10 of the Most Insane Geological Discoveries

In an age of renewed hunger for space travel, it’s easy to assume that we’ve already unlocked all the secrets of our planet. What more can we do? We’ve been to the top, we’ve sent submarines to the deepest depths, and we’ve mapped out the Earth in an extraordinary way. Signed. Done. Finished.

But how presumptuous we humans can be.

We still don’t really know what’s happening inside the Earth’s core. We still don’t fully understand how complex life suddenly appeared. Or why the Earth’s magnetic field has flipped several times. There is still a huge amount that we are yet to learn, but we are making progress. Every now and again, a geological discovery appears that leaves us with that universal sign of wonderment – wow.

And today, we’re taking you through 10 of the most insane geological discoveries. Lost continents, boiling rivers, moving mountains, and Earth’s very own natural nuclear reactor. Enjoy.

1. Hidden Ocean Beneath the Earth

If you combine all the water on Earth, including oceans, seas, rivers, and even ice in glaciers, you would arrive at a rough figure of 1.3 billion cubic kilometres (300 million cubic miles). A staggering figure, far too large for mere mortal brains. But what if I told you that there was an underground ocean, perhaps 400 to 700 km (250 to 435 miles) beneath Earth’s surface within the mantle’s transition zone, that could contain three times that amount of water? Welcome to the scarcely believable world of the Ringwoodite Reservoir.

Humans have been fascinated with what may be beneath our feet for thousands of years, but it wasn’t until the late 19th and early 20th Centuries, with books like The Lost World, At the Earth’s Core, and The Land that Time Forgot, where intrigue really bloomed.

Were there really lost worlds within the cavernous interior of Earth? It sounded vaguely plausible, until geological research revealed a core where temperatures range from approximately 4,400°C to 6,000°C (7,950°F to 10,830°F), while pressure reaches a peak of about 3.6 million atmospheres (360 GPa) at the very centre. If you struggle with atmospheres, don’t worry, we’ll just say it is 3,300 times greater than the pressure at the bottom of the Mariana Trench, the lowest point on Earth.

So no, there are no lost worlds, but research in 2014 uncovered something pretty huge. The study, led by geophysicist Steve Jacobsen from Northwestern University, found that under certain conditions found deep within the Earth’s mantle transition zone, ordinary minerals transform into entirely different structures, and one of those is ringwoodite.

Ringwoodite is still fairly mysterious, and actually we didn’t know it existed until 1969 when scientists extracted it from sections of the Tenham meteorites that fell across Western Queensland in Australia one hundred years before.

But it soon became apparent that this wasn’t a bizarre ET mineral, but rather something that is widely prevalent under our own feet, just really far down. The fascinating thing about ringwoodite is that its crystal structure can trap water — not in liquid form, but as hydroxide ions bound within the mineral itself.

In 2014, Jacobsen’s team began studying a huge region spanning below most of the continental U.S., in an area of the Earth’s mantle known as the transition zone. They came to the conclusion that, because of the vast deposits of ringwoodite, it’s highly likely that huge amounts of water are stored down there too. The way they put it:

If just 1% of the weight of mantle rock located in the transition zone was water, it would be equivalent to nearly three times the amount of water in our oceans.

So this isn’t an ocean we would ever be able to swim through, but the fact that so much water is stored within the Earth’s mantle has led to a completely different theory about how water ended up on this planet. For years, the prevailing theory was that it had been deposited here after a comet or meteor strike, but this evidence raises the possibility that our water is actually home-grown, and what we have on the surface has been forced up through earthquakes and small tectonic movements. Jacobsen said in a Guardian article:

Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight. I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet.

We tend to think about water as something that only comes from the sky, but these discoveries have completely changed that. Now we need to see rain as something that operates within a much more complex system. Perhaps the rain that falls on us today was forced to the surface because of earthquakes or volcanic activity millions of years ago.

2. The Lost Continent of Zealandia

We all remember our continents’ lessons at school. Seven of them: Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Ever wondered why so many start and end with the letter A? Well, partly coincidence, partly the structure of Latin and Greek.

The beginnings, at least, are relatively coincidental. Asia comes from the Latin name for Anatolia. Africa was named after the Afri, the Latin name for inhabitants of the lands south of the Mediterranean Sea. And America was named after the Italian explorer Amerigo Vespucci by a German cartographer, which was first Americus, then later simplified to America. Then endings are much more straightforward as female words in Latin usually end with an ‘a’.

Mystery over, and now let’s move on to a continent that you’ve probably never heard about, which certainly doesn’t start with an ‘a’– Zealandia. It covers nearly five million square kilometres (1.9 million sq miles), making it larger than India, but we don’t know about it because 94% of it lies underwater. What we see above the surface—New Zealand and a few surrounding islands—is just the highest ground of something much larger.

For a long time, this was theorised, but was far from being widely accepted. In 1995, Bruce Luyendyk, an American oceanographer and geophysicist, proposed the name and the broad concept for how it came about.

Gradually the evidence began to build, and geologists realised that the landmass beneath New Zealand was too thick and diverse to be mere oceanic crust. Then NASA’s Grace satellites got involved and started mapping tiny changes in Earth’s gravity to identify the underwater continent’s shape, with early satellite imagery showing it to be roughly the same size as Australia.

In 2017, a group of geologists formally proposed that Zealandia should be classified as a continent. Their argument was based on four main criteria: elevation, crust type, geological structure, and defined boundaries. Zealandia met all of them, despite being mostly underwater.

But the story of Zealandia begins a long way back with Gondwana. Around 80 million years ago, this supercontinent began to split and the landmasses that would eventually become Africa, South America, Antarctica, and Australia drifted apart. Zealandia was part of that system, connected to what is now eastern Australia and Antarctica. As tectonic forces pulled the region apart, Zealandia began to stretch.

This stretching thinned the continental crust, which is normally buoyant enough to sit above sea level. But as it becomes thinner, it loses that buoyancy, and over time, large portions of Zealandia gradually sank beneath the ocean’s surface. As a comparison, Zealandia’s crust is about 20 km thick (12 miles), while other continents are 30–40 km (18–24 miles). And, of course, this is not a fast process.

It took millions of years for Zealandia to reach its current state — almost entirely submerged, but still structurally intact.

Today, only New Zealand, New Caledonia, and a few islands and reefs are left of the visible Zealandia – meaning, the 8th continent of the world, has a rather light population of around 5.4 million people.

So, what about the rest? If we were to dive beneath the surface, we would find that Zealandia is mainly composed of two long, roughly parallel ridges, separated by what is known as a failed rift – which basically means the continent pulled apart and nearly split, but didn’t, leaving this depressed section of land known as a graben that later filled in. The two ridges rise about 1,000 to 1,500 metres (3200–5,000 ft) above the surrounding sea floor, with only a few rocky islands extending above sea level.

Go back 80 million years, and much of Zealandia was above ground, and things, of course, looked very different. If you go to Curio Bay in New Zealand, you will find logs from a fossilised forest that contained trees that are similar to our kauri and Norfolk pine that would have grown on the slopes of what is now Zealandia around 180 million years ago.

Unlike most continents, Zealandia — and particularly New Zealand — developed with almost no native land mammals. This created an ecosystem where birds and smaller organisms filled roles that mammals typically occupy. Flightless birds were a prime example. With no large predators around, many bird species never required the need for flight, so they never developed wings that could fly. Things were different in Zealandia.

3. The Moving Rocks of Death Valley

For years, it was a mystery that left everybody stumped. In a remote part of Death Valley National Park, there is a dry lakebed known as Racetrack Playa. It’s flat, barren, and largely featureless with hard, cracked clay, stretching for miles with very little interruption.

But in the middle of this lunar landscape are hundreds of rocks – some of which you could pick up and walk with, others that weigh over 300kg (700 lbs). OK, nothing strange so far. But the real mystery was the trail of parted sand behind them. Long, clearly defined tracks stretching across the playa, sometimes for hundreds of metres. They curve, change direction, and occasionally run parallel to one another, with each trail representing the movement of a single rock.

If you look at them, you would swear that they had been moved by humans in some Hyrox/CrossFit activity out in the desert. But there are no footprints, tyre tracks, or really anything else, apart from these lines in the sand. And for over a hundred years, this absolutely baffled people.

In 1915, a prospector named Joseph Crook visited the Racetrack Playa site and his account of the rocks, sometimes known as the sailing rocks, sparked fascination. And for decades after, interest gradually grew. The rocks appeared in Time magazine, with early theories suggesting strong winds or even magnetic forces, but these didn’t fully account for the weight of the stones.

Long-term studies began in the mid-20th century, with Bob Sharp and Dwight Carey, who started a movement monitoring program in May 1968. Stones were given a name and tracked over a 7-year period, but the findings were far from clear. Some rocks didn’t budge, others, like Mary Ann, moved 65 metres (212 ft) during that first winter alone. These studies confirmed that movement was real but sporadic, and that it did not occur during dry conditions.

The breakthrough came in 2014. Using GPS and time-lapse cameras, scientists finally observed the movement directly. It turned out that a precise combination of conditions is required: a thin layer of water must cover the playa, followed by freezing temperatures that form sheets of ice. As the ice begins to melt and break apart, the wind pushes these thin panels, which in turn slowly move the rocks.

But the reason that this rarely happens is that a very narrow set of circumstances need to occur. There has to be enough rain falling in the mountains above, which needs to make its way down to the valley floor, then temperatures need to drop quickly to freeze that water before it evaporates or simply sinks into the sand.

This all typically happens at night, but in the morning, the temperatures need to rise just enough to partly thaw the ice. And even then, if there’s no wind, the rocks aren’t going anywhere. Research back in the 1990s found that airflow can become more concentrated and intense in the playa than in other areas.

Under normal conditions, wind speeds across the playa are fairly modest — often in the range of 10 to 30 km/h (6 –18 mph) – but during winter storms, gusts can reach around 80 to 140 km/h (50 to 87 mph). And because there’s nothing to break the wind, and with a mini ice rink underneath, these magical rocks can sail through the playa.

Mystery solved.

4. The Rainbow Mountains of China

Some things just don’t look real, and in the age of CGI, AI, and whatever acronym comes next, it can be difficult to separate real from fake, fiction from reality.

The formations within the Zhangye Danxia Landform Geological Park in China are one such example. Entire hillsides are layered in bands of red, yellow, orange, and green, stretching across the terrain in long, uninterrupted lines. From a distance, the mountains appear almost painted — too uniform, too deliberate – there’s no way that’s natural.

If you happen to see these mountains at sunrise or sunset, during the peak colour months between June and October, you will be greeted by one of the most astonishing scenes anywhere on Earth. A kaleidoscope of colour – what would happen if giant children had crayons and decided to paint the mountains.

As with just about everything else on this list, this story begins millions of years ago – about 30 million, to be roughly exact. Making this, surely, the longest running art project in existence.

Back then, this region was a series of low-lying basins. Rivers carried sediment into these basins — sand, silt, and mineral-rich material — depositing it in layers over time. Each layer told its own story about what conditions were like in the region at any set time, with different minerals settling during different periods.

Iron-rich sediments, for example, would later oxidise and turn red, while other minerals settle into yellow, greens and blues. But at the time, these layers were flat, buried, and largely unremarkable – the area looked nothing like it does now.

But then the big-hitting tectonic plates, the Indian and the Eurasian, collided. OK, to say that they collided simplifies the process somewhat, so let’s walk that back a little. These two plates had, in fact, been colliding for about 25 million years before that, a process that had formed the early Himalayas and continues to push up the world’s highest mountain range to this day. However, over tens of millions of years, that slow, grinding brute force arrived in Zhangye Danxia.

The pressure of these two plates folded, tilted, and uplifted those long buried sedimentary layers, pushing them above ground and exposing them to the elements. Once they were exposed, the real work started. Wind and rain gradually wore away softer materials, carving out ridges, valleys, and steep slopes. Because the sediment layers were already tilted, erosion showed them off as long, continuous bands of colour, and over time, this created the striped appearance that we see today.

What’s amazing is just how clean and well-defined the colours are in Zhangye Danxia, which is partly due to the dry climate. With limited vegetation and relatively low rainfall, there’s less disruption to the exposed rock, allowing the patterns to remain visible. After rainfall, the area looks particularly impressive as moisture deepens the tones, making the reds richer and the yellows more vivid.

What we see looks entirely man-made, but is actually a geological anomaly that simply comes about by the presence of certain minerals. In most cases, iron oxides are responsible for the deep red colouring seen in sandstone, while oxidised minerals such as limonite or goethite tend to create yellow or brown tones, and magnetite can result in darker, almost black staining. If iron sulphide is present, it can introduce a metallic yellow colour due to its sulphur content. Green colouring, on the other hand, is usually linked to minerals like chlorite or iron-rich silicate clays.

The Rainbow Mountains is an astonishing sight to see in person, a place that looks entirely artificial in its broad colour palette, but really we’re looking at millions of years of geological history in all its vibrant splendour.

5. The Sahara’s Lost Green Age

Today, the Sahara Desert, spanning 9.2 million square kilometres (3.6 million square miles) – making it around the same size as the United States and China – is, by definition, one of the most inhospitable places on Earth.

Summer temperatures can exceed 50°C (122°F), with ground temperatures even higher, and large parts receive less than 25 mm (1 inch) of rain per year. In fact, some areas have gone years, if not decades, without measurable rainfall. The Libyan Desert, which straddles Egypt, Libya and Sudan, and the Eastern Sahara, which includes parts of southern Egypt and northern Sudan, have both experienced multi-decade dry spells. And when it does finally rain, it causes flash flooding that can be catastrophic.

Considering its vast size, it has a population of only around 2.5 million people, and the population density sits at less than 1 person per square kilometre in many areas. There’s hardly anything to drink, and with sparse vegetation – officially making it hyper-arid – and the kind of soil/sand dynamic that makes most crops quickly die, there’s not that much to eat either.

Bottom line, this is a place that few people call home, and for very obvious reasons. It may be beautiful, it may give you that brief exciting sense of foreboding as you travel through it, but it sure is inhospitable.

And that’s how you just assume it’s always been. OK, maybe if you go back ten million years there might have been an ice sheet over it because of one of our planet’s ice ages, but time spans like that are difficult for humans to process. 1 million years is hard enough. But surely if we’re talking 10,000 years, the Sahara would have been exactly the same?

Well, not really. Doubts about this first sprang up in the 19th and early 20th Centuries when cave art, most notably in the Tassili n’Ajjer region of Algeria, was discovered. Paintings and engravings from 12,000 to 4,000 years ago appeared to show a completely different Sahara to what we see today, one that was filled with wild fauna, giraffes, elephants, lions, and hippos, while later periods show domesticated cattle, horses, and eventually camels.

Later research in the mid-20th century revealed ancient lake beds, fossils of aquatic life, and the remains of human settlements deep in areas where no humans would choose to live today. In the 1970s and 1980s, radiocarbon dating of lake beds, pollen, and fossils across North Africa appeared to confirm that the Sahara had been a very different place between 14,500 and 5,500 years ago – in an era that came to be known as the African Humid Period.

Instead of sandy dunes, rocky plateaus, and barren mountains, the Sahara had vast stretches of grassland, woodland, savannah, and seasonal wetland that provided habitat for an extraordinary array of animals. And there was water – loads of it. The area was home to countless lakes and rivers, with Lake Mega-Chad, located in the modern-day Chad Basin, covering a massive 400,000 sq km (150,000 sq mi) – slightly larger than Norway.

And humans thrived here. Fishing communities lived along lakes and rivers, and early cattle herders moved across open grasslands. Tools, pottery, and burial sites show long-term habitation, with some finds stretching back 12,000 years.

Essentially, think of the Sahara today, go in the complete opposite direction, and you’ll arrive in the African Humid Period Sahara.

And this is where the story gets stranger. Because the Sahara before the African Humid Period was pretty much exactly the same as what we have today, if not bigger and even less hospitable. The African Humid Period was, in essence, the sweet spot that lasted no more than 10,000 years.

The obvious question is what caused such a drastic change and the answer lies in Earth’s orbit. Over long timescales, the shape and orientation of Earth’s orbit shift slightly. These changes, known as Milankovitch cycles, affect how sunlight is distributed across the planet. In the case of North Africa, these shifts altered the strength and reach of the African monsoon.

During the African Humid Period, increased solar heating intensified the monsoon system, pushing rainfall much further north than it does today. This brought consistent seasonal rains into what is now desert, allowing vegetation to spread and water systems to form.

As vegetation increased, it reinforced the cycle. Plants help retain moisture in the soil and influence atmospheric conditions. With more vegetation, the region could sustain more rainfall, creating a relatively stable, green environment over thousands of years.

But then, the Earth gradually tilted back the other way, and over a few thousand years, the whole process went into reverse. The monsoon stopped coming, the plants slowly died, as did the animals, and the sand eventually enveloped the Sahara to create the vast desert that we know today.

6. The Boiling River of the Amazon

Deep within the Peruvian Amazon, there is a river you really shouldn’t step into. In truth, most Amazon rivers come with a full horrifying spectrum of things that can kill you, maim you, or slowly burrow into you – highly venomous stingrays, man-eating black caimans, electric eels, flesh-eating piranhas, and the parasitic candiru fish to name just a few.

And yet, this particular river is different. It’s not what is swimming around in it that will hurt, but the fact that in some places the water temperature is a skin-roasting 95°C (203°F)

The Shanay-timpishka River, which translates as ‘boiled by the heat of the sun’ – also commonly referred to with the eye-catching name, the ‘Boiling River of the Amazon’ is a 9km (5.6 mile) tributary of the Pachitea River south of the city of Pullcapa in Central Peru. It is one of the largest documented thermal rivers in the world, but only the lower 6.3 km (3.9 mi) is thermal.

At its headwaters, the temperature is a pleasant 27°C (81 °F), but as it flows over geologic fault-zones, hot geothermal waters rise from deep in the earth and temperatures quickly rise well above what would be acceptable even in the hottest of baths. The highest temperature ever recorded in the Shanay-timpishka River was a melting 99.1 °C (210.4 °F).

So how common are rivers like this? Well, not exactly common, but also not exactly rare. You’ve got the Kerosene Creek in New Zealand, where naturally heated water flows at a steady, bath-like temperature through a forest. Rio Caliente in Costa Rica is a volcanic river with sections that reach near-hot spring heat, while the geothermal streams of Beppu in Japan, where runoff from hundreds of hot springs creates channels that behave like small thermal rivers.

Most of these share the same source – volcanic activity deep within the Earth and most remain at a comfortable enough temperature for you to visit, sit around for a few hours, and then leave with that healthy geothermal glow.

The Shanay-timpishka, on the other hand, is viciously hot and doesn’t fall into the same source category. There are no volcanoes nearby, no underground lava flows, and no steam vents rising dramatically from the earth.

Local communities have known about the river for generations, and it features in oral traditions as a place of spiritual significance. But outside the region, it remained largely undocumented, partly because of its remote location and partly because the idea itself seemed so unlikely.

One geoscientist who has looked into it is Andrés Ruzo. Ruzo was brought up in a family that moved between Peru, Nicaragua, and the United States, but he recalled growing up with stories about the mysterious boiling river in the Amazon.

In 2011, he became the first scientist granted permission by the Peruvian government to study the river and has since written a book about his experiences as well as setting up the Boiling River Project, a non-profit that aims to protect the river and the surrounding area that is being affected by deforestation.

So how does the boiling river work? Instead of the usual volcanic activity, the heat appears to come from deep underground. Rainwater seeps into the ground and travels down through cracks and faults in the Earth’s crust. As it moves deeper, it encounters hotter rocks, gradually increasing in temperature. Under the right conditions, this heated water can then rise back to the surface through fault lines, emerging as hot springs or, in this case, feeding into a river system.

While there are other examples of this around the world, we don’t know of anything of this size. And the fact that it’s so remote, and was part of a semi-mythical story told by a grandfather to his grandson, who years later trekked through the jungle to find it, makes it one hell of a story.

7. The Siberian Methane Craters

In the far north of the Yamal Peninsula in the Russian region of Siberia, the landscape is permafrost, permafrost and more permafrost. The area is around 120,000 square kilometres (47,000 sq miles) – making it half the size of the United Kingdom with a population of only around 25,000 – and that’s just part of the massive sprawling beast that is Siberia.

The name Yamal actually means ‘End of the World’ in the local Nenets language — which feels pretty accurate once you see how remote and icy it is. We’re talking vast areas covered in permafrost that has, in some places, remained frozen for thousands of years. It’s mostly flat, pretty featureless, other than some lakes and the odd forest. Or should I say, it used to be mostly flat.

In 2014, something changed. A large, perfectly circular crater was discovered in the tundra. It dropped steeply onto the ground, with smooth sides and a diameter of around 30 metres (11 feet). Think about a flat piece of paper and if you were to push a pencil through it and then withdraw it, that’s what this crater and the surrounding landscape looked like.

At first glance, it seemed obvious – a meteor or asteroid strike. But there was no clear impact site, no debris pattern that suggested something had come down from space. In fact, there wasn’t anything. It was as if the ground within this very specific circle had simply fallen away to a depth of 50 metres (165 ft).

Of course, wild theories flew right and left. Was it a meteor strike of such huge proportions that all its rock was simply obliterated? Not likely. Was it a Russian military project that had gone wrong – or had gone right, depending on what they were trying to do? Possible, but the Russian government seemed genuinely as baffled as everybody around the world.

Various agencies poured over satellite imagery and were able to pinpoint that the strange crater had appeared sometime between the 9th October and 1st November 2013. However, they weren’t able to pinpoint how it had happened. The mystery deepened. And then it deepened even more.

More craters appeared, and not just on the Yamal Peninsula, some smaller, some around the same size as the original. This essentially ruled out the possibility of a meteor strike. So bizarre Russian military experiments then? Also, no.

In 2018, a group of Russian scientists from the University of Moscow visited the area and came to the conclusion that the region was home to Earth’s first cryovolcano – or ice volcano – something that had not been found, not only on this planet, but on any of the inner planets. In fact, you need to go all the way to Enceladus, the sixth-largest moon of Saturn, around 1.2–1.7 billion km (745 million–1.06 billion miles) away, depending on its current position, to find one.

So was this the world’s first cryovolcano? Sadly, no, but they were getting closer in their thinking. When researchers drilled down through the ice, as expected, they came to a layer of thick clay permafrost. Yet they also found something sandwiched between the soil and permafrost: unusual metre-thick ponds of very salty water known as cryopegs, and just below that was a thin layer of crystallised methane-water solids, kept stable at high pressure and low temperature.

Now, all this is fine as long as everything stays nice and cold, but with climate change, this region is experiencing warmer temperatures and summers that now climb to a balmy 10°C (50 °F). That might not sound like such a bad thing in a place that experiences such bitter cold for much of the year, but the increasing warmth is causing a big problem.

With the soil layer defrosting to greater and greater depths, when the thaw reaches a cryopeg, the pressure from added meltwater forces cracks to open in the soil above. The new cracks create a sudden drop in pressure, which destabilises the methane hydrate and releases an explosive bubble of methane gas.

And so, the Siberian crater mystery was found to be the result of massive methane explosions occurring far from humans’ eyes or ears.

8. Large Low Shear Velocity Provinces

We’re going to dig down into the Earth once more, past the lost continent of Zelandia and past the vast water source tucked into all that ringwoodite. Because there’s something else down here. Something vast in scale that we still don’t really understand, something that geologists refer to as ‘large low shear velocity provinces’.

Let’s start slowly, because this is complex, hence the name. Earth is essentially an onion, and we live outside on the tunic – and yes, that is what it’s called.

The crust is Earth’s thin outer layer, ranging from about 5 to 70 km (3 to 43 miles) thick and forms the continents and ocean floors and is broken into moving tectonic plates. The mantle lies beneath and stretches about 2,900 km (1,802 miles) deep, made of hot rock that flows slowly. The outer core sits below the mantle and consists of liquid iron and nickel at extreme temperatures, and right at the centre, the inner core is a solid sphere of iron and nickel despite intense heat.

All of these layers are slowly spinning or moving, but they’re all doing their own thing. The surface has a 24-hour rotation – that’s the straightforward part. The crust moves around like a patchwork of jigsaw pieces, sometimes banging into each other; the outer core doesn’t spin like a solid, but kind of flows with complex currents. And the inner core appears to rotate at a slightly different rate to everything, either faster or slower depending on what time period is studied.

Right, now our Earth geology is set, we’re going to zoom into the mantle, where semi-solid rock moves very slowly like a liquid. You probably rarely think about Earth’s mantle, but without it, solar radiation would strip away the atmosphere over time, meaning you wouldn’t be watching this video, I wouldn’t be making this video, and Earth would be a ball of fire.

Temperatures here are extraordinary, anywhere between 4,000–6,000°C (7,200–10,800°F), and remember, this layer is around 2,900 km (1,802 miles) thick – which is about two-thirds the distance between New York and Los Angeles – all of it an ocean of small moving rock. If that doesn’t put human life into perspective, I don’t know what will.

And yet, the ocean down there isn’t clear. There are two enormous bulks, roughly opposite each other. One lies beneath Africa, the other beneath the Pacific Ocean. Everything we know about these regions comes indirectly, primarily through seismic data.

When earthquakes occur, they send waves through the Earth in all directions. By measuring how fast those waves move, and how they change direction, scientists can infer the properties of the materials they pass through. In the case of the masses in the mantle that scientists named rather vaguely, large low shear velocity provinces, something unusual happens: certain seismic waves slow down significantly, and that’s how we found them.

So, how big are we talking? Big, as in, whole continents big. The one below Africa is larger, and is thought to be around 5,000–8,000 km (3,100–5,000 miles) across and 1,000 km (620 miles) tall. That’s right, we think of our continents as flat, some with impressive mountains, but these provinces within our mantle are 3D. This one is the size of the distance from the UK to India, but is also 100 times Mt Everest going straight up.

There are several theories about their origin. One suggests that they are remnants from the early Earth, dating back billions of years to when the planet was still forming. If this is right, they could be pockets of primitive material that never fully mixed with the rest of the mantle. Another theory is that they could be the accumulated remains of subducted tectonic plates—sections of the Earth’s crust that have been pushed down into the mantle over hundreds of millions of years.

Some scientists believe they are linked to mantle plumes—columns of hot material that rise toward the surface and create volcanic hotspots. These hotspots are responsible for features like volcanic island chains and large igneous provinces, so the provinces could, in theory, be affecting all the volcanic activity going on around the world.

But, to be honest, nobody even has a remote clue what these massive bulks floating through our mantle really are, and I’m guessing that this particular mystery isn’t about to be solved anytime soon.

9. The Moving Mountains

For hundreds of years, people who knew their rocks and who visited certain mountain chains, particularly the Alps, Dinarides, Carpathians and Balkans, found something odd. The usual law of geology is that newer rock forms over older rock – and you don’t need to be a scientist to see that this makes sense.

So why did geologists in these regions keep finding older rock above younger rock? And these weren’t small patches that might be explained away as some bizarre anomaly. We’re talking entire ridges and mountains where rocks seemed to have swapped locations, and it appeared they were part of a much larger structural system. Very strange indeed.

Enter Marcel Alexandre Bertrand, a French geologist who unravelled the mystery in the early 20th Century. He named the process Nappe, which means tablecloth in French, and you’ll soon understand why.

Nappes are those strange quirks in geology where entire sheets of rock can move several kilometres horizontally. Think of a thick rug on a wooden floor. If you push it from one side, it crumples, folds, and slides forward over itself. A nappe works in a similar way, except the ‘rug’ is massive layers of rock being forced over other rocks. This happens when two tectonic plates come into contact, but instead of mountains forming upwards, the whole process moves sideways.

At the time, this theory got plenty of pushback. This was an era when understanding of tectonic activity was still relatively new and people thought the idea of mountains moving sidewards was preposterous – and you can kind of understand why. Bertrand had a theory, but wasn’t able to explain how, why, or just about anything that turns a theory into a fact.

Nevertheless, field evidence continued to accumulate. In the Alps, geologists identified massive nappes where rock units had clearly originated far from their present location, and similar structures were later found in other mountain belts, including the Himalayas and parts of North America.

In some of these locations, the same sequence of rock layers appeared multiple times, stacked on top of each other. The only plausible explanation was that these layers had been duplicated by large-scale horizontal movement. Identical fossil groups were found in rock units separated by large distances, suggesting that these rocks had once been part of the same environment before being displaced.

It seemed the evidence was indisputable, but still many refused to believe it, all the way up to the mid-20th century. With the development of plate tectonics knowledge, a proper, coherent explanation finally emerged.

As tectonic plates slowly grind together, the crust does not always behave like one solid block. Pressure builds over millions of years until huge layers of rock begin to crack and detach from the rocks beneath them. Once separated, these giant slabs can be forced sideways for astonishing distances, sometimes travelling tens or even hundreds of kilometres. If you’ve got substances like clay, salt, or water-rich rock directly underneath, they can act as lubricant to help push the heavier rocks above.

The end result is a mountain range that looks almost impossible when first studied. Older rocks can end up resting on top of younger ones because entire sections of crust have effectively been shoved over the landscape like a giant geological conveyor belt. And so, you can have ridges or sometimes even vast sections of mountains that have, quite literally, moved sideways. It’s not a fast process – we’re talking in millions of years – but it is one of the oddest geological discoveries when you think about scale.

10. Earth’s Natural Nuclear Reactor

Nuclear energy has been one of the most important breakthroughs in human history, but because of what it can do, both accidentally and when it falls into the wrong hands, we’ve become terrified of it. It is one of those highly-advanced spectres that hover over us, requiring immense scientific knowledge, precise engineering, carefully refined fuel, and tightly controlled conditions. But what if I told you the Earth could naturally create a nuclear reactor that sits just below the surface?

In 1972, workers at a uranium processing facility in France noticed something strange while analysing uranium ore shipped from Gabon. The material came from a mine near the town of Oklo, and at first glance everything appeared normal. Yet when technicians measured the uranium-235, they found its quantity to be lower than expected. The difference was tiny – the usual 0.720% vs 0.717% – but in the nuclear world, tiny discrepancies are all you need.

The world atomic, of course, comes from the word atom, the minute, yet fundamental building blocks of matter.

Uranium-235 is the isotope used in nuclear reactors and atomic weapons because its atoms split apart relatively easily, releasing huge amounts of energy in the process. So when scientists found some missing, their first thoughts weren’t positive. Had it been stolen somehow? Perhaps by a James Bond villain intent on taking over the world? Or perhaps more simply, that it had been contaminated? Or was it all just a miscalculation?

They launched an investigation, but what they found was stranger than anybody expected and certainly one of the strangest geological discoveries ever made.

Deep underground at Oklo, nature had accidentally built a functioning nuclear reactor almost two billion years ago. Now, to understand how remarkably bizarre that is, it’s worth just highlighting how difficult nuclear fission normally is to control.

Inside modern reactors, uranium atoms are bombarded with neutrons. When one atom splits, it releases energy along with more neutrons, which then strike other atoms, creating a chain reaction. Left uncontrolled, the reaction accelerates rapidly, so engineers use carefully arranged fuel rods, cooling systems, and moderators to keep the process stable. It’s a process of mind-numbing complexity that surely requires our modern Homo sapien brains.

Yet somehow, Earth itself had managed to assemble the right conditions naturally, long before humans, mammals, dinosaurs, or even complex plants existed. Two billion years ago, the planet looked utterly alien compared with today. Very low oxygen, most life existed in the oceans as simple microscopic organisms, and on land, things were desolate without almost any kind of life.

But something that there was more of was uranium-235, as ancient Earth contained a much higher percentage of fissile material than modern deposits do. And coincidentally, that percentage just so happened to sit within the range needed to sustain nuclear fission.

At Oklo, thick uranium-rich rock deposits formed underground and groundwater slowly seeped through cracks and porous rock, filling spaces around the uranium. Bizarrely, this created the perfect stable environment for the uranium atoms to split more efficiently, with the water acting as the cooling agent that is so difficult to get right in modern reactors.

Eventually, conditions crossed a critical threshold and a chain reaction began. The underground deposit started generating heat exactly like a man-made nuclear reactor and temperatures rose. That meant that the water present boiled, meaning it eventually evaporated, meaning no cooling agent and the reaction slowed and eventually stopped. Then, once the system cooled down, groundwater returned and the entire process began again.

Scientists now believe this cycle repeated itself naturally over hundreds of thousands of years. In effect, the reactor switched itself on and off automatically.

But that was just part of the discovery. When investigating further, scientists found that chemical signatures buried in the rock closely matched the waste products created inside modern reactors. This wasn’t simply an area that was experiencing fluctuating temperatures, this uranium had clearly undergone sustained nuclear fission.

Roughly 1.7 billion years ago, a small patch of land at Oklo naturally developed into a nuclear reactor that probably emitted around 100 kW of thermal power. Not a huge amount, maybe enough to power two or three commercial buildings, but it did so completely naturally, safely, and without our modern human minds.

Insane Geological Discoveries

And there we have it. 10 of the most insane geological discoveries ever made. Who knew that there were giant, continent-sized blobs moving through our mantle, that there’s a river deep in the Amazon hot enough to boil an egg in, or that the Sahara was once a lush, life-giving paradise.

We think we know the Earth

But really, we’ve barely scratched the surface.

Olivier Guiberteau

Key Takeaways

• The Earth’s mantle contains a vast reservoir of water within ringwoodite, challenging theories on water’s origin.
• Zealandia, a mostly submerged continent, was confirmed in 2017, adding an eighth continent to our planet.
• The moving rocks of Death Valley’s Racetrack Playa are driven by a combination of thin ice sheets and wind.
• The Sahara Desert was once a lush, green landscape during the African Humid Period, around 14,500 to 5,500 years ago.
• The Shanay-timpishka River in the Amazon is a naturally occurring thermal river, reaching temperatures up to 99.1°C.

Sources

• Original Side Projects video: 10 of the Most Insane Geological Discoveries
• Hero image source by ArnoBOUJIKA / openverse, by.

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