(dramatic orchestral music) [Narrator] In the driest regions of the world.

In places where clouds rarely form.

Wind and flash flooding have played key roles in shaping the landscape.

Creating dunes and eroding rocks into some of the greatest wonders on Earth.

For all their reputation as inhospitable places, deserts are full of surprises.

For they also harbor some of the most resilient plants, animals, and people in the world.

Deserts develop in the hearts of continents.

In areas sheltered from rain, by high mountains, and in the subtropics where sinking dry air prevents clouds from forming.

Including the cold deserts that sit at either pole, they cover a fifth of the land area on Earth.

When it comes to hot deserts no two look the same.

But they do have one thing in common, and that's rare or infrequent rainfall.

They are also prone to rapid evaporation, when the harsh sun strips more moisture out of the atmosphere than the weather puts in.

In either scenario, the result is little to no surface water.

(Arabian flute) The largest hot desert in Earth is the Sahara.

It stretches from the Red Sea to the Atlantic, across most of Northern Africa, covering an area that's roughly the same size as the United States of America.

The average temperature in the Sahara during the summer months is between 38 and 46 degrees Celsius.

Winds can be as strong as hurricanes and often give rise to sandstorms that can extend for more than 600 miles, covering everything in their path.

Half the Sahara receives less than three centimeters of rain a year, but climatologists say it hasn't always been this dry.

They believe the entire region was once as lush and livable as the banks of the river Nile.

(soft instrumental music) Traders have crisscrossed this vast desert for centuries.

In ancient times, they traveled exclusively on camels, carrying everything from gold and salt, to slaves.

The traders relied heavily on way-stations, such as the Siwa Oasis, one of Egypt's most isolated settlements.

Nestled in a basin some 19 meters below sea level, Siwa has hypersaline lakes, sulfurous hot pools, and over 400 natural springs.

Some of the springs are too salty for drinking, so they have been turned into swimming holes.

But others are less saline, and help to nourish extensive date and olive plantations which are central to the local economy.

The soils are also quite salty, which limits the type of crops people can grow here.

But it also helps to strengthen the bricks they make from the soil to use in the construction of their houses and shops.

On the downside, if it were to rain, the salt would accelerate the deterioration of their buildings.

Now, this is not normally an issue in the desert, but in 1926, a freak storm that brought torrential rain for three days and nights destroyed the old town and most of the ancient fortress of Shali.

With its vast sea of shifting sands, the Sahara is every bit the image most of us conjure when we try to visualize or define what a desert looks like.

But only 10% of the world's arid landscapes are made up of dunes such as this.

Some deserts regions are defined by salt flats.

Others can be quite mountainous.

The Sinai desert, which falls within the same arid belt as the Sahara, has rocky peaks that are several thousand meters high.

They include the holy mountain that lends its name to the whole peninsula.

Mount Sinai is sacred to three world religions-- Judaism, Islam, and Christianity-- and is believed to be the place where God gave Moses the stone tablets bearing the ten commandments, a set of laws that still govern the lives of millions of believers today.

At the foot of Mount Sinai is one of the oldest working Christian monasteries in the world, St.

Catherine's.

The monks who live within the confines of the monastery share their surroundings with the Jebeliya Bedouins, who have been living here for over 1400 years.

Most of their ancestors came from Eastern Europe to protect the monastery while it was being built.

And despite the desolate landscape, they clearly managed to settle in.

Thanks to the presence of water, occasionally flowing through the desert's labyrinth of eroded gullies, or Wadis, the Jebeliya have even been able to establish gardens, creating their own oases in this otherwise harsh, high altitude desert.

(Aboriginal music) In the heart of Australia's red center, a huge rock dome rises from the desert plain, completely dominating the landscape and the spiritual lives of the traditional owners of this land, the Anangu.

They believe Uluru, and the domes of nearby Kata Tjuta, were formed by their creation ancestors.

To the Anangu, Uluru is no mere rock, it is a living place, where their Tjukurpa, or spiritual law, is written in stone.

Before their creation ancestors traveled across this land, it was featureless.

There were no rocks, no caves, no waterholes or trees.

The Anangu believe that every deed and journey their creation ancestors made became imprinted in the land, and see its features as evidence of their presence.

Geologists have a completely different take on how Uluru and Kata Tjuta formed.

500 million years ago, this whole area was covered by a vast inland sea.

When it disappeared, the sea bed and, in time, the rocks beneath it were exposed.

The movement of the Earth's tectonic plates then forced the horizontal layers that formed the bedrock of Uluru into an upright position, tilting the whole sandstone mass on its end.

Over many millions of years the softer rocks eroded away, until all that remained was the iconic landmark we see in the landscape today.

The most amazing thing about Uluru is that it is just the tip of that huge slab of weathered rock, and extends a full six kilometers below the surface of the Earth.

While significant features on Uluru appear to have been shaped by the wind, geologists believe they owe much of their creation to chemical weathering.

Minerals in the rock break down or decay when exposed to air and moisture.

Surprisingly, the core color of Uluru's sandstone is not orange, but gray.

Iron rich, the sandstone rusts in contact with air.

Water also contributes to the formation of features on Uluru.

Occasional rains are common, but only total around 300 millimeters.

That's roughly a bathtub full of water, draining out across every square meter of land, over the course of a year.

But every now and then, big storms dump more than half that amount in one go, turning Uluru into a wonderland of waterfalls.

The entire landscape is transformed, but the phenomenon is always short-lived.

The water lingers in a few places, such as Mutujulu waterhole.

But with an evaporation rate nine times higher than the average annual rainfall, the rest quickly disappears.

And Uluru's more familiar "rock star" glow is restored.

If Uluru quietly defines the heart and soul of Central Australia, then Monument Valley absolutely screams the American West.

This vast, cinematic landscape, on the border of Arizona and Utah has been the go-to location for Hollywood Westerns Since the 1930s.

Director John Ford made ten films in Monument Valley, including "Stagecoach", the six-gun saga that shot actor John Wayne to fame.

The most famous geological features in this landscape are "the mittens", so named because they resemble two gloved hands with their thumbs facing inward.

Next to them, completing the overexposed trio, is Merrick Butte.

This iconic vision of the Wild West sits in the middle of Monument Valley Tribal Park, part of a much larger reservation owned and managed by the Navajo Nation.

The Navajo have many complex stories to explain how these formations were created, including one that involves a fourth world, inhabited by monsters.

Their ancestors fought and killed these beasts, leaving their carcasses to turn into stone.

The geological explanation for how these flat-topped mesas and buttes, and needle-thin spires or temples that rise up from the dead flat desert floor, is far more pragmatic.

Created over many millions of years, they are all that remain of a giant plateau that once covered the entire region.

It was uplifted by tectonic forces, then cracked and chiseled by alternating cycles of frost and heat, and slowly eroded by wind and water.

The layers in mesas, which are wider than they are tall, and buttes, which are at least as tall as they are wide, correspond to different geological periods.

Some layers are softer, and more quickly eroded than others, but the hardest layer forms a cap on top helping to protect the form beneath.

Flash flooding over the eons has carried most of the giant plateau away, leaving behind sand and siltstone, stained with red oxide, on the desert floor.

Vegetation is minimal, so habitats for wildlife are limited.

But one animal that's adapted to the harsh conditions here is the jackrabbit.

Most animals pant or sweat to keep cool, but jackrabbits have a different strategy.

They can't afford to lose moisture so they've evolved oversized ears loaded with blood vessels that help them shed excess body heat.

Beyond the main road that rattlesnakes its way through Monument Valley, there are dozens of other pinnacles, buttes, and mesas, each with a story to tell.

One of the greatest wonders of this desert is its haunting, soulful silence broken only, on rare occasions, by the rumble of an approaching storm, filling the endless sky with drama.

Cowboys and their horses are integral to the desert landscape of America.

But across the Arabian peninsula, from Jordan to Oman, Bedouins and their camels rule.

The Arabian Desert is the second largest hot desert in the world, and a surprising number of animals have adapted to its harsh conditions.

With a population in excess of 1.6 million, by far the most common animal here is the Arabian camel.

Camels can go for days without access to surface water, breaking down the fat they store in their humps to quench their thirst.

Big, thick footpads help them withstand the hot, shifting sands and rocky terrain that define the Arabian Desert.

They can close their nostrils to stop sand from getting in when the wind is whipping it into a frenzy, and have a third, transparent set of eyelids and two rows of eyelashes to protect their eyes as well.

(upbeat Arabian music) The Arabian Desert is also a stronghold for a new generation of wild Arabian Oryx.

They were once hunted to extinction on the Peninsula, but breeding and conservation programs have successfully reintroduced more than a thousand Oryx into the wild.

They are a majestic desert antelope that many historians believe is the inspiration for the mythical unicorn.

And certainly when viewed from the side, their two horns can appear as one.

Adult males will fight for supremacy using their horns as weapons, but they don't overheat during these battles, as they are able to cool the blood flowing to their brains as they breathe, through an unusual network of capillaries in their noses.

Their light body color reflects the sunlight, but in winter, their legs darken to absorb more of the desert heat.

(instrumental music) One area where they have been successfully reintroduced is Wadi Rum, also called The Valley of the Moon.

Wadi is the Arabic word for valley, and this is the largest in Jordan, set on a high plateau at the Western edge of the Arabian desert.

Winter floods and sandstorms have shaped the sandstone into natural fortresses, towers, and arches, a virtual city of iconic desert architecture, millions of years in the making.

British army officer Thomas Edward Lawrence, also known as Lawrence of Arabia, who fought alongside Arabs against the Turks during the first World War, described Wadi Rum as "vast, echoing, and God-like."

Lawrence's name is inextricably linked to Wadi Rum, and his exploits during the Arab revolt are now part of the local folklore.

The "Seven Pillars of Wisdom" are so named in honor of Lawrence's autobiography.

And Lawrence's Spring is where he is said to have bathed during his stay in Wadi Rum.

(Arabian music) Lawrence was an ally of the Bedouins, whose customs and traditions enliven the landscape to this day.

Once a nomadic people, they still pride themselves on their bravery, generosity, and hospitality, virtues that have no doubt been critical to their survival here for centuries.

Earlier inhabitants have left their mark on the landscape and soul of Wadi Rum, too.

And their story is quite literally etched in stone.

Over 20,000 prehistoric drawings or petroglyphs, and just as many inscriptions, have been found among the rocks and gorges in the valley.

They are carved into a dark layer of oxides or "desert varnish" that create a natural sheen on the rocks, helping the figures stand out.

They provide evidence of habitation and land use that dates back to the Stone Age.

Rock-solid proof that people have lived in Wadi Rum for at least 12,000 years.

(instrumental music) Deserts are places that are full of mystery, of messages left behind in the landscape by ancient civilizations.

Hieroglyphs, petroglyphs, and in the deserts of Southern Peru gigantic geoglyphs... drawings on the ground that are made by removing around 30 centimeters of soil and rock to create negative images on vast swathes of land.

The Nazca Lines, as they are known around the world, have fascinated archeologists for the better part of a century.

How were they formed?

What purpose did they serve?

They are virtually impossible to see from the ground, despite how big they are, so, the best way for scientists to study them is from the air.

In total, there are 70 geoglyphs that look like plants or animals, 300 geometric designs, and 800 perfectly straight lines, up to 50 kilometers long.

They are thought to have been made by the Nazca People, 500 to two thousand years ago.

But why and how they made them, without the benefit of an aerial perspective, is still a great mystery.

They take up a 500 square kilometer stretch of the desert, and one theory is they are some kind of calendar or serve some astronomical purpose.

More recent theories suggest the straight lines may have led to places where rituals were performed that related to the Nazcas' need for water to irrigate crops.

Some believe the spider is a sign of rain, and the hummingbird a symbol for fertility, so perhaps these geoglyphs were made to plead with the Gods for water.

Something more than nature's scant offering of less than a few millimeters a year.

(gentle instrumental music) The arid conditions here are ideal for preserving artifacts and human remains from civilizations past.

A treasure trove for present- day archeologists, coming to terms with how ancient Peruvian societies functioned.

Similar insights are being gleaned from the bones of ancient aboriginal people in Australia.

15,000 years ago, Lake Mungo, in New South Wales, was one of a chain of freshwater lakes teeming with life.

Today, it's a 22-kilometer- long dune system known as the "Great Wall of China."

It's a natural geological wonder on the desert fringes of outback Australia, eroded by wind and occasional rains that shape the landscape and open a window on the past.

As the wind blows layers of sand and silt from this dry lake bed, history springs to life.

Archeologists and park rangers working in the area, discover tools, piles of discarded shells, or middens, and animal bones nearly every other day.

To date, they have unearthed the world's oldest evidence of human cremation.

The oldest remains of modern man found outside of Africa.

This particular discovery in 1974 shocked the scientific community, for it proved that indigenous Australians had been living in this part of the country for much longer than most scholars assumed.

Mungo Man's bones, and the remains of the cremated woman they unearthed, were later dated at roughly 40,000 years old.

Decades after the scientists had finished their studies, they returned Mungo Man to his descendants, Who still maintain a connection to this ancient part of the world.

After welcoming him home, they reburied his remains, finally laying him, once and for all, to rest.

(dramatic orchestral music) It takes a great deal of fortitude to survive in the desert.

To endure the searing daytime heat, and make do with the scarcity of water.

But worldwide, more than a billion people do.

These days, many desert dwellers have access to technologies that make their lives infinitely more bearable-- air conditioning in their homes and four-wheel-drive cars to get themselves comfortably from A to B. But the legendary San, or Kalahari Bushmen, still maintain aspects of the nomadic way of life that sustained their forebears for 20,000 years.

Shifting with the seasons and availability of resources, they resisted the urge to put down roots and take up farming.

The San are the oldest inhabitants of Southern Africa and many still have an intimate knowledge of the natural world, of the animals and plants they have hunted and gathered for millennia in order to survive.

(traditional instrumental music) Women and children are traditionally the gatherers, collecting a huge variety of edible and medicinal plants and the beetle larvae the men use to poison the tips of their arrows.

Men only need to wound an animal when they're hunting, then track it as it retreats, waiting for the poison to take effect.

If their prey flees underground, they can speed up the animal's death by filling its hideout with smoke.

In this way, they are able to catch potentially dangerous animals like warthogs without risking any injury to themselves.

(ambient music) 27,000 bushmen still live in Namibia today, and although most of their ancestral lands are now protected by conservation areas, they are still permitted to hunt and gather, so long as they use traditional means.

The Kalahari is a semi-arid desert, and after good rains it can be excellent for grazing, providing food for livestock as well as wildlife.

But the Namib desert, to the west of the Kalahari, running right along Namibia's coast, is one of the driest hot deserts on Earth.

It's also said to be the oldest desert in the world, for it's existed for at least 55 million years.

(traditional percussion music) Completely devoid of surface water, its name, translated from the local Nama language, means where there is nothing.

As you might expect, most of this ancient landscape is uninhabited, save for a few settlements and camps set up to service visitors intent on seeing the raw beauty of this great natural wonder for themselves.

(flute music) Sossusvlei lies in the heart of this great barren landscape.

A sun-baked clay pan surrounded by dunes that are among the highest in the world.

The grains of sand that make up these colossal dunes have traveled over 500 kilometers from the mouth of the Orange River, the longest river in South Africa.

Washing first into the Atlantic Ocean, they've found their way north on the current, landing back on dry land, deposited by the surf.

From here they've blown inland, shape-shifting with the wind.

The Sossusvlei clay pan owes its existence to the Tsauchab River that only flows every five to ten years, draining away between the dunes rather than out to sea.

(instrumental music) Mud from the river stacks up in the hollow of Sossusvlei, and even with scant and intermittent rainfall can support a reasonable amount of vegetation.

It's hardly a place you'd expect to find life, but grasses and plants do grow in this desert, even on the Namib's gravel plains.

And that attracts the occasional two-, four-, and six-legged visitor.

Nestled in the next row of dunes beyond Sossusvlei is an even more remarkable white clay pan, fittingly named Dead Vlei.

This formed perhaps thousands of years ago after sufficient rainfall caused the Tsauchab to flood, leaving behind pools that were large enough to allow camel thorn trees to grow.

600 to 700 years ago, when the climate radically changed, the trees died.

But with no moisture in the air or soil to help them decompose, they remain in the landscape today, blackened by the scorching Namibian sun.

(traditional instrumental music) The arid conditions that define deserts around the world encourage the formation and concentration of minerals.

The Namib is the richest source of diamonds on the planet.

And the Arabian peninsula is well known for its "black gold" or oil.

But the Chihuahuan desert in Mexico holds an even more extraordinary treasure.

Buried 300 meters underground, just beyond a maze of tunnels that facilitate the operation of this lead and silver mine, lies one of the greatest geological wonders in the world.

Crystal Cave.

Intense heat from a magma chamber, five kilometers below the Earth, boiled the water that long filled this cavern, creating conditions that were perfect for dissolving and releasing minerals from the rock, and allowing them to slowly crystallize.

Over 100 million years, these gypsum crystals have just kept growing and growing, some measuring seven, eight, and even nine meters in length.

This daunting marvel was a chance discovery made when miners drained the water from the cave to prevent their operation from flooding.

Unfortunately, it's far too dangerous an environment to open to the general public, for the ambient temperature is 48 degrees, and the humidity is absolutely stifling.

Even geologists, wearing designer cooling suits, have to limit the time they spend within the cavern studying its remarkable formations.

Without the water filling this cavern, the crystals were no longer stable, so they stopped growing.

But when the mine ceased its operation in 2017 and turned off its pumps, the cave once again filled with water... preventing any further access, but on the upside, hopefully preserving this magical natural wonder forever.

(instrumental music) The Chihuahuan Desert is the largest in North America, stretching from Mexico into the Southwestern United States.

It harbors a third of all the cactus species in the world-- a desert plant that's famous for its ability to store water.

The most well-known cactus in North America is native to the Sonoran Desert, which lies to the west of the Chihuahuan, covering much of the Mexican state of Sonora and the US state of Arizona.

It is of course, the iconic Giant Saguaro, the largest cactus in the world.

These slow-growing wonders of the botanical world can take up to 75 years to grow their first arm.

They don't really take on their giant proportions until they're around 150 years old, by which time they can be as tall as a five-story building and weigh as much as eight tons.

Most of this weight is in the hundreds of liters of water they contain within them.

The Saguaro is, like most cacti, covered in spikes that help reduce water loss and prevent most animals from eating their succulent flesh.

But they clearly don't deter the industrious Gila woodpecker.

Using their beaks to excavate cavities in the Saguaro, they create perfectly cool places to raise their chicks.

Scarlet Macaws nest in Saguaros, too, and in return for free board, keep the cactus free of insects that might otherwise harm the overall health of the plant.

Lurking in the shadows of Saguaro and other cacti is the largest native lizard in the US-- the venomous Gila Monster.

They are capable of climbing Saguaros to get to a nest full of bird's eggs, but more often than not, can find an easier, meatier meal underground.

Gila Monsters can eat up to a third of their weight in one sitting, and can then go without food for several months, living off the fat they store in their tails.

Binge drinking when water is available, they can stay active for three months without dehydrating, as they store water in their bladders.

A handy adaptation to have when rainfalls are few and far between!

Gila monsters are normally solitary creatures, but when two adult males cross paths in late spring or early summer, there's a good chance a fight will break out.

Competing for the right to mate with any female Gila in the area, the male monsters wrestle, trying to pin each other to the ground.

It's a grueling fight that wages over a series of bouts that can ultimately last several hours... leaving both contestants utterly exhausted.

(Aboriginal instrumental music) Australia, the desert continent, harbors more reptiles than any other continent on Earth.

With its plentiful supply of solar radiation, the land down under became an evolutionary hotspot for creatures that depend on external sources of heat to regulate their body temperature.

And they have made themselves at home in every conceivable desert niche.

81 different species of skinks, snakes, and lizards live in Purnululu National Park, one of the nation's most iconic landscapes.

Nestled in the isolated East Kimberley region of Western Australia, between the hot, dry deserts of the midwest and the better watered North, Purnululu harbors a geological and biological marvel.

The 450 square kilometer Bungle Bungle range.

(dramatic orchestral music) Twenty million years of weathering, a mere batting of an eyelid in geological time, has produced a truly extraordinary landscape of beehive-shaped Karst sandstone domes, rising 250 meters above the semi-arid desert floor.

The dark bands that wind their way around the domes are formed by cyanobacteria, single-celled organisms that represent some of the oldest life forms on Earth.

They can be several meters wide, but only a few millimeters thick, nonetheless helping to stabilize and protect the ancient formations, acting like a bandage that stops the weather from eroding the rock beneath.

The Bungle Bungle Range is so remote, it was virtually unknown to the outside world until 1982, when a film crew captured its wonder from the air.

Even now, it's a difficult place to get to, and closed for five months of the year.

The summer heat is a prohibiting factor, but seasonal monsoon rains cut off the roads that would otherwise provide ground-level access to the geological wonder.

The domes create a massive, intricate maze.

Some gorges, such as Cathedral Gorge, are relatively wide, terminating in massive stone amphitheaters.

Others, such as Echidna Chasm, are so deep and narrow they only see the sun for a few minutes a day.

The shade makes it possible for livistona palms to grow here, thriving in the cool, moist micro-environment of the gorge.

The predominant vegetation, as it is throughout arid and semi-arid Australia, is spinifex.

But Purnululu has the highest diversity of this hardy desert grass in the country... with no fewer than 13 different species.

Some are soft, but most are needle sharp, ready to spike the calves of those who venture too close.

Spinifex acts as a deterrent to humans, but a surprising number of animals have made use of the protection they afford from predators.

Legless lizards, geckos, and spinifex hopping mice that burrow beneath the grass clumps.

They are perfectly adapted to contend with life in the desert, with the most efficient kidneys of any mammal on the planet.

Their urine is so concentrated it's solid.

(flute music) Another less well known and more compact version of the Bungle Bungles lies well to the east of Purnululu, near the remote northern territory town of Booroloola.

These giant sandstone pillars formed some 1500 million years ago.

They were once part of an ancient seabed that cracked and split as the receding water left it high and dry.

The wind and rain, over many millions of years, have eroded the sandstone into a series of skinny skyscrapers known as the "Lost City".

Local Aboriginal people still regard the site as sacred, as circumcision ceremonies were held here in the past.

Two particular trees growing in the area would have been essential to the initiation ritual.

The green plum, known to be a natural anesthetic and a species of gum, valued for its antiseptic properties.

It's easy to see why these iconic landscapes are so revered, not only by indigenous Australians, but by all who witness their splendor firsthand.

(dramatic guitar music) One of the best known desert landscapes in the world lies in the heart of Arizona.

The incomparable Grand Canyon.

Traveling across the high country of the Colorado plateau, this is a wonder you don't see coming.

(upbeat instrumental music) It doesn't loom on some distant horizon, drawing you closer by the minute.

You arrive at its rim quite suddenly, and the earth just opens up beneath your feet.

A gigantic gash more than one and a half kilometers deep, 16 kilometers wide, and nearly 450 kilometers long.

Looking out on this barren landscape is like looking back nearly two billion years in time.

The layers in the rocks are bursting with information that has helped scientists unravel the region's geological history.

The movement of the Earth's tectonic plates, which forced the whole plateau upward.

The erosive force of water, wearing parts of that formation away.

And finally, less than a million years ago, the process of volcanism, which poured lava into the western end of the canyon.

It's all here, showcased on the grandest of scales.

The rocks are ancient, but the canyon itself is relatively young, only five to six million years old.

And it's been shaped largely by water.

It's still the single most powerful force acting on the canyon today.

The Colorado River moves fairly swiftly, dropping about 670 meters over its course through the canyon.

It used to carry so much sediment, locals joked that it was "too thick to drink, and too thin to plow."

There is evidence that farming occurred in the area in the past.

Maize and corn were grown in the summer months by the Havasupai Tribes in places such as Havasupai Falls.

(dramatic orchestral music) The falls are just one of the Grand Canyon's better kept secrets, an absolute gem in its own right.

Hidden in one of the many nooks and crannies deep within America's greatest natural wonder.

For all their hostility, hot deserts are remarkable places.

They are full of incredible plants and animals that have adapted to the climate, and bursting with geological wonders that inspire.

With vast areas that are empty and silent.

Their fringes remain home to some of the most hardy and fascinating peoples on Earth... many of whom look to their future with one foot firmly in the past.