Beneath our feet lies a hidden world.
One that stretches miles into the
Earth's crust. Beyond the reach of
sunlight, beyond what we once thought
possible for life. A place of extremes
where life defies the impossible. From
ancient microbes surviving for millions
of years to bizarre organisms thriving
without sunlight, this underground world
is rewriting the very definition of life
on Earth. A vast alien-like ecosystem
thriving in extreme heat, crushing
pressure and total darkness. Here,
ancient microbes feast on minerals.
Strange organisms survive without
oxygen, and life endures in ways that
defy the rules of biology.
Welcome to Earth's deep bio.
I'm James Stewart, and you're watching
Astram Earth. In this video, we'll
uncover the secrets this underground
biosphere holds, what sorts of organisms
we can find there, the challenges they
face, and what this could all mean for
how we think of life, not just on our
planet, but on other planets, too. It's
time to go deeper and uncover the
mysteries of this unseen world.
So where exactly is this unseen world?
This is a region that extends down to at
least 5 km below the land and 10 km
below the seabed.
This deeply buried environment might not
seem like a very hospitable abode for
life compared to a tropical rainforest.
In fact, not even compared to a parched
desert or frigid glacia. But scientists
think that the deep biosphere could host
as much as 15% of all the biomass on the
planet. You've heard about
extraterrestrial life, but we're
uncovering the eerie diversity of
intraterrestrial life.
The biosphere comprising everything from
the mightiest giant redwoods down to the
tiniest microbes and viruses was once
thought to end not too far beneath our
feet. Of course, scientists knew about
creatures that spend their whole lives
in deep caves or that creep, crawl, and
borrow through the soil. But all life
was understood to take its energy
directly or indirectly from the sun,
either through photosynthesis or
consumption along the food chain,
meaning nothing could stray too far from
the light of day.
But as prospectors began to sink mines
and bore holes deep into the ground in
the early part of the 20th century, we
started to question that assumption.
Fluids extracted from deep in the
bedrock contained chemicals that seemed
to have a biological origin. And some
scientists were able to cultivate
bacteria that appeared to have been
residing far below the surface.
At first, researchers couldn't be
certain that the life that they were
detecting in these bore holes hadn't
been introduced from above by the act of
drilling itself. There's not generally a
need for drilling equipment to be
sterilized after all.
However, as scientists developed
techniques to avoid contamination from
the surface, they found that living
cells were found in nearly all the
samples that they brought up. Wherever
there were cracks or poor spaces through
which water could percolate, there was
life.
We know how different life can look if
you go just a little deeper below the
surface into caves and underground
burrows.
Strange adaptations start to emerge,
like the creepy eyeless face of the
Mexican tetra or the hairless naked mole
rat. But we're delving even deeper to
the sediments at the bottom of the ocean
and deep into the Earth's crust. What
kind of life can we expect to find
there? And what is it like?
All living things can be divided into
three domains. Bacteria, ara and ukaria.
This idea was proposed by American
microbiologist Carl Woos in 1990 and
helps us to understand the major
branching points in the tree of life
throughout the course of evolution.
Most of the life you'll be familiar with
including us belong to the ukaria.
We know what bacteria are but what about
archa? Like bacteria, they are
singleselled, but they resemble some of
the earliest life forms on Earth with a
unique kind of cell wall and genetic
makeup. Ara thrive alongside bacteria in
the deep biosphere. As smaller
unisellular organisms, they're often
better at coping with tough
environments, whether that's extreme
temperatures, high pressure, or scarce
nutrients. There's no question that the
deep biome is a difficult place to live.
So, with this in mind, let's take a look
at some of the most major findings from
our journeys below the surface.
want your digital life a little more private.
In the marine world, researchers dabbled
in shallow core sampling of ocean
sediment throughout the 20th century and
were shocked to find that cells were
present and detectable at all depths
that could be sampled. This was our
first piece of evidence that life could
exist in old sediments, some of which
were thought to have been deposited more
than a million years ago. Then began a
significant phase of ocean drilling
known as the ocean drilling program from
1983 to 2003
which gathered lots of data on the
ocean's deep sediments. And with this
data came another big shock for the
scientific community
that in fact most bacteria and archa may
be found in deeply buried sediments.
This finding prompted new waves of deep
biome exploration that continue to this
day. In 1976, scientists towing
specialized cameras along the sea floor
made the discovery of deep sea
hydrothermal vents. These vents are
ancient geological structures that spew
out a kind of hot chemical soup rich in
minerals and other nutrients. Upon later
visits to these vents in submersibles,
scientists were met by an unexpectedly
rich and vibrant community of life. So,
they started to think of these smoking
structures as a window to the deep
biosphere. And they weren't wrong. These
creatures were definitely not something
you'd find on the surface. In fact, some
vents host microbes that can function at
the boiling temperature of 100°.
Discoveries like these push the limits
of life beyond what we thought was
possible. And as a result, many
microbiologists now think the highest
temperature at which shells can function
may be closer to 150°.
But as well as extreme temperatures,
organisms living near hydrothermal vents
must cope with intense amounts of
pressure. The atmospheric pressure at
sea level is 0.1 megapascals. The
average depth of the ocean where deep
sea vents would be found is 3,800
m or 38 megapascals.
Pressure 380 times greater than you'd
experience at the sea surface. To
survive here, you'd probably have to be
what scientists call pisopilic or
pressure loving like the deep sea
bacterium photoacterium profundum SS9.
Not the catchiest name, but this species
has been adopted as somewhat of a model
organism to understand deep sea bacteria
as a group and was originally discovered
in the Philippines at a depth of 2,500
m. Pete Profundum can withstand
pressures from 0.1 to 90 megapascals.
So, it can be taken from the bottom of
the ocean and cultured at the surface
for scientists to study it. And the
results of these studies, well,
scientists found genes that allow this
bacterium to repair DNA damages caused
by high pressures. And it's actually
lower pressures like those found at the
sea surface that activate this species
stress response. This is proof that P
profundum isn't just tolerating high
pressures, but actually prefers them. At
immense depths like these, the extreme
conditions, lack of sunlight, and
primitive nutrients can really affect
the way you live. For organisms in
subseor environments, the best and
sometimes only strategy is to slow right
down. What does this mean? When energy
is scarce, all your metabolic processes
slow down. And the little energy you do
have is probably being used to repair
yourself instead of dividing and
reproducing.
Scientists have found organisms below
the sea floor with incredibly long
lifespans surviving in a kind of
metabolic stasis with little movement or
change. Microbes living in seafloor
sediments are slowly buried over time.
As more sediment and other organic
matter is deposited on top of them. This
means the further down into seafloor
sediments you go, the older the
microbial communities become. With this
information, scientists can estimate the
number of generations that have passed
since the microbes were first buried.
And the results are pretty amazing.
Researchers estimated that for a site in
Peru, a microbial community at 40 m
below the sea floor had passed through
around 11,500
generations.
It takes around 4 million years for
sediment to reach that depth. So a
simple calculation tells us that the
average generation for these microbes
lasts for nearly 350 years.
If you compare that to Eoli, which has a
generation time of just 20 minutes, you
can understand just how slow life is
when you live at the bottom of the sea.
These life forms exist on geological
time scales. So it's no wonder they
don't look like they're doing much. But
if you shift your perspective just a
bit, you realize that this is still a
complex and dynamic world where
communities respond to tectonic shifts
and geoysical forces on continental
scales.
So we know that each generation of these
microbes likes to hang around for a long
time. But how do they manage this? The
thing that surprises scientists the most
about these organisms is just how little
energy they can survive on. We humans
use about 100 jewels of energy every
second to fuel our bodily functions,
which is roughly the energy it takes to
power a ceiling fan. But in a recent
paper published in Science Advances,
scientists calculated that the average
microbe living in the ocean's deep
biosphere uses 50 billion billion times
less energy than a human.
Talk about energy conservation.
Things don't stop underwater. However,
as we go about our daily lives on the
surface, miracles are also happening
deep below the surface, too.
Within the Earth's crust, it's often in
the waters or deep fractures where we
find microbes. Against the odds, these
microbes are metabolically active, but
again, at slower rates than life on the
surface. They're often scrging around
for scraps, surviving on organic matter
that's buried within deep sediments or
travels through groundwater stores to
meet them.
As you'd expect, these aren't the best
energy sources, but it's enough for some
life to survive. However, as you go even
deeper into the bedrock, even these
sources become scarce. At the ultimate
level of deep biome survival, organisms
can only make use of hydrogen gas
generated as a byproduct of the
interaction between water and rock.
Here, cell numbers can be as low as 10
cells per milliliter. But strangely,
despite working with social resources,
these deep biome populations still have
a small degree of diversity. In fact,
the difference in species composition
between the organic carbonfed and
hydrogen gas-fed biospheres is quite
impressive with each species having its
own unique way of surviving down there.
Just like the oceans, we've discovered
some amazing species in the continental
deep biome. In one expedition to a South
African platinum mine, researchers
discovered a whole new shape of bacteria
that was previously unknown to science.
They looked like an ordinary rod-shaped
species until a cross-section revealed
not a triangle, not a square, but a
star. These stellar life forms are just
one tenth the width of a human hair. But
their shape is designed to maximize the
amount of nutrients they can absorb,
which is vital when you live in such a
depleted environment as this one.
So far, we've mainly focused on bacteria
and archa in the deep biome. And
although these groups may be more common
in subsurface environments, recent
studies have also started to uncover the
ukarotes that are also braving this
extreme lifestyle. Dr. Henrik Drake and
his colleagues presented the first
insitue finding of fungi in crystalline
rock in 2017 at a depth of 740 m. And in
2011, scientists analyzing water
extracted from rock fractures in a South
African gold mine even found
multi-ellular life. That water had been
sitting 3.6 km below the surface for at
least 3,000 years. And in it, the
researchers found minuscule worms called
neatodes, including a species that was
previously unknown to science. They
called it Hme Mafisto after
Mephistophles, the devil that loves not
the light from Dr. Fostus, which does
seem pretty fitting for a species that
lives 1.3 km deep in the Earth's crust.
There's a lot to unpack there. We've
dealt with incredibly energyefficient
microbes loving life in Earth's pressure
cooker, entirely new shapes of bacteria,
environments with only hydrogen gas to
eat, and even a species named after the
devil. Earth's deep biome has certainly
delivered so far. So, how do you even
begin to go about measuring something
that's underground and quite literally
everywhere?
Whilst it's tricky to pinpoint a
specific number for how much deep biome
life is out there, we do have a pretty
good estimate. A recent paper from the
Deep Carbon Observatory in 2018 reviewed
around 3,800 measurements of cell
concentration worldwide. Staggeringly,
they calculated there are between 200
and 600 octillion cells in the
continental subsurface alone. Well,
okay. What does that mean? Well, there's
an estimated 30 trillion cells in your
body. So, the number of cells in the
continental deep biome is 20 quadrillion
times more than that. Do bear in mind
this doesn't include subseor sediments
or groundwater stores. Though,
deep biome life is thought to occupy a
volume ranging from 2 to 2.3 billion
cubic km, which is almost twice the
volume of all the world's oceans. And
since we estimate that we've only
explored 5% of the world's oceans so
far, just think how much of the deep
biome remains untouched.
Now, we know there's a lot of deep biome
life out there. Thankfully, there's a
global project to categorize it into the
future. The Census of Deep Life involves
DCO and other partners, and its goal is
to perform a global survey of life in
continental and marine subsurface
environments using deep DNA sequencing
technology. Throughout this project,
researchers are hoping to uncover the
genetic diversity of subsurface life,
their community structure, their role in
carbon cycles, and much more. They may
even find out whether there are any
keystone species for the deep biosphere.
Keystone species are essential for the
survival of other species in an
ecosystem and are often good indicators
of ecosystem health. You may have heard
how beavers build dams that allow other
animals like fish and amphibians to
thrive. Or that looking at the lychans
growing on a tree can tell you about air
quality. Well, we might find a similar
species or group in the deep biosphere.
If it exists, it would probably be a
pioneer in colonizing the deep biome,
helping to turn it into a place where
other microbes can thrive. Scientists
are already eyeing some bacterial orders
that might be good contenders because of
their metabolic plasticity and their
presence in many of the deep microbiomes
we've studied so far. We're not there
yet, but answering some of these
questions would give us a better
understanding of how these habitats come
to be colonized in the first place and
what a healthy deep biome looks like.
Perhaps though, despite all of that, one
of the most exciting parts of this
entire concept is that it may not be
limited to just planet Earth. All of
those discoveries of intraterrestrial
life to date does beg the question,
could this kind of life exist outside of
our planet? It seems like wishful
thinking to imagine alien coral reefs or
Amazon rainforests, but an alien deep
biome might be more realistic.
Lots of the debate around this topic was
sparked by a paper published over 30
years ago. So, let's dive into some of
his claims.
In 1992, astrophysicist Tom Gold
published a landmark paper called the
deep hot biosphere. In it, he argued
that microbial life is probably as
widespread through the Earth's
subsurface as it is on the surface, but
that the rules are pretty different.
Chemical sources of energy rule over
photosynthetic ones, and temperature is
the limiting factor for survival as you
go deeper into the Earth's crust. As
we've heard from our examples of deep
biome life, gold wasn't far off from the
truth. But it was his comments about
life on other planets that really got
people talking. We sadly know the other
planetary bodies in our solar system
don't have the right conditions for
surface life. But Gold wondered whether
the same could be said for subsurface
life. We Earth life forms can be
grateful for our planet's status as a
Goldilocks planet. warm but not too warm
so that liquid water can exist on its
surface. In this respect, Earth is
unique among the solar systems planets
and moons. However, conditions in the
deep biome tend to be more consistent.
And this could be true for planets
besides Earth. Although we can't find
surface water on the planets and moons
in our solar system, that doesn't mean
there's no trace of it at all. In fact,
scientists think that at one point of
Mars was underwater. We have a great
goes into more depth on this. Do check it out. And some moons like Jupiter's
Europa or Saturn's Enceladus have
subsurface oceans beneath their icy
exterior which make themselves known in
explosive plumes. What's crazy is that
NASA have even detected organic matter
in the plumes from Enceladus with
potential to be the first building
blocks for life. It's often said on
Earth at least. Water means life. So,
it's within reason to suggest that the
same could be true for other planets,
too. With water present, you may get
similar water rock interactions to those
observed on Earth, producing hydrogen or
some other geo gas that subsurface life
would need to use as an energy source.
So although surface conditions may seem
too harsh to host extraterrestrial
microbes, they could be hiding just out
of view in the deep biomes of their home
planets. extra intraterrestrials
if you like.
As our journey beneath the surface comes
to an end, I'm quite grateful to be a
surface dweller. Many scientists say
that exploring the deep subsurface is
like exploring the Amazon rainforest.
And I'd go a step further even and say
it's like exploring a whole another
world.
Although we're not even close to
exploring the whole of the deep biome,
we've seen bacteria that can withstand
insanely high pressures, boiling
temperatures, and environments with only
hydrogen gas to eat. Conditions so
extreme that like H Misesto, you can
share a name with the devil just for
being able to survive there. Scientists
have been fascinated with this world
ever since we could first drill into the
ground or explore the oceans. And it's
possible that learning about our deep
biomes will give us a better idea of
what's going on beyond Earth's reach.
Gold famously said his ideas would have
gotten him burnt at the stake in a
different time, but it seems like now is
the perfect time to start exploring
them. In doing so, we may realize that
the deep hot biosphere is the norm
rather than the exception for planets
across the universe.