It's quite beautiful.

Living under the sea

isn't just Hollywood fantasy.

Requesting landing clearance, over.

Can we build an underwater city? Sure.

Whether we build them

to survive overpopulation or catastrophic climate change,

or to help scientists learn more about our planet.

It stands to reason

that we must push the boundaries

of ocean exploration so that we can bring back solutions.

The deep sea could teach us about our own origins

and if we can learn about how life originated here,

we might be able to learn something

about how life may have originated elsewhere.

We already know more

about the surface of the moon than the depths of our oceans.

In comparison to going to the moon

living underwater is not that complicated.

While our relationship with the ocean started

tens of thousands of years ago,

the technology that enabled humans to explore underwater

is relatively recent.

In 1943, a French Naval officer called Jacques Cousteau

invented the Aqualung, the precursor to scuba.

In his 1964 film "World Without Sun"

he explored the sea in his two-man submarine,

the Diving Saucer.

He'd park it in a garage,

which was part of his subaquatic village.

These men are the first oceanauts.

They are going to live down here for a month.

His team spent 30 days beneath the waves.

These sunken houses permit us to escape

many limitations of diving.

More habitats followed,

built by amateur enthusiasts as well as serious players,

such as the U.S. Navy and NASA.

The sea was the next frontier to be explored,

and there was interest from beyond the scientific community.

President Kennedy wrote to the U.S. Senate in 1961:

Knowledge of the oceans is more than a matter of curiosity.

Our very survival may hinge on it.

In the 1950s and '60s, that particular time period,

there's a historical context there

that makes underwater living particularly desirable.

So there are military applications,

and this is the birth of the offshore oil industry

and various underwater construction projects.

And then you also have a third reason,

which has perhaps less of an incentive,

and that's that marine biology is starting to develop.

What indeed are the limits

on flesh and blood beneath the waves?

Were people looking at the physiological effects

on the body, as opposed to say the scientific work

that could be done from those depths?

So one of the problems in underwater habitats

is that you have to change the gas mixture

that can be breathed safely at depth.

If you just breathe normal air that we breathe here,

or if you breathe pure oxygen,

it becomes toxic or you get nitrogen narcosis.

So they had to combine different types of gas

to breathe at pressure,

and they were breathing helium mixtures

and nitrogen mixtures,

which is why when you watch videos with these aquanauts,

they always have that high helium voice.

Ca va?

The seas remain largely unexplored

because of the limits of the human body.

We can only dive for a few hours.

Every breath of compressed air at depth

requires decompression after,

be it in a chamber,

or by slowly rising back up to the surface.

Without it, divers can develop decompression sickness,

also known as the bends, where nitrogen in your bloodstream

begins to bubble, damaging blood vessels

and blocking blood flow.

It's potentially lethal.

So living in an underwater habitat,

like Cousteau's aquanauts, the body stays saturated

with inert gases, enabling them to dive

and work without decompression.

If man need not return

to the surface periodically,

taking a long time to decompress

those potentially fatal bubbles within his body,

he can be infinitely more productive down below.

But one of the problems is that as soon as you have

your breathing, you're living in a helium atmosphere,

it is not very good for temperature control at all,

and if you're living in the ocean,

you can imagine it's quite cold.

So one of the problems that they had to figure out

how to adapt to is that the divers are constantly cold,

they're freezing in this helium atmosphere.

And then the other problem is that once you're staying

at depth for prolonged periods,

so unlike a submarine where you can go up,

purge the air, and go back down,

you have to develop some sort of air circulation system

that is purging CO2 constantly.

And that only really works well

if you can keep the humidity down.

If you're living in a metal container under the ocean,

it's difficult to keep the humidity down.

So controlling all of these atmospheric conditions

was one of the really big hurdles

for making it safe for people to live at depth.

A lot of these habitats came and went

in the '60s and '70s.

Can you give us some sense of the historical context?

In the 1960s and the 1970s,

this is when the space race is going on.

So there was this analog between the exploration

of inner space, the oceans and outer space

and already in the U.S., people in government,

at NASA and in the Navy were looking ahead

to future space exploration missions

and thinking that here underwater,

we have a perfect analog example

where we can already study how crews are gonna behave

in isolation in a small space,

over long periods of time.

So the Cold War is a really important context

for understanding this as well.

And the Russians were going into space

and there were a few Soviet habitats

but they never seemed like a viable,

real competition to the Americans.

So underwater competition between the Americans

and the Soviets played out with nuclear submarines

but not underwater habitats.

Nobody was colonizing the sea floor.

I think the technology was proven in the 1960s and '70s

but there were other reasons that it wasn't that useful

or proved to not be something that was necessary to do

for a long period of time.

The technology developed that allowed divers

to compress on shipboard instead, instead of at depth.

It will take two and one half hours

for their bodies to be equal to the same pressure

they will experience on the ocean floor.

So you could be compressed in a compression chamber

in a ship, then lowered in a capsule

while still under pressure,

exit the capsule, work on the oil head rig,

get back in the capsule and remain pressurized

at the surface.

And that technology did develop

out of all of these experiments with underwater habitats

but it sort of took the underwater habitats

out of the equation.

Scientists still see value in spending time under the sea.

What sort of questions are they trying to answer?

My wife is a marine microbiologist,

who's actually here if you want

to ask her questions about this.

Yeah, that'd be great.

All right.

Hi.

Hi.

I am a marine microbiologist,

mostly focusing on hydrothermal vents,

and I've been doing that for a while now.

And my advisor, my PhD advisor was the one

who first suggested that the origin of life

may have been at hydrothermal events.

Yeah. That's one of humanity's big questions, I guess.

So, you know, do you think those answers

could be at the bottom of the sea?

We like to think so.

The original idea basically was that hydrothermal vents

were kind of like a natural laboratory

because they're dominated by gradients.

So in the middle of a chimney, it's really hot,

it's water that can be up to 400 degrees Celsius,

and then two feet away,

the water's like two degrees Celsius, right?

So in between you have every temperature

you could possibly want for all kinds of reactions.

They're very hard to study

because they're at the bottom of the ocean,

thousands of meters deep,

and we can only really take samples

when we can get a ship out there.

If you had the opportunity to spend,

say a month underwater next to one of these vents,

from a scientific angle, would that be helpful?

Yeah, so there's, there's two answers there.

One is we do use submarines, so I have been there.

I've been in Alvin down to these vents

and being there in person is amazing

because you get a much better sense

of what the environment looks like

in a three-dimensional way.

Just being in that space I just felt like I had a much

better sense of what these habitats really look like

and how connected they are and whether microbes

and ingredients could flow from one vent to the next.

The thing that I would really value

whether I was present or not is just being able

to look at these things longitudinally over time.

Understanding how the microbes adapt over time

is something we really haven't addressed yet

and is something I'm working on right now

to try to understand better.

So I think there's a lot of value in that.

Now, whether I would need to be physically present

for that period of time is another question,

because I like bathrooms

and I like having food and sunlight, so maybe not.

We enjoy the adventure of going down there, but in the end,

we do want to sleep in a soft bed that's not cold and damp

at the end of the day.

The underwater habitats of the 20th century

have mostly been retired.

A couple still remain serving scientists,

but a focus on space exploration

and the rise of robotic technology has decreased the need

for humans to live beneath the waves.

But could there be a resurgence?

Fabien Cousteau, grandson of Jacques and an aquanaut,

explorer and conservationist in his own right,

spent 31 days underwater in 2014.

Can you give me a sense of the science

that can be achieved when you're underwater

for extended periods of time?

My team and I were able to execute

over three years' worth of equivalent science,

as opposed to being based from a ship above.

And that has a lot to do with the access

to the bottom world.

By being able to be based out of an underwater habitat,

it's a very unique platform, it's a very unique tool.

In the case of being saturated,

we could dive 10 to 12 hours, each of us, per day

to take advantage of that and to be able to do

much, much more research in a workday than you can

from the surface.

Additionally, as a human being,

being right on the ocean's final frontier,

you're able to do things that simply are not

as easily accessible from an ROV or an AUV or a submersible,

but there's still a human factor that needs to be integrated

into these kinds of exercises.

And with Mission 31,

we were able to use all sorts of laboratory equipment