores from the ocean floor, known as marine sediment cores, tell us that the Sahara was so dry during the Last Glacial Maximum that even our remarkably flexible, hunting and gathering ancestors couldn’t live in it. Other evidence – sediments from dried-out lakebeds, for example – tells a similar story.
And I find that really striking. Actually, more than that: chilling. A huge part of the Earth was just not habitable about 20,000 years ago. There was just no living in a desert that never got any rain, let alone on ice sheets that covered continents. It’s a reminder that, if you change Earth’s average temperature by more than a few degrees Celsius, our planet becomes a totally different and, overall, less habitable world.
Now, you know that, as Milankovitch cycles in Earth’s rotation and orbit fell out of sync, the Last Glacial Maximum gradually yielded to a warmer and, in many places, wetter climate. As we saw in our last episode, the amount of solar energy that reached the northern tropics in the summer rose until it was actually higher than it is now. That doesn’t necessarily mean that the northern hemisphere, let alone the world, was hotter than it is today – but it does mean that monsoon systems strengthened until they could bring rain deep into the Sahara.
The desert bloomed. Rivers came alive, and drained into countless new or growing lakes. One lake – Lake Chad – expanded until it was one of the biggest lakes in the world.
Dunes disappeared beneath grasses that now anchored them in place. Pollen deposits tell us that plants currently bordering the Mediterranean spread south, while the plants of today’s central Africa pushed north. They darkened the Sahara, absorbing heat, increasing evaporation, boosting rainfall, and further encouraging plant growth – a classic positive feedback.
When trees colonized the new grasslands, they created savannah landscapes that spread until they covered much of northern Africa. Savannah ecosystems are not quite wet enough to allow dense tree growth, so sunlight reaches the ground and permits grasses to flourish.
Animals followed the advance of grasses and trees. Antelopes, elephants, giraffes, ostriches, rhinoceroses and other herbivores pressed deep into the greening Sahara. So did omnivores, like monkeys and baboons. They were, of course, joined by predators and scavengers – wild dogs, jackals, hyenas, lions, and vultures.
Fossils tell us that fish swam into the resurrected rivers of the Sahara and soon found their way into new lakes. The bones of amphibians and the shells of freshwater snails reveal that the rivers formed a watery network that linked the emerging lakes, creating a vast, Sahara-straddling aquatic ecosystem.
People also migrated into the former desert. Some settled beside the rising lakes, and there carved or painted on rock shelters that provided protection from the rain and Sun. At Tassili n’Ajjer, a vast sandstone plateau in southeastern Algeria, deep in today’s desert, migrants painted hippopotamuses. At Tadrart Acacus in southwestern Libya, where years now pass with no rainfall at all, locals created rock art depicting both hippos and crocodiles.
In the cooler microclimate of Jebel ‘Uweinat, a mountain massif in the central Sahara that stretches some 25 kilometers wide, locals adorned smooth rocks with at least 1,000 paintings that record scenes from the Green Sahara. Here, representations of giraffes and gazelles and even aurochs, or wild cattle, are scattered across what is now a parched desert.
It would be a mistake to assume that rock art always depicted what life was actually like. Just west of the border separating Egypt from Libya, for example, there is an isolated mountain massif, named Jebel Arkenu, where people adorned a rock shelter with paintings of giraffes. Yet even when the Sahara was green, giraffes could not have made it atop the mountain.
The giraffes probably roamed the plains around the mountain. Or maybe the giraffes had some spiritual significance to the people of Jebel Arkenu. The point is that we should be careful about assuming that people in the distant past used art like we might use our cellphone cameras today. Art never just depicts reality; it creates meaning.
So, the migrants who pressed into the Sahara were artists – and they were hunters and gatherers. They fished in lakes, collected seaweed and grasses, and pursued big animals across the Sahara.
Yet the Pleistocene wasn’t quite ready to fade away. And its final spasm of cooling and drying would bring the bad old days back to the Sahara.
The Younger Dryas seems to have battered the Green Sahara.
When the waters of Lake Agassiz spilled into the Atlantic Ocean and temperatures plunged across the Northern Hemisphere, the Intertropical Convergence Zone migrated south, the African monsoon weakened, and much of the Sahara dried up.
Natural archives suggest that, once again, lakes evaporated, rivers ran dry, plants turned to dust, animals retreated or died out – and the dunes came back to life. For a thousand years, sand swirled across the Sahara, and communities who had fished and hunted in marshes and grasslands had little choice but to seek refuge in mountain valleys, or in oases sustained by groundwater.
A thousand years. An eternity for a person, for a community. But just a moment in the long history of climate change. A moment that had passed by about 11,500 years ago.
The rains returned, the rivers recovered, the lakes filled up, and the Sahara greened again. In the early Holocene, hunters and gatherers left their refuges within the former desert, or migrated into the Sahara from beyond its borders.
Along the western edge of the Aïr Mountains, in north-central Niger, there’s an archaeological site known as Adrar Bous that preserves a record of what happened next. Bones and artifacts reveal that a hunting and gathering community moved there soon after the Younger Dryas yielded to the Holocene. They were drawn to a reborn lake, filled by the return of Monsoon rains.
Between about 11,000 and 8,500 years ago, that lake reached a depth of about 13 meters, or nearly 50 feet. It was full of fish and freshwater snails, so the people of Adrar Bous had plenty to eat. In fact, their culture is now called the Kiffian, after the word Kiffi, meaning “fish” in the language of the Kel Aïr Tuareg people who inhabit the area today.
For about 3,000 years, the community at Adrar Bous hunted, fished, and gathered fruits, grasses and seeds on the lakeshore. Again, when we skip through climate’s history in this way, it’s easy to forget how long three millennia really are, and how remarkable it is for a small group of people to live in one place for that long – by some counts, as long as the whole history of Chinese civilization!
And it’s easy to forget the history we’re undoubtedly missing: the drama of relationships that worked and didn’t work, the heroism or cowardice of hunters and fighters, the moments of genius or revelation. All now forgotten, indeed unrecoverable.
In any case, not long after around 8,500 years ago, probably at about 8,200 years ago, the story of the first Holocene inhabitants of Adrar Bous came to an end. Another pulse of freshwater, maybe the biggest since the Younger Dryas, surged into the Atlantic. Temperatures once again plummeted across much of the Northern Hemisphere – not as they had in the Younger Dryas, but enough to reroute rains away from Adrar Bous.
The lake dried up completely. We know because dry sand covered the parched lakebed, and it shows up in the parts of sediment cores that date to the period. The people who had lived at Adrar Bous for so long, for as long as the entire history of the city of Rome, had no choice but to leave or die.
Eventually, the northern hemisphere warmed, the Monsoon rains returned, and the lake at Adrar Bous sputtered back to life. But it was a pale shadow of its former self. Now it was no more than about 10 feet deep – at most a quarter of its early Holocene depth.
People returned to Adrar Bous, but not the people who had lived there. The newcomers were Neolithic herders. They arrived with cattle, and with polished stone axes. They were shorter than the hunters and gatherers who preceded them, and they used the lake to water their herds.
The story was similar across the Sahara. After the drying about 8,200 years ago, during the 8.2K BP event, as it’s called, cattle herders spread across the recovering grasslands and occupied the banks of reborn lakes.
But the picture was complex. After all, the Sahara is vast, covering about a third of Africa, and its size makes it incredibly diverse. It didn’t, in fact it couldn’t simply switch between dry and humid periods. Aridity always set in gradually, and its progress looked different from place to place. Local ecosystems, moreover, responded in their own distinct ways. Lakes fed by groundwater survived, for example, while those that relied on rainfall – like the lake at Adrar Bous – withered away.
All these caveats aside, after about 8,000 years ago, the herders of the Sahara were living on borrowed time. The Milankovitch cycle known as the precession cycle – remember, that’s the regular wobble of Earth’s rotation on its axis – began to lower summer insolation, another word for solar radiation, around the northern tropics. Ever so slowly, the Monsoon started to weaken.
By about 7,000, maybe 6,000 years ago, much of the Sahara was in a precarious place. Plant cover had thinned across Northern Africa, as it had in previous Holocene dry periods, disrupting the feedback that had helped sustain rainfall in the Sahara. At the same time, the monsoon rains were steadily weakening.
The Sahara wasn’t today’s desert, not yet, but its grasslands were on the verge of collapse. Ecosystems had become fragile, liable to slip into arid sandscapes with relatively small shocks.
Did the herders who had spread across the Sahara cause those shocks? The population biologist Paul Ehrlich and the environmental scientist Anne Ehrlich thought so. Together, they wrote the most influential environmental catastrophe literature of the 1960s and 70s. Their book, The Population Bomb, terrified readers by warning that population was growing faster than food production, which to them meant an imminent demographic and economic collapse.
The Ehrlichs argued that the Sahara provided a warning of the environmental damage that even small groups of humans could inflict. They assumed that the desert had spread, thousands of years ago, because herders allowed their flocks to consume the grasses that once stabilized the North African savannah.
It wasn’t a surprising argument, coming from them. With The Population Bomb, they had helped popularize the idea, in the West, that people outside Europe and North America didn’t know what was best for them. The Ehrlichs believed that it was runaway population growth in Africa and Asia that would deplete Earth’s resources. I think it was natural for them to assume that, in the past, herders in Africa had also wrecked the Sahara.
But new research tells a very different story. The precession cycle actually made the Sahara most vulnerable to widespread drying about 500 to 1000 years before it decisively transitioned into a desert. Something – or someone – must have delayed that transition, rather than accelerated it.
It seems that herders – or pastoralists, to use another term – knew all about the risks of overgrazing. And of course they did! They’d lived in the green but drying Sahara for thousands of years. For millennia, they’d moved their herds with the seasons, avoiding sustained pressure on any single patch of land.
Their herds now seem to have actually benefitted grasslands by providing nutrients in dung and urine, which stimulated plant growth and mimicked the role of the wild herbivores that are essential to savannah ecosystems. That’s why grasslands can actually degrade from under-grazing, as well as over-grazing.
So, the herders or pastoralists of the Sahara hung on for as long as they could, in most places actually delaying the transition to desert. But the dynamics of the precession cycle were relentless, and ruthless. Between about 4500 and 4000 years ago, one by one, each of the Sahara’s diverse landscapes slipped back into desert. The rivers dried out, and most lakes evaporated away. The plants withered, and the animals departed.
The Green Sahara died, and today’s Sahara was born.
In one lakeshore after another, on one once-verdant plain or mountain massif at a time, the people of the Sahara faced a choice – a choice that more and more people confront today.
What do you do when the environments you know so well, the environments that sustain life, begin to change? When the climate suddenly grows less habitable, indeed uninhabitable?
In oases scattered across the Sahara, where groundwater created small, drought-resistant lakes, some people found ways to survive. A few mountain massifs also sustained human life by, for example, trapping fog and residual rainfall. And along the southern fringes of the reformed Sahara desert, life was still possible for small groups of mobile herders.
But the overwhelming majority who lived in the Green Sahara moved out of the Sahara Desert.
Many of these climate refugees migrated into the Nile Valley, where the Nile’s annual floods offered reliable water and fertile soils. Thousands of migrants seem to have joined communities that already existed in the valley. Cattle-centered economies and belief systems, desert survival strategies, and social traditions with distinct attitudes towards authority – all mingled with local cultures that depended on agriculture, trade, and specialized crafts.
Over the course of centuries, this dynamic combination may have spurred a revolution in social differentiation, in political organization, that sparked the formation of one of the world’s first great societies: ancient, Pharaonic Egypt.
The Sahara today seems timeless, indeed without time. It may feel like a permanent part of the Earth. Nothing could be further from the truth. In a sense, the Ehrlichs were right – it does provide a warning, and, perhaps, a source of hope.
On the one hand, the Sahara’s history reveals how profoundly, and how quickly, Earth’s ecosystems can transform themselves with just a little change in climate. On the other, it shows how ingeniously, how successfully, people can respond.
Today, we need to reduce our greenhouse gas emissions, urgently, to limit the changes already sweeping across our Earth. But we also need to adapt to those changes, and the changes that are yet to come.
Can we learn from the herders who survived in the Sahara, and those who left to build ancient Egypt? Will we survive, and even thrive? Will we build a new, more sustainable civilization?
Today, it’s in our hands.
For Teachers and Students
Review Questions:
- How did plate tectonics dry out the Sahara?
- What was the “Green Sahara,” and how did the precession cycle make it possible?
- How did people live in the Green Sahara? What did they do when it temporarily dried out?
- How did the (re)emergence of the Sahara Desert contribute to the emergence of ancient Egypt?
Key Publications:
Brierley, Chris, Katie Manning, and Mark Maslin. “Pastoralism may have delayed the end of the green Sahara.” Nature Communications 9:1 (2018): 4018.
Pausata, Francesco et al., “The greening of the Sahara: Past changes and future implications.” One Earth 2:3 (2020): 235-250.
Williams, Martin. When the Sahara Was Green: How Our Greatest Desert Came to Be. Princeton, NJ: Princeton University Press, 2021.
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