0:00:19 > 0:00:24Every living thing that we know to exist is found on this one rock.
0:00:28 > 0:00:32In this programme, I want to show you how almost four billion years ago,
0:00:32 > 0:00:37this rock became a home to life...
0:00:39 > 0:00:42..which has since flourished, diversified
0:00:42 > 0:00:48and evolved into the extraordinarily varied natural world we see today.
0:01:19 > 0:01:22I want to show you why our world is the only habitable planet
0:01:22 > 0:01:25we know of, anywhere in the universe.
0:01:25 > 0:01:28Now, the answer depends on the presence of a handful
0:01:28 > 0:01:32of precious ingredients that make our world a home.
0:01:36 > 0:01:39One of the most important of which is a substance vital to all
0:01:39 > 0:01:41known forms of life.
0:01:43 > 0:01:44Water.
0:01:47 > 0:01:52Our planet is the only one we know with a surface
0:01:52 > 0:01:53still drenched in liquid water.
0:01:58 > 0:02:01The story of how each drop ended up here has been hard to fathom.
0:02:03 > 0:02:04Largely because it happened
0:02:04 > 0:02:07so long ago, there's very little direct evidence.
0:02:12 > 0:02:15But in the Yucatan jungle in Mexico,
0:02:15 > 0:02:18clues to how it turned up can still be found.
0:02:20 > 0:02:25The landscape here is peppered with deep wells of water, called cenotes.
0:02:28 > 0:02:31Every civilisation on the Yucatan, be it the modern Mexicans
0:02:31 > 0:02:35or the Mayans, had to get their water from the cenotes.
0:02:35 > 0:02:39And I've got a map, a completely unbiased map, of the larger
0:02:39 > 0:02:42cenotes here, which I'm going to overlay on the Yucatan.
0:02:47 > 0:02:51And look at that - they lie in a perfect arc,
0:02:51 > 0:02:54centred around a very particular village,
0:02:54 > 0:02:56which is there,
0:02:56 > 0:03:00and it's called Chicxulub.
0:03:00 > 0:03:05Now, to a geologist, there are very few natural events that can
0:03:05 > 0:03:10create a structure, such a perfect arc as that.
0:03:14 > 0:03:18All the evidence points to just one explanation.
0:03:21 > 0:03:25We're looking at what's left of a gigantic asteroid strike.
0:03:28 > 0:03:33One that wiped out three-quarters of all plant and animal species
0:03:33 > 0:03:37when it hit the earth 65 million years ago.
0:03:37 > 0:03:40You may think that impacts from space are a thing of the past,
0:03:40 > 0:03:43a thing that only happened to the dinosaurs,
0:03:43 > 0:03:44but that's not true either.
0:03:44 > 0:03:49About 55 million kilograms of rock hits the earth every year,
0:03:49 > 0:03:52and around two per cent of that is water.
0:03:54 > 0:03:59This hints that at least some of earth's water arrived from space.
0:04:03 > 0:04:08Late in 2010, these glimpses of comet Hartley 2 arrived
0:04:08 > 0:04:09back on earth.
0:04:11 > 0:04:14They were sent by NASA's Deep Impact probe.
0:04:16 > 0:04:20From the comet's surface dust and ice spray into space.
0:04:22 > 0:04:26Analysis of this water showed that it has a very similar
0:04:26 > 0:04:29chemical composition to the water in our oceans.
0:04:31 > 0:04:35This was the first firm evidence that icy comets must have
0:04:35 > 0:04:38contributed to the formation of our world's oceans.
0:04:55 > 0:04:58Earth began life as a molten hell.
0:04:59 > 0:05:03Its internal heat drove off any trace of moisture.
0:05:07 > 0:05:11But soon the planet cooled and it's thought that water brought
0:05:11 > 0:05:16by comets condensed, contributing to the creation of the first clouds.
0:05:21 > 0:05:25Then, 4.2 billion years ago, a deluge, the like of which
0:05:25 > 0:05:30the solar system has never seen before or since, rained down...
0:05:32 > 0:05:33..forming our oceans.
0:05:45 > 0:05:50As a liquid, water molecules are held together by hydrogen bonds.
0:05:53 > 0:05:54And breaking these bonds
0:05:54 > 0:05:57and turning liquid into gas takes a lot of energy.
0:06:00 > 0:06:02In other words,
0:06:02 > 0:06:06hydrogen bonds are what makes water's boiling point high.
0:06:06 > 0:06:09High enough to have allowed it to remain on the surface
0:06:09 > 0:06:12of the earth as a liquid to the present day.
0:06:15 > 0:06:17So from quite early in its history,
0:06:17 > 0:06:21our home has been able to hang on to this most vital of ingredients.
0:06:26 > 0:06:30Water is an essential part of all metabolic processes within the body.
0:06:32 > 0:06:35It's fundamental to photosynthesis and respiration,
0:06:35 > 0:06:42and is the critical solvent in each and every one of our cells.
0:06:42 > 0:06:45But water isn't the only thing that makes our planet home.
0:06:49 > 0:06:52Complex life relies on another precious chemical.
0:06:53 > 0:06:55Oxygen.
0:06:58 > 0:07:02Understanding how earth developed an atmosphere rich in oxygen has taken
0:07:02 > 0:07:08centuries, and now we know that the secret lies with ancient bacteria.
0:07:18 > 0:07:24In 1676, a Dutchman called Anton Leeuwenhoek was trying to
0:07:24 > 0:07:28find out why pepper is spicy.
0:07:28 > 0:07:31See, they thought that there were little spikes on peppercorns
0:07:31 > 0:07:33that dug into your tongue.
0:07:33 > 0:07:35He was using the microscope,
0:07:35 > 0:07:38which had been discovered about 50 or 60 years before,
0:07:38 > 0:07:41but inexplicably had never been used for anything useful before.
0:07:41 > 0:07:43He put the peppercorns on there
0:07:43 > 0:07:45and he looked down and he couldn't see anything.
0:07:45 > 0:07:48So he thought, "OK, I'll grind them up, dissolve them in water
0:07:48 > 0:07:49"and have a look."
0:07:49 > 0:07:52When he did that, he didn't see anything interesting in the
0:07:52 > 0:07:57peppercorns, but he found that there were little animals swimming around.
0:07:57 > 0:07:59And he said that he estimated he could
0:07:59 > 0:08:02line about 100 of the "wee little creatures" -
0:08:02 > 0:08:04those were his words -
0:08:04 > 0:08:08up along the length of a single coarse sand grain.
0:08:08 > 0:08:11What Leeuwenhoek thought were animals,
0:08:11 > 0:08:14were, in all probability, not animals at all.
0:08:17 > 0:08:19Although he didn't know it at the time,
0:08:19 > 0:08:22he'd discovered a whole new domain of life.
0:08:27 > 0:08:29Bacteria.
0:08:34 > 0:08:37They are by far the most numerous organisms on the earth.
0:08:38 > 0:08:42In fact, there are more bacteria on our planet than
0:08:42 > 0:08:46there are stars in the observable universe.
0:08:49 > 0:08:53And there is one kind of bacteria more numerous than all the rest.
0:08:58 > 0:09:01One of the most striking structures I can see on this slide is
0:09:01 > 0:09:06a kind of a blue-green filament, which is a little
0:09:06 > 0:09:10colony of a type of bacteria called cyanobacteria.
0:09:14 > 0:09:18These things are incredibly important organisms.
0:09:23 > 0:09:26Fossilised cyanobacteria have been found as far back
0:09:26 > 0:09:29as 3.5 billion years ago.
0:09:33 > 0:09:37And at some point, around 2.4 billion years ago,
0:09:37 > 0:09:41they became the first living things to use pigments to split
0:09:41 > 0:09:44water apart and use it to make food.
0:09:47 > 0:09:51This evolutionary invention was incredibly complex.
0:09:51 > 0:09:54Even its name is a mouthful -
0:09:54 > 0:09:57oxygenic photosynthesis.
0:10:00 > 0:10:06It starts with a photon from the sun hitting that green pigment,
0:10:06 > 0:10:08chlorophyll.
0:10:08 > 0:10:09Chlorophyll takes that energy
0:10:09 > 0:10:14and uses it to boost electrons up a hill, if you like.
0:10:14 > 0:10:18And when they get to the top, they cascade down a molecular
0:10:18 > 0:10:22waterfall, and the energy is used to make something called ATP,
0:10:22 > 0:10:27which is essentially the energy currency of life.
0:10:27 > 0:10:31This little molecular machine is called Photosystem 2,
0:10:31 > 0:10:35and it makes energy for the cell, from sunlight.
0:10:35 > 0:10:37But when the electrons reach the bottom of that waterfall,
0:10:37 > 0:10:42they enter Photosystem One, they meet some more chlorophyll which
0:10:42 > 0:10:47is hit by another photon from the sun, and that energy raises
0:10:47 > 0:10:52the electrons up again and forces them onto carbon dioxide, turning
0:10:52 > 0:10:58that carbon dioxide eventually into sugars, into food for the cell.
0:10:58 > 0:11:00Now, why all this complexity?
0:11:00 > 0:11:03You know, why do you need these two photosystems joined
0:11:03 > 0:11:07together in this way, just to get some electrons and make sugar
0:11:07 > 0:11:09and a bit of energy out of it?
0:11:13 > 0:11:17It's because only when life coupled these two biological machines
0:11:17 > 0:11:23together, that it could split water apart and turn it into food.
0:11:23 > 0:11:25But it wasn't easy.
0:11:26 > 0:11:30The thing is that water is extremely difficult to split.
0:11:30 > 0:11:33So for a leaf to do it, for a blade of grass to do it,
0:11:33 > 0:11:38just using a trickle of light from the sun is extremely difficult.
0:11:41 > 0:11:46In fact, the task is so complex, that unlike flight or vision,
0:11:46 > 0:11:51which evolved separately many times during our history,
0:11:51 > 0:11:56oxygenic photosynthesis has only evolved once.
0:11:59 > 0:12:03In other words, the descendants of one cyanobacterium that
0:12:03 > 0:12:06worked out, for some reason, how to couple those complex
0:12:06 > 0:12:10molecular machines together in some primordial ocean,
0:12:10 > 0:12:14billions of years ago, are still present on the earth today.
0:12:21 > 0:12:26The cyanobaceria changed the world, turning it green.
0:12:28 > 0:12:31And that had a wonderful consequence.
0:12:34 > 0:12:36With this new way of living, life released
0:12:36 > 0:12:41oxygen into the atmosphere of our planet for the first time.
0:12:41 > 0:12:45And in doing so, over hundreds of millions of years,
0:12:45 > 0:12:49it eventually completely transformed the face of our home.
0:12:53 > 0:12:56Organisms started using oxygen to respire,
0:12:56 > 0:12:59yielding a lot more energy which allowed
0:12:59 > 0:13:04the development of more complex life, like plants and animals.
0:13:12 > 0:13:15With these two ingredients, oxygen and water,
0:13:15 > 0:13:21our planet has provided a home to life for billions of years.
0:13:26 > 0:13:29But how can we define what life actually is?
0:13:30 > 0:13:33The answer lies in the way that living things process
0:13:33 > 0:13:38one of the universe's most elusive properties energy.
0:13:46 > 0:13:48Energy is a concept that's central to physics,
0:13:48 > 0:13:51but because it's a word we use every day,
0:13:51 > 0:13:53its meaning has got a bit woolly.
0:13:53 > 0:13:55I mean, it's easy to say what it is, in a sense.
0:13:55 > 0:13:58Obviously this river has got energy because over the decades
0:13:58 > 0:14:02and centuries, it's cut this valley through solid rock.
0:14:04 > 0:14:07But while this description sounds simple,
0:14:07 > 0:14:10in reality, things are a little more complicated.
0:14:16 > 0:14:17Over the years,
0:14:17 > 0:14:22the nature of energy has proved notoriously difficult to pin down,
0:14:22 > 0:14:28not least because it has the seemingly magical property that it never runs out.
0:14:28 > 0:14:31It only ever changes from one form to another.
0:14:35 > 0:14:37Take the water in that waterfall.
0:14:37 > 0:14:40At the top of the waterfall, it's got something called gravitational
0:14:40 > 0:14:43potential energy, which is the energy it possesses due to
0:14:43 > 0:14:45its height above the earth's surface.
0:14:45 > 0:14:50See, if I scoop some water out of the river into this beaker,
0:14:50 > 0:14:55then I'd have to do work to carry it up to the top of the waterfall.
0:14:55 > 0:14:57I'd have to expend energy to get it up there.
0:14:57 > 0:15:02So it would have that energy as gravitational potential.
0:15:02 > 0:15:04I can even do the sums for you.
0:15:04 > 0:15:06Half a litre of water has a mass of half a kilogram.
0:15:06 > 0:15:09Multiply by the height, that's about five metres, and
0:15:09 > 0:15:13the acceleration due to gravity is about ten metres per second squared.
0:15:13 > 0:15:17So that's half, times five, times ten, is 25 joules.
0:15:17 > 0:15:21So I'd have to put in 25 joules to carry this water to
0:15:21 > 0:15:23the top of the waterfall.
0:15:23 > 0:15:27Then if I emptied it over the top of the waterfall,
0:15:27 > 0:15:29then all that gravitational potential energy would be
0:15:29 > 0:15:31transformed into other types of energy.
0:15:33 > 0:15:36Sound, which is pressure waves in the air.
0:15:36 > 0:15:40There's the energy of the waves in the river. And there's heat.
0:15:40 > 0:15:42So it'll be a bit hotter down there because the water's
0:15:42 > 0:15:46cascading into the pool at the bottom of the waterfall.
0:15:46 > 0:15:49But a key thing is, energy is conserved,
0:15:49 > 0:15:50it's not created or destroyed.
0:15:54 > 0:15:58So because energy is conserved, if I were to add up all the energy in the
0:15:58 > 0:16:02water waves, all the energy in the sound waves, all the heat energy at
0:16:02 > 0:16:06the bottom of the pool, then I would find that it would be precisely
0:16:06 > 0:16:12equal to the gravitational potential energy at the top of the falls.
0:16:15 > 0:16:20What's true for the waterfall is true for everything in the universe.
0:16:22 > 0:16:24It's a fundamental law of nature,
0:16:24 > 0:16:27known as the First Law of Thermodynamics.
0:16:28 > 0:16:33And the fact that energy is neither created nor destroyed has
0:16:33 > 0:16:34a profound implication.
0:16:36 > 0:16:37It means energy is eternal.
0:16:45 > 0:16:49Every single joule of energy in the universe today was
0:16:49 > 0:16:53present at the Big Bang 13.7 billion years ago.
0:16:56 > 0:17:00Potential energy held in primordial clouds of gas and dust
0:17:00 > 0:17:04was transformed into kinetic energy, as they collapsed
0:17:04 > 0:17:09to form stars and planetary systems just like our own solar system.
0:17:15 > 0:17:19That primordial energy was trapped deep inside new planets.
0:17:22 > 0:17:27And it's the slow release of the energy found in the earth's core
0:17:27 > 0:17:30that is thought to have kick-started life.
0:17:46 > 0:17:48Although no-one knows for sure how life began,
0:17:48 > 0:17:52it's certain that it had to have an energy source.
0:17:54 > 0:17:58One theory says that it started under extreme conditions
0:17:58 > 0:18:00almost four billion years ago,
0:18:00 > 0:18:04when the earth's energy was churning up the ocean floor.
0:18:07 > 0:18:09These are pictures from deep below the surface
0:18:09 > 0:18:13of the Atlantic Ocean, somewhere between Bermuda and the Canaries.
0:18:13 > 0:18:17And it's a place known as the Lost City.
0:18:17 > 0:18:19You can see why.
0:18:19 > 0:18:24Look at these huge towers of rock, some of them 50-60 metres high,
0:18:24 > 0:18:29reaching up from the floor of the Atlantic and into the ocean.
0:18:29 > 0:18:31It's what's known as a hydrothermal vent system.
0:18:31 > 0:18:34So these things are formed by hot water and minerals
0:18:34 > 0:18:38and gases rising up from deep within the earth.
0:18:38 > 0:18:41But the reason it's thought that life on earth may have
0:18:41 > 0:18:45begun in such structures is because these are a very unique
0:18:45 > 0:18:49kind of hydrothermal vent called an alkaline vent.
0:18:49 > 0:18:52And about four billion years ago, when life on earth began,
0:18:52 > 0:18:55sea water would have been mildly acidic.
0:18:58 > 0:19:00There was a difference in the chemical
0:19:00 > 0:19:05make-up of the water INSIDE the vent and that outside it.
0:19:05 > 0:19:09One was alkaline, the other acidic.
0:19:09 > 0:19:13And just like a battery, this difference acted as an energy store.
0:19:18 > 0:19:22When such a difference is equalised, energy is released.
0:19:22 > 0:19:25And that energy can be used to do things.
0:19:31 > 0:19:34And the vents don't just provide an energy source,
0:19:34 > 0:19:38they're also rich in the raw materials life needs.
0:19:42 > 0:19:47Hydrogen gas, carbon dioxide and minerals containing iron,
0:19:47 > 0:19:50nickel and sulphur.
0:19:51 > 0:19:53But more than that.
0:19:53 > 0:19:56See, these vents are porous, there are little chambers inside them,
0:19:56 > 0:20:00and they can act to concentrate organic molecules.
0:20:06 > 0:20:09You've got everything inside these vents.
0:20:09 > 0:20:12You've got concentrated building blocks of life
0:20:12 > 0:20:13trapped inside the rock.
0:20:17 > 0:20:20So this could be where your distant ancestors come from.
0:20:20 > 0:20:27And places like these could be the places where life on earth began.
0:20:31 > 0:20:36In these four billion years, that spark has grown into a flame.
0:20:38 > 0:20:42And a few simple organisms clustered around a hydrothermal vent
0:20:42 > 0:20:46have evolved to produce new and complex creatures.
0:20:50 > 0:20:54Today, life no longer depends on energy from the earth.
0:20:54 > 0:20:57Instead, almost all life is fuelled
0:20:57 > 0:21:02by the transformation of the sun's energy.
0:21:02 > 0:21:05As sunlight bathes our planet, it's harnessed
0:21:05 > 0:21:08and passed on from one life form to another.
0:21:10 > 0:21:14And there is one creature that embodies, more than most,
0:21:14 > 0:21:16just how that happens.
0:21:28 > 0:21:31This is the golden jellyfish.
0:21:31 > 0:21:36A unique sub-species only found in this one lake on this
0:21:36 > 0:21:40one island, in the tiny Micronesian republic of Palau.
0:21:49 > 0:21:53Golden jellyfish have evolved to do something that very few other
0:21:53 > 0:21:55animals can do.
0:21:58 > 0:22:00It really is incredible.
0:22:00 > 0:22:02As far as you can see,
0:22:02 > 0:22:07all the way down till the light vanishes, there are jellyfish.
0:22:07 > 0:22:09And you can see they've congregated in the sun.
0:22:09 > 0:22:12If you go over there to where the lake's in shade,
0:22:12 > 0:22:13there are just none.
0:22:13 > 0:22:16They're in this pool of light, beneath the sun.
0:22:16 > 0:22:18There are millions of them.
0:22:18 > 0:22:21Beautiful elegant things just floating around.
0:22:31 > 0:22:35This lake is home to over 20 million jellyfish,
0:22:35 > 0:22:41whose success comes down to a remarkable adaptation.
0:22:41 > 0:22:44Their bodies play host to thousands of other organisms.
0:22:46 > 0:22:51Photosynthetic algae that harvest energy directly from sunlight.
0:22:53 > 0:22:58And once harvested, is passed on to the jellyfish to use.
0:22:58 > 0:23:03The energy flows from sun to algae, to jellyfish.
0:23:11 > 0:23:15The ones at the surface are gently turning.
0:23:15 > 0:23:19The reason they do that is to give all their algae an equal
0:23:19 > 0:23:21dose of sunlight.
0:23:26 > 0:23:29And it's not just their anatomy that's adapted to harvest
0:23:29 > 0:23:31solar energy.
0:23:31 > 0:23:34Every morning as the sun rises,
0:23:34 > 0:23:38the jellyfish begin to swim towards the east.
0:23:41 > 0:23:46And as the sun tracks across the sky, they move back again towards
0:23:46 > 0:23:48the west, where they spend their night.
0:23:52 > 0:23:56So the jellyfish have this beautiful, intimate
0:23:56 > 0:24:01and complex relationship with the position of the sun in the sky.
0:24:05 > 0:24:08As sunlight is captured by their algae,
0:24:08 > 0:24:10it's converted into chemical energy.
0:24:13 > 0:24:16Energy they use to combine simple molecules,
0:24:16 > 0:24:22water and carbon dioxide, to produce a far more complex one...
0:24:22 > 0:24:24glucose.
0:24:25 > 0:24:29Once absorbed by the jellyfish, glucose
0:24:29 > 0:24:32and other molecules not only power their daily voyage
0:24:32 > 0:24:37across the lake, they provide the basic building blocks the jellyfish
0:24:37 > 0:24:41use to grow the elegant and complex structures of their bodies.
0:24:51 > 0:24:54So the jellyfish, through their symbiotic algae,
0:24:54 > 0:24:58absorb the light, the energy from the sun,
0:24:58 > 0:25:02and they use it to live, to power their processes of life.
0:25:02 > 0:25:05And that's true, directly or indirectly,
0:25:05 > 0:25:08for every form of life on the surface of our planet.
0:25:12 > 0:25:16Although all life uses energy in the same way, what I find
0:25:16 > 0:25:21remarkable is how spectacularly diverse our natural world is.
0:25:23 > 0:25:26From the tiniest bacteria to the tallest trees
0:25:26 > 0:25:28and the most obscure-looking animals.
0:25:30 > 0:25:32So how has life become so varied?
0:25:40 > 0:25:43We know that every living thing on the planet today,
0:25:43 > 0:25:47so every piece of food you eat, every animal you've seen,
0:25:47 > 0:25:51everyone you've ever known, or will know, in fact, every living thing
0:25:51 > 0:25:54that will ever exist on this planet,
0:25:54 > 0:25:56was descended from one speck.
0:26:00 > 0:26:05We call it the last universal common ancestor, or LUCA.
0:26:05 > 0:26:09So just as the universe had its origin in a big bang,
0:26:09 > 0:26:14all life on this planet had its origin in that one moment.
0:26:22 > 0:26:25Now, we don't know what LUCA looked like.
0:26:25 > 0:26:29We don't know precisely where it lived or how it lived.
0:26:29 > 0:26:34But we do know this - if you start to trace my ancestral line back
0:26:34 > 0:26:37to my parents, to their parents, to their parents,
0:26:37 > 0:26:42to their parents, all the way back through geological timescales
0:26:42 > 0:26:47over hundreds of thousands and millions and billions of years,
0:26:47 > 0:26:54there will be an unbroken line from me all the way back to LUCA.
0:26:57 > 0:27:00We know that, because every living thing on the planet today
0:27:00 > 0:27:03shares the same biochemistry.
0:27:03 > 0:27:09We all have DNA. It's made of the same bases - A, C, T and G.
0:27:09 > 0:27:11They code for the same amino acids.
0:27:11 > 0:27:17Those amino acids build the same proteins which do very similar jobs,
0:27:17 > 0:27:21whether you're a plant, a bacterium or a bipedal hominid like me.
0:27:27 > 0:27:30So all life uses the same fundamental biology.
0:27:32 > 0:27:38Those four bases, A, C, G and T, which code for just 20 amino acids,
0:27:38 > 0:27:44which in turn build each and every one of life's proteins.
0:27:47 > 0:27:52Be you bacteria, plant, bug or beast,
0:27:52 > 0:27:55your design comes from your DNA.
0:27:57 > 0:28:01So it's this molecule that must hold the key to understanding why
0:28:01 > 0:28:04life today is so diverse.
0:28:07 > 0:28:11We now know that the answer to why life on earth is so varied
0:28:11 > 0:28:17is actually the answer to why the DNA molecule itself is so varied.
0:28:17 > 0:28:19What are the natural processes
0:28:19 > 0:28:22that cause the structure of DNA to change?
0:28:22 > 0:28:27Well, part of the answer actually doesn't lie on earth at all.
0:28:27 > 0:28:30It lies up there amongst the stars.
0:28:30 > 0:28:35And I can show you what I mean using this, which is a cloud chamber,
0:28:35 > 0:28:39a piece of apparatus that has a unique place
0:28:39 > 0:28:41in the history of physics.
0:28:41 > 0:28:46I'm going to cool it down using dry ice, frozen carbon dioxide,
0:28:46 > 0:28:49just below minus 70 degrees Celsius.
0:28:54 > 0:28:55Put the top on...
0:28:55 > 0:28:58HIGH-PITCHED WHISTLING
0:28:58 > 0:29:00Hear that?
0:29:00 > 0:29:02That's the metal at the bottom of the tank,
0:29:02 > 0:29:05cooling down very rapidly to minus 70.
0:29:08 > 0:29:12The cloud chamber works by having a super-saturated
0:29:12 > 0:29:16vapour of alcohol inside the chamber.
0:29:16 > 0:29:18There's plenty on there.
0:29:18 > 0:29:20Now, I want to get that alcohol,
0:29:20 > 0:29:23I want to boil it off to get the vapour into the chamber.
0:29:23 > 0:29:26So I'm going to put a hot water bottle on top.
0:29:26 > 0:29:30And this is the first genuine particle physics detector.
0:29:30 > 0:29:34It's the piece of apparatus that first saw antimatter,
0:29:34 > 0:29:39and it really does consist only of a fish tank, some alcohol,
0:29:39 > 0:29:41a bit of paper and a hot water bottle.
0:30:04 > 0:30:08There, look at that. You see that cloud, that vapour trail?
0:30:11 > 0:30:13That's a cosmic ray.
0:30:13 > 0:30:18That was initiated by a particle, probably a proton,
0:30:18 > 0:30:20that hit the earth's atmosphere.
0:30:23 > 0:30:28Now imagine if one of those hits the DNA of a living thing.
0:30:28 > 0:30:31What that will do is cause a mutation.
0:30:31 > 0:30:36That mutation may be detrimental or,
0:30:36 > 0:30:38very, very occasionally, it might be beneficial.
0:30:42 > 0:30:46Mutations are an inevitable part of living on a planet like earth.
0:30:50 > 0:30:55They're the first hint of how DNA and the genes that code for
0:30:55 > 0:31:00every living thing change from generation to generation.
0:31:03 > 0:31:05Mutations are the spring
0:31:05 > 0:31:08from which innovation in the living world flows.
0:31:20 > 0:31:24But cosmic rays are not the only way in which DNA can be altered.
0:31:30 > 0:31:33There's natural background radiation from the rocks,
0:31:33 > 0:31:37there's the action of chemicals and free radicals.
0:31:37 > 0:31:40There can be errors when the code is copied.
0:31:40 > 0:31:44And then all those changes can be shuffled by sex, and indeed
0:31:44 > 0:31:50whole pieces of the code can be transferred from species to species.
0:31:50 > 0:31:55So bit by bit, in tiny steps from generation to generation,
0:31:55 > 0:31:58the code is constantly randomly changing.
0:32:01 > 0:32:07Now, whilst there's no doubt that random mutation does alter DNA,
0:32:07 > 0:32:10evolution is anything but random.
0:32:20 > 0:32:24Evolution is driven by a process called natural selection.
0:32:27 > 0:32:29And there's no better place to see how it works
0:32:29 > 0:32:32than in the forests of Madagascar.
0:32:38 > 0:32:40HOOTING CRY
0:32:43 > 0:32:45There, at the top of the tree,
0:32:45 > 0:32:49is an indri, which is the largest lemur in Madagascar.
0:32:49 > 0:32:55And the reason it's thought that we find lemurs here
0:32:55 > 0:33:00in Madagascar and Madagascar alone is because there are no simians.
0:33:00 > 0:33:06There are no chimpanzees, none of my ancestral family dating back
0:33:06 > 0:33:08tens of millions of years to out-compete them.
0:33:08 > 0:33:15So what's thought happened is that around 65 million years ago,
0:33:15 > 0:33:20one of the lemurs' ancestors managed to sail across
0:33:20 > 0:33:25the Mozambique Channel and landed here.
0:33:25 > 0:33:27There were none of those competitors here,
0:33:27 > 0:33:30and so the lemurs have flourished ever since.
0:33:32 > 0:33:38There are now over 90 species of lemur and sub-species in Madagascar.
0:33:38 > 0:33:42No species of my lineage, the simians.
0:33:56 > 0:33:59Over a vast sweep of time,
0:33:59 > 0:34:03the lemurs have diversified to fill all manner of different habitats.
0:34:06 > 0:34:10From the arid spiny forests of the south,
0:34:10 > 0:34:13to the rocky canyons in the north.
0:34:13 > 0:34:17There is something about this island that is allowing the lemurs'
0:34:17 > 0:34:21DNA to change in the most amazing ways.
0:34:29 > 0:34:32We're on the hunt for an aye-aye, the most closely
0:34:32 > 0:34:37related of all the surviving lemurs to their common ancestor.
0:34:37 > 0:34:40- Right there.- Oh, yeah! Here.
0:34:42 > 0:34:44Yes.
0:34:46 > 0:34:49The team want to attach radio collars onto the aye-ayes
0:34:49 > 0:34:51so they can track their movements.
0:34:55 > 0:34:57But first they need to find and sedate them,
0:34:57 > 0:35:00which is an incredibly tricky business.
0:35:07 > 0:35:11I mean, how you get a clean shot in this, I've no idea.
0:35:29 > 0:35:33Well, here is the aye-aye that was tranquillised last night.
0:35:33 > 0:35:37They finally got her about half an hour after we left.
0:35:37 > 0:35:39I think it was probably because we were disturbing her.
0:35:39 > 0:35:42Apparently, as soon as we'd gone, she came down the tree
0:35:42 > 0:35:43and she was tranquillised.
0:35:43 > 0:35:47And as you can see, she's pretty well sedated now,
0:35:47 > 0:35:49which is fortunate for me
0:35:49 > 0:35:54because she has certain adaptations that I wouldn't like to be deployed.
0:35:54 > 0:35:58You can see, there, her teeth.
0:35:58 > 0:36:03The teeth are very unusual for a primate. In fact, unique,
0:36:03 > 0:36:04because they carry on growing.
0:36:04 > 0:36:07So she's much more like a rodent in that respect.
0:36:07 > 0:36:10And that's so she can gnaw into wood.
0:36:10 > 0:36:14You see, aye-ayes have filled a unique niche on Madagascar.
0:36:14 > 0:36:16It's a niche that's filled by woodpeckers in many other
0:36:16 > 0:36:18areas of the world.
0:36:18 > 0:36:22What she does is she feeds on grubs and bugs inside trees.
0:36:22 > 0:36:26And to do that, she has several unique adaptations,
0:36:26 > 0:36:27of which her teeth are one.
0:36:27 > 0:36:34The most startling is this central finger here. It's bizarre.
0:36:34 > 0:36:37It's got a ball and socket joint for a start,
0:36:37 > 0:36:41so it has complete 360-degree movement.
0:36:41 > 0:36:43It feels to me almost as if it's broken,
0:36:43 > 0:36:46but it isn't, it's just you can move it around in any direction.
0:36:46 > 0:36:51And she uses that finger initially to tap on the trunk of the tree,
0:36:51 > 0:36:56and then listening to the echo from that tapping with these huge ears,
0:36:56 > 0:37:00she can detect where the grubs are.
0:37:00 > 0:37:04And then she gnaws through the wood with those rodent-like teeth,
0:37:04 > 0:37:08and then uses this finger again to reach inside the hole
0:37:08 > 0:37:11and get the bugs out.
0:37:11 > 0:37:13So the question is, why?
0:37:13 > 0:37:19How could an animal be so precisely adapted to a particular lifestyle?
0:37:19 > 0:37:22She's waking up now.
0:37:23 > 0:37:26And the answer is natural selection.
0:37:26 > 0:37:29See, what must have happened is, way back,
0:37:29 > 0:37:32when the ancestors of the lemurs, the lemuriforms,
0:37:32 > 0:37:38arrived in Madagascar, there must have been a mutation that
0:37:38 > 0:37:42lengthened the middle finger ever so slightly in one of those lemurs.
0:37:42 > 0:37:45And that must have given it an advantage.
0:37:45 > 0:37:47That must have allowed it, perhaps, to reach into little holes
0:37:47 > 0:37:49and search for grubs.
0:37:49 > 0:37:52There's some reason why that lengthened middle finger
0:37:52 > 0:37:55meant that that gene was more likely to be passed to the next
0:37:55 > 0:37:58generation, and then down to the next generation.
0:37:58 > 0:38:02So that landscape of possibilities is narrowed.
0:38:02 > 0:38:05It's narrowed because that gene persists.
0:38:05 > 0:38:10And it's persisted now for at least 40 million years,
0:38:10 > 0:38:15because this species has been on one branch of the tree of life
0:38:15 > 0:38:18now for over 40 million years.
0:38:18 > 0:38:20And so over those years that middle finger has got
0:38:20 > 0:38:22more and more specialised.
0:38:24 > 0:38:28Natural selection has allowed the aye-aye's wonderfully mutated
0:38:28 > 0:38:31finger to spread through the population.
0:38:33 > 0:38:36And this same law applies to all life.
0:38:38 > 0:38:42If you have a mutation that helps you in the struggle to survive,
0:38:42 > 0:38:44you are more likely to leave more offspring,
0:38:44 > 0:38:51and in the next generation, that mutation is more likely to survive.
0:38:54 > 0:38:59So this animal is a beautiful example, probably one
0:38:59 > 0:39:04of the best in the world, of how the sieve of natural selection produces
0:39:04 > 0:39:08animals that are perfectly adapted to live in their environment.
0:39:13 > 0:39:17This process of evolution has led to the diversity of living things
0:39:17 > 0:39:19we see on the planet today.
0:39:27 > 0:39:31Seen against the blackness of space, the earth is a fragile world.
0:39:31 > 0:39:35But seen by science, it's a world that's been crafted
0:39:35 > 0:39:39and shaped by life over almost four billion years.
0:39:47 > 0:39:50Life that could have started at the bottom of the oceans
0:39:50 > 0:39:53in hydrothermal vents,
0:39:53 > 0:39:58life that today taps into the flow of energy from the sun,
0:39:58 > 0:40:00adapting...
0:40:00 > 0:40:02changing...
0:40:02 > 0:40:05and evolving...
0:40:05 > 0:40:10to create the magnificently diverse natural world we see today.
0:40:20 > 0:40:23Subtitles by Red Bee Media Ltd