Astrum Space - Scientists Found a Lost City at the Bottom of the Ocean | Astrum Earth

Episode Date: July 9, 2026

Deep beneath the ocean lies the longest mountain range on Earth: the Mid-Atlantic Ridge. It’s a world of crushing pressure and intense volcanic activity, where nothing should survive. But when scientists scanned the sea floor, they discovered something completely unexpected. Did they find a lost city? Or something far stranger?▀▀▀▀▀▀Want to restore the planet’s ecosystems and see your impact in monthly videos? The first 100 people to join Planet Wild with my code ASTRUM7 will get the first month paid for by me: https://planetwild.com/r/astrumearth/... ▀▀▀▀▀▀Astrum's newsletter has launched! Want to know what's happening in space? Sign up here: ⁠https://astrumspace.kit.com⁠A huge thanks to our Patreons who help make these videos possible. Sign-up here: ⁠https://bit.ly/4aiJZNF

Below the surface of the Atlantic Ocean lies the longest mountain chain on Earth. It rises three kilometers above the sea floor, hidden almost entirely underwater. This is the Mid-Atlantic Ridge, a 65,000 kilometer long scar, where the Earth is literally pulling itself apart. It is a place of perpetual darkness, crushing pressure, and extreme volcanic activity. The Mid-Atlantic Ridge was something we thought we understood. We thought it was bursting with black smokers, acidic vents and even life fueled by the heat of magma. But in the year 2000, a team of scientists stumbled upon something that shouldn't exist. A towering ghostly white metropolis of spires, standing like a cathedral in the dark.

Spanning the area of a city block and towering up to 60 metres tall, They called it the Lost City. Conditions here are so hostile, so extreme that no life should be able to survive. And yet, it's teeming with trillions of residents. This is no mythical land or hidden Atlantis. This is a place that's revealing to us life's most brutal survival tactics. I'm James Stewart and you're watching Astrom Earth. Join me in this video as we go to the depths of the Mid-Atlantic Ridge to uncover how this city was built, the alien chemistry that fuels it, and why this place might hold the key to how life begun, not just here on Earth, but on icy moons across our solar system.

As we finally bring one of the strangest ecosystems ever found on planet Earth to light. On the 4th of December 2000, an expedition funded by the US National Science Foundation was sent out to dive deeper into this spectacular underwater mountain range than anyone had ever been able to before. Led by Donna Blackman of the Scripps Institute of Oceanography, Deborah Kelly of the University of Washington, and Geoffrey Carson of Duke University, their goal was a simple one. Understand the structural geology and tectonics of the mountain range. They plan to take images of the steep cliffs using a submersible, study the faults,

and work out the origin of this strange oceanic mountain. But a chance discovery changed those plants. A flicker on a camera feed 700 metres down showed ghostly shapes rising out of the darkness in a place where all they were expecting to see were normal black hydrothermal vents. But what they saw wasn't black or molten, but pale, towering and, otherworldly. At first, they didn't understand what their cameras were showing. These structures had similar characteristics to hydrothermal vents, natural hot springs on the sea floor, chimney-like structures that emit dark, particle-laden fluids, rich in metal sulphides, often

referred to as black smokers. But those shouldn't be here. They should be on the ridge axis, where it's hot, volcanic and violent, where new land is formed. not 15 kilometres away from the ridge on crust over a million years old. The weather was turning bad and they were working against the clock to get back to shore. With only enough time for one more dive in their underwater submersible Alvin, quickly the team plunged into the abyss for a better look at what the camera had first glimpsed. As they descended down in the submersible, they entered a world no one had ever seen before. What awaited them was a landscape of towering spires, some rising 60 meters high, taller than a 15-story building,

the tallest hydrothermal deposit known at the time. Their surfaces were pale, almost luminous like limestone ruins and a submerged world, but most mysterious of all was what was coming out of them. Instead of sulphide chimneys akin to normal hydrothermal vents, the team found steep-side pinnacles made largely of carbonate minerals and magnesium hydroxide. Some vents even discharged fluids around 75 degrees Celsius, while flanges trapped shimmering pools of 50 to 55 degrees Celsius water, a far cry from the 200 to 400 degrees you'd expect in typical hydrothermal vents. This area looked less like a volcanic furnace and more like a limestone citadel.

Staggeringly, the team saw that these vents hosted abundant microbial life, but lacked the kind of giant vent fauna that had become iconic elsewhere. This was not a volcanic system, but something else entirely. They named the spooky landscape The Lost City, but that was it. Their time was up, they had to get back to shore. They had glimpsed the unthinkable and then had it clutched away from them just as quickly. Ascending rapidly to avoid the weather, this voyage left them with more questions than answers. Once they returned to shore, it would force geologists, chemists and biologists to rethink what a hydrothermal vent field could be. Everything about the Lost City broke the rules.

It was in the wrong location, had the wrong chemistry, the wrong temperature, and even the wrong minerals. Hydro thermal vents were supposed to be driven by magma, but here there was no matter. and it would later transpire that area they observed on that day was just one of a cluster of more than 30 similar structures spread over an area larger than a football field To understand the significance of this we need to zoom out and look at how the Mid-Atlantic Ridge came to be in the first place Now when you think of mountain ranges you'd be right to picture something that looks like Mount Everest But 90% of the biggest mountain range on earth as we've just seen is almost in entirely underwater. The global mid-ocean ridge system, snakes around the planet like the seam on a baseball,

stretching roughly 65,000 kilometers. The Mid-Atlantic Ridge is one of the most famous segments of this monstrosity, a submerged backbone that runs right down the middle of the Atlantic Ocean. An ever-evolving boundary line between the North American plate and the Eurasian plates in the North Atlantic and the South American plate from the African plate in the South Atlantic. It was first discovered in 1853 by Matthew Fontaine Mori and confirmed as a major underwater mountain range in 1872 by the HMS Challenger expedition.

Its full continuous nature was further mapped in the 1920s with sonar and in the 1950s it was finally recognised as what we know it as today. a huge mountain range completely hidden beneath the waves. So how did a giant scar just appear in the middle of the ocean? Well, the truth behind the middle antip ridge is actually quite a straightforward one. It exists on a divergent boundary, where two tectonic plates are quite simply moving away from each other. As they separate, hot rock from the mantle rises, which causes the pressure to drop. Now, that drop in pressure allows some of the mantle to melt away, creating magma.

that magma moves upward and cools into a brand new ocean crust. In other words, the seafloor here isn't just sort of sitting around looking pretty. It's actively being manufactured and continuously manipulated along the ridge. This happens again and again and again and again over millions of years, creating a conveyor belt of rock, fresh crust forming at the ridge, older crusts being pushed outward on either side. In the case of the Mid-Atlantic Ridge, that's been happening. at roughly 2.5 centimeters per year, which sounds pretty trivial, right?

Until you realise it's been happening long enough to widen an entire ocean basin. Now, the reason we know this is happening is because the sea floor keeps a record, like a giant rocky diary of its own creation. As magma rises from the mantle, it cools quickly in seawater, and this process almost always produces basalt, and fortunately for scientists, Basalt has a rather remarkable property. As it cools, tiny crystals of iron-bearing minerals inside it act like microscopic compasses.

They align themselves with Earth's magnetic field at that exact moment and then lock permanently into place. But here's where things get strange, because Earth's magnetic field doesn't stay constant. Over geological time, it flips. North becomes south, south becomes north again and again. It's a pattern that stretches back millions of years. Now, let's apply that concept to the mid-ocean ridge.

As new basalt is constantly forming, each layer records the magnetic direction at that time. So as the seafloor spreads, that record is carried outward, frozen into the crust and the results? Bands of rock with alternating magnetic orientations, like stripes running parallel to the ridge. Now, the cool part is that because spreading happens in both directions at once, those stripes are perfectly mirrored on either side. It's like a giant barcode stamped

across the Atlantic Ocean floor. So when scientists map these magnetic patterns and link them to known reversals of Earth's magnetic field, something incredible emerged. The age of the ocean crust increases the farther you move away from the ridge. This isn't just a symmetrical pattern. It's confirmation that the Atlantic Ocean is still opening today. day right now as you watch this video. Because the Mid-Atlantic ridge spreads relatively slowly, it doesn't form a smooth volcanic dome, but instead a series of rugged, broken faults, scarts, landslides, and a central Rift Valley. In contrast, a far-spreading ridge, like the East Pacific rise, tends to have smoother volcanic crests. But make no mistake, the scales we're

talking about in this video are gargantuan, so when I say Rift Valley, quite flippantly like I did, we're talking about a valley comparable in scale to the Grand Canyon in depth and width. This ridge isn't a single unbroken line either. It's offset by Transform Fault, which are sort of like giant sideways tears in the crust, creating the zigzag pattern you see on the seafloor and now on Google Maps. Newly created oceanic crust moves away from mid-ocean spreading centres. But because Earth is spherical, this new crust can't see. spread out in flat uniform sheets. Instead, it must adjust to the planet's curved shape,

which causes cracks to form perpendicular to the axis of seafloor spreading. These cracks are known as fracture zones. When spreading centres are displaced along these fractures and the fault movement occurs in opposite directions, the crack is referred to as a transform fault. In a few rare places, the ridge rises high enough to break the surface. Actually, Iceland is a classic example of this, one of the few places on Earth where the ridge can be studied above sea level. And very helpfully, we've already made a video about how that ridge affects Iceland, by the way, which you can watch here when you finish watching this one. Finding places like this reminds me just how incredible our planet really is and how much we need to take care of it. You know, sometimes it feels like I'm just one person, what difference can I actually make?

Well, the answer is a huge one, which is why I'm just one. one, which is why I partner with Planet Wild once again. If you've watched this channel for any amount of time, you know how much I love these guys. They're like crowdfunding, but for nature. I've been a member personally for quite a while now, and their community, there's over 25,000 of us now, funds a mission to restore nature around the world every month, both on land and in our oceans. They're helping preserve incredible ecosystems just like this one, every single day as you go about your day. The cool part is they also document this and make. work on YouTube so we can actually see the impact of our contributions.

You know, right now it feels like there's wave after wave of bad news, but seeing what they're doing gives me some hope because it feels like I can actually make a difference. I don't feel as hopeless. Recently they helped build the largest biodiversity corridor in all of South America. It's amazing. And you can be part of projects just like this too. The first hundred people to sign up for this using my code Astrum 7 will get their first month paid for by me. Legit, actually, no gimmicks. Just scan this QR code on screen or click the link in the video description. After that, you can give whatever amount feels right for you, and you can also cancel at any time.

You'll see the result of your contribution in less than 30 days, and if you want to see them in action right now, check out their mission to build South America's largest biodiversity corridor with the link in the video description. But now let's head back to another awesome ecosystem, and revisit the Lost City. Slow-spreading ridges do something else, too. They can tear themselves open along long-lived faults and expose rocks from deep in the oceanic lithosphere.

This is what's happening here. When seawater penetrates those fractured mantle rocks, it reacts with primary mantle minerals such as olivine in a process called serpentinization, and it's this that changes everything. That reaction generates heat, hydrogen, methane and extremely alkaline fluids, similar to the hydrothermal vents sites have been accustomed to seeing, but these ones behave completely differently.

When those fluids mix with cold seawater, they precipitate carbonate and brucite, a natural mineral form of magnesium hydroxide, characterized by its soft, pearly to wax the appearance and white, grey or pale green colour. And it's exactly that reaction. that builds those giant pale chimneys the team saw in the Lost City. But why is that so significant?

Well, what this revealed is that the Lost City is not driven in the familiar way. There is no roaring magma chamber beneath a volcanic ridge crest, essentially. We're talking about seawater infiltrating deep fractures in mantle rock, being chemically transformed, and then returning to the ocean fully loaded with hydrogen, methane, and alkalinity. Just trying to imagine that. Not only does this play show that life doesn't need sunlight to survive, perhaps the most significant aspect of hydrothermal vents, but it also shows life doesn't even need volcanic heat.

Life can survive on chemistry alone. These fluids are energy bonanzas, creating a unique environment for microbial communities. The Lost City is a scientific anomaly. While Black Smokers can support giant tube worms, the Lost City is dominated by microbes. The chimneys are lined with thick biofilms of archaea, ancient organisms that don't breathe oxygen or eat plants. They consume the hydrogen and methane produced by the rocks themselves. That's their lunch.

Living on the surface of these towers are swarms of tiny translucent shrimp, snails and amphipods. Because the environment is so stable, evolution has actually been given the time to slowly but surely create this highly specialized ecosystem. Which, by the way, is the reason it's not just scientists here on Earth interested in the Lost City. NASA is also keeping a close eye on things as well, because if life can exist here, powered only by the reaction between water and rock, then it could exist on Enceladus, one of Saturn's moons, or even Europa, one of Jupiter's moons. Both have similar properties, rocky cores and liquid oceans, albeit hidden under thick icy crusts, making the Lost City, not just an earthly wonder, but the potential blueprint for finding, life in the cosmos, which is obviously pretty cool. But before we get too far ahead of ourselves and run off to other planets,

which is what Ashthram space is for, there is still much more to uncover here on our planet and in the Lost City. And this place has thrown up even more striking revelations in the years since. The 2000 discovery was spectacular. There is no doubt about that. But it was also incomplete. The team still didn't know exactly how old the field was, whether the towers were fixed, in a place or migrating, how far venting extended across the Mid-Atlantic Ridge, or even where the Lost City was a one-off. The fact they'd only had time for that one miraculous, but single dive, made those uncertainties especially acute. The first major answers arrived in different stages. After three agonising years filled with theories and speculation,

virtually the same team returned in 2003, aboard the Woods Hole Oceanographic Institute's research vessel Atlantis. The star of the show this time was their autonomous Benthic Explorer, or Abe, a free swimming robotic vehicle deployed above the mountain each night from Atlantis. Now, Abe was able to do something the scientists could not, and follow pre-programmed glide paths to produce sonar maps of unprecedented resolution in the vent site area, around 700 meters below the surface, shining both a literal and metaphorical light on this hidden world. In addition to Abe's relentless work, the team also collected a total

of 114 rock, 173 vent fluid, and 153 microbiological samples. They also made 19 dives to the vent site areas, aboard Atlantis' manned research submarine, Alphiolitan. and their patience was rewarded. They were able to map a dozen vent structures, spread over an area about a square kilometer, including one structure they nicknamed Poseidon, standing nearly 61 meters tall. But there were still big questions to answer. How long had these things been sat here, glowing away in the Atlantic Ocean without anyone realising it?

Within a few years, isotope and radio carbon work gave us the answer. The Lost City had been active for at least 30,000 years. But it still wasn't a firm answer, a nice round number to take home. Thanks to a combination of high-resolution bathymetry, basically just precise detailed mapping of underwater terrain, image mosaics and direct observations. Those 30,000 years quadrupled. Scientists now estimated the Lost City had been around for at least 120,000 years. But there was still something missing. The thing is, up until now, scientists weren't quite sure if this place was a total fluke,

a freak of beautiful nature the accidentally stumbled upon, or whether there were more systems like it. So, Noah and the Schmidt Ocean Institute combined forces, expanding their search and launched a new expedition called In Search of Hydro Thermal Lost Cities. This time, they didn't just focus on one area, but focused their efforts along a 700km section of the Mid-Atlantic Ridge. The expedition used a modern layered search strategy. Shipboard multi-beam mapping, CTD, conductivity temperature depth,

which involves using an instrument package on a wire to look for traces of hydrothermal activity. ORP plume sensing, or oxidation reduction potential, an environmental monitoring technique that measures the ability of water to oxidise or reduce, and ROV Sebastian with a real-time methane sensor. In other words, they threw the kitchen sink at this. What they found was both thrilling and humbling. The team discovered three new hydrothermal vent fields, all-black smoker style,

and generated high-resolution maps over large areas of the sea floor. Whilst this was still quite an impressive discovery, what they did not find was the Lost City's long-loss twin. But that wasn't necessarily the worst. worst news. In its own right, this discovery proved to be scientifically valuable. It suggested that Lost City is either genuinely rare, or that the exact combination of tectonics, rock exposure, fluid flow and preservation needed to build those giant carbonate towers is harder to find than they'd hoped. So they pressed on. Around the same time in 2023,

the International Ocean Discovery Program tackled the problem head on, taking a more direct approach and drilling a borehole on the southern wall more than a kilometre below the sea floor. This is far, far beyond any previous drilling success ever recorded in a peridotite-dominated system like this. This was significant. What they did essentially was pull up a long, coherent piece of the altered upper-me. mantle from the Lost City neighborhood, something that had never been done before. It gave research as one of the best direct samples yet of the rock column feeding this kind of system

and established a new benchmark for studying mantle hydration and serpentinization near Lost City. Now, after that potted chemical history, you're welcome, by the way, you may have noticed one thing standing out, or rather only one thing standing out. Over a 17-year period of grueling academic work, scientists still hadn't found another lost city. Well, sort of. Things get a bit complicated here, and in the interest of not spiraling myself into a chemistry vortex, my head isn't really fried. I'll keep things brief, but of course, if you do want to know more, shout in the comments, and we can do a follow-up. The search for a twin lost city reached a fever pitch, and teams were out there doing everything they could to find something they thought couldn't exist. until 2017 when they thought they'd found it.

Far deeper, at a depth of around 3,100 metres in a region of the southwest Indian Ridge. Something was discovered that behaved very much like Lost City. Slightly underwhelmingly, the scientists named it the old city. It was an alkaline field driven by serpentinization, those rock water reactions, rather than volcanic magma. Bingo, this is it. there was one crucial difference.

The old city is more like a chemical twin rather than a physical one. At the depth the old city operates at, and you can see what it looks like here on screen. The crushing pressure and different fluid dynamics likely make it far harder for 60-meter-tall carbonate towers to form and survive, so it looks pretty different. Instead, this place is more like a village, if I'm being kind, than a metropolis. Don't news heart just yet, though, if you're still rooting for this bizarre family tree to be. completed because things aren't over yet. Noah Chief Scientist Dr David Butterfield, leather mission as part of the search for hydrothermal

lost cities. The expedition was conducted on the Schmidt Ocean Institute's new research vessel Valcore and it too brought something astonishing to the surface. Equipped with one of the most advanced methane sniffers ever built, the research vessel arrived at a massive underwater feature called the Pui-de-Fol volcano. This was another volcanic ventfield discovered on the mid-Atlantic ridge at a depth of 2,000 meters. All of a sudden, sensors started screaming. Huge plumes of methane and hydrogen were rising from the depth, the exact chemical fingerprint of the lost city.

On board, the excitement was electric. Was this it? Had they finally found a second white metropolis? As the ROV sub-Astean, which gets me every time, reached the sea floor, the mystery deepened. This wasn't another Lost City, but instead another massive high-temperature black smoker field. These vents were screaming at 340 degrees Celsius, hot enough to melt lead. Instead of the cooler alkaline slow cooker chemistry of the Lost City, this area was a volcanic furnace and a spectacular find.

The first vents discovered in this 640-kilometer stretch of the ridge in over 40 years. but even so it wasn't the twin they were looking for. To me, reliving these discoveries with you now makes the original lost city even more of a miracle. To get those white 15-story carbonate towers, you need a perfect goldy locks kind of balance, mantle rock, low heat, and loads of time. And that, as it turns out, is not just rare, it's unique.

While the old city in the Indian Ocean prove the chemistry exists elsewhere, The original lost city remains the only place where nature has built a literal cathedral out of Earth's own breath. But there's a problem. You see, this city is under threat. All of these incredible scientific efforts are a blessing in so many ways, but they're also kind of a curse. The fact I'm sat here making a video about this unique place, telling everyone where it is, advertising it, well, that could also be viewed as a problem.

It's not just NASA and Noah keeping an eye on what's going on here. deep-sea miners are also targeting the Mid-Atlantic Ridge. Commercial interests are sizing up the mineral-rich crust surrounding these vents, as companies and governments seek to dominate mineral trade and gain rare earth autonomy, without much thought for what might stand in the way. Scientists warn that destroying these sites could mean losing the answers to the origin of life before we've even finished reading them. It's a timely reminder that Lost City is still a frontier.

the bottom of the Atlantic in the crushing darkness. The rocks are breathing. The water is turning to stone. Life is finding a way against all odds and we need to protect it. I know there's a lot to digest in this video. The chemistry took me a while to get my head round too, I must admit, but when I did, when I was finally able to process and compute just how special this place was, is it all became worth it. The deepest truth in the story is the 2000 discovery didn't actually solve a mystery at all. No, instead it created one. The Lost City began as an accidental find on a geological survey and every major revisit since has revealed a system that is older, stranger, more chemically subtle and more consequential than the first

stunned dive team could have ever known. Whilst I go about my day, my quest to do everything as quickly as I can rushing through live ticking stuff off my to-do list, you name it, I'm going to stop in the about this place? For over 100,000 years, this hidden system has endured, not as a violent eruption but as a slow patient engine, reshaping our understanding of what a living world can be. A world where slow and steady wins the race. Don't forget to subscribe to Astrom Earth if you like this video or learn something new. And let me know in the comments what you think of this discovery. Had you heard of it before? Did it surprise you? And do you think one day in the future, we might find another just like it.

Let me know down below. Don't forget, before you go, we have that great offer for you with Planet Wild. First hundred people to sign up get their first month paid for by me. If you want to do something right now for the planet, if this video has inspired you,

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