Below the surface of the Atlantic Ocean
lies the longest mountain chain on
Earth.
It rises 3 kilometers above the sea
floor. Hidden almost entirely
underwater.
This is the Mid-Atlantic Ridge, a 65,000
km 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 m 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 teameming 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
Astramm 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 Jeffrey 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 plans. A flicker on a
camera feed 700 meters 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 particleladen
fluids rich in metal sulfides, 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 forming, not
15 km 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 a submersible, they entered a world
no one had ever seen before. What
awaited them was a landscape of towering
spires, sun rising 60 m high, taller
than a 15story building. The tallest
hydrothermal deposit known at the time.
Their surfaces were pale, almost
luminous like limestone ruins in a
submerged world. But most mysterious of
all was what was coming out of them.
Instead of sulfide chimneys akin to
normal hydrothermal vents, the team
found steepsided pinnacles made largely
of carbonate minerals and magnesium
hydroxide.
Some vents even discharge fluids around
75° C, while flanges trap shimmering
pools of 50 to 55° C water, a far cry
from the 200 to 400° 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. Hydrothermal vents were
supposed to be driven by magma. But
here, there was no magma chamber. 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 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 plate 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 Mory 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 recognized 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 antic
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 crust being
pushed outward on either side. In the
case of the Mid-Atlantic Ridge, that's
been happening at roughly 2.5 cm per
year, which sounds pretty trivial,
right? until you realize 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
bassalts. And fortunately for
scientists, bassalt has a rather
remarkable property. As it cools, tiny
crystals of ironbearing 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 bassalt 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 result 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 mapped 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, 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, scars,
landslides, and a central rift valley.
In contrast, a fast-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 is 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 centers. But
because Earth is spherical, this new
crust can't 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
centers 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.
another awesome ecosystem and revisit the lost city.
Slow spreading ridges do something else
too. They can tear themselves open along
longived 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
serpentonization.
And it's this that changes everything.
That reaction generates heat. hydrogen,
methane, and extremely alkaline fluids,
similar to the hydrothermal vents
scientists 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 waxy
appearance and white gray or pale green
color. 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
try and imagine that. Not only does this
place 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
tubeworms, the lost city is dominated by
microbes. The chimneys are lined with
thick bofilms of archa, 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 anthropods. 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 Ash 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
midatlantic ridge, or even whether 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 agonizing years filled with
theories and speculation, virtually the
same team returned in 2003 aboard the
Woods Hull 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 m below
the surface, shining both a literal and
metaphorical light on this hidden world.
In addition to Abee'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's manned research
submarine, Alvin, 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 m 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 realizing it? Within a
few years, isotope and radiocarbon 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
highresolution bathimemetry, 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 they 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
Hydrothermal Lost Cities.
This time they didn't just focus on one
area, but focused their efforts along a
700 km 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. OP
plume sensing or oxidation reduction
potential. an environmental monitoring
technique that measures the ability of
water to oxidize or reduce an ROV
Sebastian with a realtime 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 highresolution 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 lost twin. But that wasn't
necessarily the 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 carbonet 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 headon, taking a
more direct approach and drilling a ball
hole on the southern wall more than a
kilometer 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 mantle from the lost city
neighborhood, something that had never
been done before. It gave researchers
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
serpentonization 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 sparring myself into a
chemistry vortex, my head is already
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 m 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 serpentonization, those rock
water reactions rather than volcanic
magma. Bingo. This is it. Except 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 me 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 lose 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
led the mission as part of the search
for hydrothermal loss cities. The
expedition was conducted on the Schmidt
Ocean Institute's new research vessel,
Valkor, 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 Pu Def Volcano. This was
another volcanic vent field discovered
on the midatlantic ridge at a depth of
2,000 m. 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 Subastion,
which gets me every time, reached the
seafloor, the mystery deepened. This
wasn't another lost city, but instead
another massive high temperature black
smoker field. These vents were screaming
at 340° C, 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 km 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 15story carbonate towers, you need
a perfect Goldilocks kind of balance.
Mantel 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 proved 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
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 mineralrich 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. At 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 around, 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 stun dive team could have ever
known. Whilst I go about my day and my
quest to do everything as quickly as I
can, rushing through life, ticking stuff
off my to-do list, you name it, I'm
going to stop and think about this
place. For over a 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.
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discovery. Had you heard of it before?
Did it surprise you? And do you think
one day in the future, we might find
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