00:00You're flying over the Sahara Desert in a small light aircraft, when you spot something
00:05truly weird.
00:07It seems to belong to a very different part of the world, the ocean.
00:11But what ocean can be huge enough for this monstrous sea star to dwell there?
00:17You descend and realize that it's not a sea star.
00:21It's a towering dune with a pretty unique shape, and it's not alone.
00:27From afar, these magnificent sand structures look a bit like pyramids.
00:32They have pointed tops and radiating arms.
00:35Called star dunes, they're the most complex and largest desert dunes in the world.
00:40They're the tallest of their kind, but that's not the coolest thing about them.
00:45Researchers have found similar formations on Mars, and even on one of Saturn's moons,
00:51Titan.
00:52Star dunes aren't super rare, but they're especially widespread in southeastern Morocco
00:57near the border with Algeria.
00:59That's where you're flying at the moment, and the breathtaking dune you're marveling
01:03at is Lella Lallia, probably the most famous of them all, a giant 330 feet tall.
01:10Scientists believe that it formed in less than 1,000 years.
01:14How about doing some research to find out more about these unusual formations?
01:18There, I see a great spot for landing!
01:22Star dunes got their name because of their multi-armed shapes.
01:26They form in areas where winds change direction throughout the year.
01:29But even though you can find them in different places on our planet, there is just one confirmed
01:34star dune in the rock record, the collective record of Earth's development reflected
01:39in preserved rocks.
01:41The star dune in question is in Scotland, and it's ancient, from about 250 million
01:47years ago.
01:48That's all we know about super old star dunes, probably because we don't know what
01:53to look for to identify one.
01:57Another problem, star dunes often form in remote locations, which makes them extremely
02:01difficult to study.
02:03Imagine reaching the nearest settlement, then somehow traveling who knows how many miles
02:08to the dune itself, and then slogging up several hundred feet of shifting sand.
02:14I'll pass.
02:15But you can go since you've already landed, and the dune is right here in front of you.
02:21Currently, you're in a dune field called Erg Shaby.
02:25Lucky for you, this area has long become a popular tourist stop.
02:30Look, in the distance, there are hotels and even a good road!
02:36Scientists who examined Lele Lalea before you used ground-penetrating radar to find
02:41out more about the sand formation.
02:44This equipment can detect the tiniest differences in sand grain sizes and water content under
02:49the surface of the dune.
02:51That's how you can create a picture of its interior layers.
02:57Look out!
02:58Phew!
02:59It was a close call.
03:00See this trench?
03:01The researchers dug such trenches to take samples of long-buried sands and then examined
03:06them.
03:07It's a pretty cool process.
03:09The thing is, while buried deep inside, the quartz in the sand accumulates radiation coming
03:14from natural sources within our planet.
03:17We can compare the grains of quartz to miniscule rechargeable batteries.
03:21They can store the energy they get from radiation.
03:24When researchers bring them to the laboratory, they can make the grains release that energy,
03:29which comes out in the form of light.
03:32Scientists can measure the brightness and say when the sand enjoyed sunlight for the
03:36last time.
03:38Now when those experts who dug the trenches looked inside Lele Lalia, they were shocked.
03:44The enormous formation turned out to be very young, for a dune of course.
03:49You'd expect a dune that is several hundred feet tall to be pretty old, like thousands
03:53or tens of thousands of years.
03:55But that wasn't the case, well at least not entirely.
03:59The upper part of the dune has turned 900 just recently.
04:05But look at the sand near the base of the dune.
04:07Yep, right there.
04:09Well it was buried there around 12 or 13 thousand years ago, representing ancient dunes in the
04:15area.
04:17Those good old dunes were active for a couple thousand years, and then something went wrong.
04:22Because for a whopping 8 thousand years, the sand wasn't accumulating there.
04:26A mystery?
04:28Scientists might have an explanation.
04:31You see, the first part of this quiet period occurred during the time when the climate
04:35became warm and wet.
04:37Yep, even in the Sahara.
04:39It happened about 11,700 years ago.
04:43It was the end of the last ice age and the beginning of a new era, the Holocene.
04:48And guess what?
04:49The Sahara went green!
04:51It started blooming like your local botanic garden.
04:54Plants started popping up all over the place, stabilizing the sand.
04:58If you had visited the Sahara during that period, you wouldn't have recognized this
05:02place.
05:03But you would have likely come across humans wandering marshy landscapes and hunting for
05:07food.
05:09Researchers have found pottery fragments and stone tools on one side of Lele Lalea.
05:16That's true.
05:17As sand dunes form and then shift throughout their lives, they swallow and protect ancient
05:22remnants of life.
05:24Just dig well enough, and you might find something that will provide you with a window into the
05:29past.
05:30It can be ancient fossils, anything from fossilized shells and corals to prehistoric plants.
05:37Those can offer precious insights into the history of our planet and the living beings
05:41once inhabiting certain regions.
05:44Now it might come as a shock, but in the Sahara Desert, scientists have uncovered well-preserved
05:50marine reptiles and fossilized fish within the layers of those ancient sand dunes.
05:56They are the remains from the time when the Sahara was covered with a sea millions of
06:01years ago.
06:03Anyway, it's time to leave that ancient paradise if you want to survive.
06:08Four thousand years ago, the wet period came to an end, and the Sahara dried out again.
06:13Interestingly, our dune didn't begin building up right away.
06:17For some time, sand probably blew through but didn't accumulate.
06:22Or the dune could have started growing in a different location.
06:25But it's a valid theory since scientists have discovered recently that Lelulalia shifts
06:30around 1.6 feet every year.
06:33It also accumulates about 6,400 tons of sand every year.
06:40Now if you've been inspired by your dune trip and are now eager to explore more of them,
06:44I've got some unpleasant news for you.
06:47Unfortunately, although there might be star dunes locked in sandstones around the globe,
06:52they're super tricky to detect.
06:55The problem is, dunes are huge, but they lack a single distinguishing feature.
07:00So you'd really need large exposed beds of rock if you want to get a wide enough view
07:05to identify a star dune.
07:07On the bright side, there surely are places where it might be possible to do such research,
07:12but you should be ready to know that it might be just a set of various features that look
07:17like other dunes.
07:19But if you combine them, you'll say, ah, it's likely to be a star dune!
07:25Comment below if you'd like to go on a trip in search of a star dune!
07:28Meanwhile, we'll continue our journey.
07:31You decide to have some rest and start climbing down the side of the dune.
07:35That's when you begin hearing it, terrible, haunting sounds.
07:40Are there ghosts nearby?
07:43Worry not, you're safe.
07:44You might have heard of a phenomenon called singing sands.
07:48As you walk down some sandy slopes, you disturb the grains of sand.
07:52They rub against each other, producing friction that creates those eerie melodies.
07:57With each step, the sand beneath your feet comes alive in a ghostly choir of whistles
08:02and whispers.
08:04The sounds range from low hums to loud, high-pitched wails, as if an otherworldly symphony is echoing
08:10through the dunes.
08:12But of course, scientists have their own very practical explanation.
08:16Attributing this phenomenon to the right atmospheric conditions combined with the unique size,
08:22shape, and moisture content of the grains.
08:25Now you've almost made it all the way to the bottom of the dune.
08:29But beware of slip faces!
08:31When a sand dune reaches a certain steepness, it develops a slope.
08:36That's the very slip face I was talking about.
08:38This slope is usually on the leeward side of the dune and sheltered from the prevailing
08:43wind.
08:44Sand grains start accumulating on the windward side, slowly creeping along the dune's gentle
08:50slope.
08:51At one point, they reach the top, gravity takes over, and they start sliding down, triggering
08:56a cascading effect.
08:58It looks like a miniature sand avalanche, and I wouldn't want to end up in its way.
09:03That's it for today!
09:07So hey, if you pacified your curiosity, then give the video a like and share it with your
09:11friends!
09:12Or if you want more, just click on these videos and stay on the Bright Side!
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