0:00:05 > 0:00:09Everything around us exists somewhere on a vast scale,
0:00:09 > 0:00:11from cold to hot.
0:00:13 > 0:00:18The tiniest insect, all of us, the Earth, the stars,
0:00:18 > 0:00:21even the universe itself, everything has a temperature.
0:00:25 > 0:00:27I'm Dr Helen Czerski.
0:00:27 > 0:00:31In this series, I'm going to unlock temperature's deepest mysteries.
0:00:35 > 0:00:39Across three programmes, I'm going to explore the extremes of the
0:00:39 > 0:00:40temperature scale.
0:00:41 > 0:00:44From some of the coldest temperatures,
0:00:44 > 0:00:49to the very hottest, and everything in between.
0:00:49 > 0:00:53I'm a physicist, so my treasure map is woven from the fundamental
0:00:53 > 0:00:57physical laws of the universe, and temperature is an essential part of that.
0:00:58 > 0:01:01It's the hidden energy contained within matter...
0:01:03 > 0:01:07..and the way that energy endlessly shifts and flows.
0:01:08 > 0:01:10It's the architect that has shaped our planet...
0:01:13 > 0:01:15..and the universe.
0:01:16 > 0:01:19It's not often that I get up at 5am to watch a pond,
0:01:19 > 0:01:20but this one is worth watching.
0:01:27 > 0:01:32This time, I'm going to explore the narrow band of temperature that has
0:01:32 > 0:01:33led to life.
0:01:35 > 0:01:37From the origins of life in a dramatic place
0:01:37 > 0:01:39where hot meets cold...
0:01:40 > 0:01:44You're bringing together these chemical ingredients that could
0:01:44 > 0:01:47start producing some of the building blocks of life.
0:01:47 > 0:01:51..to the latest surgery that's using temperature to push the human
0:01:51 > 0:01:55body to the very limits of survival.
0:01:55 > 0:01:59Temperature is in every single story that nature has to tell,
0:01:59 > 0:02:02and in this series, I'll be exploring why, what temperature means,
0:02:02 > 0:02:07how it works, and just how deep its influence on our lives
0:02:07 > 0:02:08and our world really is.
0:02:39 > 0:02:43This is a Painted Lady butterfly and it's been kept cool,
0:02:43 > 0:02:47at around six degrees, but as it sits in the sun,
0:02:47 > 0:02:51it's warming itself up, fluttering its flight muscles...
0:02:52 > 0:02:54..and getting ready to fly.
0:02:55 > 0:02:59These insects can't control their own body temperature, so they're
0:02:59 > 0:03:02reliant on heat from the sun.
0:03:04 > 0:03:05And there he goes.
0:03:09 > 0:03:14The butterfly's survival depends on its delicate relationship with temperature.
0:03:16 > 0:03:20And that's true of every living thing on our planet,
0:03:20 > 0:03:25plant or animal, large or small.
0:03:25 > 0:03:28Everything depends on temperature for its existence.
0:03:33 > 0:03:36And that relationship is as complex as it's profound.
0:03:39 > 0:03:43On the road to all of this, all this colour and smell and
0:03:43 > 0:03:46movement that's alive, there's a story,
0:03:46 > 0:03:50and it's the story of the intricate dance of life along a tightrope
0:03:50 > 0:03:52stretching from hot to cold.
0:04:07 > 0:04:11There's only one place in the universe where we're absolutely
0:04:11 > 0:04:14sure that life exists, and that is here on Earth,
0:04:14 > 0:04:18but it's hard not to look up into the night sky and wonder what else
0:04:18 > 0:04:20might be living out there.
0:04:20 > 0:04:22And as astronomers started to learn about our solar system,
0:04:22 > 0:04:26they looked at the other planets and wondered what might be living there.
0:04:26 > 0:04:32Perhaps there are monsters on Venus or an entire civilisation on Mars.
0:04:32 > 0:04:36Because after all, those planets seem to be in the same sort of
0:04:36 > 0:04:40position as us - not so close to the sun that they got fried
0:04:40 > 0:04:43and not so far away that they were frozen.
0:04:43 > 0:04:46And that led to the concept of a habitable zone,
0:04:46 > 0:04:49a distance from the sun that was just right for life.
0:04:51 > 0:04:54But it turned out not to be that simple.
0:04:55 > 0:04:59Our nearest neighbour, Venus, just a little closer to the sun,
0:04:59 > 0:05:04has a surface temperature of over 450 degrees Celsius.
0:05:06 > 0:05:10While on Mars, the next planet out, it's minus 60.
0:05:13 > 0:05:17Temperatures far more extreme than Earth, making life impossible.
0:05:19 > 0:05:23But even Earth's own temperature isn't what you might expect.
0:05:25 > 0:05:29If you average out the temperatures across the planet,
0:05:29 > 0:05:32you get a rather pleasant 14 degrees Celsius.
0:05:35 > 0:05:38But that's around 30 degrees warmer than might be expected,
0:05:38 > 0:05:40given the Earth's distance from the sun.
0:05:42 > 0:05:47At 30 degrees colder, you'd expect Earth to be completely different.
0:05:47 > 0:05:49A barren, desolate world.
0:05:52 > 0:05:55So why is our planet warmer than it appears it should be?
0:06:01 > 0:06:06The answer lies in one of the most intriguing substances to be found
0:06:06 > 0:06:08anywhere in the universe.
0:06:08 > 0:06:11SWELLING MUSIC PLAYS
0:06:23 > 0:06:26This is the Skogafoss waterfall in Iceland.
0:06:27 > 0:06:32Every day here, hundreds of millions of litres of water tumble down
0:06:32 > 0:06:33towards the sea.
0:06:35 > 0:06:37MUSIC PLAYS
0:06:48 > 0:06:52More than 70% of Earth's surface is covered with water,
0:06:52 > 0:06:54but that wasn't always the case.
0:07:00 > 0:07:01Early in our planet's history,
0:07:01 > 0:07:05when the surface was far too hot for liquid water,
0:07:05 > 0:07:09this planet was shrouded in a thick atmosphere of carbon dioxide and
0:07:09 > 0:07:14water and all you would've seen from space was the white cloud tops.
0:07:14 > 0:07:19But as the planet cooled, the rains began and a deluge shifted most of
0:07:19 > 0:07:22that water from the atmosphere to the oceans.
0:07:22 > 0:07:25And then when the rain finished and the clouds cleared,
0:07:25 > 0:07:30the liquid of our blue planet was on show to the universe for the first time.
0:07:33 > 0:07:37Ever since, the sheer physical power of water has been carving and
0:07:37 > 0:07:39shaping the surface of our planet.
0:07:41 > 0:07:46And crucially for our story, all this water has had huge consequences
0:07:46 > 0:07:48for the Earth's temperature.
0:07:53 > 0:07:57To understand why, we need to delve into the strange
0:07:57 > 0:08:00world of water at the molecular scale.
0:08:00 > 0:08:04And that journey begins with a chance discovery that revealed for
0:08:04 > 0:08:07the first time what water is actually made of.
0:08:09 > 0:08:13In 1766, a reclusive scientist called Henry Cavendish,
0:08:13 > 0:08:17added various metals to a liquid called spirits of salt,
0:08:17 > 0:08:20now known as hydrochloric acid.
0:08:22 > 0:08:25And what he saw was something that he called inflammable air,
0:08:25 > 0:08:28but today we know as hydrogen.
0:08:28 > 0:08:32And Cavendish was the first person to recognise its significance and
0:08:32 > 0:08:34to do experiments on it to test its properties.
0:08:37 > 0:08:40Cavendish collected the gas given off by his experiment.
0:08:41 > 0:08:46When he had enough, he took a flaming splint and put it next to the opening...
0:08:51 > 0:08:53BOOM
0:08:53 > 0:08:54..with explosive results!
0:08:56 > 0:08:59Afterwards, Cavendish noticed something intriguing.
0:09:01 > 0:09:05On the inside of the glass vessel there were tiny droplets of a clear
0:09:05 > 0:09:10liquid and he wondered what that was, he tasted it, he smelt it
0:09:10 > 0:09:13and he came to the conclusion that it was water.
0:09:13 > 0:09:17And so Cavendish was the first person to realise that water was a
0:09:17 > 0:09:22combination of hydrogen and oxygen and today we know that the chemical
0:09:22 > 0:09:26formula is H2O, two hydrogens and one oxygen.
0:09:26 > 0:09:31And that sounds beautifully simple but still, water is one of the most
0:09:31 > 0:09:32fascinating molecules we know of.
0:09:37 > 0:09:41The molecular structure of water is the key to why Earth's temperature
0:09:41 > 0:09:43is warmer than you might expect.
0:09:46 > 0:09:50Yet it's in a cold place that I can begin to uncover why that is.
0:09:53 > 0:09:56This is Jokulsarlon Lagoon in Iceland.
0:10:01 > 0:10:03Isn't this all stunning?
0:10:03 > 0:10:07All these bits of glacier that have just fallen off from up there.
0:10:09 > 0:10:11We take scenes like this for granted.
0:10:11 > 0:10:15This is our impression of the Arctic and the Antarctic,
0:10:15 > 0:10:16floating icebergs,
0:10:16 > 0:10:20but from a material science point of view this, that thing,
0:10:20 > 0:10:23is really weird because it's floating.
0:10:23 > 0:10:27With almost everything else, when you cool things down and freeze them,
0:10:27 > 0:10:31the solid will sink to the bottom of the liquid but water is different.
0:10:31 > 0:10:33It floats.
0:10:36 > 0:10:41As a liquid, the molecules of water are constantly sliding past each
0:10:41 > 0:10:45other, always on the move, but as it freezes,
0:10:45 > 0:10:51their positions become fixed in a regular hexagonal lattice.
0:10:51 > 0:10:56Ice floats because the molecules in the lattice are taking up more space
0:10:56 > 0:10:59than in the liquid, which makes ice less dense than water.
0:11:02 > 0:11:06This happens because of the forces holding the molecules in position.
0:11:09 > 0:11:13Something I can more easily show you with water in its liquid state.
0:11:15 > 0:11:20I've got some plastic pipe here and a proper Icelandic woolly jumper,
0:11:20 > 0:11:22because it's made of wool and therefore it's good at charging up
0:11:22 > 0:11:24the plastic.
0:11:24 > 0:11:28So this pipe now has an electric charge and what I'm going to do...
0:11:30 > 0:11:32..is put it near a stream of water.
0:11:32 > 0:11:36And you can see that it bends the stream really strongly...
0:11:37 > 0:11:40..and all the water is doing is falling but it's being pulled
0:11:40 > 0:11:42towards the electric field.
0:11:43 > 0:11:48The reason for this phenomenon lies within the water molecules themselves.
0:11:50 > 0:11:52This is the water molecule, so we've got two Hs,
0:11:52 > 0:11:56that's the H2 and then O is the oxygen at the top
0:11:56 > 0:11:59and the charge on the molecule isn't evenly distributed,
0:11:59 > 0:12:03so it's more positive around here and it's more negative up there.
0:12:03 > 0:12:05So when the stream of water comes down,
0:12:05 > 0:12:08it's got all these molecules moving round inside it.
0:12:08 > 0:12:11When you bring the electrical field close, some of those molecules
0:12:11 > 0:12:14will flip around so that their opposite charge is attracted in to
0:12:14 > 0:12:19the electric field, so the whole stream of water moves.
0:12:19 > 0:12:23It's such a simple demo but it shows you that the water molecule
0:12:23 > 0:12:25itself has uneven charge distribution.
0:12:25 > 0:12:29And this has a huge effect on how water behaves.
0:12:29 > 0:12:33Within the liquid, the negatively charged oxygen atom from one
0:12:33 > 0:12:36molecule is pulled towards the
0:12:36 > 0:12:39positively charged hydrogen atoms of
0:12:39 > 0:12:41another, creating a strong
0:12:41 > 0:12:44attraction known as a hydrogen bond.
0:12:44 > 0:12:46And these bonds are key to water's
0:12:46 > 0:12:48influence on Earth's temperature.
0:12:51 > 0:12:56Hydrogen bonds are so strong that it takes a lot of energy to break them.
0:12:56 > 0:13:00And that means that the water in the Earth's oceans can absorb a huge
0:13:00 > 0:13:06amount of heat energy from the sun without changing from a liquid to a gas.
0:13:07 > 0:13:12The oceans act like a huge store of energy, and as they move they
0:13:12 > 0:13:18distribute heat from the equator to cooler latitudes north and south.
0:13:21 > 0:13:25But it's not only in the oceans that water plays a part in Earth's temperature.
0:13:29 > 0:13:33The bonds between water molecules in liquid water are very strong but
0:13:33 > 0:13:37provide enough energy and they'll break apart and then you get what's
0:13:37 > 0:13:40all around me in the air here - water vapour.
0:13:43 > 0:13:46And in this form, as vapour in the atmosphere,
0:13:46 > 0:13:50water has perhaps its greatest influence.
0:13:50 > 0:13:52The atmosphere traps the sun's heat,
0:13:52 > 0:13:55a process known as the greenhouse effect.
0:13:56 > 0:13:59But although we tend to associate this with carbon dioxide,
0:13:59 > 0:14:03it's actually water vapour that accounts for much of the trapped heat.
0:14:08 > 0:14:11I've got a thermal camera here,
0:14:11 > 0:14:16and if I point it at the sand and the pebbles, what you can see is
0:14:16 > 0:14:19that they're bright, they're radiating away energy.
0:14:19 > 0:14:23And you can see it's just the surface because if I dig down a little way,
0:14:23 > 0:14:27down in the hole, everything is very dark blue.
0:14:27 > 0:14:32The red areas are warmer and what's happening is that they're emitting
0:14:32 > 0:14:34infrared radiation.
0:14:34 > 0:14:39So the sun heats up the surface and then because the surface is warm,
0:14:39 > 0:14:43infrared radiation travels back up into the atmosphere.
0:14:43 > 0:14:44Now, here's the thing.
0:14:44 > 0:14:47The visible light went straight through the atmosphere,
0:14:47 > 0:14:50but the infrared doesn't.
0:14:51 > 0:14:55And one of the main things that stops it is water vapour.
0:14:56 > 0:15:01The water molecules are able to bend and stretch in three different ways,
0:15:01 > 0:15:03which allows them to absorb a lot of energy.
0:15:05 > 0:15:09So as the infrared gets up into the atmosphere,
0:15:09 > 0:15:12hits all those water molecules, some of it's absorbed,
0:15:12 > 0:15:13and once it's been absorbed,
0:15:13 > 0:15:16the important point is it isn't going straight up to space any more.
0:15:16 > 0:15:19It then gets scattered in lots of different directions
0:15:19 > 0:15:21and some of it comes back down to Earth.
0:15:23 > 0:15:24It's a huge difference.
0:15:24 > 0:15:27That invisible water vapour in the air is playing a huge role
0:15:27 > 0:15:28in keeping us nice and warm.
0:15:39 > 0:15:41Were it not for the water in the oceans
0:15:41 > 0:15:44and the atmosphere keeping Earth's temperature warm and stable,
0:15:44 > 0:15:49our planet would be as inhospitable as Venus or Mars.
0:15:51 > 0:15:54But the influence of temperature on life goes far deeper
0:15:54 > 0:16:00because the story of how life itself began is a story of temperature.
0:16:02 > 0:16:05And it starts with Earth's complex geology.
0:16:13 > 0:16:15This is the Gunnuhver vent in Iceland
0:16:15 > 0:16:17and it's impossible to come here
0:16:17 > 0:16:20and not wonder what's causing all of this.
0:16:20 > 0:16:24What there is beneath my feet is a magma pool
0:16:24 > 0:16:27and seawater is seeping in through cracks and fissures
0:16:27 > 0:16:29and when it hits the hot rock, it boils.
0:16:29 > 0:16:34And all of this is just the spout of a gigantic natural kettle.
0:16:41 > 0:16:43This is a thermal vent.
0:16:43 > 0:16:47It gives us a rare glimpse of the heat at the Earth's core.
0:16:47 > 0:16:50But here, at the surface of the planet,
0:16:50 > 0:16:54isn't the only place where such vents exist.
0:16:54 > 0:16:58Similar vents can be found deep on the ocean floor
0:16:58 > 0:17:02and even in this dark, inhospitable place,
0:17:02 > 0:17:05many of them are teeming with life,
0:17:05 > 0:17:09a profusion of organisms found in few other places on Earth.
0:17:11 > 0:17:15It's a spectacle that Dr John Copley from the University of Southampton
0:17:15 > 0:17:16has seen first-hand.
0:17:18 > 0:17:20When you get a moment to pause and think,
0:17:20 > 0:17:23you're struck by how you are next to
0:17:23 > 0:17:25a truly awesome force of nature.
0:17:28 > 0:17:31John is part of a research project
0:17:31 > 0:17:35exploring the life that exists around these deep sea vents.
0:17:37 > 0:17:40The stuff that is gushing out, what's in it?
0:17:40 > 0:17:43That is a very hot mineral-rich fluid.
0:17:43 > 0:17:46How hot? Well, these vents, 401 degrees C.
0:17:46 > 0:17:49- Which is enormous! Enormous! - Yeah, and it's still liquid.
0:17:49 > 0:17:52It doesn't boil into steam because of the pressure.
0:17:52 > 0:17:54Because we're at 500 times atmospheric pressure,
0:17:54 > 0:17:56it's still liquid,
0:17:56 > 0:18:01and it's mineral rich because that hot fluid is the end product
0:18:01 > 0:18:05of seawater percolating down into the ocean crust.
0:18:05 > 0:18:08There it's reacting with the surrounding rocks
0:18:08 > 0:18:11and it's leaching a lot of minerals and elements from those rocks,
0:18:11 > 0:18:15so we've got microbes that can use some of those dissolved minerals
0:18:15 > 0:18:16as an energy source.
0:18:16 > 0:18:19There's some thinking that these sorts of places
0:18:19 > 0:18:22might have been where life originated.
0:18:22 > 0:18:24What makes them so good for that?
0:18:24 > 0:18:26When we're making a temperature measurement
0:18:26 > 0:18:29at the throat of one of these vents and we're reading 401 degrees,
0:18:29 > 0:18:31if we move that temperature probe
0:18:31 > 0:18:33a few centimetres in that flow coming out of the top
0:18:33 > 0:18:36of that, what we call chimney, it will drop off by 120 degrees.
0:18:38 > 0:18:41And then the chemistry is changing over that distance as well,
0:18:41 > 0:18:44from being really rich in these dissolved minerals
0:18:44 > 0:18:45to being much more influenced by,
0:18:45 > 0:18:49you know, normal seawater, and that's mixing, so we've got changes
0:18:49 > 0:18:52in chemistry and in temperature over very, very small spaces.
0:18:53 > 0:18:57And that means you can get very exciting reactions.
0:18:57 > 0:19:00Reactions will run more rapidly at higher temperatures
0:19:00 > 0:19:03and you're bringing together these chemical ingredients
0:19:03 > 0:19:06that could start producing some of the building blocks of life.
0:19:08 > 0:19:11Even looking at the pictures feels like you're looking at something
0:19:11 > 0:19:14very primitive, that there was one moment at some point
0:19:14 > 0:19:17that might have happened in an environment like this
0:19:17 > 0:19:19that just tipped chemistry into biology
0:19:19 > 0:19:21and it's a huge thought.
0:19:21 > 0:19:24When we explore these today, we become aware that, you know,
0:19:24 > 0:19:26there are several thousand of these out there
0:19:26 > 0:19:27dotted around the world's oceans
0:19:27 > 0:19:29and they are roiling away all the time.
0:19:29 > 0:19:32Give yourself millions of years and at some point it was enough
0:19:32 > 0:19:35and it tipped things over to give us life
0:19:35 > 0:19:37from just physics and chemistry.
0:19:40 > 0:19:42If life did begin at these vents,
0:19:42 > 0:19:44then to move beyond them,
0:19:44 > 0:19:47it would require a different source of energy altogether,
0:19:47 > 0:19:50one that wasn't limited to these rare pockets of heat
0:19:50 > 0:19:52from the Earth's core.
0:20:01 > 0:20:05And that source was revealed by a chance discovery
0:20:05 > 0:20:07in the 18th century,
0:20:07 > 0:20:09by a scientist who wasn't even looking for it.
0:20:12 > 0:20:15In the 1770s, there was a Dutch physician called Jan Ingenhousz
0:20:15 > 0:20:17and he was a medical doctor
0:20:17 > 0:20:19who had become famous for smallpox inoculations.
0:20:19 > 0:20:21But he had a lively mind.
0:20:21 > 0:20:24He paid attention to the science of his day,
0:20:24 > 0:20:27and that decade he turned his mind to leaves.
0:20:29 > 0:20:33Ingenhousz had recently read of an experiment involving plant leaves
0:20:33 > 0:20:37submerged in water and how this had resulted in bubbles
0:20:37 > 0:20:39containing a mystery gas.
0:20:41 > 0:20:45Some scientists of the day thought that the bubbles were attracted by the leaves
0:20:45 > 0:20:48from the water, but Ingenhousz wasn't convinced
0:20:48 > 0:20:49and he did his own experiments.
0:20:49 > 0:20:53The first observation that he made was that the bubbles didn't form
0:20:53 > 0:20:54when the leaves were in shadow,
0:20:54 > 0:20:57but they did form when you put them in the sunlight
0:20:57 > 0:20:58and he checked very carefully
0:20:58 > 0:21:00that it wasn't just the warmth of the sun,
0:21:00 > 0:21:02it was actually the light itself.
0:21:04 > 0:21:07And the gas wasn't coming from the water.
0:21:07 > 0:21:09It seemed to be coming from the leaves.
0:21:11 > 0:21:15Ingenhousz tested the gas and discovered that it was pure oxygen.
0:21:17 > 0:21:20He had uncovered one of the most fundamental processes
0:21:20 > 0:21:22in all of nature.
0:21:23 > 0:21:25Photosynthesis.
0:21:28 > 0:21:31Plants absorb energy from the sun
0:21:31 > 0:21:35and use it to break molecules of water into hydrogen and oxygen.
0:21:37 > 0:21:40The oxygen is released, as Ingenhousz observed.
0:21:42 > 0:21:45And just as important is what happens to the hydrogen.
0:21:45 > 0:21:50It combines with carbon dioxide to form carbohydrates,
0:21:50 > 0:21:52specifically sugars,
0:21:52 > 0:21:55making the plants a store of energy.
0:21:59 > 0:22:01By tapping into the energy from sunlight,
0:22:01 > 0:22:04life could now move away from the thermal vents
0:22:04 > 0:22:07and spread across the globe,
0:22:07 > 0:22:11first in the oceans and eventually onto land.
0:22:13 > 0:22:16Endlessly harvesting energy from the sun
0:22:16 > 0:22:20and locking it into the chemical bonds of sugar molecules,
0:22:20 > 0:22:24a process that's crucial to almost all life on Earth today.
0:22:26 > 0:22:29That stored energy is important, because when it's stored
0:22:29 > 0:22:31it can be released as required,
0:22:31 > 0:22:35and that's what powers almost all life on Earth.
0:22:39 > 0:22:42The sugars formed in photosynthesis
0:22:42 > 0:22:45are the beginning of almost every food chain.
0:22:45 > 0:22:49Further up the chain, complex life forms unlock that energy,
0:22:49 > 0:22:54using it as the fuel that powers the thousands of chemical reactions
0:22:54 > 0:22:56that take place in their cells to keep them alive.
0:22:58 > 0:23:02But here, temperature poses an intriguing problem.
0:23:04 > 0:23:06At everyday temperatures,
0:23:06 > 0:23:10most biochemical reactions happen too slowly to sustain life.
0:23:14 > 0:23:19To make them happen fast enough requires a special kind of molecule,
0:23:19 > 0:23:22one that itself can only exist
0:23:22 > 0:23:24within the tiniest band of temperature.
0:23:25 > 0:23:27And there's an easy way to show you.
0:23:31 > 0:23:33I've got two glasses here,
0:23:33 > 0:23:37both of them have a little bit of corn-starch in water
0:23:37 > 0:23:40and a little bit of iodine, which is what's made them purple,
0:23:40 > 0:23:43and I'm going to add some of my own saliva using one of these,
0:23:43 > 0:23:47and a cheek swab, just to one of them. Here we go.
0:23:48 > 0:23:49Lovely.
0:23:49 > 0:23:51I'm going to stir it into that one.
0:23:55 > 0:23:59Starch is present in foods like bread and potatoes.
0:23:59 > 0:24:02It's a complex carbohydrate with long-chain molecules.
0:24:04 > 0:24:07And over five minutes we can see that adding saliva
0:24:07 > 0:24:11to our starch mixture has caused an obvious change.
0:24:12 > 0:24:14You can see that the one with the spit in
0:24:14 > 0:24:16has definitely changed colour.
0:24:16 > 0:24:18A chemical reaction's happened
0:24:18 > 0:24:20and it's actually one that happens all the time in all of us,
0:24:20 > 0:24:23both in our mouths and further down our digestive system.
0:24:24 > 0:24:27What's going on is that there's an enzyme,
0:24:27 > 0:24:29a biological catalyst in my saliva
0:24:29 > 0:24:34which is breaking that carbohydrate down into simple sugars.
0:24:34 > 0:24:38And enzymes like this are the root of all biology
0:24:38 > 0:24:40because they speed reactions up.
0:24:40 > 0:24:44They don't change what happens, but they make them happen faster.
0:24:46 > 0:24:50There are 3,000 different types of enzymes in our body.
0:24:50 > 0:24:52Each one speeds up a specific reaction,
0:24:52 > 0:24:56sometimes more than a million times.
0:24:56 > 0:25:01Behind every process in our body - breathing, moving, thinking -
0:25:01 > 0:25:04lies a series of very precise reactions
0:25:04 > 0:25:06powered by particular enzymes.
0:25:07 > 0:25:10Enzymes are fabulous little biological machines
0:25:10 > 0:25:13but they've got a limitation connected to temperature.
0:25:13 > 0:25:17Like most chemical reactions, if you increase the temperature,
0:25:17 > 0:25:19an enzyme will work a little bit faster,
0:25:19 > 0:25:23until you increase the temperature past a certain point,
0:25:23 > 0:25:25and at that point, everything stops happening.
0:25:27 > 0:25:29And there's a simple reason why.
0:25:33 > 0:25:37An egg white is made of protein molecules.
0:25:37 > 0:25:40The reason its colour and texture change when cooked
0:25:40 > 0:25:43is that those protein molecules change in structure
0:25:43 > 0:25:44when they get hot.
0:25:46 > 0:25:49Enzymes are also proteins.
0:25:49 > 0:25:50Like the egg white,
0:25:50 > 0:25:54if they get too hot their structure changes permanently
0:25:54 > 0:25:58and they're no longer able to perform their specialised function.
0:25:58 > 0:26:03So keeping them at precisely the right temperature is crucial.
0:26:05 > 0:26:07Just think about all the places you find life,
0:26:07 > 0:26:09very cold places in the bottom of the ocean,
0:26:09 > 0:26:11very hot places in deserts,
0:26:11 > 0:26:14all these different environments that life can survive,
0:26:14 > 0:26:16they've all got one challenge in common,
0:26:16 > 0:26:18and that's to keep their enzymes functioning
0:26:18 > 0:26:21and the first way to achieve that challenge
0:26:21 > 0:26:23is to keep your enzymes at the right temperature.
0:26:23 > 0:26:27And that's the critical link between life and temperature.
0:26:30 > 0:26:34Plants and animals that live in the oceans have it relatively easy
0:26:34 > 0:26:37thanks to the water providing a stable temperature environment.
0:26:39 > 0:26:42But living on land has always presented
0:26:42 > 0:26:44much more of a temperature challenge,
0:26:44 > 0:26:48one that I can fully appreciate in a most unlikely place.
0:26:55 > 0:26:58Budleigh Salterton, on the English south coast,
0:26:58 > 0:27:00has long been a popular holiday spot.
0:27:01 > 0:27:04And two centuries ago, tourists went mad
0:27:04 > 0:27:07for a souvenir they couldn't get elsewhere.
0:27:15 > 0:27:17Quite a few of the locals made a bit of extra cash
0:27:17 > 0:27:20by selling the strange stones they found on the beach.
0:27:20 > 0:27:24They didn't know what they were but they gave them names, snake stones,
0:27:24 > 0:27:26vertiberries and devil's fingers.
0:27:27 > 0:27:31It was only when the fossilised remains of much larger organisms
0:27:31 > 0:27:35were discovered here that people realised what these trinkets were.
0:27:37 > 0:27:40Ancient animals, long since extinct.
0:27:47 > 0:27:51This stretch of the British coast is an extraordinary record
0:27:51 > 0:27:54of how life on Earth has evolved down the ages.
0:27:55 > 0:27:59And what I am interested in is how it's been affected by temperature.
0:28:01 > 0:28:06Perhaps the most striking example is these distinctive red cliffs,
0:28:06 > 0:28:11a clue to a period more than 240 million years ago,
0:28:11 > 0:28:15that was probably one of the hottest times the world has known.
0:28:17 > 0:28:21Helping me decipher the landscape is geologist Nicky Hewitt.
0:28:23 > 0:28:24This is called a ventifact,
0:28:24 > 0:28:27a stone that's been sandblasted by the wind.
0:28:27 > 0:28:30This comes from the top layer just underneath the yellow layer
0:28:30 > 0:28:34that you see there. The bottom is rough where it's stayed flat.
0:28:34 > 0:28:35With the wind sandblasting it
0:28:35 > 0:28:37and the back side away from the wind direction,
0:28:37 > 0:28:40it's just a little bit rougher than the other two.
0:28:40 > 0:28:41We're looking at the same sort of rocks
0:28:41 > 0:28:43that you find in the Sahara today.
0:28:43 > 0:28:46So even though we're on a beach now and you cannot imagine
0:28:46 > 0:28:49an environment that is more different to the Sahara, and yet,
0:28:49 > 0:28:53240 million years ago, that's what that was, the middle of a desert.
0:28:54 > 0:28:56Exactly. The middle of a much bigger desert.
0:29:01 > 0:29:04These cliffs are a relic of what is thought to be
0:29:04 > 0:29:07one of the hottest deserts ever to exist on Earth.
0:29:08 > 0:29:11A desert that formed part of a vast supercontinent.
0:29:16 > 0:29:19If we were here 240 million years ago,
0:29:19 > 0:29:21the Earth would have looked very different and this is it?
0:29:21 > 0:29:24This is all of the continents of the world,
0:29:24 > 0:29:28mashed together into one great big continent that was called Pangaea.
0:29:28 > 0:29:30The UK is sitting about here.
0:29:30 > 0:29:34You've got to imagine the equator coming across here at an angle
0:29:34 > 0:29:38and so the UK is in the northern arid zone,
0:29:38 > 0:29:40where the Sahara Desert lies today.
0:29:40 > 0:29:44- So we'd have been very hot and dry in there.- Absolutely.
0:29:44 > 0:29:46The weather in the centre of this continent
0:29:46 > 0:29:48would have been much, much more extreme
0:29:48 > 0:29:50than it could ever be on any of the continents today,
0:29:50 > 0:29:54just because you can get so much further away from the sea.
0:29:54 > 0:29:56So it sounds horribly hostile.
0:29:56 > 0:29:59The rocks that we're looking at here show no vegetation,
0:29:59 > 0:30:01no fossils, nothing.
0:30:01 > 0:30:03But then as time progresses,
0:30:03 > 0:30:06the continents were moving very, very gently further north
0:30:06 > 0:30:09and the climate was getting a little bit gentler.
0:30:09 > 0:30:13A little bit more rain was falling, a little bit less heat.
0:30:13 > 0:30:16Then you start to see the animals, the reptiles,
0:30:16 > 0:30:17and the plants coming in.
0:30:22 > 0:30:26It's estimated that the Pangaean desert would have reached
0:30:26 > 0:30:30upwards of 50 degrees Celsius, making life here almost impossible.
0:30:32 > 0:30:34But just as the continents had come together,
0:30:34 > 0:30:39so they drifted apart and life returned to this part of the land.
0:30:46 > 0:30:48Yet even in less extreme conditions,
0:30:48 > 0:30:51life on land faces a temperature challenge.
0:30:52 > 0:30:57The fluctuations between night and day and from season to season
0:30:57 > 0:31:01mean that animals need to be able to control their body temperature.
0:31:04 > 0:31:07Throughout most of the history of animal life,
0:31:07 > 0:31:09there's one method that's endured.
0:31:09 > 0:31:11I've come to Colchester Zoo
0:31:11 > 0:31:14to meet an animal that's perfected it.
0:31:18 > 0:31:20- Right, have to ask you to wait there.- All right.
0:31:20 > 0:31:22His keeper, Glen Fairweather,
0:31:22 > 0:31:25is taking me behind the scenes to meet him.
0:31:25 > 0:31:26Telu!
0:31:27 > 0:31:28Telu!
0:31:30 > 0:31:32Come on. That's it.
0:31:32 > 0:31:35Good boy. Here he comes.
0:31:35 > 0:31:38This is Telu, an adult male Komodo dragon.
0:31:38 > 0:31:41That is a lot of lizard. He's enormous!
0:31:41 > 0:31:43- He is big. Yeah. - A slightly clumsy lizard.
0:31:44 > 0:31:46Komodo dragons like Telu
0:31:46 > 0:31:50are the largest lizard to be found anywhere on earth.
0:31:52 > 0:31:55- OK, well, I'm just going to give Telu a little snack.- OK.
0:31:57 > 0:31:59Oh, didn't notice it.
0:31:59 > 0:32:03He's... He's having a good look around there.
0:32:03 > 0:32:04Oh.
0:32:05 > 0:32:11Fantastic. In the wild, dragons will eat 10 to 12 meals a year, maybe.
0:32:11 > 0:32:1412 meals a year sounds like almost nothing.
0:32:14 > 0:32:18They have a very slow metabolism, so it would take Telu several weeks
0:32:18 > 0:32:21to digest a large meal of 10, 15, 20 kilos.
0:32:22 > 0:32:27The reason Telu eats so little is that he's cold-blooded.
0:32:27 > 0:32:30Instead of using energy from his food to warm himself up,
0:32:30 > 0:32:33he takes in heat from his surroundings.
0:32:34 > 0:32:39In his natural habitat in Indonesia, he'd do that by basking in the sun.
0:32:39 > 0:32:43In captivity, he has special lamps to provide both heat
0:32:43 > 0:32:45and ultraviolet light.
0:32:47 > 0:32:50This unique footage filmed at Chester Zoo
0:32:50 > 0:32:54shows how rapidly a Komodo dragon can alter its body temperature.
0:32:55 > 0:32:59In just 90 minutes, this animal's body warms
0:32:59 > 0:33:03from its night-time temperature of 22 degrees to 35 degrees.
0:33:07 > 0:33:10To stay active for the rest of the day,
0:33:10 > 0:33:13it must now keep its body temperature within a narrow range,
0:33:13 > 0:33:16between 34 and 36 degrees.
0:33:18 > 0:33:22Observing Telu, palaeontologist Dr Darren Naish
0:33:22 > 0:33:24can tell me how they do it.
0:33:25 > 0:33:27So he's in front of his heat lamp
0:33:27 > 0:33:29and he's done something quite distinctive,
0:33:29 > 0:33:31which is sort of spread himself out flat.
0:33:31 > 0:33:33Why has that happened?
0:33:33 > 0:33:36Yeah, in order to basically be the best shape
0:33:36 > 0:33:38to absorb as much heat as possible from the environment,
0:33:38 > 0:33:41a lot of reptiles adopt specific poses
0:33:41 > 0:33:43and the most obvious thing they do
0:33:43 > 0:33:45is they do spread out and flatten the rib cage,
0:33:45 > 0:33:47so they're presenting a larger surface area to the sun.
0:33:47 > 0:33:51What Telu here is doing is absorbing heat from his heat lamp.
0:33:51 > 0:33:53He's also receiving heat from the ground,
0:33:53 > 0:33:55which has obviously been warmed by the heat lamp,
0:33:55 > 0:33:56and through his own behaviour
0:33:56 > 0:33:59he's very good at controlling his temperature,
0:33:59 > 0:34:02keeping it quite high and in a very specific band.
0:34:07 > 0:34:11Being cold-blooded does come with an obvious limitation.
0:34:12 > 0:34:15You need enough heat in your environment.
0:34:16 > 0:34:19We definitely do see a massive drop-off in the diversity
0:34:19 > 0:34:21of cold-blooded reptiles like lizards
0:34:21 > 0:34:23once you get away from the equator,
0:34:23 > 0:34:25once you get further towards the north,
0:34:25 > 0:34:29so clearly they are disadvantaged in cooler environments.
0:34:29 > 0:34:31Today, we mostly associate cold-blooded animals
0:34:31 > 0:34:36with places where there are warm conditions year round.
0:34:43 > 0:34:46So for cold-blooded animals, the challenge of keeping warm enough
0:34:46 > 0:34:50tends to limit them to the hotter regions of the planet.
0:34:52 > 0:34:54To thrive in the cooler places,
0:34:54 > 0:34:57you need a different way to keep your body temperature
0:34:57 > 0:34:58warm and stable.
0:35:00 > 0:35:02And evidence for this comes
0:35:02 > 0:35:05from perhaps the last group of animals you'd expect.
0:35:07 > 0:35:10When I was a kid, I spent a couple of years being dinosaur mad
0:35:10 > 0:35:14and I remember the excitement of being taken to an exhibition
0:35:14 > 0:35:16of Chinese dinosaur fossils
0:35:16 > 0:35:19and I remember loving the picture that painted
0:35:19 > 0:35:22of a different version of Earth, these giant lizards,
0:35:22 > 0:35:26cold-blooded slow animals roaming the swamps.
0:35:26 > 0:35:31Well, here today there is another exhibition of Chinese dinosaurs
0:35:31 > 0:35:32but the specimens here
0:35:32 > 0:35:36paint a completely different picture of that world.
0:35:47 > 0:35:49Dr Adam Smith is a curator
0:35:49 > 0:35:52at Wollaton Hall Natural History Museum.
0:35:54 > 0:35:56When I was a kid growing up,
0:35:56 > 0:35:59the picture of the environment that dinosaurs lived in
0:35:59 > 0:36:04was a swampy environment surrounded by volcanoes but we now know
0:36:04 > 0:36:06that dinosaurs were much more diverse than that
0:36:06 > 0:36:08and the environments that they occupied
0:36:08 > 0:36:11were much more diverse than that as well.
0:36:11 > 0:36:13Some of them were adapted for living in forests,
0:36:13 > 0:36:17some were adapted for living in open landscapes,
0:36:17 > 0:36:18some lived on the shore,
0:36:18 > 0:36:21even quite snowy areas would have been occupied by dinosaurs.
0:36:25 > 0:36:28For decades, the spread of dinosaurs into cooler regions
0:36:28 > 0:36:31away from the tropics posed the question...
0:36:33 > 0:36:37..how could cold-blooded creatures survive in colder climates?
0:36:39 > 0:36:43And then in 1996, a fossil was discovered in China
0:36:43 > 0:36:44that changed everything.
0:36:47 > 0:36:51So this specimen is obviously beautifully preserved. What is it?
0:36:51 > 0:36:56This is a genuine fossil of a sinosauropteryx dinosaur.
0:36:56 > 0:37:00It was living in a climate that was similar to northern Europe
0:37:00 > 0:37:03and so you would have had warm seasons and cold seasons
0:37:03 > 0:37:05and the special thing about it is that,
0:37:05 > 0:37:08in addition to the bones being preserved,
0:37:08 > 0:37:11we have evidence of the soft tissues as well.
0:37:11 > 0:37:14You can see it most clearly running along the back of the tail here,
0:37:14 > 0:37:15this dark line,
0:37:15 > 0:37:19and especially at the very tip of the tail, it looks very tuft-like.
0:37:22 > 0:37:27The dark line on this 125-million- year-old sinosauropteryx fossil
0:37:27 > 0:37:32is only faint, but it's tantalising evidence
0:37:32 > 0:37:36for something you wouldn't expect on a dinosaur.
0:37:39 > 0:37:41It's very similar to the downy material
0:37:41 > 0:37:44that you find on a newly hatched chick.
0:37:44 > 0:37:48And that's why this has been interpreted as feathers.
0:37:48 > 0:37:51So this is a dinosaur and it's got feathers?
0:37:51 > 0:37:54They're not true feathers as you would think of as a bird's feathers
0:37:54 > 0:37:58but they were the structures that led to true feathers.
0:37:58 > 0:37:59They're fuzzy feathers,
0:37:59 > 0:38:01so they've been given the name proto-feathers.
0:38:05 > 0:38:08For palaeontologists, these fuzzy feathers
0:38:08 > 0:38:10were a spectacular revelation.
0:38:12 > 0:38:16The fuzz in the dinosaur suggests that they were using it
0:38:16 > 0:38:20for insulation and in that case you would expect the dinosaurs
0:38:20 > 0:38:23to be generating their own heat rather than basking in the sun
0:38:23 > 0:38:25to get warm from the outside environment.
0:38:29 > 0:38:31Cold-blooded animals tend not to have feathers,
0:38:31 > 0:38:36in part because their skin needs to absorb heat from the environment.
0:38:37 > 0:38:41So this animal, that suggests, was not cold-blooded?
0:38:41 > 0:38:44It's very likely, based on the evidence from the feathers,
0:38:44 > 0:38:46that this particular dinosaur was warm-blooded.
0:38:49 > 0:38:54This discovery is helping scientists to reimagine the world of dinosaurs.
0:38:58 > 0:39:00In the case of these dinosaurs,
0:39:00 > 0:39:02we know that they were very active animals,
0:39:02 > 0:39:06very agile dinosaurs, very intelligent animals as well.
0:39:13 > 0:39:15It's now thought that many dinosaurs
0:39:15 > 0:39:18may have been at least partly warm-blooded.
0:39:21 > 0:39:24This would have made them less reliant on the sun
0:39:24 > 0:39:26and allowed them to thrive in cooler habitats.
0:39:28 > 0:39:31Had an asteroid impact not contributed to their extinction,
0:39:31 > 0:39:33some of them might still exist today.
0:39:39 > 0:39:43The dinosaurs that did survive evolved into modern birds,
0:39:43 > 0:39:44which are warm-blooded.
0:39:47 > 0:39:51And alongside them grew the rapidly expanding class
0:39:51 > 0:39:53of warm-blooded mammals.
0:40:02 > 0:40:04Birds and mammals use the energy from food
0:40:04 > 0:40:06to generate their own body heat,
0:40:06 > 0:40:11and one area that is particularly sensitive to temperature
0:40:11 > 0:40:13is the brain.
0:40:13 > 0:40:19This powerful but fragile organ generates intense heat of its own,
0:40:19 > 0:40:23so animals need a way to keep it at precisely the right temperature.
0:40:29 > 0:40:32On a cold, rainy day like this in Colchester...
0:40:33 > 0:40:36..nobody here is thinking that they're too warm.
0:40:36 > 0:40:40But these animals have some amazing adaptations to keep them cool
0:40:40 > 0:40:43in the really hot weather in Africa.
0:40:46 > 0:40:49I am meeting Dr Chris Basu from the Royal Veterinary College,
0:40:49 > 0:40:52who's an expert in giraffe physiology.
0:40:53 > 0:40:57The brain itself is an organ which produces a lot of heat, so even when
0:40:57 > 0:41:00they're not doing particularly anything taxing, the brain is very
0:41:00 > 0:41:02metabolically active, so it's producing loads of heat.
0:41:04 > 0:41:07A giraffe's natural habitat is hot,
0:41:07 > 0:41:10sometimes well above 30 degrees Celsius,
0:41:10 > 0:41:14so these animals have had to adapt to dissipate heat.
0:41:15 > 0:41:18Their distinctive markings have long been thought to
0:41:18 > 0:41:20play a role in camouflage,
0:41:20 > 0:41:24but take a look at them with a thermal imaging camera and
0:41:24 > 0:41:25something more is revealed.
0:41:27 > 0:41:31You might expect the giraffe's body to be all the same temperature
0:41:31 > 0:41:33and therefore a uniform colour,
0:41:33 > 0:41:37but instead the dark patches are still visible,
0:41:37 > 0:41:40and the colour shows they are actually warmer
0:41:40 > 0:41:42than the surrounding skin.
0:41:42 > 0:41:44Beneath those spots is actually
0:41:44 > 0:41:47quite an intricate network of blood vessels.
0:41:47 > 0:41:50So, blood vessels bring blood to the surface, to the skin,
0:41:50 > 0:41:52and they can actually radiate heat through those blood vessels.
0:41:52 > 0:41:54So when you look at those spots,
0:41:54 > 0:41:57you can almost think of those spots as thermal windows -
0:41:57 > 0:41:59they're getting rid of heat through those spots.
0:42:00 > 0:42:05These markings are crucial to keeping the giraffe's body cool.
0:42:05 > 0:42:08But keeping the brain at the right temperature is so important
0:42:08 > 0:42:11that it needs its own cooling system,
0:42:11 > 0:42:15one of the most sophisticated adaptations in the animal kingdom.
0:42:16 > 0:42:18And it all starts with its nose.
0:42:20 > 0:42:22When the giraffe breathes in,
0:42:22 > 0:42:27the air helps water in the moist lining of its nostrils to evaporate,
0:42:27 > 0:42:31which in turn cools the blood in the underlying blood vessels,
0:42:31 > 0:42:33much like when we sweat.
0:42:36 > 0:42:40And the next crucial step is what happens when this cooler blood
0:42:40 > 0:42:42heads back towards the heart.
0:42:42 > 0:42:46At the base of the brain is a structure called the carotid rete,
0:42:46 > 0:42:49where heat can be transferred from the warmer blood
0:42:49 > 0:42:53travelling to the brain to the cooler blood from the nose.
0:42:53 > 0:42:58It's thought that this helps cool the blood arriving from the heart
0:42:58 > 0:43:00before it reaches the brain,
0:43:00 > 0:43:03preventing the brain from overheating.
0:43:03 > 0:43:05We can think of it as like a heat exchanger.
0:43:05 > 0:43:07It drops the temperature by about two degrees,
0:43:07 > 0:43:10but the really clever thing is they can actually adapt this mechanism
0:43:10 > 0:43:12based on the environmental conditions.
0:43:12 > 0:43:16It sounds an amazingly practical, efficient way of losing heat.
0:43:16 > 0:43:18It means that they can just respond to their environment,
0:43:18 > 0:43:20they're really quite responsive.
0:43:23 > 0:43:27Giraffes have evolved in this very distinctive way to cope with heat.
0:43:30 > 0:43:35But if there's one animal that's found a way to live in pretty much
0:43:35 > 0:43:39every temperature environment on Earth, from deserts to poles...
0:43:40 > 0:43:41..it's us.
0:43:43 > 0:43:47So how does the human body cope with extremes of temperature?
0:43:51 > 0:43:54To show you, I first need to generate a lot of heat.
0:43:56 > 0:43:59So I've come to my badminton club to train with my coach, Stuart.
0:44:01 > 0:44:04We are used to the idea that our body temperature is 37 degrees,
0:44:04 > 0:44:07but we don't often think about just how hard our system has to work
0:44:07 > 0:44:09to make sure that's true.
0:44:09 > 0:44:12I do a lot of sport, so I run around all the time,
0:44:12 > 0:44:15and that sort of exercise puts a lot of stress on the system,
0:44:15 > 0:44:18and the body has a challenge to get rid of that heat.
0:44:24 > 0:44:29While Stuart puts me through my paces, my body has two jobs to do.
0:44:32 > 0:44:35So, on court I'm thinking about what my muscles are doing,
0:44:35 > 0:44:37how I'm moving, but while all that's going on,
0:44:37 > 0:44:39my body has another challenge,
0:44:39 > 0:44:41which is getting rid of all the heat I'm generating.
0:44:43 > 0:44:46One obvious way my body does this is to sweat.
0:44:47 > 0:44:51But to see what else I'm doing, I'm using the thermal imaging camera.
0:44:53 > 0:44:56This will show the temperature of the interface between
0:44:56 > 0:44:58my skin and the surrounding air.
0:44:59 > 0:45:03The lighter and brighter the colour, the hotter the temperature.
0:45:06 > 0:45:09Watching the thermal footage of me playing is fascinating
0:45:09 > 0:45:11because there's so much detail.
0:45:11 > 0:45:14You can see that my surface temperature is different
0:45:14 > 0:45:15in different places.
0:45:15 > 0:45:18My face is obviously very warm, under my arms are very warm.
0:45:18 > 0:45:21All of the places where there's blood flow close to the surface,
0:45:21 > 0:45:24those show up really, really brightly.
0:45:24 > 0:45:27And the really interesting bit here is when you look
0:45:27 > 0:45:30just after I've stopped, and you can see how hard my body
0:45:30 > 0:45:32is working to get rid of that heat.
0:45:32 > 0:45:36My blood vessels on my arms are just shining out
0:45:36 > 0:45:38because they're so warm.
0:45:39 > 0:45:43That's because when we're getting too hot, our brain tells
0:45:43 > 0:45:46the blood vessels supplying our skin to widen.
0:45:49 > 0:45:52This increases the flow of blood to the surface of the skin,
0:45:52 > 0:45:54where it can dissipate heat.
0:45:58 > 0:46:02And this shifting of blood to and from the skin's surface
0:46:02 > 0:46:06is an extremely effective way to control our body temperature.
0:46:07 > 0:46:10It helps prevent our bodies from overheating
0:46:10 > 0:46:14and keeps them within a very narrow and safe window of temperature.
0:46:19 > 0:46:22The amazing thing about this is I run around in this sports hall
0:46:22 > 0:46:25all the time and I never have to think about this,
0:46:25 > 0:46:26my body just takes care of it all.
0:46:31 > 0:46:35But when we get cold, our bodies face the opposite challenge -
0:46:35 > 0:46:38not dissipating heat, but hanging on to it.
0:46:44 > 0:46:47To understand how our bodies deal with cold,
0:46:47 > 0:46:51I've come to the University of Portsmouth to experience it
0:46:51 > 0:46:52in a rather unusual way.
0:46:55 > 0:46:58I'm pretty good with physical discomfort but I hate being cold,
0:46:58 > 0:47:01and I'm a fidget and I hate sitting still,
0:47:01 > 0:47:04and both of them are about to happen to me at the same time.
0:47:06 > 0:47:09Putting me through this challenge is Professor Mike Tipton,
0:47:09 > 0:47:12an expert in cold water survival.
0:47:12 > 0:47:17He's going to immerse me in water that's 18 degrees Celsius,
0:47:17 > 0:47:21nearly 20 degrees below my normal core body temperature.
0:47:23 > 0:47:25And to see how the cold affects me,
0:47:25 > 0:47:28Mike has got a simple manual task for me to perform,
0:47:28 > 0:47:32which I'll repeat after I've spent time in the water.
0:47:32 > 0:47:34Three, two, one, go.
0:47:38 > 0:47:39Now come back.
0:47:39 > 0:47:42- That's good.- OK. - Well done.- Right, done.
0:47:42 > 0:47:44You've done that, yeah, 22 seconds.
0:47:44 > 0:47:45- OK.- I will remember that.
0:47:46 > 0:47:50It's time for the big plunge.
0:47:50 > 0:47:53I suddenly have immense sympathy for witches in the 16th century.
0:47:57 > 0:48:01Four, three, two, one, go.
0:48:10 > 0:48:12Oh, it's horrible.
0:48:12 > 0:48:15It's amazing how the urge to breathe is very sudden.
0:48:16 > 0:48:21As soon as I am submerged, my survival mechanisms kick in.
0:48:21 > 0:48:24I have started to shiver - about a minute ago, I started to shiver.
0:48:24 > 0:48:28Yeah, the skin receptors are sending messages into the brain saying,
0:48:28 > 0:48:30"You've got a very cold skin,"
0:48:30 > 0:48:32and so that's being integrated in the centre of the brain,
0:48:32 > 0:48:35the hypothalamus of the brain is saying,
0:48:35 > 0:48:37"We need to start generating heat."
0:48:37 > 0:48:39And that's why you have started shivering.
0:48:39 > 0:48:44Shivering is my body's attempt to counteract the cold by producing
0:48:44 > 0:48:48its own heat to prevent my vital organs from dropping in temperature.
0:48:49 > 0:48:53But in these conditions, shivering, alone, isn't enough.
0:48:54 > 0:48:57A drop in my core temperature of just two degrees Celsius
0:48:57 > 0:49:00would cause hypothermia.
0:49:00 > 0:49:02So after half an hour, I've reached my limit.
0:49:03 > 0:49:07- I think it's probably time to bring you out.- OK!
0:49:07 > 0:49:08Ready? Here we go.
0:49:11 > 0:49:16As I'm winched out of the water, the thermal imaging camera reveals
0:49:16 > 0:49:19another of my body's responses to the cold.
0:49:19 > 0:49:23Dark blue areas indicate where my surface temperature has dropped
0:49:23 > 0:49:29dramatically as blood is diverted away from the cold water.
0:49:29 > 0:49:32The body will sacrifice the extremities
0:49:32 > 0:49:35in order to preserve the internal organs.
0:49:35 > 0:49:38And you will have people who have got frostbite,
0:49:38 > 0:49:42they are losing extremities, but to preserve
0:49:42 > 0:49:45their heart and brain temperatures, because once those
0:49:45 > 0:49:49temperatures fall, then it's a threat to survival.
0:49:49 > 0:49:51So what we're going to do now is just ask you to do
0:49:51 > 0:49:53that nut and bolt test again.
0:49:53 > 0:49:55Three, two, one, go.
0:49:57 > 0:50:00My wrists are very cold and I feel that's stopping me moving
0:50:00 > 0:50:02- my fingers very well. - That's it, done?
0:50:02 > 0:50:05- Done.- Oh, there we are. - Yeah.- Bang on a minute.
0:50:05 > 0:50:06Really? Three times!
0:50:06 > 0:50:09So 22 seconds before, a minute afterwards.
0:50:10 > 0:50:13This experience has made me realise
0:50:13 > 0:50:16just how vulnerable to cold we all are.
0:50:16 > 0:50:20In fact, what enables us humans to survive and thrive
0:50:20 > 0:50:24in cold temperatures isn't our in-built survival mechanisms,
0:50:24 > 0:50:26it's something else.
0:50:27 > 0:50:31Our physiological responses to cold really wouldn't let you
0:50:31 > 0:50:35move very far away from your equatorial origins.
0:50:36 > 0:50:38You know, once you start getting into zero degrees overnight,
0:50:38 > 0:50:41the level of heat production, the level of heat retention
0:50:41 > 0:50:44you have got will have been very limiting.
0:50:44 > 0:50:49And the really important thing is that it's underpinned by intellect.
0:50:49 > 0:50:53We have been using clothing for 75,000 years,
0:50:53 > 0:50:55we've been using fire for a million years.
0:50:55 > 0:50:58Now, as soon as you have done that, you've got a source of heat
0:50:58 > 0:51:01and a source of light, you can cook food, your diet can change.
0:51:01 > 0:51:03You are a tropical animal
0:51:03 > 0:51:05that's taken those origins with it thermally,
0:51:05 > 0:51:09so you've recreated, as I say, a microclimate next to your skin
0:51:09 > 0:51:12which would be the same as if you were living naked
0:51:12 > 0:51:15in the 28-degree environment from which you evolved.
0:51:18 > 0:51:20While all life on Earth has adapted
0:51:20 > 0:51:23to survive the temperature of its habitat,
0:51:23 > 0:51:28only we humans are able to create micro-habitats of our own.
0:51:28 > 0:51:32We can maintain our ideal temperature wherever we go
0:51:32 > 0:51:34thanks to our intelligence.
0:51:39 > 0:51:43But human ingenuity hasn't just enabled us to manipulate
0:51:43 > 0:51:45the temperature of our environment.
0:51:47 > 0:51:52It's also allowed us, in very special circumstances,
0:51:52 > 0:51:55to push the boundaries of life itself.
0:51:59 > 0:52:02It's 8am and a team at Papworth Hospital are getting ready
0:52:02 > 0:52:06to perform a radical type of surgery.
0:52:06 > 0:52:08It involves cooling a patient's body
0:52:08 > 0:52:11to a temperature that would normally be fatal,
0:52:11 > 0:52:13taking them to the edge of life.
0:52:17 > 0:52:20Justine has a life-threatening condition.
0:52:20 > 0:52:23Clots are blocking the blood vessels in her lungs,
0:52:23 > 0:52:26leaving her struggling for breath.
0:52:26 > 0:52:28I've continuously got a tightness in my chest.
0:52:28 > 0:52:31Just doing normal things, like going up and down the stairs,
0:52:31 > 0:52:32I'm out of breath.
0:52:32 > 0:52:35It's quite daunting but I know, obviously,
0:52:35 > 0:52:38I've got to have this operation. If I don't,
0:52:38 > 0:52:41I don't know how long I'm going to be able to continue for.
0:52:41 > 0:52:44So I know that I have to do it in order to be able to
0:52:44 > 0:52:47take my little girl to the park and play.
0:52:58 > 0:53:00It's down to surgeon David Jenkins
0:53:00 > 0:53:03to remove the clots from Justine's lungs.
0:53:03 > 0:53:06But while blood is flowing through her lungs,
0:53:06 > 0:53:09the operation is impossible.
0:53:09 > 0:53:13Well, the main problem is the lungs usually have five litres of blood
0:53:13 > 0:53:15every minute being pumped through them.
0:53:15 > 0:53:18For this operation we need a completely clear field
0:53:18 > 0:53:20in the small vessels in the lungs,
0:53:20 > 0:53:23so the only way to do that is to drain all the blood out of the body.
0:53:25 > 0:53:30Removing a patient's entire blood supply is a truly extraordinary
0:53:30 > 0:53:35procedure and David is a leading specialist in the technique.
0:53:35 > 0:53:39Once Justine is under anaesthetic, the first step is to divert
0:53:39 > 0:53:42her blood supply to a heart-lung machine.
0:53:42 > 0:53:45At this stage, her blood is still delivering fresh oxygen
0:53:45 > 0:53:50to her vital organs and, crucially, to her brain.
0:53:50 > 0:53:51- Running OK?- It's running well.
0:53:53 > 0:53:55At David's command,
0:53:55 > 0:53:58the machine drains all Justine's blood from her body.
0:53:59 > 0:54:05Now we are in this critical window where there is no blood flow
0:54:05 > 0:54:07going through Justine's body,
0:54:07 > 0:54:09and David is able to see
0:54:09 > 0:54:13inside the pulmonary arteries to clear the blockages.
0:54:15 > 0:54:18He can now begin to remove the clots from her lungs.
0:54:20 > 0:54:24But he has to work against the clock because without blood circulating,
0:54:24 > 0:54:27Justine no longer has a supply of oxygen.
0:54:29 > 0:54:33Normally, the human brain can only survive for around four minutes
0:54:33 > 0:54:37without fresh oxygen before permanent damage occurs.
0:54:39 > 0:54:42But in the controlled environment of the operating theatre,
0:54:42 > 0:54:46Justine is being kept alive by temperature.
0:54:47 > 0:54:49Cooling to 20.
0:54:49 > 0:54:51Before David began to operate,
0:54:51 > 0:54:55Justine's body was slowly cooled to just 20 degrees.
0:54:57 > 0:55:01This is the key to the entire procedure.
0:55:01 > 0:55:05Her body is in a temporary state of stasis.
0:55:05 > 0:55:08At this temperature, the function of her brain is slowed down
0:55:08 > 0:55:12and it can survive 20 minutes without oxygen.
0:55:14 > 0:55:19The process is being supervised by anaesthetist Dr Joe Arrowsmith.
0:55:19 > 0:55:22Our body has all these mechanisms to stop us getting that cold -
0:55:22 > 0:55:24why isn't she shivering?
0:55:24 > 0:55:26Well, the anaesthetic I've given her
0:55:26 > 0:55:28has disabled all of those mechanisms.
0:55:28 > 0:55:32I've paralysed her skeletal muscle, so she physically cannot shiver.
0:55:34 > 0:55:37To reduce the need for oxygen as much as possible,
0:55:37 > 0:55:40the team have cooled Justine's brain still further.
0:55:42 > 0:55:44We have this cap wrapped around Justine's head
0:55:44 > 0:55:48and it has got a continuous flow of ice-cold water that comes
0:55:48 > 0:55:51from this ice bath here with freezer ice packs in.
0:55:51 > 0:55:56What we believe this does is keep the outer centimetre or two of
0:55:56 > 0:55:59the brain slightly cooler than the rest of the brain,
0:55:59 > 0:56:02so where the grey matter is, where all of the cell bodies
0:56:02 > 0:56:05and most of the metabolism is, so we think that buys us
0:56:05 > 0:56:08just a little bit of extra brain protection.
0:56:08 > 0:56:12The right side is done and we managed to do that
0:56:12 > 0:56:14in just under 15 minutes.
0:56:14 > 0:56:17So that's good, and we're back on the heart-lung machine now.
0:56:19 > 0:56:23With the clots removed, Justine's blood is returned via the machine.
0:56:24 > 0:56:28It gradually warms up her blood, and in turn her body.
0:56:29 > 0:56:33And after a while, her heart spontaneously restarts.
0:56:36 > 0:56:38The patients who go through this procedure
0:56:38 > 0:56:41live through something incredible.
0:56:41 > 0:56:45They are taken to the edge of life and brought back.
0:56:45 > 0:56:49And the skill and the delicacy of the process
0:56:49 > 0:56:51is just amazing to watch.
0:56:53 > 0:56:55And it's all made possible by control of temperature.
0:56:58 > 0:57:00After six hours in surgery,
0:57:00 > 0:57:04Justine has safely returned from her incredible journey
0:57:04 > 0:57:05down the temperature scale.
0:57:08 > 0:57:10And what's really exciting is that
0:57:10 > 0:57:13our ability to manipulate temperature
0:57:13 > 0:57:17is beginning to open up a whole new field of medical possibilities.
0:57:23 > 0:57:25We are alive, you and I,
0:57:25 > 0:57:28which means that we are directly connected to the web of life
0:57:28 > 0:57:31that covers this planet and extends back through
0:57:31 > 0:57:33almost all of its history.
0:57:33 > 0:57:36And all of that web, in all of its variety,
0:57:36 > 0:57:40only exists within a very narrow temperature range,
0:57:40 > 0:57:43and we barely appreciate the temperatures of life.
0:57:44 > 0:57:48But next time you hold someone's hand or give them a hug,
0:57:48 > 0:57:52it's worth remembering that it's not just about the physical gesture,
0:57:52 > 0:57:54you're sharing the warmth of life.
0:57:55 > 0:57:59And it's a nice thought that that shows just how intimately
0:57:59 > 0:58:01temperature and life are intertwined.
0:58:06 > 0:58:10Next time, I'll be exploring the incredible science of heat.
0:58:10 > 0:58:13What temperatures does it reach on the inside there?
0:58:13 > 0:58:14100 million degrees.
0:58:14 > 0:58:16That's just a ludicrous number!
0:58:17 > 0:58:20I'll reveal how our ability to harness heat
0:58:20 > 0:58:23lies behind some of humanity's greatest achievements...
0:58:25 > 0:58:28..and promises a future of almost unlimited power.