00:00When you imagine an epic scene in the desert, with its crushing sun, its infinite dunes, and its almost supernatural oases,
00:08it is natural to imagine the mythical Sahara, isn't it?
00:11Yet, what would you say if you were told that 11,000 years ago, this vast sea of burning sand had a radically different appearance?
00:19Of course, no one was there to testify to this.
00:22But it is said that at that time, what we now call a desert, was a real Eden,
00:28dotted with lakes, rivers, green meadows, and even forests.
00:33So, where did all this water go?
00:36There are many stories about these ancient times when the deserts were covered with jungle and luxurious forests,
00:44until an upheaval, whether it be climate change or titanic earthquakes,
00:49transformed these fertile lands into arid dunes.
00:52But what would you think of a hypothesis, according to which the Sahara would have been transformed into a desert by human activities and... goats?
01:00Over the millennia, the Sahara has experienced alternations marked between wet and dry periods,
01:06mainly due to slight variations in the orbital inclination of the Earth,
01:11influencing the amount of solar radiation received by the atmosphere.
01:15There were even phases called African wet periods,
01:19where abundant rains metamorphosed this arid landscape into a screen of sparkling greenery.
01:25However, between 8 and 4,500 BC, an unusual phenomenon shook the region.
01:31Some areas went from a humid climate to an arid climate far too quickly for this to be explained only by orbital variations.
01:39In a relatively short period of time, the greening Sahara gave way to the desert we know today.
01:45If you ask scientists about the reason for this change, they will undoubtedly evoke a bad parameterization of the data.
01:53This jargon may seem nebulous, so allow us to translate,
01:57it means that they themselves are not sure and that they still lack several pieces of the puzzle.
02:03By analyzing old samples of soil and pollen, however, researchers have detected an intriguing tendency.
02:09Where shepherds, humans accompanied by their domestic animals, had to stay, the vegetation seemed to be changing.
02:17To believe that every time these men and their herds crossed green expanses,
02:22they left behind them only bushes and desert landscapes.
02:26What an irony!
02:28It seems that the overgrowing practiced by these populations has contributed to drying the atmosphere,
02:34because the plants, by releasing moisture, participate in the formation of clouds.
02:39This deforestation would have intensified the sun, thus precipitating the end of the humid periods.
02:45Moreover, it is likely that our ancestors made an excessive use of the burn to grow their land,
02:52accelerating the advance of the desert.
02:55In any case, scientists agree that this luxurious Sahara would have become a desert again,
03:01even in the absence of human intervention, a phenomenon attributed to the natural cycles of the earth.
03:07It is therefore useless to put the entire responsibility of this brutal transition on man.
03:12This change could simply reflect the interactions between vegetation and dust cycles.
03:18It remains difficult to determine the causes of these changes, as the factors are interconnected.
03:23During the last humid period, the Sahara was home to hunter-gatherers.
03:27With its gradual drying, these populations turned to farming to meet their needs,
03:33but it is just as conceivable that overgrowing has contributed to accelerating the degradation of the landscapes.
03:40So, what is the real origin of this phenomenon?
03:43The egg or the hen?
03:45In this particular case, the human or the cow?
03:48The evidence available today does not yet allow to decide.
03:52Nowadays, we can say that water is no longer an insurmountable problem in the Sahara,
03:57despite its desert immensity and the fact that the air of the green forests has changed.
04:02Technology offers unprecedented solutions, such as the Nubi Basin, the largest underground water reservoir in the world.
04:09This hydraulic treasure, located on the eastern border of the desert,
04:13extends over four countries in North-East Africa, Sudan, Chad, Libya and Egypt.
04:19It covers about 2 million square kilometers and contains nearly 150,000 cubic kilometers of underground water.
04:25It is enough to see the infrastructure deployed during its implementation.
04:29It is the largest irrigation project on the planet, making possible a prosperous life in the heart of the Sahara.
04:34But imagine living in the Sahara with a single source of water.
04:38It seems inconceivable, doesn't it?
04:40However, the ancient Garamonte have achieved this, not only by surviving, but by thriving for nearly a millennium.
04:47Despite the absence of swamps or rivers feeding their desert refuge.
04:51These ingenious pioneers were the precursors of urban life in the heart of the sands,
04:56to the point of attracting the attention of the Romans, who could only admire their genius.
05:00While many considered them as simple nomads,
05:03the Garamontes built a real empire under one of the most hostile climates on the planet.
05:08But what was their secret?
05:10They showed remarkable ingenuity by digging a vast underground network to exploit a gigantic aquifer.
05:16They literally extracted every drop of water from the depths of the dunes.
05:20But recent studies reveal that, although they were laborious and ingenious,
05:25the Garamontes also benefited from a good dose of luck.
05:29The Garamontes had an underground aquifer, which led the water to a hill,
05:33where they set up more than 500 fogueras, remarkable irrigation systems,
05:38some extending over more than 4 kilometers.
05:41These devices functioned like a straw, allowing the irrigation of their crops for nearly a century,
05:47especially since low rainfall was enough to recharge the system.
05:51However, the lack of rain eventually exhausted this aquifer.
05:55To exploit the resources again, it would have been necessary to dig more tunnels
05:59and mobilize a larger number of workers.
06:02A complex task in a context marked by food and water shortages.
06:06You can probably guess what happened to the Garamontes in such conditions.
06:10The disappearance of Garamonte culture seems to be linked to several factors.
06:14Climate change probably played a role,
06:17but it is also plausible that they overexploited their water reserves.
06:21At the time, the Sahara was a fertile region,
06:24thanks in particular to the ingenious irrigation systems put in place.
06:27However, fossil water being a non-renewable resource,
06:31the phreatic aquifers gradually dried up,
06:34seemingly precipitating the decline of this kingdom from the end of the 7th century.
06:38This decline evokes the story of someone who wins a huge pact,
06:41dilapidates his wealth and finds himself returning to a much less enviable daily life
06:46once his savings are exhausted.
06:48Moreover, even if the Garamontes had left behind them some evidence of their wisdom,
06:53it is very likely that we never managed to understand it.
06:57We do not know the language they used,
07:00and their texts remain almost entirely indescribable to this day.
07:04Let's go back to the Sahara.
07:06This desert was formed about 4,500 years ago,
07:09but today we have a fascinating view of life at this time,
07:12thanks to natural parks in Africa.
07:15These places house an extraordinary open-air art gallery,
07:18with more than 15,000 paintings and ancient engravings,
07:21illustrating the daily life of the inhabitants of some 11,000 years ago.
07:25Finally, if the engravings are not enough
07:27and you want to discover a real desert transformed into a flower garden,
07:31a trip to California is necessary.
07:33You can observe one of the most beautiful natural phenomena there,
07:36the superfluorescence.
07:38Imagine an explosion of colors,
07:40orange, green, pink,
07:42in an arid desert after several years of rain in usually dry areas.
07:47This dazzling spectacle, visible from space,
07:50makes the desert a living painting of a rare beauty.
07:53This rare phenomenon also manifests itself in other arid and desert areas,
07:57notably in West Africa and Australia,
08:00in Western Australia and Chile.
08:02These regions, where summers are arid and dry,
08:05benefit from a soft and humid air in winter,
08:08offering a perfect setting for spectacular flowering.
08:11The flower seeds buried in the sand of the desert
08:14can wait for decades before germinating.
08:17When the scorching sun eliminates all the herbs
08:20and enough rainfall comes to moisten the soil,
08:23it is as if the seeds decided that their time had come.
08:27At that moment, hundreds of thousands of tourists flock
08:31to immortalize these landscapes
08:33and share their enchanting clichés on social networks.
08:36Alas, this influx represents a serious threat to these fragile flowers.
08:40If you visit such sites,
08:42be sure not to pick them up or crush them.
08:45Stay on the marked paths,
08:47do not leave any waste,
08:49and limit yourself to taking pictures
08:51while leaving only your footsteps behind you.
08:54Is it clear?
08:55Very good!
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