From Ice to Fire: The Incredible Science of Temperature (2018): Season 1, Episode 2 - A Temperature for Life - full transcript

Dr. Helen Czerski: Everything
around us exists somewhere

on a vast scale from
cold...to hot.

Whether living or dead,
solid or liquid, visible or

invisible, everything
has a temperature.

It's the hidden energy
contained within matter.

And the way that energy
endlessly shifts and flows

is the architect that
has shaped our planet

and the universe.

Across three programs,
we're going to explore

the extremes of the
temperature scale,

from some of the coldest
temperatures...



to the very hottest

and everything in-between.

This time, the narrow band
of temperature that's

led to life.

From the origins of life in
a dramatic place,

where hot meets cold...

Man: You're
bringing together these

chemical ingredients that
could start, you know,

producing some of the
building blocks for life.

Czerski: to the latest surgery
that's using temperature to

push the human body to the
very limits of survival...

Temperature is in
every single story

that nature has to tell,

and in this series
we'll show you why.



[Birds chirping]

This is a painted lady
butterfly, and it's been kept

cool, around 6 degrees,
but as it sits in the Sun, it's

warming itself up, fluttering
it's flight muscles,

and getting ready to fly.

These insects can't control
their own body temperature,

so they're reliant on
heat from the Sun.

And there he goes.

The butterfly's survival
depends on its unique

and delicate relationship
with temperature.

And that's true of each
and every living thing

on our planet.

Plant or animal,

large or small,

everything depends on
temperature for its existence.

And that relationship is far
more complicated than you

might think.

There's only one place in
the universe where we're

absolutely sure that
life exists...and that is

here on Earth.

And for many years, it was
thought that the reason why

the Earth was so unique
lay in its distance

from the Sun.

Not close enough to be too hot
for life, or far away enough

to be too cold.

And this gave rise to the
idea of a habitable zone,

a distance from the Sun that
was just right for life.

[Dogs barking]

But it turns out that it's
not quite that simple...

because the Earth's
temperature isn't what you

might expect.

If you average out
temperatures across the

planet, from deserts to poles,
you get a very pleasant

14 degrees Celsius.

But that's around 30
degrees warmer than might be

expected, given the Earth's
distance from the Sun.

So why is our planet warmer
than it appears it should be?

The answer lies in one of the
most intriguing substances to

be found anywhere
in the universe...

and yet one of the most
commonplace here on Earth.

[Water rushing]

This is the Skogafoss
waterfall in Iceland.

Every day here, hundreds of
millions of liters of water

tumble down towards the sea.

More than 70% of Earth's
surface is covered with water,

but that wasn't
always the case.

Early in our planet's history
when the surface was far too

hot for liquid water,
this planet was shrouded

in a thick atmosphere of
carbon dioxide and water.

And all you'd have seen from
space is the white cloud tops.

But as the planet cooled,
the rains began, and a deluge

shifted most of that water
from the atmosphere to

the oceans.

And then when the rain
finished and the clouds

cleared, the liquid of our
blue planet was on show to the

universe for the first time.

Ever since, the sheer physical
power of water has been

carving and shaping the
surface of our planet.

And crucially for our story,
all this water has had huge

consequences for the
Earth's temperature.

To understand why, we need to
delve into the strange world

of water at the
molecular scale.

And that journey begins with a
chance discovery that revealed

for the first time what
water is actually made of.

In 1766,
a reclusive scientist,

Henry Cavendish, added various
metals to a liquid called

Spirits of Salt, now known
as Hydrochloric acid.

And what he saw was something
that he called inflammable air,

but today we know as
hydrogen, and Cavendish was

the first person to recognize
its significance and to do

experiments on it to
test its properties.

Cavendish collected the gas
given off by his experiment.

When he had enough, he took a
flaming splint and put it next

to the opening....

[Loud whoosh]

with explosive results.

[Loud whoosh]

Afterwards, Cavendish
noticed something intriguing.

On the inside of the glass
vessel, there were tiny

droplets of a clear liquid,
and he wondered what that was.

He tasted it, he smelt it,
and he came to the conclusion

that it was water.

And so Cavendish was the first
person to realize that water

was a combination of
hydrogen and oxygen.

And today, we know that the
chemical formula is H2O--

2 hydrogens and 1 oxygen.

And that's sounds beautifully
simple, but still, water is

one of the most fascinating
molecules we know of.

The molecular structure
of water is the key to why

Earth's temperature is
warmer than you might expect...

yet it's in a cold place where
we can begin to understand

just why that is.

This is Jokulsarlon lagoon,
in Iceland.

Isn't this all stunning?

All these bits of glacier
that have just fallen off

from up there.

We take scenes like this for
granted. This is our impression

of the Arctic and the
Antarctic, floating icebergs.

But from a material
science point of view this,

that thing, is really weird,
because it's floating

with almost everything else.

When you cool things down and
freeze them, the solid will

sink to the bottom
of the liquid.

But water is different.

It floats.

As a liquid, the molecules of
water are constantly sliding

past each other,
always on the move.

But as it freezes, their
positions become fixed

in a regular,
hexagonal lattice.

Ice floats because the
molecules in the lattice are

taking up more space than in
the liquid, which makes ice

less dense than water.

This happens because of the
forces holding the molecules

in position,

something that's more easily
seen with water in its

liquid state.

I've got some plastic pipe
here and a proper Icelandic

woolly jumper, because it's
made of wool and therefore

it's good at charging
up the plastic.

So this pipe now has an
electric charge, and what I'm

gonna do is put it near a
stream of water, and you can

see that it bends the
stream really strongly.

And all the water's doing is
falling, but it's being pulled

towards the electric field.

The reason for this phenomenon
lies within the water

molecules themselves.

This is the water molecule.
So we've got two Hs.

That's the H2, and then O is
the oxygen at the top.

And the charge on the molecule
isn't evenly distributed

so it's more positive
round here, and it's more

negative up there.

So when the stream of water
comes down, it's got all these

molecules moving
round inside it.

When you bring the electrical
field close, some of those

molecules will flip around,
so that their opposite charge

is attracted in to the
electric field, so the whole

stream of water moves.

And it's such a simple demo,
but it shows you that

the water molecule itself has
uneven charge distribution.

And this has a huge effect
on how water behaves.

Within the liquid,
the negatively charged oxygen

atom from one molecule is
pulled towards the positively

charged hydrogen atoms of
another, creating a strong

attraction known
as a hydrogen bond.

And it's this bond that
explains water's role

in distributing heat
around the planet.

Hydrogen bonds are so strong,
that it takes a lot of energy

to break them.

And that means that the water
in the Earth's oceans can

absorb a huge amount of heat
energy from the Sun, without

changing from a
liquid to a gas.

The oceans act like a
huge store of energy.

And as they move, they
distribute heat from

the Equator to cooler
latitudes north and south.

But it's not only in the
oceans that water plays a part

in Earth's temperature.

While the bonds between liquid
water molecules are extremely

strong, heat them up enough,
and they'll break apart,

turning all that
liquid into a vapor.

And in this form, as vapor
in the atmosphere, water has

perhaps its greatest
influence.

The atmosphere traps the Sun's
heat, a process known as

the Greenhouse Effect.

But though we tend to associate
this with carbon dioxide,

it's actually water
vapor that accounts for much

of the trapped heat.

I've got a thermal camera
here, and if I point it

at the sand and the pebbles,
what you can see is that

they're bright, they're
radiating away energy.

And you can see it's just the
surface, because if I dig down

a little way down in the hole,
everything is very dark blue.

The red areas, though,
are warmer, and what's

happening is that they're
emitting infrared radiation.

But while visible light can
travel straight through the

atmosphere, infrared can't.

And one of the main
things that stops it

is water vapor.

The water molecules are able
to bend and stretch in

3 different ways, allowing them
to absorb a lot of energy.

So as the infrared
gets up into

the atmosphere, hits all those
water molecules, some of its

absorbed and once it's been
absorbed, the important point

is it isn't going straight
up to space anymore.

It then gets scattered in
lots of different directions,

and some of it comes
back down to Earth.

It's a huge difference.

That invisible water vapor in
the air is playing a huge role

in keeping us nice and warm.

Were it not for the water

in the oceans and the
atmosphere keeping Earth's

temperature warm and stable,
our planet would be as

inhospitable as
Venus and Mars.

But the influence of
temperature on life goes

far deeper.

Because the story of how
life itself began is a story

of temperature,

and it starts with the
Earth's complex geology.

[Wind blowing loudly]

This is the Deildartunguhver
vent in Iceland,

and it's
impossible to come here

and not wonder what's
causing all of this.

What there is beneath my feet
is a magma pool, and sea water

is seeping in through
cracks and fissures.

And when it hits the
hot rock, it boils.

And all of this is just
the spout of a gigantic

natural kettle.

This is a thermal vent.

It gives us a rare glimpse of
the heat at the Earth's core.

But here at the surface of the
planet isn't the only place

where such vents exist.

Similar vents can be found
deep on the ocean floor.

And even in this dark,
inhospitable place, many

are teeming with life,

a profusion of organisms found
in few other places on Earth.

It's a spectacle that Dr. Jon
Copley from the University

of Southampton
has seen firsthand.

Copley: When you get a moment to
pause and think, you're struck

by how you are next to a truly
awesome force of nature.

Czerski: Jon is part of a
research project exploring the

life that exists around
these deep sea vents.

Stuff that's gushing out,
what's in it?

Copley: That's a very hot
mineral-rich fluid.

How hot? Well, these vents--
401 degrees C.

Which is enormous!
Enormous!

Copley: Yeah,
and it's still liquid.

It doesn't boil into steam
because of the pressure,

because we're at 500 times
atmospheric pressure.

It's still liquid.

And it's mineral-rich because
that hot fluid is the end

product of seawater
percolating down into

the ocean crust.

There it's reacting with the
surrounding rocks and it's

leaching a lot of minerals
and elements from those rocks.

So we've got microbes that can
use some of those dissolved

minerals as an energy source.

Czerski: There's some thinking
that these sorts of places

might have been where
life originated.

What makes them
so good for that?

Copley: When we're making a
temperature measurement

at the throat of one of these
vents, and we're reading

401 degrees, if we move that
temperature probe a few

centimeters in that flow
coming out of the top of that

what we call "chimney," it'll
drop off by 120 degrees.

And then the chemistry is
changing over that distance as

well from being really rich
in these dissolved minerals to

being much more influenced by,
you know, normal sea water

and that's mixing.

So we've got changes in
chemistry and in temperature

over very, very small spaces.

And that means you can get
very exciting reactions.

Reactions will run
more rapidly at higher

temperatures, and you're
bringing together these

chemical ingredients that,
you know, could start producing

some of the building
blocks for life.

Czerski: Even looking at the
pictures, feels like you're

looking at something very
primitive, that there was one

moment at some point that
might have happened

in an environment like this
that just tipped chemistry

into biology and
it's a huge thought!

When we explore these
today, we become aware that,

you know, there are several
thousand of these out there

dotted around the world's
oceans, and they're roiling

away all the time.

Give yourself millions of
years, and at some point,

it was enough.

And it tipped things over,
you know, to give us life from

just physics and chemistry.

Czerski: If life did begin at
these vents, then to move beyond

them, it was going to need
a different source

of energy altogether...

one derived not from the
heat of the planet, but from

somewhere else.

And that source was revealed
by a chance discovery

in the 18th century by a
scientist who wasn't even

looking for it.

In the 1770s, there was a
Dutch physician called

Jan Ingenhousz, and he was a
medical doctor who'd become

famous for smallpox
inoculations.

But he had a lively mind.

He paid attention to the
science of his day, and that

decade he turned his
mind to leaves.

Ingenhousz had recently read
of an experiment involving

plant leaves submerged in
water, which had resulted

in the appearance of
bubbles of a mystery gas.

Some scientists of the day
thought that the bubbles were

attracted by the leaves from
the water, but Ingenhousz

wasn't convinced and he
did his own experiments.

The first observation that
he made was that the bubbles

didn't form when the leaves
were in shadow, but they did

form when you put them
in the sunlight.

And he checked very carefully
that it wasn't just the warmth

of the Sun, it was
actually the light itself.

And the gas wasn't
coming from the water.

It seemed to be
coming from the leaves.

Ingenhousz tested the gas
and discovered that it was

pure oxygen.

He had uncovered one of the
most fundamental processes

in all of nature.

Photosynthesis.

Plants absorb energy from
the Sun and use it to break

molecules of water into
hydrogen and oxygen.

The oxygen is released,
as Ingenhousz observed.

And just as important is
what happens to the hydrogen.

It combines with carbon
dioxide to form carbohydrates,

specifically sugars, making
the plants a store of energy.

By tapping into the energy
from sunlight, life could now

move away from thermal vents
and spread across the globe,

first in the oceans
and eventually onto land...

endlessly harvesting energy
from the Sun and locking it

into the chemical bonds of
sugar molecules, a process

that's crucial to all
life on Earth today.

The sugars formed

in photosynthesis are
the beginning of almost every

food chain.

Further up the chain, complex
life forms unlock that energy,

using it as the fuel
that powers the thousands

of chemical reactions that
take place in their cells to

keep them alive.

But here, temperature poses
an intriguing problem.

At our everyday temperatures,
most biochemical reactions

happen too slowly
to sustain life.

To make them happen fast
enough requires a special kind

of molecule, one that itself
can only exist within the

tiniest band of temperature.

And there's a simple
way of showing this.

I've got two glasses here,
both of them have a little bit

of corn starch in water and a
little bit of iodine which is

what's made them purple.

And I'm gonna add some of my
own saliva using one of these

and a cheek swab just
to one of them.

Here we go.

Lovely.

And I'm gonna stir
it into that one.

Starch is present in foods
like bread and potatoes.

It's a complex carbohydrate
with long-chain molecules.

And over 5 minutes, we can
see that adding saliva to our

starch mixture has caused
an obvious change.

You can see that the one with
the spit in has definitely

changed color.

A chemical reaction's
happened, and it's actually

one that happens all the time
in all of us, both in our

mouths and further down
our digestive system.

What's going on is
that there's an enzyme,

a biological catalyst in my
saliva, which is breaking that

carbohydrate down
into simple sugars.

And enzymes like this are
the root of all biology,

because they speed
reactions up.

They don't change what
happens, but they make them

happen faster.

There are 3,000 different
types of enzymes in our body.

Each one speeds up a specific
reaction sometimes more than

a million times.

Behind every process in our
body--breathing, moving,

thinking--lies a series of
very precise reactions powered

by particular enzymes.

Enzymes are fabulous
little biological machines,

but they've got a limitation
connected to temperature.

Like most chemical reactions,
if you increase the

temperature, an enzyme will
work a little bit faster,

until you increase the
temperature past a certain

point, and at that point
everything stops happening.

And there's a
simple reason why.

An egg white is made
of protein molecules.

The familiar way its color
and texture change when cooked

is because those protein
molecules change in structure

when they get hot.

Enzymes are also proteins.

Like the egg white, if they
get too hot, their structure

changes permanently,

and they're no longer able
to perform their

specialized function.

So, keeping them at precisely
the right temperature

is crucial.

Plants and animals that
live in the oceans have it

relatively easy, thanks to
the water providing a stable

temperature environment,

but living on land has
always presented much more

of a temperature challenge.

The fluctuations between night
and day and from season to

season mean that animals need
to be able to control their

body temperature.

Throughout most of the history
of animal life, there's one

method that's endured.

And there's one animal here
at Colchester Zoo that's

perfected it.

Man: All right, so I'll
ask you to wait there.

Czerski: All right.

His keeper
is Glenn Fairweather.

Fairweather: Telu!

Telu!

Come on.
That's it.

Good boy.
Here he comes.

This is Telu, an adult
male Komodo dragon.

Czerski: That is
a lot of lizard.

- He's enormous.
- He is big, yeah.

Czerski: Slightly
clumsy lizard.

Komodo dragons, like Telu,
are the largest lizard to be

found anywhere on Earth.

Fairweather: OK, well I'm just
gonna give Telu a little snack.

Czerski: OK.

Oh, didn't notice it.
Ha ha!

He's having a good
look around there.

- Oh.
- Yeah.

Fairweather: Fantastic.

In the wild, dragons will eat
10 to 12 meals a year, maybe.

12 meals a year
sounds like almost nothing.

Fairweather: They have a very
slow metabolism, so it would

take Telu several weeks to
digest a large meal

of 10, 15, 20 kilos.

Czerski:
The reason Telu eats so little

is that he's cold-blooded.

Instead of using energy from
his food to warm himself up,

he takes in heat from
his surroundings.

In his natural habitat in
Indonesia, he'd do that simply

by basking in the Sun.

In captivity, he has special
lamps to provide both heat

and ultraviolet light.

This unique footage filmed at
Chester Zoo, shows how rapidly

a Komodo dragon can alter
its body temperature.

In just 90 minutes,
this animal's body warms from

its nighttime temperature of
22 degrees, to 35 degrees.

To stay active for the
rest of the day,

it must now keep its body
in a narrow range

of between 34
and 36 degrees.

Paleontologist Dr. Darren
Naish explains how they do it.

So he's in front of
his heat lamp, and he's done

something quite distinctive,
which he's sort of spread

himself out flat.

Why has that happened?

Yeah, in order to
basically be the best shape to

absorb as much heat as
possible from the environment,

a lot of reptiles
adopt specific poses.

And the most obvious thing
they do is they do spread out

and flatten the rib cage so
they're presenting a larger

surface area to the Sun.

What Telu here is doing
is absorbing heat from his

heat lamp.

He's also receiving heat from
the ground which has obviously

been warmed by the heat lamp
and through his own behavior.

He's very good at controlling
his temperature, keeping it

quite high and in a
very specific band.

Czerski: Being cold-blooded does
come with an obvious limitation.

You need enough heat
in your environment.

Naish: We definitely do see
a massive dropoff

in the diversity of cold-
blooded reptiles like lizards

once you get away from the
Equator, once you get further

towards the north, so clearly
they are disadvantaged

in cooler environments.

Today, we mostly associate cold-
blooded animals with places

where there are warm
conditions, year-round.

Czerski: So, for
cold-blooded animals,

the challenge of
keeping warm enough

tends to limit them
to the hotter regions

of the planet.

To thrive in cooler places,
you need a different way to

keep your body
temperature warm and stable.

And evidence for this comes
from perhaps the last group

of animals you'd expect.

Dr. Adam Smith is a curator
here at Wollaton Hall Natural

History Museum.

Smith: When I was a kid
growing up, the picture

of the environment that
dinosaurs lived in was

a swampy environment
surrounded by volcanos.

But we now know that dinosaurs
were much more diverse than

that, and the environments
that they occupied were much

more diverse than
that as well.

Some of them were adapted for
living in forests, some were

adapted for living
in open landscapes.

Some lived on the shore.

Even quite snowy areas
would have been occupied

by dinosaurs.

Czerski: For decades, the spread
of dinosaurs into cooler regions

away from the tropics
posed a question.

How could large cold-blooded
creatures survive

in colder climates?

Then, in 1996, a fossil was
discovered in China that

changed everything.

So this specimen is obviously
beautifully preserved.

What is it?

Smith: This is a genuine fossil
of a Sinosauropteryx dinosaur.

It was living in a climate
that was similar to

Northern Europe, and so you
would have had warm seasons

and cold seasons.

And the special thing about
it is that in addition to

the bones being preserved, we
have evidence of the soft

tissues as well.

You can see it most clearly
running along the back

of the tail here, this
dark line, and, especially

at the every tip of the tail,
it looks very tuft-like.

Czerski: The dark line on this
125-million-year-old

Sinosauropteryx fossil is only
faint, but it's tantalizing

evidence for something you
wouldn't expect on a dinosaur.

Smith: It's very similar to the
downy material that you find

on a newly hatched chick.

And that's why this has been
interpreted as feathers.

Czerski: So this is a dinosaur,
and it's got feathers.

Smith: And not true feathers
as you would think of as

a bird's feathers, but they
were the structures that led

to true feathers.

They're fuzzy feathers,
so they've been given

the name proto-feathers.

Czerski: For paleontologists,
these fuzzy feathers were

a spectacular revelation.

Smith: The fuzz in the dinosaurs
suggests that they were using

it for insulation.

And in that case, you would
expect the dinosaurs to be

generating their own heat,
rather than basking in the Sun

to get warm from the
outside environment.

Czerski: Cold-blooded animals
tend not to have feathers,

in part because their skin
needs to absorb heat from

the environment.

So this animal, that
suggests, was not cold-blooded?

It's very likely,
based on the evidence from the

feathers, that this particular
dinosaur was warm-blooded.

This discovery is helping
scientists to reimagine

the world of dinosaurs.

Smith: In the case of these
dinosaurs, we know that they

were very active animals,
very agile dinosaurs,

very intelligent
animals as well.

[Water rushing]

[Roars]

Czerski: It's now thought that
many dinosaurs may have been

at least partly warm-blooded.

This would have made them less
reliant on the Sun and allowed

them to thrive in
cooler habitats.

Had an asteroid impact
not contributed to their

extinction, some of them
might still exist today.

The dinosaurs that did survive
evolved into modern birds,

which are warm-blooded.

And alongside them grew
the rapidly expanding class

of warm-blooded mammals.

Birds and mammals use the
energy from food to generate

their own body heat.

And one area that's
particularly sensitive to

temperature is the brain.

This powerful but fragile
organ generates intense heat

of its own.

So animals need a way to
keep it at precisely

the right temperature.

And that's especially true
of us big-brained humans.

We're used to the idea that
our body temperature is

37 degrees, but we don't often
think about just how hard our

system has to work to
make sure that's true.

I do a lot of sport, so I run
around all the time, and that

sort of exercise puts a lot
of stress on the system,

and the body has a challenge
to get rid of that heat.

One obvious way our bodies
do this is to sweat.

But to see what else is going
on, we need to use a thermal

imaging camera.

This will show the temperature
at the interface between the

skin and the surrounding air.

The lighter and brighter
the color, the hotter

the temperature.

Watching the thermal footage
of me playing is fascinating

because there's
so much detail.

And you can see that my
surface temperature's

different in different places.

So my face is
obviously very warm.

Under my arms are very warm,
all the places where there's

blood flow close
to the surface.

Those show up really, really
brightly, and the really

interesting bit here is
when you look just after

I've stopped.

And you can see how hard my
body is working to get rid

of that heat.

My blood vessels on my arms
are just shining out, 'cause

they're so warm.

That's because when we're
getting too hot, our brain

tells the blood vessels
supplying our skin to widen.

This increases the flow
of blood to the surface

of the skin, where it
can dissipate heat.

The shifting of blood to and
from the skin's surface is

an effective way to control
our body temperature.

It helps keep our bodies
within a very narrow and safe

window of temperature,
even during the most

intense exercise.

The amazing thing about this
is, I run around in this

sports hall all the time,
and I never have to think

about this.

My body just takes
care of it all.

But when we get cold,
our bodies face

the opposite challenge.

Not dissipating heat,
but hanging onto it.

To understand how our bodies
deal with cold, we've come to

the University of Portsmouth
to meet Professor Mike Timpton,

an expert in
cold-water survival.

Woman: Further round.

OK, have to go back in
there a sec.

Czerski: He's going to show us
what happens when the human body

is immersed in a tank of water
that's been chilled down to

18 degrees Celsius,

nearly 20 degrees below
normal core body temperature.

The test begins with a few
simple manual tasks that will

be repeated later.

Plimpton: 3, 2, 1, go.

Now come back.

- That's good, well done.
- OK.

- Right, done.
- Yep, 22 seconds.

- OK.
- We'll remember that.

[Click]

Finally the test can begin.

I sudden have immense
sympathy for witches

in the 16th century.

4, 3, 2, 1, go.

Czerski: Oh, it's horrible.

It's amazing how the urge
to breathe is very sudden.

With the body now submerged,
its survival

mechanisms kick in.

I have
started to shiver.

About a minute ago,
I started to shiver.

Timpton: The skin receptors are
sending messages into

the brain saying, "You've got
a very cold skin."

And so that's being integrated
in the center of the brain,

the hypothalamus of the brain,
that's saying, "We need to

start generating heat."

And that's why you've
started shivering.

Czerski: Shivering is the body's
attempt to counteract the cold

by producing its own heat
to prevent vital organs from

dropping in temperature.

I heard that. Yeah.

But in these conditions,
shivering alone isn't enough.

A drop in core temperature of
just 2 degrees Celsius would

cause hypothermia, so after
half an hour, Mike calls

a halt to proceedings.

Timpton: I think it's probably
time to bring you out.

- OK.
- You ready? Here we go.

It's at this point that the
thermal imaging camera reveals

another of the body's
responses to cold.

Dark-blue areas indicate where
the surface temperature has

dropped dramatically, as blood
is diverted away from

the cold water.

Timpton: The body will sacrifice
the extremities in order to

preserve the internal organs.

And you'll have people who
have got frostbite, they're

losing extremities, but,
to preserve their heart

and their brain temperatures,
because once those

temperatures fall, then
it's a threat to survival.

So what we're going to do
now is just ask you to do that

nut and bolt test again.

3, 2, 1, go.

Czerski: My wrists are very cold
and I feel that's stopping me

moving my fingers very well.

That's it.
Done. No, there we are.

- Yeah.
- Bang on a minute.

Really?
So 3 times?

22 seconds before,
a minute afterwards.

Czerski: What this test shows

is just how vulnerable the
human body is to cold.

In fact, what enables us
humans to survive and thrive

in cold temperatures isn't our
inbuilt survival mechanisms.

It's something else.

Timpton: Our physiological
responses to cold really

wouldn't let you move very
far away from your

equatorial origins.

You know, once you start
getting into 0 degrees

overnight, the level of heat
production and the level

of heat retention you've got
will have been very limiting.

And the really important
thing is that it's underpinned

by intellect.

We've been using
clothing 75,000 years.

We've been using fire,
for 1 million years.

Now as soon as you've done
that, you've got a source

of heat, you've got
a source of light.

You can cook food,
your diet can change.

You are a tropical animal
that's taken those origins

with it thermally.

So you've re-created a
microclimate next to your

skin, which would be the same
as if you were living naked

in a 28-degree environment
from which you evolved.

Czerski: While all life on Earth
has adapted to survive the

temperature of its habitat,
only we humans are able to

create
micro-habitats of our own.

[Barking]

We can maintain our ideal
temperature wherever we go,

thanks to our intelligence.

But human ingenuity hasn't
just enabled us to manipulate

the temperature of
our environment.

It's also allowed us, in very
special circumstances, to push

the boundaries of life itself.

It's 8 A.M., and a team from
Papworth Hospital is getting

ready to perform a
radical type of surgery.

It involves cooling
a patient's body to

a temperature that would
normally be fatal, taking them

to the very edge of life.

Justine Giller has a life-
threatening condition.

Clots are blocking the blood
vessels in her lungs, leaving

her struggling for breath.

Giller: I've continuously got
a tightness in my chest,

just doing normal things like
going up and down the stairs.

I'm out of breath.

It's quite daunting, but I
know obviously I've got to

have this operation.

if I don't, I don't know how
long I'm gonna be able to

continue for.

So, I know that I have to do
it in order to be able to take

my little girl to
the park and play.

[Sniffs]

It's down to surgeon David
Jenkins to remove the clots

from Justine's lungs.

But while blood is
flowing through her lungs,

the operation is impossible.

Jenkins: Well, the main problem
is that lungs usually have

5 liters of blood every minute
being pumped through them.

And for this operation,
we need a completely clear

field in the small
vessels in the lungs.

So the only way to do that
is to drain all the blood out

of the body.

Czerski: Removing a patient's
entire blood supply is a truly

extraordinary procedure,
and David is a leading

specialist in the technique.

Once Justine is under
anesthetic, the first step is

to divert her blood supply
to a heart-lung machine.

At this stage, her blood is
still delivering fresh oxygen

to her vital organs
and, crucially, her brain.

- Running OK?
- It's running well.

At David's command,
the machine drains all of

Justine's blood from her body.

He can now begin to remove the
clots from her lungs, but he

has to work against the clock.

Because without blood
circulating, Justine no longer

has a supply of oxygen.

Normally, the human brain
can only survive for around

4 minutes without fresh
oxygen before permanent

damage occurs.

But in the controlled
environment of the operating

theatre, Justine is being
kept alive by temperature.

Over the past two hours,
Justine's body has slowly been

cooled to just 20 degrees.

This is the key to the
entire procedure.

Her body is in a temporary
state of stasis.

At this temperature,
the function of Justine's

brain is slowed down, and
it can survive 20 minutes

without oxygen.

The process is being
supervised by anesthetist

Dr. Joe Arrowsmith.

Our body has all these
mechanisms to stop us getting

that cold.

Why isn't she shivering?

Arrowsmith: Well, the anesthetic
I've given her has disabled all

of those mechanisms.

I've paralyzed her skeletal
muscle, so she physically

cannot shiver.

Czerski: To reduce the need for
oxygen as much as possible,

the team have cooled Justine's
brain still further.

Arrowsmith: We have this cap
wrapped around Justine's head,

and it's got a continuous flow
of ice-cold water that comes

from this ice bath here
with freezer ice packs in.

What we believe this does is
keep the outer centimeter or two

of the brain slightly
cooler than the rest

of the brain, where the
brain matter is where all

of the cell bodies and most of
the metabolism is, and so we

think that buys us just
a little bit of extra

brain protection.

Jenkins: So the right side
is done, and we managed to do

that in just under 15
minutes, so that's good.

And we're back on the
heart-lung machine now.

Czerski: With the clot removed,
Justine's blood is returned

via the machine.

It gradually warms up her
blood and, in turn, her body.

And after a while, her heart
spontaneously restarts.

After 6 hours in surgery,
Justine has returned safely

from her remarkable journey
down the temperature scale...

a living testament to how
our ability to manipulate

temperature is beginning
to open up a whole new field

of medical possibilities.

We're alive, you and I,
which means that we're

directly connected to the
web of life that covers this

planet and extends
back through almost all

of its history.

And all of that web, in all
of its variety, only exists

within a very narrow
temperature range.

And we barely appreciate
the temperatures of life.

But next time you hold
someone's hand or give

them a hug,
it's worth remembering that

it's not just about the
physical gesture.

You're sharing
the warmth of life.

And it's a nice thought that
that shows just how intimately

temperature and life
are intertwined.