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00:00A huge discovery in South America raises questions about early human history in the region.
00:07Why would they come here with the dry conditions, limited resources and low oxygen?
00:12It's not exactly a welcoming environment.
00:15A terrifying discovery deep within a Saudi Arabian cave leaves experts searching for answers.
00:22Could they be here as victims or were they the predators themselves?
00:26And a haunting audio phenomenon found in the Gobi Desert baffles scientists.
00:33It's almost unbelievable that it's actually happening, but where could the sound be coming from?
00:40Astonishing discoveries unearthed from the depths of the desert.
00:47Ancient lost cities.
00:50Forgotten treasures.
00:53Mysterious structures.
00:56Extraordinary curiosities, once lost to the sands of time, are finally revealed.
01:02As new technology uncovers remarkable tales hidden beneath the deserts of the world.
01:08The secrets in the sand will finally be exposed.
01:26In the Puno district of southern Peru, high up in the Andes Mountains, is Lake Titicaca.
01:34Covering around 8,300 square kilometres, this immense lake is the largest body of fresh water in South America.
01:42The lake and basin are thought to have been created millions of years ago, when a huge earthquake rattled this
01:49part of the Andes.
01:51And it sits at an astounding 3,800 metres above sea level.
01:56The highlands in Lake Titicaca basin are really inhospitable.
02:01It's cold and dry, and because of the altitude, there isn't much oxygen in the air.
02:09It's a largely treeless, resource-thin environment.
02:13But despite this, the area has a rich human history, dating back thousands of years.
02:20Around 30 kilometres west of the lake, a local man discovered a scattering of artefacts buried in the sandy ground.
02:29He keeps coming across ancient projectile points on his land, so he asks archaeologists working nearby to come and have
02:36a look.
02:37Excavating an area of around 37 square metres, at about 30 centimetres deep, reveals dark stains where the earth has
02:46been blackened by ash from fires.
02:48This indicates a human presence from hundreds, possibly even thousands of years ago.
02:54The discovery was made near Muya Fasiri, a community of Ayamara people.
02:59The Ayamara are a large indigenous group who've lived in this region since before the Inca took control in the
03:0615th century CE.
03:08Nowadays, the Ayamara number around 3 million people, spread out across Peru, Bolivia, Argentina and Chile.
03:15They're mostly herders and farmers, despite living in harsh environments, high up in the Andes.
03:20Their lands became a vital part of the Incan Empire, but they weren't pushovers and regularly revolted against the Inca.
03:30So maybe this is an old Ayamara site?
03:34The team eventually uncovered over 20,000 artefacts, but about 40 centimetres below ground, something else grabbed their attention.
03:44It's human remains, a body in a flexed position, oriented towards the east.
03:51Buried with it are two projectile points.
03:54One is near the pelvic area, and the other is touching the right forearm.
03:59Based on the skull and jawbone, it's determined that this is a male.
04:03And the dental wear patterns indicate that he was between 25 and 30 years old when he died.
04:08Given the style of the projectile points that they found, it's estimated that the remains are between 7 and 9
04:15,000 years old, predating the Ayamara by thousands of years.
04:20So who were these people?
04:22Further excavation of the site, now named Willamaya Parta, revealed another four burial sites containing human remains.
04:31But unlike the first grave, they didn't contain any artefacts.
04:35This lack of grave goods isn't really that surprising.
04:39These people were likely hunter-gatherers who moved around a lot and didn't carry much with them.
04:45As the team continued digging, they discovered another set of human remains, buried around 85 centimetres below ground.
04:53It's fragments of a skull, teeth and parts of various leg bones.
04:58But that's not all.
04:59There are 24 stone artefacts with the body, most of them in a tidy pile near the hip.
05:06So clearly this was a person treated with reverence.
05:09But who were they?
05:12About a kilometre to the north of Willamaya Parta, another burial site had been discovered 18 years earlier.
05:20It contained the remains of 16 individuals, two of whom showed evidence of violent trauma.
05:27One of the bodies had a large hole in the left parietal bone, and a dart point was found between
05:33the ribs and the sternum.
05:34It looks like this person likely suffered a violent death. Given all the projectile points found in the area, maybe
05:41there was a battle between these two groups.
05:43These highland communities would have been exploring new and fragile cooperative dynamics that could have led to competition.
05:48But radiocarbon dating shows that the remains discovered with evidence of injury nearby are over a thousand years younger than
05:57the ones found with the grave goods at Willamaya Parta.
06:01The team conducted a study of the bones, analysing their stable oxygen and carbon isotopes.
06:08The higher the elevation where people live, the lower the number of oxygen isotopes will be present, and the greater
06:15the number of carbon isotopes.
06:17Based on the results, it's determined that these people lived permanently at high altitude, but lower than the Titicaca Basin.
06:24So it's likely that this area was used for seasonal habitation.
06:28But why would they come here with the dry conditions, limited resources and low oxygen? It's not exactly a welcoming
06:35environment.
06:38Further excavations uncovered something unexpected, given the area's inhospitable reputation.
06:46There are fragments of animal bones, mostly large mammals, like deer and camels, but there are 106 unidentified fragments.
06:55This is quite surprising, given the scarcity of vegetation and the overall dryness of the region.
07:01It doesn't seem to be able to support such a diverse range of wildlife.
07:05As the team took a closer look at the artefacts left in the burial site at Willamaya Parta, the role
07:10of the individual became clearer.
07:12These are tools for hunting big game. Given the presence of so many animal bones, this area was probably used
07:20as a seasonal hunting ground.
07:23The projectile points would have been for bringing down the animals, probably with an outloddle, a spear-throwing device used
07:30by ancient hunters.
07:31The knives would have been used for removing the animals' organs, and the scrapers and stones were for processing the
07:37animals' hides.
07:38Because most of the tools were found in a neat pile next to the body, they were likely placed there
07:44in a container of some kind, probably a leather satchel that disintegrated over the years.
07:49This was a symbolic act of respect shown to a skilled hunter.
07:52The team attempted to further analyse the bones to gather more information, but they were too degraded to be studied
08:00for certain attributes.
08:01However, a new form of testing may be able to unlock their secrets.
08:06A recently developed technique examined the proteins in the enamel of the teeth.
08:11Specifically, a protein called amylogenin.
08:15And the tested sample provided a surprising result!
08:29In Peru, on the shores of Lake Titicaca, archaeologists examining the remains from the burial at Willa Mayaparta had a
08:37stunning realisation.
08:40The remains belonged to a woman, between 17 and 19 years old.
08:45This is a major discovery, because it's often assumed that in early hunter-gatherer societies, the males did all of
08:53the hunting.
08:54This discovery wasn't the first time that a prehistoric female, thought to be a hunter, had been found.
09:01In 1989, road workers accidentally unearthed human remains in a gravel quarry, near the town of Buell in south-central
09:10Idaho.
09:11Analysis of the bones revealed that the individual was a paleo-Indian woman, who was roughly between 17 and 21
09:18years old when she died, about 10,000 years ago.
09:21Along with the body, they found several grave goods, including a tool made of bone and a large stem projectile
09:27point, similar to what was discovered at Willa Mayaparta.
09:30It's not just these hunting discoveries that are causing people to rethink traditional gender roles in the ancient world.
09:38There's also significant evidence to suggest that some prehistoric women were not only hunters, but celebrated warriors defending their people
09:49as well.
09:50A team of researchers had recently performed DNA analysis on the remains of a 13-year-old Scythian child warrior,
09:58discovered in Siberia in 1988.
10:02For decades, the scientific community assumed that it was a male, because they found a quiver with arrows, a birch
10:09bow and an axe with the body, grave goods that are traditionally associated with males.
10:14But the DNA revealed that the remains actually belonged to a female, thought to have died about 2,600 years
10:20ago.
10:21In order to expand on the significance of the findings at Willa Mayaparta, researchers analyzed burials across the Americas, studying
10:30429 sites, dated between 8 and 14,000 years ago.
10:36They found that only 27 of them had the tools for hunting big game.
10:42Surprisingly, 10 of these sites contained the remains of females.
10:47Based on this data, the team concluded that between 30 and 50% of prehistoric big game hunters might have
10:55been female.
10:56But some aren't convinced.
10:57It's a very small sample size to arrive at such a sweeping conclusion.
11:02It's also important to remember that the interpretation of grave goods is not so cut and dry.
11:08Certain practices may differ across cultures and generations.
11:12But given the sheer volume of hunting artifacts found with the body, it's safe to assume that the female remains
11:18found at Willa Mayaparta belong to a hunter of some renown.
11:22While the team admit that further research is required to substantiate the conclusions of the study, the discovery, along with
11:30the growing body of evidence across the field, may just force us to reconsider our preconceived notions about the role
11:38of women in prehistoric societies.
11:50The Arabian Peninsula features not only extensive areas of arid landscapes of sand and rock, but also huge lava fields
11:59or Harat.
12:01One of these fields, named Harat Kaibar, covers 14,000 square kilometers of Saudi Arabia.
12:09The Harat Kaibar contains a wide range of volcanic rock types and extraordinary landforms.
12:15And there are over 400 kilometers of unexplored passages and at least 40 lava tubes here.
12:21These tubes are natural tunnels created by a lava flow.
12:26At the end of an eruption, after the lava starts flowing, it drains and leaves these tunnels, caves and entire
12:33cave systems beneath the ground.
12:37While exploring and mapping this fascinating landscape, speleologists, or cave scientists, ventured deep underground inside a cave known as Ung
12:47Jasan and uncovered something truly terrifying.
12:51Deep within this enormous lava cave system is a massive cache of bones, hundreds of them.
12:57And beyond what's visible, there are presumably many, many more underneath the layers of undisturbed sediment.
13:04Not only is this a horrific boneyard, but animal snarls echoing from the depths of the cave, believed to be
13:11made by wolves, are enough to send you running for the surface.
13:17The volcanic field was formed by multiple eruptions along a 100 kilometer vent system over a period of 5 million
13:23years.
13:24And the most recent eruption on record happened between 13 to 1400 years ago.
13:29Archaeologists were called in to investigate Ung Jasan, the longest lava tube in Arabia, measuring 1,481 meters.
13:39Its length is divided into three separate passages by two areas of structural collapse.
13:46The average height of the cave's passages are 8 to 12 meters, with a 45 meter width.
13:53Ung Jasan travels underground from east to west.
13:56The western passage, where the huge cache of bones was found, has only one entrance and is 341 meters long.
14:05While there are a few other smaller deposits and scattered bones in other areas of the tunnel, the extraordinary quantity
14:12of bones found at the end of the western passage are likely the work of predators,
14:17who are creatures of habit and tend to bring their prey back to the same location again and again.
14:22Given the piles of bones and the accompanying bone-chilling growls, Ung Jasan earned the nickname Wolf Den.
14:30So maybe that's what it is, the den of some very well-fed wolves.
14:37The Arabian Wolf is a desert-adapted subspecies native to the Arabian Peninsula and is a protected species in Saudi
14:45Arabia.
14:47Arabian Wolves are one of the smallest subspecies of wolf on the planet.
14:51Their small stature likely helps them adapt to life in a hot, dry climate.
14:58While wolves do use caves as dens, they tend to stick to the mouth of the cave.
15:02So a wolf den nearly 350 meters underground would be very out of character.
15:09Radiocarbon dating of a selection of the bones proves that they range in age from 6,839 to 439 years
15:17old.
15:17This is a wide expanse of time in which many more varieties of wildlife would have been living in the
15:23region.
15:23The bones were inspected for weathering, chemical corrosion, abrasion and carnivore or rodent damage.
15:31They ranged from completely recognizable, with scraps of dehydrated tissue still attached,
15:37to highly decayed bone fragments and splinters.
15:40But two skull fragments were of particular interest.
15:45These two skull calves are undoubtedly human.
15:49Could they be here as victims or were they the predators themselves?
15:53However, there is no significant evidence of human presence in the wolf den.
15:57The volume of bones in the Western passage, including the human skulls, are not likely the result of human activity.
16:06Each bone and fragment was examined under 10 to 20 times magnification,
16:11with different exposures to thoroughly study the remains.
16:15Then the bones with areas of unique surface damage or wear were examined under 80 times magnification,
16:22and showed compelling results.
16:2442% of the bones show evidence of having been eaten by carnivores.
16:29This includes gnaw marks, partially digested bones and rounding from licking.
16:34So humans are definitely off the table.
16:36Some of the tooth impressions are linked to rodents.
16:39And there are a number of distinct quills found throughout the length of Umjursan.
16:44Perhaps porcupines, known as the bone collectors of the animal kingdom, could be responsible.
16:50The cave dwellings of an African crested porcupine are littered with hundreds if not thousands of bones.
16:57And though small, porcupines have been known to take on and kill large cats.
17:03While porcupines dune on items like bone and wood to shave down their perpetually growing incisors,
17:10they're actually herbivores.
17:12So it's unlikely that a porcupine, or even a prickle of porcupines, would have taken down so much large prey,
17:19and dragged them underground just to gnaw on the bones.
17:23Carnivores capable of this kind of damage include large cats, like lions, cheetahs and leopards.
17:30Many of which are critically endangered or extinct in this part of the world.
17:35Asiatic or Persian lions lived across the Arabian Peninsula until the 19th century, but now only survive in India.
17:43The largest Asiatic cheetah is now only found in Iran.
17:47And there are less than 200 Arabian leopards left in the wild in the mountains of Saudi Arabia.
17:53These big cats could have been on the prowl in this region during the early Holocene period,
17:58and would have enjoyed the variety and quantity of the remains found here as part of a healthy cat diet.
18:04However, big cats don't tend to live in such deep caves, and they prefer dining on their prey right out
18:10in the open.
18:12Turning back to Um Jasan, archaeologists examined the tunnel floor for further clues.
18:17Among the sediment and guano deposits, they found hundreds of fossilized fecal specimens known as coprolites.
18:25The majority of coprolites collected here have a white appearance with a crumbly texture and globular shape,
18:31with either a single pellet or fused pellet appearance.
18:34This feces is consistent with one carnivore in particular, the hyena.
18:39While not the largest carnivorous predator, what they lack in size, they make up for in design.
18:45Their distinct and powerful necks and elongated front legs allow them to pull and move-kill over great distances.
18:54Striped hyenas are cave-dwelling predators who do call Saudi Arabia home.
18:59They're a smaller species than their famed African cousins, weighing only 50 kilograms.
19:05And hyena poop is famously white, due to its high calcium content, as a result of digesting so much bone.
19:14They have a digestive system that kills the bacteria in scavenged meat.
19:19And their powerful jaws and razor-sharp teeth can reduce whole skeletons, hooves and all,
19:24to these piles of fragments and undigested bone sharks.
19:29Then we have the cave itself.
19:31Hyenas are not as nomadic as many other predators, and have a distinct family structure that binds them together in
19:38groups called cackles.
19:39As such, hyenas actually spend a lot of their time hanging out in cavernous dens, complete with the bones of
19:46all the creatures they prey on.
19:48One den was even found at 490 metres deep into a cave.
19:52That's 150 metres deeper than the den at M'Gersan.
19:59Experts confidently believe that the cache of bones at the bottom of the western passage of M'Gersan belonged to
20:06a striped hyena den.
20:08This is where the hyena cackle not only filled the cave with the evidence of their feasts,
20:14but likely the wailing and laughter hyenas are known for, which could explain the terrifying sounds the Discovery team heard
20:22echoing from the depths of the cave.
20:34Across the huge inhospitable expanse of North Africa's Sahara Desert is Tunisia's Gulf of Harmomet.
20:42Tunisia's climate varies considerably due to the influence of the Mediterranean Sea and the Sahara Desert.
20:49Given its strategic location on the Mediterranean, it has seen an incredibly diverse range of people trading with, settling in
20:56and even colonising the area over thousands of years, giving it a unique history.
21:04In the days following a very heavy windstorm, beachgoers noticed something odd emerging from the sand in the shallow waters
21:11of the Gulf.
21:13Strange shaped stones just beneath the waves.
21:17Wind and water are always chipping away at coastlines, altering these landscapes over time.
21:23But these rocks seem entirely out of place on the seafloor.
21:28Perhaps they're manmade.
21:31Strange items have been known to wash up on shores after storms.
21:35Everything from beached whales and trash to shipwrecks and bottled messages.
21:40So while these rock formations are unnatural, they're not entirely unique given the circumstances.
21:48As word of their discovery spread, teams of interested investigators descended upon the Gulf in search of answers.
21:54Divers took to the water and quickly discovered that these aren't displaced rocks, nor are they rubbish shifted by the
22:02storm.
22:03These are blocks, 100% manmade building blocks with right angles and hewn flat surfaces.
22:10Actually, given the amount of algae present, these stones have clearly been underwater for a very long time.
22:18So where did they come from?
22:22Expanding their underwater search, not only did they find more blocks, but they discovered connecting foundations and structures, poking up
22:31from the sand and sea growth.
22:33A few loose stones could be explained, but intact building foundations? That's a surprise.
22:40Whatever it is we're looking at used to be above the water.
22:43So what happened here?
22:53A discovery lost to the sands of Nabil Tunisia had perplexed archaeologists.
23:00Limestone has been extensively used as building blocks in the Mediterranean basin since the first constructions made by humans.
23:09Expanding their search on land, the archaeologists hope to encounter ruins that could help explain their findings.
23:16In the grassy area just beyond the beach is a massive foundation made of similar blocks to the ones found
23:23in the water.
23:24It's palatial, and it appears to be built around a central water feature and courtyard structure.
23:30Its design is reminiscent of classic Roman villas dated to the middle of the 4th century.
23:37It's as elegant and well designed as those found 1,300 kilometres away in Rome.
23:43Were the Tradesians fans of Roman design? Who built these and why?
23:48Thousands of years ago, the entirety of the Mediterranean Sea and every surrounding piece of land that touched the water
23:55was absorbed into the booming Roman Empire.
23:58Over 2,000 years ago, the northern coast of Africa was prized for its fertile agricultural lands, and it became
24:05known as the breadbasket of the empire due to its abundant supply of grain.
24:10Considering the number and quality of historic Roman sites found across Tunisia, the area was clearly favoured by the elites
24:19of the empire.
24:20Palatial villas for the wealthy, functional aqueducts, ornate bathhouses, and communal sites for entertainment were built throughout the country at
24:28great expense.
24:30Signs of the Roman good life exist across the Gulf region of Tunisia.
24:35But there are no ruins of farms in the immediate vicinity, so where did this wealth come from?
24:42On the grounds of the villa, known as the House of Nymphs, there is an intricately decorated ceramic basin, complete
24:49with a mosaic inlay, featuring the image of the god Oceanus surrounded by fish, that could offer some insight.
24:57The artwork implies a bounty of fish from the sea.
25:00Perhaps the seaside community was flourishing due to a thriving fishing industry.
25:05Teams of experts were called in to examine the site, and using drone imaging, they were able to create a
25:12connected grid of all the known structures on land and beneath the water.
25:17The submerged discoveries appeared to match the layout and engineered design of the above-ground ruins.
25:24This combines the known area on land with another 20 hectares of structures in the Gulf into one large connected
25:31site or city.
25:33Few historical records exist for the area, but the references we do have indicate this could be the rumoured Roman
25:39metropolis of Neapolis, founded by Julius Caesar after his war against Pompey.
25:46Neapolis was originally established in the 5th century BCE as a Phoenician outpost.
25:51The Phoenicians were an ancient civilisation of merchants, traders and colonisers, originating in the eastern Mediterranean, primarily located in modern
26:02Lebanon and coastal Syria.
26:04But the city was lost to the Romans in 146 CE.
26:09It's likely due to its frequent and often violent changes in government that there are so few records of its
26:15history.
26:16But with little to go on, and nearly half the site underwater, investigations must continue.
26:24On the periphery of the underwater site, divers located a large foundation with giant embedded tanks.
26:34Hundreds of them.
26:37The tanks are often built in sets of three.
26:40They're about two metres deep and they are lined with ancient concrete.
26:44They appear to be connected through pipes from the outer tanks to the inner, larger basin.
26:51These tanks are very familiar.
26:53They've been found throughout the Roman Empire, but rarely in these numbers.
26:57These are garum tanks.
27:00Garum tanks are vats, where ungutted fish are salted, seasoned, left to liquefy, ferment and then dry in the sun.
27:10The bacteria present in the fish intestine is the secret ingredient of the fermentation process.
27:16It's a very smelly, very long process that results in the collection of a clear fish sauce in the central
27:23basin,
27:23which is packed with protein and flavour.
27:26Historians believe it was served along with meats, vegetables and fruits, and was even thought to be an aphrodisiac.
27:34Continuing the exploration of the beachside area, experts came across another large ruin.
27:40But this wasn't a Roman villa. It appeared to have a more functional design.
27:45Along the grounds of this large property are more garum tanks.
27:49These above-ground ruins even contain the pungent residue of fish bones and guts.
27:54So it's likely this was a Roman garum factory.
27:59Garum was the favourite condiment of the Empire, and due to its extreme salt content, it could last for years.
28:04The underwater discovery of hundreds of tanks here, combined with the tanks on land,
28:09point to this city being a major production hub.
28:13If this were a successful garum factory town, the producers would need some way to package and sell their liquid
28:20gold throughout the Empire.
28:23Amphora was just the ticket. They were a specific type of two-handled ceramic vessel used to transport liquids, including
28:31garum.
28:33Amphoras that are believed to have been made in Neapolis feature a ring-like rim, moulded outer face with a
28:40thin, elongated neck, and wide, three-grooved handles.
28:44And they have been found throughout the Roman Empire.
28:48What we now know is that Neapolis became the hub of garum production for the Roman Empire.
28:54But there is something fishier than the smell of garum going on here.
28:57How did 20 hectares of the city end up underwater?
29:01Lost the world for millennia.
29:10The discovery of ancient garum facilities in Neapolis explains the affluence of the region at the time.
29:18But the mystery of the structures found in Tunisia's Gulf of Harmomet remains unsolved.
29:26The Mediterranean and northern coast of Africa sit on very active tectonic plates, leading to increased earthquake activity.
29:36It's possible a quake could have wreaked this kind of havoc, but there are no records or physical evidence here
29:44of any earthquake capable of dropping a city into the sea.
29:48While no earthquakes were registered at that time along the African coast, nearly 2,000 kilometers away in Alexandria, records
29:57show that the city was devastated by a massive tsunami.
30:02On the 21st of July 365 CE, the Roman historian Armianus Marcellinus wrote,
30:10The solidity of the whole earth was made to shake and shudder, and the sea was driven away.
30:16Its waves were rolled back and it disappeared, before returning to destroy the city in its wake.
30:26Over 80% of tsunamis are caused by earthquakes. By following the displaced soil and sediment samples from the bottom
30:33of the Mediterranean, experts are able to track Alexandria's tsunami to its source.
30:38It's believed, based on the current evidence, that the wave originated as a result of an earthquake at the island
30:44of Crete, 654 kilometers away from Alexandria.
30:49It's estimated that the quake would have had a rating of up to 8.5 on the Richter scale, in
30:54order to have caused the devastation registered along the coasts of North Africa, Spain and Greece.
30:59That's a huge earthquake. And yet, no major wave came to Neapolis' shores.
31:06So it wasn't an earthquake or a tsunami that sunk half the city.
31:11Whatever happened in Neapolis seems to have taken a slower and more insidious path.
31:20Experts now believe that the Crete earthquake and subsequent tsunami had another unexpected consequence.
31:27An underwater landslide off the coast of ancient Neapolis.
31:32If proven true, it would have had a huge destabilizing effect on the coastline of Tunisia.
31:38As the undercurrent swept sands deeper into the sea, the ground along the coast would have been infiltrated by water.
31:45The theory is that Neapolis likely suffered from liquefaction, which ultimately led to the city sinking into the sea.
31:56Liquefaction occurs when loosely packed waterlogged soil, at or near ground level, loses its strength or structural integrity in response
32:05to vibration in the ground.
32:08The loss of major elements of the city and its garum production would have felt a huge blow to the
32:14Roman Empire, which itself was already nearing the point of collapse.
32:19Interestingly, waves were the key to finding the lost city of Neapolis as well as the source of its demise
32:26so many years ago.
32:30Today, the modern town of Neapolis stands watch over what remains of the ancient Roman city, both above and below
32:40the sea, a testament to the unique and connective history of the area.
32:56Towering 300 meters above the expanse of southern Mongolia's Gobi Desert, the sand dunes at Hongar and El's are a
33:05dramatic change from the otherwise flat surroundings.
33:09The Gobi stretches across a variety of different ecoregions. Sand dunes give way to hard-packed rock desert, which transitions
33:17to salt marshes and lakes.
33:20But one thing that the entire region has in common is how little rain it receives. Only about 40 millimeters
33:27a year.
33:28That's an incredibly low amount of rainfall. To put things into perspective, Australian deserts average around 250 millimeters a year.
33:37The dunes are some of the biggest and most magnificent in Mongolia, drawing people from far and wide.
33:46But it's not just the dunes that draw gasps of wonder.
33:50Researchers visiting the area encountered an otherworldly deafening sound that made their bodies vibrate.
34:01It's all-encompassing. The sound is this low-pitched drone that sounds as though it's coming from everywhere all at
34:07once.
34:08It's a rich baritone, almost as if someone or some thing is singing.
34:15It's almost unbelievable that it's actually happening. But where could the sound be coming from?
34:21It's a pretty frightening sound. It adds to the mystery of this entire area, which occupies a dramatic and important
34:29space in human history.
34:33Over the course of centuries, travelers and tradesmen alike struggled their way across this ruthless environment.
34:40And because of this, we have many accounts detailing their experiences.
34:44The researchers began to investigate this auditory phenomenon that has mystified everyone who's ever encountered it, since it was first
34:54recorded in a 9th century Chinese manuscript.
34:58In the 13th century, Marco Polo also famously wrote about a certain inexplicable sound that terrified everyone who encountered it.
35:07The singing can last for more than a minute, and it registers at a pretty low frequency and at over
35:13100 decibels. This is incredible. It's louder than a jet engine.
35:19The sounds appear to be originating from far away. Some people say that they're actually spirits residing between the dunes,
35:26looking to lure people away from their companions.
35:31It'd be hard to prove that spirits are at work here. And although there are plenty of things in this
35:36world that can't be explained, the scientists believe that this is not one of them.
35:43If you've ever heard a swarm of locusts or cicadas, you might think that they could cause such a disruptive
35:48sound. But when you listen closely, these sounds in the desert are very different.
35:56And while earthquakes have been known to make loud, booming sounds, there's been no seismic activity picked up around the
36:02dunes when this sound occurs.
36:05So if it isn't the result of animals or plate tectonics, you wonder if it could be the sand that
36:10has something to do with it. It's the one thing there's a lot of around here.
36:16This bizarre audio phenomenon has been puzzling the scientific community for many years. Their search for answers led them to
36:26the continent of Australia.
36:31The sands at Hayams and Whitehaven Beach famously emit loud squeaks when people walk across them.
36:40But these mousy squeaks are much shorter than the meditative sounds heard among the dunes of Mongolia. They're also more
36:47high pitched.
36:49They don't really compare whatsoever. Measurements reveal that they're in the 500 to 2500 hertz range, whereas these sounds in
36:57Mongolia measure below 300 hertz, a much lower frequency.
37:02Of course, this is a totally different sound. But could the physical mechanisms causing the sand to squeak be similar
37:10to what's happening in the Gobi Desert?
37:13Examination of the sands at the Australian beaches revealed that this high pitched sound only happens if the sand grains
37:20are composed of quartz and have a rounded shape.
37:25The squeak happens when the similarly sized quartz grains rub against each other and start vibrating. The vibration then transfers
37:33its energy to the tiny air pockets surrounding the sand grains. This energy then reaches our ears in the form
37:40of a squeak.
37:42Also, the sand only squeaks as a result of someone or something interacting with it. But in the Gobi, even
37:49if the scientists don't make a move, this noise will still occur.
37:54Research reveals that it's not only in Mongolia where people have witnessed the phenomenon. The singing sands have been encountered
38:03in many of the world's deserts.
38:05There are reports of these booming or singing sounds in the deserts of Morocco and Oman.
38:11And in the US, the Eureka Dunes of Death Valley have mystified visitors for years.
38:19The Eureka sand dunes are the tallest dunes in the state of California. They rise approximately 200 meters from the
38:27desert floor.
38:30Researchers noticed that when the wind picked up, these strange sounds increased in frequency.
38:37Wind can cause a whole range of sounds, but it doesn't have the capacity to cause these feelings of vibrations
38:43inside the body.
38:46While observing the dunes, they notice that sand avalanches are triggered by the wind.
38:51A sand avalanche happens when the angle of the sand accumulated at the top of a dune reaches a critical
38:59point where it's incapable of supporting its own weight.
39:02Usually, a couple of seconds after the avalanche, this booming singing sound occurs.
39:09So it's possible that the sand's movement is somehow causing these sounds.
39:15In order to better understand what processes were taking place, the scientists used an instrument known as a geophone, a
39:23device used to measure vibrations.
39:26If the earth, or in this case the sand, is vibrating, the geophone will detect this.
39:33They placed the geophone not on the face of the dune, but on the flat ground beneath it.
39:38They then triggered a sand avalanche and waited to see if the geophone registered anything.
39:44Sure enough, the geophone registers the vibrations rippling through the dune and continuing along the valley floor.
39:52So the sand is somehow causing these sounds.
39:55But there has to be more at play here.
39:58Additionally, when the sand on the valley floor is agitated, the geophone picks up the vibrations.
40:03This means the grains of sand are rubbing against each other.
40:06But most importantly, the telltale drone remains absent.
40:10So whatever is happening must exclusively involve the structure of the sand dune.
40:16Hoping that the dune itself may shed some light on the mystery, the researchers considered its structure and formation.
40:25A dune is essentially created by wind blowing sand across a landscape.
40:30As it does, little piles begin to accumulate.
40:33And as more and more sand gathers on top of these piles, a gap is formed in front of them.
40:39As it grows, it does so in layers.
40:42And we're talking tons of sand here.
40:45Remember, these dunes are hundreds of meters tall.
40:48As the dune gets bigger, the sand in its core is compacted by all of the sand that's above it.
40:56A dune can only reach a certain height.
40:58When an opposing side reaches an angle of around 33 degrees, it will self-regulate, releasing avalanches that cascade down
41:07its face.
41:10Ground penetrating radar reveals that the top layer of the dune is around one and a half to two meters
41:15of loosely packed sand.
41:17Below that is a super densely packed mass of sand that's almost like concrete.
41:23But it's on top of the outer layer where the avalanching occurs.
41:27Curious about the properties of this top layer, the scientists looked at its seismic velocity, its ability to carry seismic
41:35waves.
41:36The physical properties of the dune's top layer allow the vibration to travel through it at a specific velocity.
41:43While the dense concrete-like sand below it only reflects the vibrations right back at it.
41:50The scientists theorize that as the sand is avalanching, the vibrations created by the moving sand are trapped and reverberate
41:59throughout the top layer.
42:01The top layer is acting like an amplifier of the vibrations caused by the sliding sand.
42:08This has the same effect that the body of a guitar has.
42:12When you strum a chord, you don't get any reverberating sound unless you have the body of an instrument to
42:18capture it.
42:20Amazingly, it creates its own feedback loop, which, as we've heard, can be both terrifying and beautiful.
42:28The phenomenon of the singing sands can be characterized as nature's true instrument, playing these long drawn-out notes for
42:38humanity since time began.
42:41gotten the most terrifying hello, a very beautiful,撒 Tillman, and flying in, and climbing.
42:45Do you do now?
42:45I'm aBook and I'm a renowned scholar.
42:47You can find that when you make your own eigene technology.
42:47It's not the most vulnerable, but you can find that as humans as humans as humans as humans.
42:48You can find that a human love.
42:50You can find that she can.
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