I spend a ridiculous amount of time reading about space, distant planets and everything happening millions of miles above our heads, but it occurred to me recently that we have an entire planet beneath our feet that we haven't even come close to exploring. We know an extraordinary amount about Earth's interior thanks to geology and seismic research, but when it comes to physically drilling down and examining what's actually there, our accomplishments are surprisingly limited.
Which brings me to one of the strangest scientific projects I've ever read about, the Kola Superdeep Borehole in northern Russia, where Soviet scientists spent decades drilling more than seven miles into the Earth's crust, only to discover that some of their assumptions about what was down there were completely wrong.
You may have heard of this project already, although there's a decent chance you know it from one of those ridiculous internet stories about scientists accidentally drilling into Hell and recording people screaming from underground. I promise we'll get to that because the whole thing is absolutely bizarre, but the actual scientific discoveries are considerably more interesting than a fictional recording of tortured souls.
The fact that scientists managed to drill more than seven miles into solid rock, found water and evidence of ancient life, and still barely scratched the surface of our planet is fascinating enough without inventing anything supernatural.
The Cold War Had Scientists Racing Underground Too
During the 1960s, the United States and Soviet Union were competing over just about everything, most famously the race to put humans on the Moon. Because, sending people into space wasn't quite enough of a scientific challenge, both countries were also interested in exploring what was happening beneath the Earth's surface.
The United States had launched an ambitious research effort called Project Mohole, which aimed to drill through the ocean floor and eventually reach the Earth's mantle. Scientists chose the ocean because oceanic crust is generally much thinner than continental crust, meaning they had a better chance of reaching the boundary between the crust and mantle without drilling an absolutely unreasonable distance.
Unfortunately, Project Mohole ran into technical difficulties, financial problems and political disagreements, and Congress stopped funding it in 1966. The project did demonstrate that drilling from a ship in deep water was possible, which eventually helped advance ocean drilling research, but scientists never reached the mantle.
The Soviet Union had its own plans, and in May 1970, drilling began on the Kola Peninsula in northwestern Russia, not far from the Norwegian border. The location was selected partly because it sits within the Baltic Shield, a region of incredibly ancient continental crust that scientists wanted to study directly.
Their goal was to drill approximately 15 kilometers, or 9.3 miles, into the crust, collecting rock samples and measuring the geological conditions along the way.
I think it's important to point out that the Soviet project wasn't simply trying to beat the Americans to the mantle. Kola was primarily designed to investigate the structure, composition and physical properties of the continental crust, which meant the scientists could accomplish an enormous amount of research without ever reaching the next major layer of the Earth.
Of course, that didn't make the engineering challenge any less ridiculous.
How Do You Even Drill a Hole Seven Miles Deep?
When I first saw photographs of the Kola Superdeep Borehole, I was expecting something enormous, perhaps a giant opening in the ground that looked like the entrance to an underground mine. Instead, the famous opening is covered by a metal cap roughly the size of a dinner plate, which is a pretty underwhelming appearance for one of the greatest drilling achievements in human history.
The borehole itself is narrow, measuring only around nine inches across in some sections, and the project involved multiple drilling paths extending downward through the rock.
Scientists weren't digging out a giant underground tunnel or building something people could climb into. They were using specialized drilling equipment to cut through the crust while bringing cylindrical samples of rock, called drill cores, back to the surface for analysis.
Now imagine trying to do that at depths where the equipment stretches for kilometers, temperatures are increasing, rock layers are changing and the pressure is enormous. Every time something broke, became stuck or needed replacing, the engineers faced the rather unpleasant task of dealing with equipment buried miles underground.
And things definitely broke.
In 1984, a serious equipment failure interrupted drilling after the project had already passed 12 kilometers. The team eventually continued by drilling along a different path, because recovering from a failure several miles underground isn't exactly a matter of running to the hardware store for a replacement part.
By 1989, the borehole had reached its greatest depth of 12,262 meters, approximately 40,230 feet or 7.62 miles.
That record still matters today, although there's an important distinction between the deepest borehole and the longest one. Modern oil and gas wells can extend for greater distances because they curve and travel horizontally beneath the surface. Kola remains the deepest vertical penetration into Earth's crust, even though its actual drilling paths weren't perfectly straight.
And despite reaching more than seven miles underground, the scientists were still inside the continental crust.
The average distance from the Earth's surface to its center is approximately 6,371 kilometers, meaning Kola's extraordinary depth represents only about 0.2 percent of that journey. We spent nearly two decades drilling toward the center of our planet and managed to travel less than one quarter of one percent of the way there. I'm not entirely sure whether that makes me more impressed with the engineers or more intimidated by the size of the Earth.
Scientists Expected to Find Basalt, but the Rocks Had Other Plans
One of the most important discoveries from the Kola project involved a geological boundary that researchers thought they understood before drilling began.
Scientists have used seismic waves to study Earth's interior for more than a century. When earthquakes occur, they produce waves that travel through the planet, and those waves change speed depending on the properties of the materials they encounter.
By measuring those changes, geologists can make remarkably detailed estimates of what's happening underground without physically digging through every layer.
The problem is that seismic data requires interpretation, and sometimes more than one geological explanation can account for the same observations.
Before the Kola project, some researchers believed a change in seismic wave behavior several kilometers beneath the surface represented a transition from granitic rocks to denser basaltic rocks. This was part of a relatively simple model of continental crustal layering that scientists wanted to investigate.
Except when the drill reached the predicted depths, the expected basaltic layer wasn't there.
Instead, researchers encountered ancient metamorphic rocks, including gneisses, along with complicated geological structures, fractured zones and changes in the physical properties of the rock itself.
Gneiss, if you're unfamiliar with it, is a metamorphic rock that forms when older rocks are subjected to intense heat and pressure. Depending on the original material, it can contain minerals such as quartz, feldspar and mica, often arranged in distinctive bands.
The important discovery wasn't simply that they found a different kind of rock than expected. It was that the change in seismic wave behavior didn't necessarily mean the rock had changed from granite to basalt.
Fractures, metamorphism, deformation and other geological properties could also influence those measurements.
Essentially, scientists had been interpreting part of the crust using a model that turned out to be too simplistic for that region.
I love discoveries like this because they demonstrate something people occasionally misunderstand about science. Scientists don't necessarily spend their careers proving that everything they already believe is correct. Some of the most valuable research happens when their predictions turn out to be wrong, and they have to figure out why.
There Was Water Miles Beneath the Surface
This might be my favorite part of the entire project because I think most of us imagine that once you travel far enough underground, everything must become a solid mass of rock with very little room for anything else.
And to be fair, that's not an unreasonable assumption considering the amount of pressure involved.
But researchers studying the Kola borehole discovered evidence of fluids within fractures and mineral-bearing zones at depths where they hadn't expected such extensive fluid activity.
We're not talking about enormous underground lakes or a secret ocean hidden beneath Russia, which is unfortunately how some websites have decided to describe the discovery. Instead, scientists identified water and other fluids associated with cracks, faults and altered minerals in the deep crystalline rocks.
Some fluids can originate from geological processes involving heat, pressure and chemical reactions, while others can move through connected fractures over long periods of time. The exact origin and history of a particular fluid depends on the rocks and geological conditions involved.
What made the findings significant was that parts of the deep continental crust were far more fractured and capable of transmitting fluids than earlier models had suggested.
Researchers have continued studying Kola rock samples for decades, including examining tiny pockets of fluid trapped inside minerals. A study published in Scientific Reports in 2020 even investigated unusual concentrations of gold nanoparticles within ancient fluid inclusions from the borehole.
Yes, actual gold nanoparticles trapped in geological fluids. Apparently, the Earth has been conducting its own complicated chemistry experiments for billions of years without asking us whether we understand any of them.
One clarification worth making is that the discovery of water at depth doesn't automatically mean scientists found a reservoir of water that had been sitting untouched for two billion years. Determining the age and origin of underground fluids requires specific geological and chemical evidence, and the Kola findings involve several different fluid-related processes.
What we do know is that the deep crust is considerably more chemically active and complicated than a simple collection of solid rock layers would suggest.
They Also Found Evidence of Ancient Life
As if the unexpected fluids weren't interesting enough, accounts of the Kola research program also describe microscopic fossil material associated with rocks and geological processes several kilometers beneath the surface.
A scientific review published in Communications Earth & Environment in 2026 discusses reworked fossil plankton at approximately six kilometers deep, along with evidence of fluids moving through the crust.
Now, before anybody starts imagining tiny prehistoric creatures happily swimming around in underground water at temperatures approaching 400 degrees Fahrenheit, that's not what the discovery means.
Plankton are organisms that drift in water, and their fossilized remains can become incorporated into sediments and other geological materials. Over enormous periods of time, those materials can be buried, transformed by heat and pressure, and affected by geological deformation or fluid movement.
Finding ancient biological material within a deep geological setting doesn't mean those organisms originally lived at that depth, and it certainly doesn't prove that plankton can survive under the extreme conditions near the bottom of the borehole.
The research is fascinating because it provides another way to investigate the geological history of the rocks and the processes that have changed them over time.
Some of the rocks collected from Kola belong to the Archean Eon, a period of Earth's history stretching from approximately four billion to 2.5 billion years ago. That's long before dinosaurs, forests, animals or anything resembling the world we recognize today.
But it's not older than life itself, because evidence indicates that microbial life already existed during the Archean.
I find it genuinely difficult to comprehend that scientists could bring pieces of rock to the surface that had formed billions of years before humans existed, then study their chemistry and mineral structures to reconstruct some small piece of our planet's history.
I get excited when I find an interesting fossil at a museum, so I can only imagine what it must've felt like to examine material recovered from more than six miles beneath the Earth's surface.
The Heat Was a Much Bigger Problem Than Anyone Expected
The original plan was to drill 15 kilometers down, but the engineers eventually encountered conditions that made continued drilling increasingly difficult.
One of the biggest problems was temperature.
Scientists knew the Earth's interior becomes hotter with increasing depth, but the temperatures encountered at Kola were substantially higher than the project had originally anticipated.
Reports commonly describe temperatures reaching around 180°C, or 356°F, at great depth, while some later scientific reviews report temperatures exceeding 200°C in the deepest sections.
For comparison, water boils at 100°C, or 212°F, at normal atmospheric pressure. Of course, water behaves differently under the enormous pressures found deep underground, so you can't just imagine the bottom of the borehole as a giant pot of boiling water.
The rocks weren't turning into molten lava either, despite what some internet explanations might lead you to believe.
What happens to rock under extreme temperatures and pressures is much more interesting than that. Although we tend to think of rock as completely rigid, it can deform under prolonged stress, and the conditions deep within the crust can cause the surrounding material to behave differently from rocks at the surface.
At Kola, the combination of heat, pressure, rock deformation and drilling difficulties made it increasingly challenging to maintain a stable borehole and keep the equipment functioning properly.
Some accounts from the project even describe problems recovering intact drill cores, with samples fragmenting as they were brought to the surface and the surrounding pressure changed.
Imagine spending an enormous amount of time drilling for a particular piece of ancient rock, only to have it arrive in fragments after you've hauled it up from miles underground. I'd be a little irritated.
By 1989, the deepest drilling path had reached its record depth, but attempts to continue the project and work through technical problems carried on into the 1990s.
Unfortunately, the engineering challenges weren't the only problems the scientists were about to face.
Then the Soviet Union Collapsed
The Soviet Union dissolved in 1991, bringing enormous economic and political changes that affected scientific research throughout the former Soviet states.
A project requiring specialized equipment, hundreds of workers and a substantial research budget was suddenly operating in a very different financial environment. Combined with the enormous technical difficulties of drilling any deeper, the loss of funding made continued progress increasingly unrealistic.
Although work on additional drilling paths continued into the 1990s, the project never surpassed its 1989 depth record, and drilling eventually came to an end.
The site remained associated with scientific research for years afterward, but the enormous drilling infrastructure was gradually abandoned. Today, photographs show deteriorating industrial buildings, rusted equipment and the famous metal cap covering the borehole.
There's something a little sad about seeing the remains of what was once such an ambitious scientific undertaking, particularly knowing how much effort went into reaching that depth…but the project certainly wasn't a failure.
Scientists recovered thousands of rock samples, collected measurements of temperatures and physical properties, and gathered an extraordinary amount of information about the structure of the continental crust.
Some of those samples are still studied today, which means the scientific value of the project didn't disappear when the drilling stopped.
Considering how expensive and technically difficult it is to obtain material from those depths, I imagine researchers will be finding new things to investigate in the Kola samples for quite some time.
So Where Did the Story About Scientists Hearing Screams from Hell Come From?
Okay, now we can talk about the ridiculous part.
At some point, the Kola Superdeep Borehole became associated with one of the strangest urban legends of the late twentieth century, a story claiming Soviet scientists had drilled so deeply that they accidentally opened a passage into Hell.
According to different versions of the legend, researchers supposedly encountered an enormous underground chamber, lowered a heat-resistant microphone into the opening and recorded thousands of people screaming in agony. Naturally, this story spread through sensational publications, religious broadcasts and eventually the internet, where it became one of those mysteries people continue sharing regardless of how many times it's been debunked.
The legend is commonly known as the Well to Hell, and recordings claiming to capture the screams have circulated online for years.
There's just one fairly significant problem with the whole thing. There's no credible scientific evidence that anything like this happened…of course. The actual Kola research program produced geological measurements, rock samples, temperature data and studies of the Earth's crust. It didn't produce verified recordings of human screams, and scientists didn't discover an enormous underground chamber filled with supernatural activity.
The story also frequently places the borehole somewhere in Siberia, despite the actual drilling site being on the Kola Peninsula in northwestern Russia, which is a pretty substantial geographical mistake to make when you're supposedly revealing one of humanity's greatest discoveries.
Investigations into the legend have traced its spread through sensational reporting and embellished retellings rather than legitimate scientific publications. I suppose the actual explanation, involving fractured crystalline rocks, geothermal gradients and seismic discontinuities, doesn't have quite the same potential for a terrifying YouTube thumbnail.
Personally, I think finding unexpected fluids and billions-of-years-old rocks miles beneath the surface is considerably more fascinating than a fabricated horror story, but apparently I'm not the target audience for those videos.
What Did the Kola Superdeep Borehole Actually Teach Us?
The biggest achievement of the Kola project wasn't simply breaking a depth record, although reaching more than 12 kilometers into solid rock was an extraordinary engineering accomplishment.
It was the opportunity to examine parts of the Earth's continental crust that scientists had previously studied primarily through indirect measurements and geological models.
The project provided valuable evidence about the ancient rocks beneath the Baltic Shield, challenged assumptions about seismic boundaries, revealed deep fractures and fluid activity, and demonstrated how dramatically temperature and pressure can complicate our understanding of the underground environment.
It also highlighted why combining different scientific methods is so important.
Seismic waves allow scientists to investigate enormous regions of Earth's interior, while drilling provides actual rock samples and direct measurements that can help test those interpretations. Neither method replaces the other, and together they allow geologists to develop a much more accurate picture of what's happening beneath the surface.
Kola has also helped researchers understand some of the engineering challenges involved in ultradeep drilling, which remains relevant as companies and scientists investigate deep geothermal energy, underground resources and other technologies requiring access to extreme environments.
In fact, a major scientific review published in February 2026 revisited the Kola discoveries alongside modern ultradeep drilling projects, demonstrating that research conducted decades ago continues to inform how scientists approach the Earth's interior.
That's something I find particularly wonderful about projects like this. The scientists involved couldn't possibly have predicted every future application of the information they were collecting, but their work created a foundation that researchers can continue building upon long after the original equipment has stopped working.
We Know So Much About Space, but We've Barely Explored Beneath Our Feet
I think what fascinates me most about the Kola Superdeep Borehole is the perspective it gives us on our own planet.
We have spacecraft exploring the outer reaches of our solar system, telescopes observing galaxies billions of light-years away, and satellites capable of measuring tiny changes in the Earth's surface from hundreds of miles overhead.
Meanwhile, the deepest vertical hole we've ever drilled into the crust extends just over seven and a half miles beneath our feet.
To be clear, that doesn't mean we know almost nothing about Earth's interior. Modern geology, seismology, mineral physics and other scientific methods have taught us an enormous amount about the structure and behavior of our planet without requiring us to drill all the way through it.
But there's still a fascinating difference between studying something indirectly and physically recovering a piece of it.
It's one thing to calculate what temperatures and pressures should exist at a particular depth based on our models. It's another thing entirely to lower instruments into that environment, recover actual pieces of rock, and discover that some of those predictions were wrong.
And that's exactly what makes the Kola project so important.
It reminds us that even the world we live on every single day contains extraordinary scientific mysteries, and that understanding those mysteries often requires us to question things we thought we already knew.
The scientists at Kola didn't reach their original target of 15 kilometers, and they certainly didn't reach the Earth's mantle, but they managed to collect information from a part of our planet that no previous drilling project had explored to that depth.
They discovered unexpected geological structures, evidence of fluid movement, ancient rocks and conditions that challenged their assumptions about the deep crust.
And perhaps my favorite part is that some of the most important discoveries weren't the things they originally expected to find.
After spending years trying to understand the world beneath us, the researchers ended up with an entirely new collection of questions about how Earth's crust actually works.
I suppose that's one of the things I love most about science. Every time we manage to answer something that's puzzled us for years, we seem to discover another dozen things we hadn't even thought to ask.
The Kola Superdeep Borehole might not look particularly impressive today, with its abandoned buildings and small metal cap, but beneath that ordinary-looking piece of industrial history is a reminder of just how much effort humans are willing to put into understanding the world around us.
Considering that we've only managed to drill about 0.2 percent of the distance to the Earth's center, I'd say we still have a pretty unreasonable amount of exploring left to do.
Which is wonderful, really, because I can't imagine anything more boring than living on a planet where we'd already figured everything out.
A rock and mineral sample kit would give me a very enjoyable way to keep looking at the geology part. Put the pieces out on the table, compare the colors and textures and let me get distracted by what’s inside the planet for a change.
Related Reads You Might Enjoy:
The Earth’s Core Is Leaking Gold: A Hidden Alchemy Beneath Our Feet
The Ring of Fire Is Waking Up: Quakes, Eruptions, and Tsunamis
The Mountains That Breathe Fire: Volcanoes Most Likely to Erupt in Our Lifetime
When the Moon Rang Like a Bell: NASA’s Apollo Mystery That Still Echoes
Scientists Think the Earth Might Be an Intelligent Entity, Here’s What That Actually Means
The Shattered Planet That Lives On: What Vesta Tells Us About Cosmic Ruins
The Secret Life of Soil: Why Healthy Dirt Might Be Smarter Than You Think
Works Cited
Zhu, G., and H. Huang. “Ultradeep Drilling Beyond 10 km Revealing New Insights into Earth Systems and Resources.” Communications Earth & Environment, 2026. Research article.
Popov, Yuri A., et al. “New Geothermal Data from the Kola Superdeep Well SG-3.” Tectonophysics, vol. 306, 1999, pp. 345–366. Research article.
Wrigley, Charlotte. “Going Deep: Excavation, Collaboration and Imagination at the Kola Superdeep Borehole.” Environment and Planning D: Society and Space, 2023. Research article.
Prokofiev, V. Yu., et al. “Exceptional Concentrations of Gold Nanoparticles in 1.7 Ga Fluid Inclusions from the Kola Superdeep Borehole, Northwest Russia.” Scientific Reports, vol. 10, 2020. Research article.
National Research Council. 50 Years of Ocean Discovery: National Science Foundation 1950–2000. National Academies Press, 2000. Project Mohole history.
Kozlovsky, Y. A., editor. The Superdeep Well of the Kola Peninsula. Springer-Verlag, 1987.
Snopes. “The Well to Hell.” Fact-check and history of the urban legend.
