00:00You fly over the Sahara desert aboard a small light aircraft when you see something really strange.
00:07It seems to belong to a world very different from the one that is under your eyes.
00:12To the ocean.
00:13But what ocean can be big enough to shelter such a monstrous starfish?
00:18You go down and you realize that it is not a starfish,
00:22but an imposing dune whose shape is quite unique.
00:26And there are others.
00:27From afar, these magnificent sand structures look a bit like pyramids.
00:32They have a pointed top and star-shaped branches.
00:35With the name of starfish, they are the largest and most complex dunes in the world.
00:41Researchers have discovered similar formations on Mars and even on Titan, one of Saturn's moons.
00:48Starfish are not very rare.
00:50They are particularly common in the southeast of Morocco, near the border with Algeria.
00:56It is this region that you are flying over.
00:59And the dune that amazes you is called Lala Lalia.
01:04It is probably the most famous of them all.
01:07A giant 100 meters high, scientists think it formed in less than a thousand years.
01:13What would you say to go explore these singular formations?
01:17This is an ideal place to land.
01:20Starfish, of course, owe their name to their shape.
01:24They are found in regions where the winds change direction throughout the year.
01:29They are present in different parts of our planet.
01:32However, there is only one official starfish in the rock record,
01:37where all geological data relating to the evolution of the Earth are assigned.
01:41The starfish in question is in Scotland, and it is very old.
01:46It is about 250 million years old.
01:49That's all we know about these strange formations.
01:53Because we don't know what to look for to identify them.
01:56Another problem, starfish often form in remote places,
02:01which makes them extremely difficult to study.
02:04Imagine that you reach the nearest village,
02:07that you then travel, I don't know how many kilometers, to the dune itself,
02:11and that you then have to climb several hundred meters of slippery sand.
02:15Would you try the adventure?
02:17But since you have already landed and the dune is right in front of you,
02:20why not?
02:21After all, you have arrived in a dune field called Erg Shebi.
02:25Fortunately for you, this area has long been a very popular place for tourists.
02:30Look, in the distance, there are hotels and even a practical road.
02:35Scientists who have examined Lala Lalia before you,
02:39have used a georadar to find out more about this sand formation.
02:44This radar allows you to detect the slightest size differences
02:47between the grains of sand and the water content under the surface of the dune.
02:51This is how it is possible to create an image of the interior layers of the dune.
02:56Be careful, it was not easy.
02:58Do you see this trench?
03:00Researchers have dug it to take samples of the sand buried there and analyze them.
03:05A really interesting process.
03:07Indeed, when it is buried deeply,
03:09the quartz contained in the sand absorbs the radiation
03:12from the natural sources of our planet.
03:15We can therefore compare the grains of quartz to tiny rechargeable batteries.
03:19They can store the energy they draw from these radiations.
03:22Once in their laboratory,
03:24the researchers make sure that the grains release this energy,
03:27which manifests itself in the form of light.
03:30Scientists then measure this luminosity,
03:33which tells them when the sand was last exposed to sunlight.
03:39When the experts who dug these trenches looked inside Lala Lalia,
03:44they were amazed.
03:46The huge formation was actually very young.
03:49For a dune, of course.
03:51We would expect a dune several hundred meters high to be quite old.
03:55That is, it dates back several thousand or tens of thousands of years.
03:59But this is not the case here.
04:01The upper part of the dune was 900 years old very recently.
04:04But look at the sand near the base of the dune.
04:07Yes, right there.
04:09It was buried about 12,000 or 13,000 years ago,
04:12like the oldest dunes in the region.
04:15These old dunes were active for several thousand years,
04:18then something went wrong.
04:20For 8,000 years, the sand did not accumulate in this place.
04:24A mystery?
04:25Scientists may have an explanation.
04:28A first period of calm took place at a time
04:31when the climate was warm and humid.
04:34Yes, we are talking about the Sahara.
04:36It dates back to about 11,700 years.
04:39It was the end of the last glacial period
04:42and the beginning of a new era, the Holocene.
04:45And guess what?
04:47The Sahara then became green.
04:49It started to bloom like a pretty botanical garden.
04:52Plants began to grow everywhere, stabilizing the sand.
04:56If you had visited the region at this time,
04:58you would not have recognized it.
05:00However, you would probably have met humans
05:03wandering from swamp to swamp.
05:05And hunting for food.
05:07Researchers found fragments of pottery
05:09and stone tools on one side of the Alalaliya.
05:13Yes, the sand dunes form and move throughout their life,
05:17swallowing and protecting the remains
05:19that we leave on our way.
05:21You just have to dig enough
05:23and you will find something
05:25that will open a window to the past.
05:27It can be ancient fossils,
05:29shells, corals,
05:31or prehistoric plants.
05:33These fossils provide us with precious information
05:36on the history of our planet
05:38and on the beings who inhabited these regions.
05:41This may seem surprising,
05:43but in the Sahara desert,
05:45scientists discovered marine reptiles
05:47and fossilized fish
05:49well preserved in the lower layers
05:51of these ancient sand dunes.
05:53These are the remains of the time
05:55when the sea covered the Sahara
05:57millions of years ago.
05:59Anyway, if you want to survive,
06:02it's time to leave this ancient paradise.
06:044,000 years ago,
06:06the wet period was over
06:08and the Sahara dried up again.
06:10Note that our dune
06:12did not start to form right away.
06:14For a while,
06:16the sand moved here and there,
06:18but did not accumulate.
06:20It is also possible
06:22that the dune began to develop
06:24in another place.
06:26It's an interesting theory.
06:28Scientists have recently discovered
06:30that Lala, the lia,
06:32moves about half a meter per year
06:34and that it accumulates
06:36about 6,400 tons of sand each year.
06:38If your trip to the dunes
06:40has inspired you
06:42and that you now want to explore others,
06:44I have bad news to announce.
06:46Alas,
06:48even if there are dunes
06:50starry all over the world,
06:52they are very difficult to detect.
06:54The problem
06:56is that they are huge,
06:58but that they have no distinctive sign.
07:00Therefore,
07:02you need very large stone beds
07:04exposed if you want to have
07:06a sufficiently wide view to identify
07:08a starry dune.
07:10And there are certainly places
07:12where it is possible to carry out such research.
07:14But you will need to be able to recognize
07:16a whole set of different characteristics.
07:18And being very attentive
07:20and studying a lot,
07:22you may one day come across
07:24one of these mysterious starry dunes.
07:26Comment below if you want
07:28to go in search of one of these wonders.
07:30In the meantime,
07:32let's continue our journey.
07:34You decide to rest
07:36and you begin to descend along the dune.
07:38It is then that you hear strange
07:40and disturbing noises.
07:42Are there ghosts around?
07:44Do not worry, you are safe.
07:46Have you ever heard of a phenomenon
07:48called singing sand?
07:50By descending a sandy slope,
07:52you move the grains of sand
07:54against each other,
07:56creating this sinister music.
07:58At each step, the sand under your feet
08:00is animated like a heart of ghosts
08:02whistling and whispering.
08:04These noises go from deaf rumbling
08:06to high rumblings.
08:08It is as if a symphony of another world
08:10resonated in the dunes.
08:12But, of course, scientists
08:14have their own explanation.
08:16They attribute this phenomenon
08:18to the right atmospheric conditions,
08:20as well as to the size, shape
08:22You have almost reached the foot of the dune,
08:24but be careful not to slip.
08:26When a sand dune reaches
08:28a certain degree of inclination,
08:30it forms a slope
08:32and it becomes very slippery.
08:34This slope is generally
08:36on the side under the wind of the dune
08:38and sheltered from the dominant wind.
08:40The grains of sand begin to accumulate
08:42on the exposed side to the wind,
08:44slowly climbing along
08:46the soft slope of the dune.
08:48At some point, they reach the top.
08:50Gravity takes over
08:52and they begin to slide down,
08:54triggering a cascade effect.
08:58It looks like a miniature avalanche.
09:00And it is better not to be
09:02on its way.
Comments