Original subtitles

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.