0:00:07 > 0:00:09I've spent most of my life trying to understand
0:00:09 > 0:00:12the forces that shaped our planet,
0:00:12 > 0:00:14and as a geologist, it always seemed to me
0:00:14 > 0:00:17that rocks were right at the heart of things.
0:00:21 > 0:00:26But now, I'm discovering it's not only volcanoes and colliding continents
0:00:26 > 0:00:29that have driven the Earth's greatest changes,
0:00:29 > 0:00:33because at crucial moments in its history,
0:00:33 > 0:00:36another force has helped create the planet we live on...
0:00:37 > 0:00:39...plants.
0:00:39 > 0:00:41Just look at this seed.
0:00:41 > 0:00:46It's small, it's brown, it weighs hardly anything. Looks pretty ordinary.
0:00:46 > 0:00:49But, actually, nothing could be further from the truth,
0:00:49 > 0:00:52because what it will become is truly extraordinary.
0:00:59 > 0:01:02These are giant sequoias.
0:01:02 > 0:01:05Some are over 3,000 years old.
0:01:08 > 0:01:12And sequoias are the largest single life form on Earth.
0:01:13 > 0:01:15All from a tiny seed.
0:01:17 > 0:01:19Yet, even that pales into insignificance
0:01:19 > 0:01:23when compared to what the whole of the plant kingdom's done
0:01:23 > 0:01:25throughout the history of our planet.
0:01:25 > 0:01:28It's a whole new story about our Earth...
0:01:30 > 0:01:36...told through remarkable images, captured for the very first time,
0:01:36 > 0:01:39and the latest scientific discoveries.
0:01:41 > 0:01:44I love this. This is just fantastic.
0:01:54 > 0:01:58This programme is about just one type of plant,
0:01:58 > 0:02:02the most underrated but perhaps the most important of all.
0:02:03 > 0:02:07One that, by taking on and conquering the rest of the plant kingdom,
0:02:07 > 0:02:12shaped the face of the planet and went on to help create human civilisation.
0:02:12 > 0:02:16This is the story of the rise of that underdog.
0:02:32 > 0:02:36For hundreds of millions of years, throughout the time of the dinosaurs,
0:02:36 > 0:02:38forests ruled the land.
0:02:42 > 0:02:46It was so warm, trees extended over most of the Earth.
0:02:47 > 0:02:53Imagine the Arctic and Antarctic without ice, carpeted with forests.
0:02:57 > 0:03:01Welcome to the planet of the trees.
0:03:09 > 0:03:14Today, isolated remnants of those expansive forests still exist
0:03:14 > 0:03:19and here in East Africa is one of the most impressive.
0:03:19 > 0:03:24The Katago Cloud Forest rises out of the dry plains of Kenya.
0:03:30 > 0:03:34Cloaked in moisture, it's much the same as it was then.
0:03:38 > 0:03:40Ah! Oh, at last!
0:03:40 > 0:03:41Look at that.
0:03:44 > 0:03:46But millions of years ago,
0:03:46 > 0:03:50a challenger to the old dominant trees came onto the scene.
0:03:53 > 0:03:55And the best way to find it is to climb right down
0:03:55 > 0:03:58into the depths of the forest.
0:04:00 > 0:04:02It's never really elegant, this.
0:04:02 > 0:04:06This is when the adrenaline thrill starts to come in.
0:04:08 > 0:04:11To be honest, I'm not quite sure after you get to...
0:04:11 > 0:04:14There's a little lip, just seems to go straight down.
0:04:23 > 0:04:26This is the oldest forest in Africa up here.
0:04:26 > 0:04:32A relic, really, of the time when trees dominated the planet.
0:04:33 > 0:04:40So, this really has a... a feeling of descending into that ancient lost world.
0:05:06 > 0:05:09Back then, trees ruled
0:05:09 > 0:05:12because wood gave them the strength to grow ever taller
0:05:12 > 0:05:15and to gorge on the sunlight all plants need.
0:05:22 > 0:05:23As you descend,
0:05:23 > 0:05:29you get a real sense of how trees bully and overshadow everything below.
0:05:35 > 0:05:38We've come about ten metres just into the canopy.
0:05:38 > 0:05:41(CHUCKLES) And I've nicked the cameraman's light metre,
0:05:41 > 0:05:44just to see what the light levels are doing.
0:05:44 > 0:05:48And already, they've dropped by about a third.
0:05:54 > 0:05:56(WHISPERS) Oh, God, finally.
0:05:56 > 0:05:59Now, let's see... see how that light's doing.
0:06:01 > 0:06:03That's gone down by a half.
0:06:03 > 0:06:07These huge trees here have stolen half the light.
0:06:13 > 0:06:16Down here, the trees are intimidating.
0:06:20 > 0:06:23But it's not complete gloom.
0:06:25 > 0:06:29Patches of sunlight do break through to the forest floor.
0:06:31 > 0:06:35And those shafts of precious light offer the chance
0:06:35 > 0:06:36for a new type of plant,
0:06:36 > 0:06:40one that would come to take on the trees.
0:06:45 > 0:06:49So, how did scientists discover the identity of the challenger?
0:06:50 > 0:06:53It's all thanks to a rather enchanting piece of research
0:06:53 > 0:06:57involving what's inside this little box.
0:06:57 > 0:06:59You'll never guess what it is.
0:07:00 > 0:07:05This is a piece of fossilised dinosaur poo.
0:07:05 > 0:07:07It stinks.
0:07:07 > 0:07:08Phew.
0:07:08 > 0:07:10It's from a titanosaur sauropod,
0:07:10 > 0:07:13which is kind of like a brontosaurus,
0:07:13 > 0:07:16my favourite dinosaur as a kid.
0:07:16 > 0:07:18It weighed about 100 tonnes,
0:07:18 > 0:07:22which makes me think that this is just a fragment of something the size of...
0:07:22 > 0:07:25I don't know, really. Something big, anyway.
0:07:25 > 0:07:28Scientists love fossil poo. Coprolites, we call it.
0:07:28 > 0:07:31They tell us about the diet of animals, and particularly,
0:07:31 > 0:07:34about the plants that were around when dinosaurs were here.
0:07:34 > 0:07:37And when scientists analysed this one a few years ago,
0:07:37 > 0:07:41they found it contained something really strange.
0:07:43 > 0:07:49Under the microscope, the scientists saw a fragment of a plant.
0:07:49 > 0:07:53It had a distinctive pattern, these figure-of-eight nodules.
0:07:54 > 0:07:56They turned out to be the defining feature
0:07:56 > 0:08:00of a family of plants they were astonished to see.
0:08:00 > 0:08:01The grasses.
0:08:04 > 0:08:07It was from 66 million years ago,
0:08:07 > 0:08:13evidence for the earliest grass ever found, called matleitis.
0:08:18 > 0:08:19From its humble birth,
0:08:19 > 0:08:23grass would eventually become one of the most dominant forces on our planet.
0:08:33 > 0:08:37But its rise would be a David-and-Goliath battle with the trees.
0:08:43 > 0:08:45BIRD SONG
0:08:47 > 0:08:51You can still find descendants of those early challengers today.
0:08:57 > 0:08:59Plants like this.
0:09:00 > 0:09:05And we think these are similar to what the first grasses must have looked like.
0:09:05 > 0:09:09You can just imagine 'em struggling away on the forest floor,
0:09:09 > 0:09:13just feeding off little scraps of light making it through the canopy.
0:09:14 > 0:09:17It's wonderful to think that dinosaurs the size of houses
0:09:17 > 0:09:23were trampling through forests like this, just grazing on little patches of grass.
0:09:29 > 0:09:34But the dinosaurs' days of grazing were about to end abruptly.
0:09:42 > 0:09:4865 million years ago, an asteroid ten kilometres across killed them off.
0:09:57 > 0:10:00The grasses survived.
0:10:01 > 0:10:06But in turn, they would face their own crisis.
0:10:11 > 0:10:13What was coming had nothing to do
0:10:13 > 0:10:16with the plants and animals that lived on Earth.
0:10:16 > 0:10:19It was all to do with the atmosphere,
0:10:19 > 0:10:23and that was changing for the most surprising of reasons.
0:10:27 > 0:10:30Our air contains carbon dioxide.
0:10:30 > 0:10:33It's the gas that plants need to breathe to stay alive.
0:10:36 > 0:10:41But between 50 and 30 million years ago, this gas began to disappear...
0:10:43 > 0:10:45...threatening all plants.
0:10:53 > 0:10:59The crisis started with the creation of huge mountain ranges like the Himalayas...
0:11:07 > 0:11:11...the biggest period of mountain building in Earth's history.
0:11:19 > 0:11:24The freshly exposed rock was washed away.
0:11:27 > 0:11:31Some of the minerals ended up in the sea.
0:11:38 > 0:11:41And here they sucked the carbon dioxide gas out of the air,
0:11:41 > 0:11:46combining with it to form an entirely new type of rock.
0:11:51 > 0:11:53Limestone.
0:11:55 > 0:11:58I can show you that limestone's got carbon dioxide in it,
0:11:58 > 0:12:01because if I put a little bit of acid on it,
0:12:01 > 0:12:03it should fizz like mad.
0:12:09 > 0:12:12What this is doing is it's liberating carbon dioxide
0:12:12 > 0:12:14that had been in the ancient atmosphere
0:12:14 > 0:12:19and has now for the last few million years been locked away in this rock.
0:12:28 > 0:12:33By 30 million years ago, as the mountains had risen,
0:12:33 > 0:12:36the level of carbon dioxide fell.
0:12:37 > 0:12:42In fact, carbon dioxide levels dropped to a sixth of what they were beforehand,
0:12:42 > 0:12:44which is an enormous fall,
0:12:44 > 0:12:47and for the plant kingdom it meant crisis.
0:12:51 > 0:12:54Without enough vital carbon dioxide,
0:12:54 > 0:12:58many plants, including the grasses, were struggling to survive.
0:13:18 > 0:13:21One way to reveal the impact this had on plants
0:13:21 > 0:13:24is to look at a clever bit of human machinery.
0:13:28 > 0:13:30The car engine.
0:13:33 > 0:13:38Because what's under the bonnet shares surprising similarities with plants.
0:13:45 > 0:13:47The car engine relies on two things to work.
0:13:47 > 0:13:51It needs petrol and it needs oxygen from the air.
0:13:51 > 0:13:55Inside the engine, these two are combined to release the energy
0:13:55 > 0:13:57to power the car.
0:13:57 > 0:14:00It's called combustion.
0:14:00 > 0:14:02ENGINE STARTS
0:14:10 > 0:14:15Like the engine, plants also need a gas from the air to work,
0:14:15 > 0:14:18in their case the carbon dioxide.
0:14:22 > 0:14:24So, for plants... ENGINE STARTS
0:14:24 > 0:14:26...the collapse of carbon dioxide levels
0:14:26 > 0:14:30were similar to a car engine starved of oxygen.
0:14:32 > 0:14:36If I block the air intake, you can feel the engine stuttering away,
0:14:36 > 0:14:41because it's struggling to get the oxygen that it needs to work.
0:14:44 > 0:14:47With less carbon dioxide in the atmosphere,
0:14:47 > 0:14:50plants also began to stutter.
0:14:52 > 0:14:56But the grasses were evolving a new and ingenious invention.
0:14:57 > 0:15:01ENGINE RUNNING Again, the engine provides a parallel.
0:15:03 > 0:15:06There's a piece of shiny machinery here that any petrol-head will recognise.
0:15:06 > 0:15:09What that does is the opposite of my hand.
0:15:09 > 0:15:12It forces more oxygen into the engine.
0:15:12 > 0:15:14It's called a turbocharger.
0:15:21 > 0:15:24More oxygen means that the petrol burns more fiercely
0:15:24 > 0:15:28and that means more power, power enough to do this.
0:15:31 > 0:15:34(LAUGHS)
0:15:34 > 0:15:36Whoo-hoo!
0:15:47 > 0:15:51Evolution often comes up with our cleverest solutions
0:15:51 > 0:15:53during desperate times.
0:15:56 > 0:15:59And one group of plants, the grasses, turned this crisis
0:15:59 > 0:16:02into an opportunity.
0:16:07 > 0:16:08Grasses like this.
0:16:08 > 0:16:12This is elephant grass, which is one of the fastest-growing plants in the world.
0:16:12 > 0:16:16In three months, right, this stuff grows four metres.
0:16:16 > 0:16:19That's that much every day.
0:16:19 > 0:16:21This phenomenal growth rate was only possible
0:16:21 > 0:16:26because of a technology that evolved 30 million years ago,
0:16:26 > 0:16:31a design so effective that, if you were a mechanic, you'd be blown away.
0:16:38 > 0:16:41The new grasses came up with the equivalent of a turbocharger
0:16:41 > 0:16:44inside the leaves.
0:16:48 > 0:16:53It's in the cells of the leaves that photosynthesis occurs,
0:16:53 > 0:16:57where carbon dioxide is combined with water to make sugar.
0:17:00 > 0:17:03But the new grasses created an add-on,
0:17:03 > 0:17:07rings of specialist cells known as bundles.
0:17:09 > 0:17:12It all acts as a miniature pump,
0:17:12 > 0:17:16sucking in and concentrating vital carbon dioxide.
0:17:23 > 0:17:26So, although there was less carbon dioxide in the air,
0:17:26 > 0:17:30the grasses had the edge over other plants.
0:17:41 > 0:17:43Hm.
0:17:43 > 0:17:47You know, when you study the planet, you're so used to seeing the big events,
0:17:47 > 0:17:50like, I don't know, ice sheets melting and volcanoes erupting.
0:17:50 > 0:17:54But with the rise of turbocharge grasses
0:17:54 > 0:17:56you've got something that's the tiniest of events.
0:17:56 > 0:18:00It's something almost invisible tucked away
0:18:00 > 0:18:03inside the leaf of a plant.
0:18:03 > 0:18:07It's what makes the story of plants just so fascinating.
0:18:12 > 0:18:16The grasses had found a way to survive the crisis.
0:18:22 > 0:18:25But forests still ruled the world.
0:18:29 > 0:18:32The huge trees had also survived.
0:18:36 > 0:18:42Then the underdog unleashed a devastating new weapon.
0:18:53 > 0:18:57Eight million years ago, by now the climate had altered.
0:18:58 > 0:19:01Much of the earth was dryer than ever before.
0:19:04 > 0:19:09It was the moment grasses had been waiting for.
0:19:14 > 0:19:19The grasses had evolved unique properties that made them especially flammable.
0:19:20 > 0:19:24When dry, they became like a tinderbox.
0:19:25 > 0:19:28All they needed was the spark.
0:19:37 > 0:19:42Today there's an ideal place to see what happened eight million years ago.
0:19:49 > 0:19:52Here in the national parks of South Africa,
0:19:52 > 0:19:57rangers deliberately start huge fires to manage the land.
0:20:02 > 0:20:08And for me it's the perfect opportunity to see how back then grasses exploited fire.
0:20:09 > 0:20:12So, we've got a chopper coming right down this line
0:20:12 > 0:20:15dropping incendiaries all the way along here.
0:20:17 > 0:20:20Chief fire-starter is Chris Austin.
0:20:21 > 0:20:25He coordinates the helicopter crew as they drop pellets onto the grass.
0:20:25 > 0:20:28Artificial lightning strikes.
0:20:31 > 0:20:35What'll happen is that they just sit there, they just open up, ignite,
0:20:35 > 0:20:36and then you just see them erupt.
0:20:39 > 0:20:43- Next 46 seconds, which is quite a long time. - 46 seconds? That's nice and precise.
0:20:43 > 0:20:46- There we go. There's one. - There we go. Come and have a look.
0:20:46 > 0:20:49- Yeah, there's probably another one there.- There it is.
0:20:49 > 0:20:51It should ignite now.
0:20:51 > 0:20:53- There she goes.- There.
0:20:53 > 0:20:58And then over here we've got ourselves another one.
0:20:58 > 0:21:02So, this line, this whole line now, is just gonna go up into a wall of flames.
0:21:02 > 0:21:03Another one there.
0:21:03 > 0:21:04Is it safe now here?
0:21:04 > 0:21:08She's gonna go up slope, yeah? She's gonna go away from us?
0:21:08 > 0:21:11Of course, if the wind's pushing it, it'll accelerate.
0:21:11 > 0:21:13You can see it's being pulled by the slope.
0:21:13 > 0:21:16Oh, I can feel it burning my face already.
0:21:18 > 0:21:20Look at that. That's amazing.
0:21:21 > 0:21:24It's just a wall of smoke and flame.
0:21:24 > 0:21:26Unbelievable.
0:21:31 > 0:21:36The most aggressive fire that I've seen moved at more than three metres a second, which is...
0:21:36 > 0:21:39- That's phenomenal.- It's really quick. You can't outrun it.
0:21:39 > 0:21:43The fires that kill people are grassland fires, because they're so fast-moving.
0:21:46 > 0:21:48And that's not all.
0:21:48 > 0:21:53Grass burns in a special way, a way that was devastating to its enemies.
0:21:57 > 0:21:58(GIGGLES)
0:21:58 > 0:22:00I've kind of fallen into it.
0:22:02 > 0:22:05To discover more about its properties,
0:22:05 > 0:22:08I've volunteered to enter into the heart of the fire.
0:22:09 > 0:22:12This stuff that's going in now is not kind of medical monitoring.
0:22:12 > 0:22:15This is actually for monitoring the temperatures of the fire.
0:22:15 > 0:22:19It's a thermocouple wire. It's gonna go running down...in this case down my leg.
0:22:19 > 0:22:23- It's probably the first time this has been done.- First time I've ever done this with a guy!
0:22:23 > 0:22:25(LAUGHS) First time you've put your...
0:22:25 > 0:22:28First time you've put your hand down a man's trousers.
0:22:28 > 0:22:30If you get stuck, that's us virtually married.
0:22:30 > 0:22:35Once in the flames, we hope to combine readings from the heat sensors on my suit,
0:22:35 > 0:22:37with a thermal-imaging camera
0:22:37 > 0:22:41to reveal the secrets of a grass fire.
0:22:46 > 0:22:48OXYGEN HISSES The fire is picking up speed.
0:22:49 > 0:22:54I can't believe I'm seeing this. It's starting to come towards us.
0:22:54 > 0:22:58This just seems like one of the daftest things I've done.
0:23:07 > 0:23:09Look at the flames!
0:23:10 > 0:23:13Grass fires are very different from other fires.
0:23:13 > 0:23:17The readings show that the hottest area of the fire,
0:23:17 > 0:23:19the white parts on this image,
0:23:19 > 0:23:22is not in the burning grass but a metre above it.
0:23:25 > 0:23:29The temperature here is over 360 degrees.
0:23:30 > 0:23:32OXYGEN HISSING
0:23:32 > 0:23:35Grass ignites more easily than other plants
0:23:35 > 0:23:38and it's transformed into a volatile gas.
0:23:41 > 0:23:46This grass rises and burns even hotter than the grass itself,
0:23:46 > 0:23:50making it one of the fiercest and fastest fires in nature.
0:23:50 > 0:23:53OXYGEN HISSING
0:24:02 > 0:24:04SIGHS AND SNORTS
0:24:05 > 0:24:08OXYGEN HISSES Ah.
0:24:10 > 0:24:13Oh, I know this feels... It sounds really strange,
0:24:13 > 0:24:16but it was actually quite a privilege to be in there.
0:24:16 > 0:24:18You know, normally if you're stuck in one of them,
0:24:18 > 0:24:20you just don't come out.
0:24:20 > 0:24:24It's great, at one point, the flames came up, and I just looked down,
0:24:24 > 0:24:27and it was just lapping against the mask.
0:24:27 > 0:24:30SNORTS You kind of feel sorry for the trees.
0:24:58 > 0:25:02The next day, the fire still smoulders.
0:25:02 > 0:25:05It's so strange.
0:25:05 > 0:25:09Why did grasses evolve to encourage fires to take hold...
0:25:10 > 0:25:14...ripping through the landscape and destroying plant life?
0:25:15 > 0:25:18It seems suicidal.
0:25:19 > 0:25:22Grasses don't just encourage fires to start.
0:25:22 > 0:25:24They're also designed to survive them.
0:25:24 > 0:25:28In fact, they're the most fire-resistant plant on earth
0:25:28 > 0:25:30and you can see here, this all looks scorched.
0:25:30 > 0:25:34How can it still... Look at the charcoal and smoke there.
0:25:34 > 0:25:38But the thing is, if you just peel this back, you quickly find that...
0:25:38 > 0:25:41Look at that. A lot of that's still alive.
0:25:42 > 0:25:44In fact the trick, really,
0:25:44 > 0:25:48the solution to why grasses can survive isn't on the surface.
0:25:48 > 0:25:50It's just below the surface.
0:25:50 > 0:25:56Cos if you open up these stalks, you can see that right here is a little bud.
0:25:56 > 0:26:00It's stuck under a... a kind of insulated thick coating.
0:26:00 > 0:26:03It's kind of tucked away in its underground bunker.
0:26:03 > 0:26:06It's still alive.
0:26:06 > 0:26:09So, you look around here and you just think everything's dead.
0:26:09 > 0:26:11And that tree... that tree certainly is.
0:26:11 > 0:26:16But the grass...the grass is just biding its time. It's very much alive.
0:26:19 > 0:26:24You know, this scene... this could easily be a scene from eight million years ago
0:26:24 > 0:26:29where the grasses just really quickly recover and recolonise.
0:26:29 > 0:26:33And the sneaky bit is they do it much faster than trees.
0:27:02 > 0:27:06In the wake of this onslaught, the forest started breaking up.
0:27:10 > 0:27:13The grasses were on a land grab,
0:27:13 > 0:27:17conquering the territory once held by the trees.
0:27:25 > 0:27:29The expanding grasses turned the earth into a flammable planet,
0:27:29 > 0:27:31a...a fireball world.
0:27:31 > 0:27:34It must have seen about a million trees burned
0:27:34 > 0:27:38and black ash filled the sky for hundreds of thousands of years.
0:27:38 > 0:27:41And for the trees, this was apocalypse.
0:27:51 > 0:27:53The world was ablaze.
0:27:54 > 0:27:59The challenger had sparked a revolution that was changing the face of the planet.
0:28:10 > 0:28:16But the global rise of grasses wasn't just reshaping plant life.
0:28:16 > 0:28:19It was transforming the animal kingdom too.
0:28:20 > 0:28:24So, how do we know this?
0:28:43 > 0:28:46The effects of the spreading grasses have been revealed by...
0:28:46 > 0:28:49not one of the most elegant pieces of forensic science.
0:28:49 > 0:28:52Part of the evidence had been discovered here in North America
0:28:52 > 0:28:55and it comes literally straight from the horse's mouth.
0:28:55 > 0:28:57Come on.
0:28:57 > 0:28:58HORSE SNORTS Whoa!
0:29:03 > 0:29:04IAIN GRUNTS
0:29:06 > 0:29:08When an animal eats a plant,
0:29:08 > 0:29:12the carbon of the plant is absorbed into its teeth.
0:29:12 > 0:29:17Studying the teeth tells you whether the herbivore has eaten the leaves of trees...
0:29:17 > 0:29:18or the new grasses.
0:29:18 > 0:29:20Yeah.
0:29:20 > 0:29:22All right?
0:29:22 > 0:29:28And the fossil teeth from millions of years ago tell a remarkable story.
0:29:31 > 0:29:35This is the result of the scientific analysis of tooth enamel
0:29:35 > 0:29:38from herbivores in North America.
0:29:38 > 0:29:41You can see down here this is us going back in time in millions of years.
0:29:41 > 0:29:45Now, the thing is, up to about eight million years to about here
0:29:45 > 0:29:48you can see that herbivores are largely eating shrubs and trees.
0:29:48 > 0:29:50But then there's a really dramatic change
0:29:50 > 0:29:52between seven and six million years ago.
0:29:52 > 0:29:55And, after that, they're eating grasses.
0:29:55 > 0:29:58And the thing is, this sudden switchover isn't confined to North America.
0:29:58 > 0:30:01Here's a graph for South America.
0:30:01 > 0:30:04And here's a graph for Africa and also for Asia.
0:30:04 > 0:30:07You put them together. Look at that.
0:30:08 > 0:30:10What these graphs tell is the same story
0:30:10 > 0:30:15and that is in a period of about one million years, a geological instant,
0:30:15 > 0:30:18the world's herbivores dramatically change their diet,
0:30:18 > 0:30:20so that they're eating the new grasses.
0:30:28 > 0:30:32This discovery proves that, by six million years ago,
0:30:32 > 0:30:34grasses were dominating the land.
0:30:40 > 0:30:44It was a domination that would have striking consequences for many animals...
0:30:50 > 0:30:52INSECT BUZZES
0:30:59 > 0:31:04...and it involved another piece of clever engineering from the grasses.
0:31:09 > 0:31:13Ah, this is it. This is the stuff that I've been looking for.
0:31:13 > 0:31:17This is the sharp stuff. I'm pretty sure of it.
0:31:17 > 0:31:19Let's have a little look.
0:31:21 > 0:31:23Ah, you...
0:31:23 > 0:31:25Ooh. Oh.
0:31:25 > 0:31:28That's something we've all done in the past.
0:31:28 > 0:31:30Cut ourselves on a blade of grass.
0:31:30 > 0:31:32Look at that.
0:31:32 > 0:31:34I'm bleeding.
0:31:34 > 0:31:36But have you ever wondered why that happens?
0:31:36 > 0:31:39It's actually all to do with something that coats
0:31:39 > 0:31:40the edge of the leaf.
0:31:48 > 0:31:52Grass extracts a mineral called silica from the soil.
0:31:56 > 0:32:01The silica is built into row upon row of tiny daggers along the leaf.
0:32:04 > 0:32:07It's a defence to discourage animals from eating it.
0:32:11 > 0:32:13Although tiny,
0:32:13 > 0:32:19these weapons led to one of the biggest extinctions of mammals in Earth's history.
0:32:21 > 0:32:24The world had been full of many different plant eaters
0:32:24 > 0:32:26including the vast balachetherium.
0:32:26 > 0:32:28SNORTING AND GROWLING
0:32:30 > 0:32:34These 20-tonne beasts were the largest mammals ever to exist.
0:32:35 > 0:32:37They fed off trees and shrubs.
0:32:37 > 0:32:41But, as their food source disappeared, these animals died out.
0:32:43 > 0:32:46SNORTING AND GROWLING
0:32:50 > 0:32:52In North America alone,
0:32:52 > 0:32:57grasses led to the extinction of over half of all plant-eating mammals.
0:33:02 > 0:33:04But some herbivores thrived.
0:33:07 > 0:33:09It's all down to the teeth again.
0:33:09 > 0:33:12Who would have thought that gnashers could be so important?
0:33:12 > 0:33:16You can see how the survivors coped, with this skull here.
0:33:16 > 0:33:21They developed harder teeth to bite through that silica-edged grass.
0:33:21 > 0:33:26And also longer grinding teeth so that it didn't matter if they got worn down.
0:33:26 > 0:33:28The creatures adapted.
0:33:28 > 0:33:33And this is one of the results, the jaw of a modern-day horse, like Tank here.
0:33:43 > 0:33:44By six million years ago,
0:33:44 > 0:33:49the triumph of grasses had caused the death of many types of animals,
0:33:49 > 0:33:52while creating vast herds of new ones,
0:33:52 > 0:33:56the more familiar plant eaters we know today.
0:34:02 > 0:34:06ELEPHANTS TRUMPETING But that's just the start.
0:34:06 > 0:34:09Because if you've got herbivores consuming silica-rich grasses,
0:34:09 > 0:34:13all that mineral has to go somewhere...
0:34:15 > 0:34:17...as manure.
0:34:17 > 0:34:23The herds of herbivores were producing millions of tonnes of manure every day.
0:34:27 > 0:34:29It's washed away into rivers...
0:34:31 > 0:34:33...until finally it reached the ocean.
0:34:35 > 0:34:38And within it was all that silica.
0:34:44 > 0:34:49It's out in the oceans that things really began to take off.
0:34:49 > 0:34:51Because it's out here that there's creatures
0:34:51 > 0:34:54that are addicted to this silica.
0:34:57 > 0:35:00These creatures are microscopic...
0:35:01 > 0:35:03...a few hundredths of a millimetre across.
0:35:05 > 0:35:09They're diatoms, a type of green algae.
0:35:11 > 0:35:16Diatoms are wonderfully delicate, like some kind of alien architecture.
0:35:20 > 0:35:25But essential for the construction of their tiny skeletons is silica.
0:35:29 > 0:35:30Five million years ago,
0:35:30 > 0:35:34they were feasting on huge amounts of silica from the grasses.
0:35:38 > 0:35:41For the diatoms, it was like Christmas.
0:35:41 > 0:35:43Their numbers exploded.
0:35:51 > 0:35:56And diatoms are crucial because they form the foundation of the ocean's food chain.
0:35:57 > 0:36:02With more diatoms came huge shoals of anchovies and herring that eat them.
0:36:02 > 0:36:07This in turn attracts predators like seabirds and dolphins
0:36:07 > 0:36:09and even bigger hunters.
0:36:16 > 0:36:20But it's from space you really appreciate their importance.
0:36:20 > 0:36:23They appear as vast green blooms.
0:36:25 > 0:36:28When they bloom, they cover over a tenth of the oceans.
0:36:29 > 0:36:34They're green because like plants diatoms contain chlorophyll
0:36:34 > 0:36:38and like plants they all release oxygen.
0:36:38 > 0:36:40SQUAWKING
0:36:43 > 0:36:46Those photosynthesising diatoms
0:36:46 > 0:36:49produce about a quarter of the oxygen in the atmosphere.
0:36:49 > 0:36:53So, if you like, every fourth breath you take on average
0:36:53 > 0:36:55has been exhaled by the diatoms.
0:36:56 > 0:36:59They really are the lungs of the ocean.
0:37:02 > 0:37:08It's remarkable what the humble grasses had achieved by five million years ago.
0:37:11 > 0:37:15A once-forested planet was now dominated by open plains.
0:37:22 > 0:37:278,000 different species of grasses covering a quarter of all land.
0:37:29 > 0:37:30ELEPHANTS TRUMPET
0:37:30 > 0:37:34They'd selected which animals would live or die.
0:37:38 > 0:37:42And they'd fundamentally altered the oceans
0:37:42 > 0:37:45playing a crucial role in the make-up of our atmosphere.
0:37:50 > 0:37:56Yet perhaps the most important impact of this remarkable plant was still to come.
0:38:02 > 0:38:05The impact on our story.
0:38:08 > 0:38:10Human beings.
0:38:17 > 0:38:21And that's why I've come to the savanna of West Africa.
0:38:24 > 0:38:28I'm in Senegal to see a scientific first.
0:38:28 > 0:38:30It's a discovery that's got profound implications
0:38:30 > 0:38:33for our understanding of our own past,
0:38:33 > 0:38:37because it's here in Africa that our earliest ape ancestors emerged.
0:38:40 > 0:38:42Five million years ago,
0:38:42 > 0:38:45why did one group of apes leave the trees for the savanna
0:38:45 > 0:38:49and develop so differently, eventually becoming human?
0:38:49 > 0:38:54Well, the chimpanzees here might provide some answers.
0:38:54 > 0:38:57Because unlike almost all other chimps in Africa,
0:38:57 > 0:39:01the ones here in Fongoli live on grasslands.
0:39:03 > 0:39:06- Jill!- Heh-hey!- Hey!- Welcome.
0:39:06 > 0:39:07I'm Iain.
0:39:07 > 0:39:11It's what makes them so fascinating to anthropologist Jill Pruetz.
0:39:11 > 0:39:14- All this is HQ, chimp HQ? - Yeah, this is home base.
0:39:14 > 0:39:16Every day we take off wherever they're at.
0:39:21 > 0:39:24Jill has spent ten years studying the Fongoli chimps.
0:39:30 > 0:39:35She's most interested in parallels between the unusual behaviours of these chimps
0:39:35 > 0:39:38and what might have happened during the evolution of human beings.
0:39:38 > 0:39:41Settled round the waterhole like that.
0:39:41 > 0:39:43CHIMPS SCREECHING
0:39:50 > 0:39:51I wasn't expecting that.
0:39:51 > 0:39:54I guess I was expecting them kind of swinging through the trees.
0:39:54 > 0:39:57But look at them. They're just ambling along on all fours.
0:39:57 > 0:40:03Perfectly happy down here on the ground walking through the grass.
0:40:03 > 0:40:06And they look so human. I know, it's obvious. Really obvious thing to say.
0:40:06 > 0:40:09But they just look so human.
0:40:13 > 0:40:17The Fongoli chimps have other human attributes.
0:40:19 > 0:40:24They are proficient at using tools like sticks for collecting termites.
0:40:26 > 0:40:28Many chimps in Africa catch termites this way,
0:40:28 > 0:40:33although these chimps do it more than any others.
0:40:38 > 0:40:44But what makes them really special is a hunting technique, one that is unique.
0:40:45 > 0:40:48I think that probably the most exciting discovery made
0:40:48 > 0:40:52was that they hunt with tools, which before we thought only humans did.
0:40:52 > 0:40:54How is that?
0:40:54 > 0:40:57They'll fashion branches into sort of like a spear
0:40:57 > 0:40:59and they'll use it to jab into these tree holes,
0:40:59 > 0:41:03where you have another kind of primate, a bush baby.
0:41:03 > 0:41:06And then they jab it into the hole.
0:41:07 > 0:41:09Jill's filmed this remarkable behaviour,
0:41:09 > 0:41:12the first time it's ever been recorded.
0:41:15 > 0:41:21It shows a chimp using a spear he's made to stab and kill a mammal,
0:41:21 > 0:41:23a bush baby.
0:41:27 > 0:41:31Yeah, that was something that... again, we used to define humans.
0:41:31 > 0:41:34- Really?- Yeah.- See, that's starting to blur the boundaries.- Yeah.
0:41:39 > 0:41:41CHIMPS SCREECHING
0:41:47 > 0:41:49The chimps of Fongoli are the only ones in the world
0:41:49 > 0:41:53that have been observed using spears to hunt mammals.
0:41:53 > 0:41:55CHIMPS SCREECHING
0:41:56 > 0:41:59Jill believes they've had to come up with this behaviour
0:41:59 > 0:42:02to cope with the harsh and dry grasslands.
0:42:04 > 0:42:07It's a more hostile habitat than the forest
0:42:07 > 0:42:10so the chimps here have to be smarter.
0:42:15 > 0:42:20And Jill has discovered a final extraordinary behaviour of these chimps.
0:42:20 > 0:42:22BIRDSONG
0:42:25 > 0:42:31It also reveals more about how our ancient ancestors might have evolved
0:42:31 > 0:42:32as they moved out of the forests.
0:42:35 > 0:42:38This is a nice one, I think, from the wet season.
0:42:38 > 0:42:42- So, this is a grassland.- I can see a group of them in there.
0:42:42 > 0:42:45- There are three, four of them.- You can see 'em just above the grass.
0:42:45 > 0:42:49But watch... watch what they'll need to do here.
0:42:53 > 0:42:58(LAUGHS) One of them just stood up!
0:42:58 > 0:43:01I mean, he obviously has to do that to see over the grass.
0:43:01 > 0:43:04I want to see that again. Yeah, let me see that.
0:43:14 > 0:43:18Many scientists think this is perhaps a mirror of what happened
0:43:18 > 0:43:22as our own forebears stood up on the grasslands for the first time.
0:43:24 > 0:43:28It allowed them to keep an eye out for predators and prey...
0:43:29 > 0:43:33...and eventually to evolve walking.
0:43:33 > 0:43:37That's incredible to see chimps in the wild standing proud in the savanna grassland.
0:43:37 > 0:43:40- Yeah, yeah.- And looking incredibly comfortable as well.
0:43:40 > 0:43:42It's exciting to see it.
0:43:43 > 0:43:47It's the grasslands that's driving and encouraging them to... develop that way.
0:43:47 > 0:43:52- What, to be more resourceful, more resilient?- I think so. They have to be creative and resilient.
0:43:52 > 0:43:58I've just got this weird feeling that I'm looking at a bit of video from four, five million years ago.
0:43:58 > 0:44:01- Do you know what I mean? That could be the scene.- Mm-hm.
0:44:03 > 0:44:07Here at Fongoli you can actually see what scientists think happened
0:44:07 > 0:44:10when grasses shaped our ancient ancestors
0:44:10 > 0:44:15and encouraged them to make those first upright steps onto the savanna.
0:44:15 > 0:44:19And it really brings home how our human journey
0:44:19 > 0:44:21began on the grasslands.
0:44:40 > 0:44:46Over the next five million years, these ape men continued to evolve in Africa...
0:44:48 > 0:44:52...until eventually they became homo sapiens.
0:44:54 > 0:44:58And then 100,000 years ago, these new people,
0:44:58 > 0:45:02for they really were people now, like you and me,
0:45:02 > 0:45:04began to migrate across the rest of the world.
0:45:07 > 0:45:12At this point in time, our ancestors were hunter-gatherers.
0:45:14 > 0:45:17They were living a tough life in small family groups,
0:45:17 > 0:45:21killing wild animals and collecting berries and roots to eat.
0:45:23 > 0:45:25But grasses hadn't finished with us...
0:45:26 > 0:45:32...because they'd trigger the greatest revolution in humankind's existence.
0:45:40 > 0:45:42SCRAPES EARTH
0:45:47 > 0:45:50It's not in Africa but here in southern Turkey
0:45:50 > 0:45:55that archaeologists believe they've discovered why that revolution happened.
0:45:58 > 0:46:01The place is called Gobekli Tepe.
0:46:04 > 0:46:09For me, this is one of the most exciting sites of modern archaeology,
0:46:09 > 0:46:13because here at Gobekli Tepe are some of the oldest buildings in the world.
0:46:13 > 0:46:17They date to nearly three times the age of the first Egyptian pyramids.
0:46:17 > 0:46:19And there's a real... there's a real mystery here.
0:46:19 > 0:46:21Who built this place?
0:46:21 > 0:46:25And more importantly, how could they have done it?
0:46:40 > 0:46:45This astonishing structure is 12,000 years old.
0:46:46 > 0:46:50It lay buried and undiscovered until 1994.
0:46:52 > 0:46:54Hello.
0:46:54 > 0:46:55Hello again.
0:46:55 > 0:46:58The archaeologist who unearthed it is Klaus Schmidt.
0:46:58 > 0:47:03- It's great to be here. - Welcome in enclosure C.- Enclosure C!
0:47:03 > 0:47:08What a place! It's spectacular, isn't it? I mean, these are great.
0:47:08 > 0:47:09Big question is, "who were they"?
0:47:09 > 0:47:14One thing is very important. Never a face is depicted. They are always faceless.
0:47:14 > 0:47:18- I saw you working on a very sophisticated one here.- Yeah.
0:47:18 > 0:47:19This looks amazing. What is it?
0:47:19 > 0:47:23It's a masterpiece of craftsmanship. It's made from one stone.
0:47:23 > 0:47:25And we have a flat relief of a boar,
0:47:25 > 0:47:27and we have this high relief of a leopard.
0:47:27 > 0:47:30This is an extremely complex society.
0:47:30 > 0:47:33Yes, and this is a surprise. We didn't expect this.
0:47:33 > 0:47:38What we are doing here, we are at a chapter in world history,
0:47:38 > 0:47:41a chapter which we didn't know existed before.
0:47:41 > 0:47:42Yeah.
0:47:45 > 0:47:49To construct Gobekli Tepe with its 50-tonne megaliths
0:47:49 > 0:47:53would have needed a huge army of well-organised workers.
0:47:57 > 0:48:01Yet 12,000 years ago was the Stone Age,
0:48:01 > 0:48:04a time when people were supposed to be hunter-gatherers
0:48:04 > 0:48:06living in small groups.
0:48:09 > 0:48:15How did they sustain the numbers essential to build such a vast temple?
0:48:23 > 0:48:26The answer lies a short distance away.
0:48:43 > 0:48:48Within sight of Gobekli Tepe are the Karacadag Mountains.
0:48:48 > 0:48:52Here something happened at this time that would change our world forever.
0:48:59 > 0:49:03It was all to do with one particular type of grass.
0:49:05 > 0:49:10It's an ancient type of wheat which grew totally wild, just as it does today.
0:49:10 > 0:49:12It's called einkorn wheat.
0:49:16 > 0:49:2112,000 years ago was a time before farming.
0:49:21 > 0:49:25The people here would have been desperate for whatever nutrition they could gather.
0:49:30 > 0:49:33Yet collecting it presented a huge problem.
0:49:33 > 0:49:35Let me show you why.
0:49:36 > 0:49:40When the head of the wheat's ripe, then just the tiniest of touches,
0:49:40 > 0:49:41and look what happens.
0:49:41 > 0:49:44It just scatters everywhere.
0:49:48 > 0:49:52And that's because the seed is attached to the plant so precariously.
0:49:52 > 0:49:55Imagine if you were trying to collect enough seed for a meal.
0:49:55 > 0:49:57I mean, I can hardly even see where they are.
0:49:57 > 0:50:00There's one. Ah, don't...
0:50:00 > 0:50:02It would drive you mad.
0:50:10 > 0:50:13Frankly, it's hard to believe anyone would bother.
0:50:13 > 0:50:19But everything was about to change, triggered by a crucial event.
0:50:21 > 0:50:25A tiny alteration in the genetic makeup of a wild wheat plant.
0:50:26 > 0:50:28Just one gene.
0:50:28 > 0:50:31In just one single plant.
0:50:31 > 0:50:33CHILDREN CHATTER
0:50:36 > 0:50:40That mutation has been traced back to here,
0:50:40 > 0:50:42just 30 kilometres from Gobekli Tepe.
0:50:47 > 0:50:48If you look closely
0:50:48 > 0:50:51you can see the difference between the two types of wheat.
0:50:55 > 0:50:57In the original wild wheat,
0:50:57 > 0:51:02a special ridge of cells between the stalk and the seed breaks down
0:51:02 > 0:51:04as the plant ripens
0:51:04 > 0:51:07and this allows the seed to fall away.
0:51:10 > 0:51:15But in the wheat with the genetic mutation these cells remain as a solid band.
0:51:20 > 0:51:23It means the new wheat never lets go of its seeds.
0:51:25 > 0:51:29Under normal circumstances in the wild that would doom the plant,
0:51:29 > 0:51:31because it just couldn't scatter the seeds.
0:51:31 > 0:51:33Look, you bang it and nothing happens.
0:51:33 > 0:51:39But it turns out that for one animal species this trait was really beneficial.
0:51:39 > 0:51:40Us.
0:51:56 > 0:51:58LOW CHATTER
0:52:05 > 0:52:08Because the seed remained on the stalk after it had ripened,
0:52:08 > 0:52:12it meant that not only could the people who lived here collect more grain,
0:52:12 > 0:52:13they could also begin to farm it.
0:52:13 > 0:52:17In other words they could take some of the spare seeds at the end of a season,
0:52:17 > 0:52:21put it back in the ground and then harvest the new plants the following year.
0:52:21 > 0:52:24It was the dawn of domesticated wheat.
0:52:38 > 0:52:41And this wheat gave us bread.
0:52:43 > 0:52:46A fabulously concentrated form of energy.
0:52:46 > 0:52:50It could be carried, it could be divided up, it could be stored.
0:52:52 > 0:52:56And in turn, bread would lead to something even bigger.
0:53:03 > 0:53:06In order to build Gobekli Tepe,
0:53:06 > 0:53:10the Stone Age people turned their back on hunter-gathering.
0:53:13 > 0:53:15They became the first farmers.
0:53:20 > 0:53:2412,000 years ago, they began to sustain themselves with bread...
0:53:25 > 0:53:28...made from the grass we call wheat.
0:53:34 > 0:53:36Now they could feed the huge workforce
0:53:36 > 0:53:40required to construct such a vast and sophisticated temple.
0:53:43 > 0:53:46The mystery of Gobekli Tepe was solved.
0:53:47 > 0:53:52People had been hunter-gatherers, and now this site marks the end of that time,
0:53:52 > 0:53:54the end of that period and the beginning of a new age.
0:53:57 > 0:54:01So Gobekli Tepe is part of that chain reaction? It's a cultural...
0:54:01 > 0:54:03- The people in Gobekli Tepe... - Yeah.
0:54:03 > 0:54:06...are the first people having bread also in their villages,
0:54:06 > 0:54:08not only here but also in the villages.
0:54:08 > 0:54:12- That's incredible to think that these were the first people to taste bread.- Yeah.
0:54:12 > 0:54:18And the idea, then, that it was bread that was the kind of energy source, essentially, the sustenance.
0:54:18 > 0:54:21Exactly, exactly. It's a turning point in world history.
0:54:39 > 0:54:41There's one last thing that I find intriguing.
0:54:43 > 0:54:46Our ancestors must have felt that they were the masters of this new crop,
0:54:46 > 0:54:49in the same way that we still feel today about farming.
0:54:49 > 0:54:52You know, we are in control of the plants that we grow and harvest.
0:54:52 > 0:54:56But think of it for a minute from the wheat's point of view.
0:54:56 > 0:54:59I mean, here's a plant that's done something really clever.
0:54:59 > 0:55:03It's attracted an animal that's prepared to sow it, to nurture it,
0:55:03 > 0:55:07to protect it from competitors and scavengers.
0:55:07 > 0:55:10It's also prepared to disperse its seed by hand
0:55:10 > 0:55:13without the plant having to do a single thing.
0:55:15 > 0:55:18So, it begs the question, who's using who?
0:55:31 > 0:55:36Human beings had now invented a way of harnessing the power of plants
0:55:36 > 0:55:40and once invented it could never be reversed
0:55:40 > 0:55:45because farming allowed us to come together in bigger and bigger groups,
0:55:45 > 0:55:49to build villages, towns, and eventually cities.
0:56:01 > 0:56:04A world once dominated by forests and dinosaurs
0:56:04 > 0:56:07had given way to a world of our own making.
0:56:16 > 0:56:21I've always been fascinated by how our planet changes over time,
0:56:21 > 0:56:24over the four and a half billion years of Earth history.
0:56:24 > 0:56:27And what's astounding is how important plants have been
0:56:27 > 0:56:31in changing that original lifeless rock
0:56:31 > 0:56:35into this vital and vibrant world that we live in today.
0:56:35 > 0:56:37Our home.
0:56:39 > 0:56:44Over this series we've seen how plants gave us the oxygen and the atmosphere.
0:56:47 > 0:56:51We've watched as the rise of flowers painted a drab world
0:56:51 > 0:56:52with brilliant colour.
0:56:54 > 0:56:57And we've discovered how plants shape the animal kingdom.
0:57:04 > 0:57:09And, for us, the humble grasses play the most important role of all.
0:57:09 > 0:57:12They drove the rise of our apelike ancestors
0:57:12 > 0:57:17and ultimately triggered the birth of civilisation.
0:57:17 > 0:57:21Plants made us and the world we live in.
0:57:33 > 0:57:38Subtitles by Red Bee Media Ltd