Skip to playerSkip to main contentSkip to footer
GreatBritish1
  • 2 days ago
HTGAP episode 1
Transcript
00:00:00I spent most of my life trying to understand the forces that shaped our planet.
00:00:13And as a geologist, it always seemed to me that rocks were right at the heart of things.
00:00:23But now, I'm discovering it's not only volcanoes and colliding continents
00:00:28that have driven the Earth's greatest changes.
00:00:32Because at crucial moments in its history, another force has helped create the planet we live on.
00:00:40Plants.
00:00:42Just look at this seed.
00:00:44It's small, it's brown, it weighs hardly anything.
00:00:47It looks pretty ordinary.
00:00:48But actually nothing can be further from the truth because what it will become is truly extraordinary.
00:00:58These are giant sequoias.
00:01:05Some are over 3,000 years old.
00:01:11And sequoias are the largest single life form on Earth.
00:01:15All from a tiny seed.
00:01:18Yet even that pales into insignificance when compared to what the whole of the plant kingdom's done throughout the history of our planet.
00:01:29They harmless light from a star, bringing energy to our world.
00:01:34They and their ancestors created a life-giving atmosphere.
00:01:38And breathed an oxygen that was made two and a half billion years ago.
00:01:47They sculpted the very surface of the Earth.
00:01:51And they drove the evolution of all animals.
00:01:55What are we here?
00:01:57Including our own ancestors.
00:01:58It's a whole new story about our Earth.
00:02:08Told through remarkable images.
00:02:11Captured for the very first time.
00:02:16And the latest scientific discoveries.
00:02:19Wish me luck.
00:02:20This is the start of that story.
00:02:30How plants took a barren alien rock, our planet, and transformed it into the home we know today.
00:02:36What do we know today?
00:02:54It's a long way down.
00:02:57I'm in central Vietnam.
00:03:00And I'm descending into one of the largest caves in the world.
00:03:03Look at those structures.
00:03:05Absolutely fantastic.
00:03:12At seven kilometres long, this is known as Hansong Dung.
00:03:20It's a dark alien world.
00:03:23Down here, very little is alive.
00:03:26But I'm not here for the cave.
00:03:33Oh, look at that.
00:03:38For goodness sake.
00:03:43It looks like the roof has collapsed.
00:03:46And the rainforest has just invaded.
00:03:48It's a rainforest inside a cave.
00:03:51After being in the darkness and the black for ages.
00:03:55Look at that.
00:03:56You just suddenly see brilliant green.
00:03:59This isn't the entrance.
00:04:02We're three kilometres into the heart of the cave system.
00:04:06It's a thriving lost world with towering polyalthea trees.
00:04:15And home to strange creatures like this Vietnamese flat-backed millipede.
00:04:20Isn't that incredible?
00:04:21It's got antlers.
00:04:23You really feel as if you've left the confines of that cave and just escaped really into this fantastic forest.
00:04:38It's a wonderland really.
00:04:40This rainforest exists because of one thing above all.
00:04:45Something which has enabled plants to colonise almost everywhere on Earth.
00:04:52Light.
00:04:56Light which has travelled 150 million kilometres from the sun.
00:05:01Plants have this truly remarkable ability to harness energy from outer space to produce food.
00:05:11It's this ability to eat the sun.
00:05:14To manufacture life from light.
00:05:17It's allowed plants to dominate our planet.
00:05:23This is the most important natural process on Earth.
00:05:26It's how the plant kingdom has transformed a lifeless planet into a living world.
00:05:42But it wasn't always like this.
00:05:47And to see how it started, we need to go back three billion years.
00:05:56To begin with, our planet was like an alien world.
00:06:05There was very little oxygen.
00:06:09The atmosphere was a cocktail of toxic gases.
00:06:13Like methane and sulphur dioxide.
00:06:17The land was lifeless.
00:06:20This barren salt pan in southern Kenya is as close as you can get in the modern day Earth to that ancient world three billion years ago.
00:06:32But the one crucial difference between the planet then and the planet now is that back then, it had been burnt to a crisp.
00:06:38That's because the primitive atmosphere couldn't screen out the sun's powerful ultraviolet rays.
00:06:53Back then, these UV rays were hundreds of times stronger than they are now.
00:06:58Nothing could survive on land.
00:07:08Yet all this was about to change.
00:07:12A momentous event that would create the planet's first life-supporting atmosphere.
00:07:19This event, between three and two and a half billion years ago, was the single greatest turning point in the history of life on Earth.
00:07:33And it was all brought about by the earliest ancestors of plants.
00:07:38Here at the Sishin Iron Mine in South Africa, evidence of that epic event can still be unearthed today.
00:07:57But to get to it, you need a bit of help.
00:08:0030 seconds.
00:08:06In.
00:08:23That has 200,000 tonnes of iron ore just been blasted apart.
00:08:27These explosions open a cross-section back in time to the distant origins of the plant kingdom.
00:08:43This is iron ore.
00:08:44It's so heavy.
00:08:46Now, pure iron's got this metallic glint.
00:08:50It's shiny, but you can see that this, it's got loads of red in it.
00:08:53And it's red for a really simple reason.
00:08:57It's rusted.
00:08:58It's rusted because it's come into contact with oxygen.
00:09:01Oxygen produced by the very first burst of life.
00:09:09The miners want the ore for its iron content.
00:09:12But I'm going to use this iron oxide for a very different reason.
00:09:16Something I don't think's ever been done before.
00:09:19Just why I'm a wee bit excited.
00:09:23I've taken a chunk of the iron oxide rock and had it ground up into a fine powder.
00:09:31It's then been turned into a solution.
00:09:34One I'm hoping will allow me to take a breath from the planet's earliest oxygen.
00:09:41Oxygen made by the ancient ancestors of plants.
00:09:44And now what I'm going to do is kind of jump start it really with this battery.
00:09:50I'm going to attach a lead and pass an electric current through it.
00:09:54And we should see a simple reaction.
00:09:59Oh, yeah, yeah.
00:10:01Yeah, there's some bubbles coming off.
00:10:03These bubbles are the gas oxygen.
00:10:08It's being released for the first time in over two and a half billion years,
00:10:14when it was locked away in the rock.
00:10:17There's a lovely little train of them just rising up to the top of the test tube
00:10:21and falling in a little pocket of gas.
00:10:22You're never sure with these experiments whether you're really going to get it or not,
00:10:28but that's exactly what I was hoping to see.
00:10:33In just one hour, I've collected enough to fill the whole test tube.
00:10:36The thing is, this isn't any old oxygen.
00:10:46This is oxygen that's come from those iron bands.
00:10:49The very oxygen that changed our planet.
00:10:53In fact, I can't resist it.
00:10:55We have to.
00:11:01I can't believe it.
00:11:02I'm breathing oxygen that was made two and a half billion years ago.
00:11:08It's all gone.
00:11:10Liberated from the rocks now.
00:11:12It's up there somewhere.
00:11:16These iron bands tell a remarkable story.
00:11:20Oxygen was now flooding the Earth's atmosphere.
00:11:23It cleaned out the planet's toxic gases.
00:11:33Leaving the sky a clear blue for the first time.
00:11:42Geologists call it the Great Oxidation Event.
00:11:46And it certainly was an event.
00:11:48This was an irreversible change between two very different worlds.
00:11:51A planet with virtually no free oxygen.
00:11:55And a planet full of oxygen.
00:11:57This was the greatest change in the history of life on Earth.
00:12:04So how did this great event happen?
00:12:07The answer lies with the first burst of life,
00:12:11which emerged not on the hostile land, but under water.
00:12:15Back then, water acted as a liquid sunscreen to the dangerous UV rays.
00:12:23Under the protection of water, the earliest organisms on Earth evolved
00:12:28in the form of tiny bacteria.
00:12:31And here in East Africa is a rare chance to see what it would have been like.
00:12:36This is Lake Magaddy.
00:12:38The waters here are just super salty.
00:12:40I can feel it nipping away at my feet.
00:12:43But the bacteria I'm wading through are close descendants of the very first microorganisms that lived 3 billion years ago.
00:12:55It's fantastic to think that swimming in the top layer here are some of the most primitive life forms on Earth.
00:13:04And those bacteria, just like the ones all that time ago, have got something surprising about them.
00:13:09They're purple.
00:13:18These are hallow bacteria.
00:13:20And they didn't just occupy the occasional lake.
00:13:23Much of the world's oceans were purple too.
00:13:30Imagine that from outer space.
00:13:34A purple Earth.
00:13:39The purple bacteria lived by harnessing energy from the sun.
00:13:47But they only used part of the light.
00:13:50Some rays passed deeper into the water.
00:13:54And over time, down there, a different type of bacteria evolved.
00:14:00They had to live off the colours of light left over.
00:14:04This made them appear green.
00:14:06These were the green bacteria.
00:14:10This seemingly arbitrary event, a bacteria absorbing one colour of light rather than another, would have colossal repercussions for the planet.
00:14:21Over time, these green bacteria, a type of cyanobacteria, came to dominate the waters of the world.
00:14:31Eventually, as we'll see, these green microorganisms became the ancestor of all plants on Earth.
00:14:40And because right from the start they were reflecting green light, the stalks of the plants became green, and the leaves were green.
00:14:47In fact, that's why all plants on Earth became green, from the grasses to the forests.
00:14:53And it's also why, today, instead of living on a purple planet, we've got a green one.
00:14:58We've got a green one.
00:15:08But it wasn't just about colour.
00:15:11Because the green bacteria did something their purple cousins couldn't.
00:15:15They produced oxygen.
00:15:16They would breathe life into the lifeless land.
00:15:26Without them, the story of our planet would be more like that of Mars.
00:15:30How the green bacteria did this is so complex that scientists still grapple with the details.
00:15:43I've come to the Eden Project in Cornwall to try to understand it.
00:15:50I'm to be the subject of an experiment that's never been attempted before.
00:15:55Hi. Hello there.
00:15:57I'm the guinea pig. Doctor, I presume.
00:15:59Indeed. Dan Martin.
00:16:01Hiya. Hi, Katrina. Hi.
00:16:03Nice to meet you. This is fantastic.
00:16:05Incredible, isn't it?
00:16:07I'm about to be locked inside this airtight chamber.
00:16:10I hope to experience first-hand my very own great oxidation event.
00:16:16OK, everyone, I'm going to start reducing the oxygen concentration in here now.
00:16:20The first step is to lower oxygen levels closer to those of the early Earth.
00:16:29So, first of all, this is going to mount your heart rate and your oxygen levels.
00:16:33OK.
00:16:34So, if we pop that and we can just have a look here.
00:16:37It's a lack of oxygen that complex life, like us, can't operate at for long.
00:16:43So, at the top is your heart rate.
00:16:46How's that? Is that really high?
00:16:47I think you might be a little bit anxious about going in there.
00:16:51I am, a little bit.
00:16:52I'm sure your resting heart rate's not normally 95.
00:16:55No, I have been thinking a lot about it, I have to say.
00:16:58My vital signs have been monitored, along with the oxygen levels in my blood.
00:17:03Now it's time to be sealed inside the chamber for the next 48 hours.
00:17:08I'm as ready as a liver beer guy, so can we all open this door?
00:17:15Wish me luck.
00:17:17Oh, it's small, isn't it?
00:17:22Oxygen levels in the air are normally 21%.
00:17:32Inside the chamber, they're far lower.
00:17:36Just over 12%.
00:17:38At these concentrations, the cellular activity in my body and brain is starting to slow down.
00:17:47Go.
00:17:49Green, yellow, red, green, yeah, it's kind of orange, purple, blue.
00:17:57You'll find that thinking becomes a little bit slower.
00:18:02My hand-to-eye coordination is being impaired.
00:18:07You can put them in any order you like.
00:18:10That's the way.
00:18:12Can you just tell us how exactly are you feeling?
00:18:13Yeah, it's funny, I felt very slow.
00:18:16Yeah, that slow, slowness is there, definitely.
00:18:23The doctors calculate that at the rate I use up oxygen,
00:18:27if it carried on like this, I'd be unconscious in just 24 hours.
00:18:32Your oxygen saturation, sort of 88%.
00:18:36If that was your level in hospital, we'd be pretty worried about you right now.
00:18:39The next crucial step is to see if the 300 plants in here with me
00:18:45can produce enough oxygen to keep me alive.
00:18:50It's all to do with a wondrous ability they inherited from those green bacteria.
00:18:56It's photosynthesis, of course.
00:19:00I think we can have the lights on, please.
00:19:03To kick-start it, you need light.
00:19:06You need light.
00:19:09Wow, suddenly the lights hit.
00:19:18Plants use photosynthesis to live and grow,
00:19:21and most importantly for me, to make oxygen.
00:19:28Photosynthesis is an intricate process that science is still trying to unlock.
00:19:33But the production of oxygen is one of its key features.
00:19:40To understand what's happening, you need to enter a complex and microscopic world.
00:19:47Inside every leaf, of every plant on the planet, are the direct descendants of those first green bacteria.
00:19:57Magnify a leaf a thousand times and you can see them.
00:20:02They're known as chloroplasts, packed into every cell.
00:20:07They still behave a bit like bacteria.
00:20:12This is real footage of them moving towards a flash of light.
00:20:22They're just five thousandths of a millimetre across.
00:20:27And it's inside chloroplasts that photosynthesis happens.
00:20:32Light rays from the sun are made of photons.
00:20:38They're tiny, fast-moving particles of electromagnetic energy.
00:20:44When they hit the surface, the energy of the photons is captured by a ring,
00:20:49called the light-harvesting complex.
00:20:59Inside this structure, the energy of two photons is used to split a water molecule.
00:21:04It's ripped into its two elements, hydrogen and oxygen.
00:21:19The plant uses the hydrogen to live and grow.
00:21:22But right now I'm interested in the other part of the water.
00:21:28The part plants pump out as a waste product.
00:21:32The oxygen.
00:21:33Scientists have calculated that the 300 plants in here with me
00:21:52should raise oxygen levels in this chamber from 12 to 21% within 48 hours.
00:21:58I'm finding out how reliable the process of photosynthesis really is.
00:22:10It is quite concerning. You've been very busy this afternoon.
00:22:14A lot of activity, so...
00:22:16We need to restrict the amount that you're talking.
00:22:19And really get you resting as much as possible.
00:22:22Not dashing around the chamber any more.
00:22:24This is doctor's orders. Bed rest.
00:22:26Night-night.
00:22:28Night-night.
00:22:34As I drift off to sleep, the 11,000 leaves go to work.
00:22:43They have 30 cubic metres of the box to fill.
00:22:48Some plants, like this maize and the banana plant,
00:22:53are particularly efficient at pumping out oxygen.
00:22:54So you can see the increase every hour here.
00:22:55That's incredible, really.
00:22:56Yeah.
00:22:57They're really pushing out a lot of oxygen, as you can see.
00:23:00Every hour, my plants are producing over 40 litres of oxygen.
00:23:04Hi.
00:23:05It's Katrina.
00:23:06We're now 41 hours in.
00:23:07Really?
00:23:0841 hours in?
00:23:09Yeah.
00:23:10Yeah.
00:23:11So the oxygen levels are still climbing gradually every hour, so it's going really well.
00:23:15With my vital signs returning to normal, I'm now a top attraction at the Eden Project.
00:23:16Hello.
00:23:17Hello.
00:23:18Hello.
00:23:19Hello.
00:23:20Can you see him?
00:23:21What are you doing in that box?
00:23:22He looks very happy in there, doesn't he?
00:23:23He looks very happy in there, doesn't he?
00:23:24He's measuring his oxygen levels.
00:23:25Eat your heart out, David Blaine.
00:23:26Finally after 40 long hours, oxygen levels are almost back to normal.
00:23:51after 48 long hours, oxygen levels are almost back to normal. The plants have triumphed.
00:24:05Whee! Oh, I'm out. Ah, I survived it. Fantastic. It's amazing. I was just thinking that I've
00:24:15survived, but actually, I guess I've really survived because of them, because of the plants.
00:24:21I leave here thinking that I needed those plants way more than they needed me. It's easy to
00:24:27think of this as just an experiment, but to me, when you're lying in there, you realise
00:24:31that this place is a metaphor for something much bigger, for the planet really, and for
00:24:36our relationship with plants through photosynthesis to keep life going. The early earth was like
00:24:45my chamber. It was transformed from a world with very little oxygen to a world rich in oxygen.
00:24:53And all that oxygen began to do something else. High in the stratosphere, it created ozone.
00:25:00This was a protective blanket, which enveloped the earth and blocked most of the sun's dangerous
00:25:11UV rays. It meant that for the first time in the planet's history, plants could move on to
00:25:19the land. But it was no small step. The thing is, if you'd been protected by water for billions
00:25:37of years, then the move to the land was going to be a root shock. Yet over 400 million years
00:25:44ago, plants finally made that leap. Surprisingly, the best evidence for these pioneers doesn't
00:25:54come from some exotic corner of our planet, but from Britain. I've come to just outside the
00:26:05village of Rhiney in North East Scotland to see this. A stone wall. But not just any stone
00:26:11wall, of course. For me, this is the most important stone wall in the history of science.
00:26:24Scotland was located well south of the equator and looked like another world. Hot springs and
00:26:41geysers boiled out across a rocky and barren landscape. But something else was happening.
00:26:53A scientist discover when they came across some curious markings on this wall. And this is one
00:26:59of them. Look at this. You see these really strange, elongated kind of shapes here. And at
00:27:05first people just didn't really know what they were. They thought maybe at first it was some
00:27:09kind of lava. But when they looked really closely, especially when they got it cut and polished,
00:27:14this rock literally came alive. Because you can see these dark features here. They realised that this
00:27:28was something that was once living. And when they were alive, this is what they looked like.
00:27:36Just a few centimetres tall, they're called aglophyton. Bulbous shapes on the end of naked stems.
00:27:53A time before leaves or roots. Yet somehow these bizarre life forms survived along the water's edge.
00:28:02What geologists had found right here in Scotland were some of the earliest pioneering plants to make
00:28:08that giant leap. To colonise the land. And around this time, all along the margins of lakes and rivers,
00:28:21primitive plants were coming ashore. For the first time when viewed from space, the land began to look alive.
00:28:33The beginning of a transformation from hostile world to fertile earth.
00:28:43Yet this wasn't a full-scale invasion. Just a toehold.
00:28:49Plants were still tied to the water's edge, unable to head inland and penetrate the harsh, rocky surface.
00:28:58But all this was about to change.
00:29:04Plants evolved and inspired the solution to the problem. A brilliant device for collecting water and nutrients.
00:29:10And something that they never really had before. Roots.
00:29:14Cambodia. The 12th century temple here at Taprom is a wonder of civilisation.
00:29:31But it's also a wonder of the natural world.
00:29:34Although the roots of these strangler things are very different from the first ones to evolve,
00:29:40it's a superb place to reveal how roots allowed plants to invade inland.
00:29:50Roots are hugely powerful. I mean, I love this one.
00:29:53Look at it, prizing its way into that roof, just lifting that whole structure up.
00:29:58And then boring down here through these stone blocks and then disappearing.
00:30:02Just tiny pressures exerted over decades and centuries.
00:30:09Add these up and you get phenomenal strength.
00:30:14A pressure of up to 10 kilograms per square centimetre.
00:30:18Around 400 million years ago, the first roots appeared.
00:30:23And gave plants the ability to smash up the rocky planet.
00:30:32And this created a vital ingredient for life on land.
00:30:39When the tiny broken up fragments of rock get mixed up with kind of dead plant material,
00:30:44it ends up as this ideal environment for storing water.
00:30:50An environment that we call...soil.
00:30:56Today, soil covers 40% of the planet's land.
00:31:00It takes a long time to form.
00:31:03A thousand years to make just two centimetres of soil.
00:31:06But it's essential for plant life.
00:31:09Just as it was back then.
00:31:14Because the primitive, leafless plants could now break free from the water's edge.
00:31:22Roots and the soil they created made plants unstoppable.
00:31:28Allowing them to colonise inland for the first time.
00:31:33An invasion that would have a dramatic influence on all life on Earth.
00:31:46For millions of years, animals had been confined to the rivers and oceans.
00:31:52Now they could finally emerge from the water.
00:31:55And get an idea of those first tentative steps by travelling back in time with a creature that's barely changed for 500 million years.
00:32:08I've come to the east coast of America, where these ancient creatures still come ashore at dusk to mate.
00:32:28Here they are.
00:32:30Horseshoe crabs.
00:32:34Looks like something from another planet.
00:32:36You can see the two main eyes here, but they've got something like ten eyes scattered across their body.
00:32:44And the really weird bit is if you lift them up.
00:32:49I mean, look at that.
00:32:51For a start they've got five pairs of legs.
00:32:53One, two, three, four, five.
00:32:55Whereas normal crabs just have four.
00:32:57They're actually more related to the scorpion than to normal crabs.
00:33:00Look at that.
00:33:01But the really interesting bit is tucked under here.
00:33:05You've got these things called bookgills.
00:33:07Look at that there.
00:33:09It's like sheaves of a book.
00:33:11And that allows them to extract oxygen, not just from the water, but also from the air.
00:33:16It's an amazing breathing apparatus.
00:33:18Got to put her back now.
00:33:21Come on, dear.
00:33:23There you go.
00:33:29As long as they're kept moist, these lung-like gills enable the crabs to stay out of water for days at a time.
00:33:37Fossils show that horseshoe crabs appeared on land at least 400 million years ago.
00:33:44They're some of the first animals ever to come ashore.
00:33:55Amphibians and insects soon followed.
00:33:59Oxygen allowed them to move onto land.
00:34:02But something else was also enticing them.
00:34:08It's funny.
00:34:09Plants create oxygen as a waste product.
00:34:11And it's that waste product that has transformed our atmosphere.
00:34:16But, of course, the main reason that plants photosynthesize is to create sugars.
00:34:21Sugars that are vital for plants to live and to grow.
00:34:24And also provide a source of food for all animals.
00:34:27Plants make this sugar from water, carbon dioxide from the air, and energy from the sun.
00:34:43And, again, it all happens in those tiny chloroplasts.
00:34:52We've seen how light splits water into oxygen and hydrogen.
00:34:57Well, the plant takes that hydrogen and combines it with carbon dioxide to make sugar.
00:35:05By exposing a plant to carbon dioxide tagged with a radioactive marker, you can see the sugar being created.
00:35:18For the first time, scientists have imaged its creation and movement through a plant.
00:35:22In this case, maize.
00:35:28As soon as carbon dioxide is sucked into the plant cells, they begin to glow.
00:35:35This is the actual moment that photosynthesis turns the carbon dioxide into sugar.
00:35:41In just 15 minutes, the newly formed sugar is sent to the roots for storage.
00:35:52The plant can then use this sugar to grow and thrive.
00:35:59That's why photosynthesis is nature's most astonishing achievement.
00:36:03The ability of plants to be powered by light from beyond our planet sets them apart from all other life.
00:36:12And that connection with that star, our sun, makes plants a foundation stone for all living things.
00:36:20It's just such a wonderful thought.
00:36:22400 million years ago, leafless plants were flourishing like never before.
00:36:37But a dramatic transformation of the atmosphere was about to throw plants into a global crisis.
00:36:45Not only would it change their shape, it would change all life on our planet.
00:36:52This is Lake Tarawera in New Zealand.
00:37:13This ancient landscape is home to a plant that 360 million years ago
00:37:22confronted that crisis and came up with an inspired solution.
00:37:30Looks like the land that time forgot, doesn't it?
00:37:33Just that strange mixture of different shapes of plants and trees.
00:37:37Really unfamiliar and alien.
00:37:39It's almost primeval.
00:37:40The early plants had become victims of their own success.
00:37:48They were gorging on so much carbon dioxide in the atmosphere that they were using it up.
00:37:55Levels plummeted by 90%.
00:37:58Without enough of this vital gas, plants began struggling.
00:38:05If they couldn't find a way to breathe in more carbon dioxide, they'd suffocate.
00:38:11The early plants, plants like these gorgeous ferns here, came up with a remarkable new structure.
00:38:22Large flat surfaces that house within them a complex breathing apparatus.
00:38:26We call them leaves.
00:38:34Leaves were the answer to all plants' breathing problems.
00:38:38They massively increased their surface area by over a hundredfold,
00:38:44allowing them to absorb far more carbon dioxide.
00:38:47Now, for the first time, shade was cast by a beautiful and delicate canopy, like these Dixonia.
00:39:00These ferns are incredible.
00:39:03They like giant umbrellas.
00:39:07The key to this advanced breathing apparatus is on the underside of each fern leaf.
00:39:13They're microscopic holes called stomata.
00:39:20Filmed in action with an electron microscope, this is them opening and closing.
00:39:26Speeded up 140 times.
00:39:38There are thousands of stomata on every leaf on Earth.
00:39:41They allow a single fern to breathe in five litres of carbon dioxide a day.
00:40:00The evolution of leaves, rich in stomata, save plants from suffocation.
00:40:04But leaves also allowed plants to capture more light.
00:40:13This in turn field fierce competition.
00:40:16Each plant desperate for the sun's rays.
00:40:21This family squabble would lead to a new type of plant.
00:40:25One that would have surprising repercussions for the planet.
00:40:34How do we know?
00:40:36Well, it's all thanks to some rare evidence here in Nova Scotia in Canada.
00:40:39To reach it, you have to abseil to the bottom of this 30-metre cliff.
00:40:48Here, scientists discovered the remains of a mysterious world.
00:40:53You know, this is just the best way to see rocks.
00:40:58You really feel as if you're a time traveller, peeling back the layers of history one by one as you go down.
00:41:03I mean, these rocks are over 300 million years old.
00:41:11But it's what's locked inside the rocks at the base of this cliff that took scientists' breath away.
00:41:16These fossilised remains are just spectacular.
00:41:26I mean, look at the texture.
00:41:28You can tell it's a plant, but this isn't some big shrub or overgrown fern.
00:41:33You can see here, look, you can get traces of bark.
00:41:37And down here, you can see there's some roots coming off.
00:41:40This is completely extinct. You don't get this anymore.
00:41:42What I'm actually crouching beside is one of the planet's very early tree trunks.
00:41:48And not just one tree, cos look here.
00:41:50There's another one here.
00:41:53There's another one there.
00:41:57This is a fossil forest.
00:42:02These lepidodendron trees had strange diamond-shaped bark.
00:42:08Each diamond sprouting a needle-like leaf.
00:42:10Over 300 million years ago, they made up the planet's first tropical forests.
00:42:19Found in swamps throughout the Earth's tropics, these first forests were so extensive, you'd have seen a band of dark green from space.
00:42:39And all those new leaves were pumping out oxygen.
00:42:47So much that levels of oxygen increased to not far off double what they are today.
00:42:53It was having a very odd effect on animals.
00:43:00In particular, insects and their cousins.
00:43:05Instead of lungs, invertebrates have simple breathing tubes that rely on diffusion for oxygen to reach their internal organs.
00:43:15The size of these animals is therefore limited by the concentration of oxygen in the air.
00:43:23Increase the oxygen, just as the first forest did, and things get interesting.
00:43:29Do you see these markings on the rock here?
00:43:37There's two lines of little dents, one here and one here.
00:43:41They are fossilised footprints that date back to the very early forests.
00:43:45When scientists first studied them, they realised they weren't made by some reptile or amphibian.
00:43:50They were made by a millipede.
00:43:53Now, here is one of the biggest millipede species alive in the Earth today.
00:44:01That's pretty big.
00:44:02Using the tracks for scale, it's clear the ancestors of this little fellow were massive.
00:44:22Called Arthropluridae, it was over two metres long.
00:44:29The forests would have been terrifying.
00:44:33With giant scorpions and giant spiders.
00:44:40And not just on the land.
00:44:43I think the most impressive of all were the dragonflies.
00:44:47I mean, most modern dragonflies have wingspans up to ten centimetres across,
00:44:52but back then they were way larger.
00:44:54Some were up to a metre across.
00:45:02These mega-neura were the largest insects ever to take to the skies.
00:45:11But in this oversized world, pumped with oxygen, the plant kingdom still reigns supreme.
00:45:20Then, 230 million years ago, a new group of animals emerged from the shadows of the swampy forests.
00:45:30They would become the largest creatures to roam the Earth.
00:45:33And they were ready to do battle with the kingdom of the plants.
00:45:38I'm talking, of course, of dinosaurs.
00:45:40It's the meat-eaters that get all the press.
00:45:48But recent research has revealed that out of the 700 species discovered, over two-thirds were herbivores.
00:45:58Vegetarians ruled.
00:46:02Led by the biggest herbivores in history.
00:46:06The sauropods.
00:46:11To discover the impact of these huge dinosaurs on the plant kingdom,
00:46:16I've come to an animal sanctuary to see it in the flesh.
00:46:19Unfortunately, this place doesn't have a living sauropod, but what it does have is the biggest herbivore that the planet's got to offer.
00:46:32The African elephant.
00:46:34Come and meet Butch.
00:46:36This beautiful four-ton elephant can help me truly appreciate the staggering size of the dinosaurs.
00:46:43Can we go up?
00:46:56Now, Butch here is about as big as a big African bull gets.
00:47:00And, you know, that's already...
00:47:02What's that?
00:47:04Four metres high.
00:47:06But if we want to get to the height of a sauropod, we have to go much higher.
00:47:10Six metres, we've got to be higher than that.
00:47:14We're now at eight metres.
00:47:16Still got to go higher.
00:47:18Where are we at?
00:47:19Ten metres now.
00:47:20A bit higher than that.
00:47:22We're still not at the height of a sauropod yet.
00:47:25Okay, we're getting there. Nearly.
00:47:27Okay.
00:47:29Fight.
00:47:32So my head's now about 12 metres,
00:47:35which is about the height of a four-storey building,
00:47:38and also the height of a sauropod.
00:47:40And the thing is, on the end of a nine-metre neck,
00:47:44this is the skull of a sauropod.
00:47:49It seems quite small,
00:47:51but the point was that this had to be manoeuvrable and nimble
00:47:55to get right up at that high-level foliage.
00:48:00Sauropods were like nothing else a planet had ever seen.
00:48:03They weighed more than ten times an African elephant.
00:48:10Now, Butch here eats about 90 kilograms of foliage every day,
00:48:14which is roughly about that much hay.
00:48:17But scientists have estimated that sauropods
00:48:20eat about 1,500 kilograms of hay every day.
00:48:23In other words, about 20 times that daily diet.
00:48:27Or 50 bales of hay.
00:48:30Now, if you imagine,
00:48:32you've got herds of about 30 sauropods,
00:48:35much bigger than these beasts here,
00:48:37and you realise that the plant kingdom
00:48:39was up against the ultimate salad predator.
00:48:42150 million years ago,
00:48:48dinosaurs were stripping the land of vast swathes of foliage.
00:48:52For the first time,
00:48:55the plant kingdom was under serious attack
00:48:58from another dynasty.
00:49:02To fight back,
00:49:04plants began to evolve a whole arsenal of defences
00:49:07for their precious leaves.
00:49:08Here in California,
00:49:13we can see just how intense this arms race was
00:49:16in one of the world's most unusual gardens.
00:49:21It's full of a group of bizarre and extremely rare plants
00:49:25called cycads,
00:49:27that once they made up a quarter of all plants on Earth.
00:49:36This is incredible.
00:49:39Exactly the kind of place you'd expect a dinosaur just to pop out.
00:49:47To stave off attack from those ravenous dinosaurs,
00:49:49cycads developed some clever lines of defence,
00:49:52and the most obvious being physical weapons
00:49:55like needles and spikes and...
00:49:57I can't...
00:49:59These are vicious.
00:50:01The main point was to make leaves as painful as possible to eat.
00:50:05These defences came in all shapes and sizes.
00:50:20And some plants also spice things up with chemical weapons.
00:50:23This is a Traps Valley psyched from South Africa, but it's pretty typical in that
00:50:33the leaves contain a nerve age and that if you ingest it causes vomiting,
00:50:38diarrhoea, paralysis of the limbs, and then of course, death.
00:50:41Now obviously I'm not going to eat one of these, but I can eat a plant whose ancestors emerged
00:50:48around the time of the dinosaurs and who also have a chemical weapon,
00:50:52and that is...
00:50:54a chilli.
00:50:56In particular, a harbarnus chilli.
00:50:59Which is supposed to be one of the most powerful in the world.
00:51:05There's a chemical in here called capsicum,
00:51:07but it's contained in the fruit,
00:51:11and that essentially is a toxin.
00:51:16Ah!
00:51:21Which is, at this precise moment,
00:51:27burning and inflaming all of my mouth.
00:51:31Oh my gosh.
00:51:32The thing is, the toxins in the cycads, right?
00:51:40They were...
00:51:42they were far more powerful even than chillies.
00:51:45Oh my gosh.
00:51:47So you can imagine what...
00:51:49the dinosaurs were had to endure.
00:51:51Oh my!
00:51:53I could have to...
00:51:59Ah!
00:52:00I can't even say how sore that is.
00:52:04Ah!
00:52:08Mmm.
00:52:10Mmm.
00:52:12Eat a chilli, they said.
00:52:14It'll be funny, they said.
00:52:18You know what, forget about cycads.
00:52:20That could have brought down a 70-tonne sore point.
00:52:22Oh!
00:52:23Oh!
00:52:28And the arms race didn't stop there.
00:52:31Ah!
00:52:32Plants evolved a new tactic.
00:52:35Not so much a line of defence,
00:52:38as a line of communication.
00:52:40We know that when some plants are attacked,
00:52:44they activate a quick-acting toxin that deters herbivores.
00:52:51Now we're discovering that this defence goes even further.
00:52:57Because plants can actually warn other plants
00:53:01that a herbivore is eating them.
00:53:02And at last, scientists here at Exeter University
00:53:12are beginning to listen in to this hidden conversation.
00:53:19They're finding that when plants are attacked,
00:53:22they also release an unseen gas from the leaves.
00:53:25What it does is extraordinary.
00:53:31And this will be the first time it's been captured on film,
00:53:35using specialist imagery.
00:53:37These two Arabidopsis plants are being put inside a chamber.
00:53:44A third plant is then cut to mimic an attack.
00:53:47It's added to the undamaged plants.
00:54:02The chamber is sealed.
00:54:03The plant leaves are now releasing the gas.
00:54:19As they do so, their biological activity can be seen changing.
00:54:30Something remarkable happens.
00:54:33The gas triggers a change in the biological activity
00:54:37in the two neighbouring plants.
00:54:44They have detected the message warning them to protect themselves.
00:54:58Scientists don't know all the details of this plant language,
00:55:00but increasingly they believe there's a chatter between plants all around us.
00:55:09I think most people assume that plants lead a rather passive life.
00:55:13That they're static and unresponsive.
00:55:16That's just not true.
00:55:18In reality, they move, they sense, they communicate.
00:55:22It's almost as if they show a kind of intelligence.
00:55:24For 200 million years, the dinosaurs and the plants were locked in a titanic evolutionary battle.
00:55:37Each trying to gain the upper hand.
00:55:41But it was now that some plants played their trump card.
00:55:46They use wood to grow taller and taller.
00:55:47And in California's Sierra Nevada, I'm about to find out just how tall.
00:55:55To do that, I need the help of biologist Jim Spickler.
00:55:56Ready as I'll ever be.
00:55:57Take your time.
00:55:58I mean, we're...
00:55:59What I was going to do.
00:56:00We've got some time.
00:56:01Absolutely.
00:56:02What I was going to do.
00:56:03We've got some time.
00:56:04Absolutely.
00:56:05Yeah.
00:56:06This is the grandest example of a tree.
00:56:07This is the grandest example of a tree.
00:56:08This is the grandest example of a tree in Sierra Nevada.
00:56:09In Sierra Nevada, I'm about to find out just how tall.
00:56:13To do that, I need the help of biologist Jim Spickler.
00:56:20Ready as I'll ever be.
00:56:21Take your time.
00:56:22I mean, we're...
00:56:23What I was going to do.
00:56:24We've got some time.
00:56:25Absolutely.
00:56:26This is the grandest example of them all.
00:56:36The giant sequoia.
00:56:40What you see is just impossible for your mind to process.
00:56:43The scale is so large and...
00:56:45Oh, it's extraordinary.
00:56:47I feel like it's a bit of Lord of the Rings.
00:56:56Oh, what a great tree.
00:57:1570 million years ago, the ancestors of this type of tree,
00:57:20the conifers, got ever taller.
00:57:24This was the ultimate in plant construction.
00:57:29Conifers like the giant sequoias raised their precious leaves out of reach.
00:57:37The dinosaurs were no longer the biggest organisms on earth.
00:57:42That title had been well and truly won back by these giants of the plant kingdom.
00:57:50This is so tall.
00:57:52But I've still got, I don't know, another third to go.
00:57:56The thing is, by using wood to grow really tall like this,
00:58:00it gave trees another advantage over plants
00:58:02because it allowed them first pick of the sun's strongest rays.
00:58:06And the thing is, of course, for plants, light means success.
00:58:09If you had a satellite image of the dinosaur era 70 million years ago,
00:58:20you'd see the earth like it had never been before,
00:58:23and never would be again.
00:58:27The climate was so warm, the poles had no ice.
00:58:30Instead they were covered with conifers, a vast polar forest.
00:58:39And the mighty sequoia trees were not just found in small areas of the Sierra Nevada as they are today.
00:58:45They were global, stretching along the Pacific coast and as far south as Australia.
00:58:52How far are we from the, from the top then?
00:58:59We're getting close.
00:59:01Oh, that's extraordinary.
00:59:04Extraordinary.
00:59:09This is it.
00:59:11This is the top of the tree.
00:59:13Whoo.
00:59:15Unbelievable.
00:59:17It's staggering to think that using just a gas, carbon dioxide, and a liquid, water,
00:59:31together with light energy from beyond our world,
00:59:35you can construct a cathedral of wood 90 metres tall.
00:59:47Since they first appeared, plants and their ancestors have revolutionised our planet.
00:59:56They created oxygen for the atmosphere.
01:00:01Which had allowed them to conquer the land and transform rock into soil.
01:00:09In turn, fuelling the explosion of all life.
01:00:12From a barren, alien planet, plants had made a living Earth.
01:00:19And left on its own, the world would have continued like this.
01:00:24Dominated by large dinosaurs and endless forests.
01:00:29If at 65 million years ago something happened it would change everything.
01:00:33A chance of end it would have dramatic consequences not just for plants but for all life.
01:00:37And it would originate not on Earth but in outer space.
01:00:52The asteroid would kill off the dinosaurs.
01:00:55And the next chapter would see the triumph of a whole new group of plants.
01:00:59Flowers transformed the bond between animal and plant.
01:01:07Even sculpting the very planet itself.
01:01:11Above all, plants would drive our human story.
01:01:16But all that was still to come.
01:01:18Yes it is still to come.
01:01:19With the same reproduction of the creature and Possibly.
01:01:21That it was still in character and a culminator.
01:01:25And that ten that gap is still to come.
01:01:27MR CHURCH
01:01:39Transcription by CastingWords