Colours of Earth Colour: The Spectrum of Science

We live in a world ablaze with colour.

Rainbows and rainforests, oceans and humanity.

Earth is the most colourful place we know of.

It's easy to take our colourful world for granted.

Red, yellow and blue are some of the first words we learn

but the colours we see are far more complex

and fascinating than they appear.

Each one has its own story to tell.

I'm Dr Helen Czerski.

I'm a physicist and I'm fascinated by colour.

In this series, I'm going to uncover exactly what it is, how it

works and how it has written the story of our planet.

'I'll seek out the colours that transformed the Earth,

'from a ball of rock to a vivid jewel...'

This salt and this colour

has a little bit more to it than meets the eye.

'..and the colours that life has used to survive and thrive.'

So these insects are broadcasting a code. It's almost like Morse code.

This is communication in colour.

'And I'm going in search of the colours that

'exist beyond the rainbow...'

When we look at it in infrared, it completely lights up.

We're observing the invisible.

'..to discover why our future will be shaped by colours our eye

'can't even perceive.'

We've developed a completely new technology that can image people.

That's a huge step forward.

I'm going to tell our story from an unusual perspective...

..by looking at 15 colours that made the world and us.

Just look at all of this.

Blue lake, green trees, blue sky, red and yellow apple.

The Earth is a fantastically colourful place.

These colours emerged deep in the past.

Each one is a clue to a vital process that has shaped the Earth.

And each helps answer a fundamental question -

how did our world come to be this way?

In this programme, I'm going in search of five colours that

tell the story of our planet.

It's a story that begins with light.

Our planet is bathed in light from our nearest star...

..the sun.

When we think of the colour of the sun, we usually think of yellow,

and it certainly looks yellowish at the moment,

but it isn't really that colour.

The yellow hue of the sun conceals the real nature of sunlight.

Hidden within each sunbeam are the secrets of colour -

what it is and what it does.

I'm on my way to a place where I can reveal the essence of sunlight.

This is the Big Bear Solar Observatory,

set on a lake in the mountains of Southern California.

It's the largest solar telescope in the world.

Professor Dale Gary is director of the observatory.

The intriguing question is, what makes this unusual spot

a good place to study the workings of the sun?

Why would you build an observatory here, in the middle of a lake?

Here, we want to observe in the daytime,

and that's when the land would normally be heating up.

So what we want to do is be in the vicinity of a lake,

have a nice, cool lake that keeps the sun's heat from heating up

the atmosphere above it.

High-altitude lakes are the perfect place to observe the sun.

For most of human history, people thought sunlight was pure

and unchangeable.

The bright orb in the sky bathes the world in light,

pure, white light.

But then came one of the biggest revelations in science,

which came about when Sir Isaac Newton experimented with a prism.

Isaac Newton was the first person to appreciate

the significance of a really simple experiment.

When he did it, he blacked out a room in his house

and just let in a single sunbeam through a chink in the curtains.

And in front of that he put a prism,

something that was relatively new at that time.

I've got a much more sophisticated set-up here

because I'm taking advantage of this fantastic solar telescope,

and this is a modern prism,

but Isaac Newton would absolutely have recognised this experiment.

When the light comes through the prism,

the prism slows it down and it bends it.

And what Isaac Newton saw coming out of the prism told him

something really fundamental about the nature of light.

And it was this.

This is the visible spectrum,

from red through orange and yellow

through green and blue and all the way to violet.

White light isn't an absence of colour,

it's all the colours folded in together.

And what Newton realised is that if you put those components back

together, you get white light once more.

But that white light hides within in it all

the ingredients for our visual world.

What we'd believed to be pure,

immutable white light was actually a vivid spectrum.

At one end, shorter wavelengths of light that we see as blue

ranging through to the other end,

longer wavelengths of light that we see as red.

The combination of different wavelengths of light

is what creates every hue and shade that we can see.

It's an amazing thought - that light can't exist without colour...

..and colour can't exist without light.

Today, nearly four centuries after Newton's revelation,

the solar astronomers at Big Bear are able to study

the sun in intricate detail, helping to reveal another

fundamental truth about what colour actually is.

By using filters to look at the sun in all the different

colours of the spectrum, scientists can detect

features on its surface that were previously unknown.

It's a seething, dynamic world

where vast magnetic fields can spit matter and energy

out into space, sending them rippling through the solar system.

So here, we see lots of features here

that are following the magnetic field, so these linear...

-They look like twisted ropes, almost.

-That's right.

And the twisting is actually an indication of stored energy.

They begin to twist and some of it starts to unravel,

so when they unravel enough, it becomes very sudden

and you see this flare occur over just a few minutes.

-Oh, wow!

-And then suddenly, the flare is generated.

This is really thrilling. What I've just seen is a solar flare -

a massive ejection of electromagnetic energy from the sun.

These are some of the highest-energy events in our solar system.

Each one is capable of sending the same energy

as a billion nuclear bombs hurtling towards our planet.

So the sun very occasionally launches things out into space

and if the Earth is in the firing line, we feel their influence.

That's right. And it can be as often as a couple of times a month.

When they do arrive, then you can have magnetic disturbances which

can affect satellite signals and GPS signals...

..and cellphones and the power grids...

..and then actually cause great currents to flow and

destroy transformers, and that can be very bad for a big power system.

It's easy to think of the sun as just a sort of yellow

circle in the sky but, in fact, it's a dynamic system. It's doing things

and it's sending material out in our direction.

Yes.

If the sun didn't have magnetic fields and this activity,

it would be as boring as most astronomers believe it is.

SHE LAUGHS

The Earth is bathed in a colossal flood of energy from the sun.

A tiny part of that energy is the sunlight we see.

All light, and therefore all colour, carries energy...

..and the variety of different wavelengths

leads to another essential truth about colour.

This is Betelgeuse - a star that's glowing red.

This colour tells us its temperature is about 3,000 degrees Celsius.

From this, we know we're looking at an ageing star

coming to the end of its life.

And this is Sirius - a star that's glowing blue.

This colour indicates a temperature of nearly 10,000 degrees,

so we know it's a younger and hotter star.

So colour isn't just energy, it's also information,

and astronomers have learned to read the information

contained in colour to discover what different stars are made of.

As Newton first did with his prism,

they bend the light from a star to break it into its colour spectrum.

Dark lines in the spectrum

mark the presence of specific chemical elements,

each of which absorbs a precise wavelength of coloured light.

So the pattern of dark lines reveals exactly which

elements are present in the star.

And what of our own sun?

This view from the International Space Station shows how it

looks to the rest of the universe.

Here, above Earth's atmosphere, it glows a milky white.

This is the sun's true colour.

It's a striking view,

one that only a handful of humans have seen with their own eyes.

Below, you can see the sun's reflection on the Earth's

surface, and it is a rich yellow,

the colour that we Earthbound humans see when we look at the sun.

That's because when sunlight reaches the Earth,

it interacts with our planet's thick atmosphere.

The blue wavelengths are scattered, making the sky blue...

..and the sun appear yellow.

As the sun sets, our view of its colour becomes ever more distorted.

The atmosphere acts like a giant version of Newton's prism,

bending the light first to orange then red and,

if the conditions are just right, a brief and final glimpse of green.

And in the darkness of night,

we can perhaps best appreciate the full significance of colour.

There's a huge richness in the colourful world around us,

offering all kinds of clues as to what's going on,

but we can only see those colours

because there's light shining on them.

If there's no light, no colour, no information.

It's only in sunlight that the Earth explodes in colour.

And there's one colour that seems to dominate our world.

But the paradox of blue is that

while it seems to be all around us, very rarely is it solid or tangible.

Blue's absent from the palate of the land itself

and scarce in the plants and animals that inhabit it.

There are exceptions, striking to our eye because they're unusual.

IT SQUAWKS

This scarcity meant that our early human ancestors had very

little contact with the colour blue.

It's almost entirely absent from ancient art and literature...

..and many languages still don't have a specific word for it, even today.

Perhaps that's because it's always out of reach.

We can't touch the blueness of the sky

or capture the deep blue of the oceans.

Yet, in some remote corners,

the Earth does harbour this elusive colour.

The way it got there

provides a clue to how our vivid planet came into existence.

And to get my hands on it, I'm about to enter a very different world.

David Margulies is an artist, historian

and devotee of the colour blue.

In his London studio, he works with some of the rarest minerals

and pigments on Earth.

Among them all, the most spectacular are the blues.

And one blue in particular takes pride of place on his shelves.

This is a piece of lapis lazuli that's come from the one

mountain in Afghanistan.

So the important thing here is this blue colour

and that is lapis lazuli.

It is. It was the most precious and most expensive of all the pigments.

There aren't many blue things in nature,

so this must have been a spectacular thing to display and to find.

Someone had walked through the mountains of Afghanistan

and come across a blue stone.

And it makes me wonder whether they believed that the sky had

fallen to the Earth and turned to rock.

I love that idea, the sky that had fallen into a rock.

That's exactly what it looks like, isn't it?

'The colour is so stunning.

'I can imagine the impact it must have made when lapis first

'arrived in Europe, when trade routes from the east opened up.'

It was seen as extremely valuable.

In Renaissance Italy it was

so expensive it was the equivalent of the price of gold.

To have this was a status symbol

and the most visible way of having it was to put it on a painting

cos you could paint this colour onto a big canvas

and show that you had this commodity.

So it's not a subtle way of displaying your status.

-It's saying, for everyone to see...

-I don't think it's subtle at all.

I think the most important aspect is that lapis

does have a slightly mystical quality.

So, when it came to painting,

quite often the blue was used

to paint the robes of Mary.

Probably the most famous artist to have used it is Titian.

'There's something entrancing about this colour,

'but to discover what it can tell us about our planet,

'I need to do what painters do,

'and get right inside this rock.'

An artist is presented with a lump of this rock,

and they have to make paint out of it. What do they do?

-They hammer it.

-Not very sophisticated.

Hammer it until it gets smaller and smaller.

It's quite satisfying, this.

This is the first time it's been a colour cos this has never seen daylight before.

That bit of rock I've just smashed has just become

a colour for the first time.

So the next one along... So now we've got a lot of broken up bits,

-and you can start to see blue powder...

-That's right.

..and that's what the pigment is, it's the powder,

-when it becomes a powder.

-That's right.

It's a horrible noise. It's such a horrible noise.

You might smell it as well.

Oh! There's a really strong smell of sulphur.

It is sulphur. Sulphur is what makes the rock blue.

And then the final stage,

when it's broken down, is what we've got in the last one here.

This is the bluest thing I've ever seen.

'It's the chemistry of this rock that creates its colour.

'Sulphur more often produces yellowish compounds...

This is lovely, lovely stuff.

'..but in lapis lazuli, the unique combination of sulphur with

'other elements, produces this deep, rich blue we call ultramarine.'

And this is it. This is the final step.

The blue powder has been mixed with oil and some wax

and it's a paint.

And so this rock that looks like it fell from the sky

is becoming sky all over again.

When we look at this, we just see a blue rock,

but the secret to that colour is hidden in the atoms

that make this up.

But the atoms themselves aren't enough.

To get this you need to transform them.

For a transformation to this dramatic blue

you need the sorts of pressures and temperatures

with which planets are forged.

Humans have made lapis a part of our culture in exquisite, delicate ways.

But its origins couldn't be more different,

and they're certainly a very long way from a sophisticated art gallery.

'I've come high into the mountains of Southern California,

'one of the few places on the planet where lapis lazuli can be found.

'It takes a unique set of conditions to produce the vivid colour

'of this rock,

'and Professor George Rossman,

a geologist at the California Institute of Technology,

'is going to help me understand how it formed.'

Here's an example. The blue is kind of interesting.

It comes from sulphur.

The important thing is we have to get three sulphur atoms,

and we have to line them up in a row - one, two, three atoms in a chain,

trapped inside a cage inside the mineral, to make this happen.

'It takes extreme temperatures

'and pressures to force sulphur atoms to combine in this particular way.

'So the very existence of this rock is a telltale sign of the powerful

'forces that formed our planet, and are still at work deep within it.'

When we look at this, we see this amazing colour,

and everyone loves looking at it, but, really, what we're looking at is

evidence, direct evidence, that this was deep down in the Earth's crust.

Oh, this has been down in the cauldron of geological fire,

down 35km, 40km below the surface.

And then that has to get taken into a really active geological area

to be heated up.

Molten rock came in, rock like this one right here,

and then the heat from this rock started a series of chemical reactions.

So it's a very specific type of oven, that.

Oh, yes.

So it would have been red hot that deep down,

and then as it came up it became blue.

Absolutely correct. Through earthquakes and tectonic activity

these rocks have been slowly brought up over tens of millions of years,

so they're now 2km to 3km above sea level.

It's an amazing process.

This rock has been deep down into the Earth's crust

and it's been transformed by the processes that shape our planet.

And its colour is a reminder of that.

It's appropriate that that colour is blue, perhaps,

because we live on a blue planet.

'Just how dominant this colour truly is, is a fairly recent discovery.

'It's only within the past 60 years,

'when humans got into space and gained the ability to look back at ourselves,

'that we've been able to see our planet in its colourful entirety.

'A single photograph, taken a quarter of a million miles from Earth,

'changed our view of our home, forever.

'On Christmas Eve, 1968,

'as Apollo Eight made its way around the dark side of the Moon,

'astronaut Bill Anders picked up his camera

'and began to take pictures.'

I just clicked away and just kept turning,

and I took at least a dozen, maybe 50 pictures,

one of which was selected by others to be Earthrise.

'This is phenomenal.'

Out of the lunar horizon came this beautiful blue.

'Earthrise depicted our home planet

'in a way that nobody back on Earth had ever seen before...

'Let there be light. And there was light.'

'..a planet dominated by the colour blue.'

Even though we were hard-bitten test and fighter pilots,

this thing was beautiful.

'Our home is defined by this single colour.

'A vibrant blue orb,

'suspended against the blackness of the cosmos.

'It's from this vast expanse of space

'that one of our most celebrated colours emerged.

'It's a colour we've worshipped for millennia.

'Wars have been fought over it,

'and yet its very presence on the face of the Earth is an accident.

'There's an extraordinary story here,

'one that reveals the next great force that shaped our planet.

'And to tell it,

'I'm going to start somewhere most of us would never normally get to see.'

I'm somewhere close to central London, but I can't tell you where

and that's because I'm on my way to a secret location.

'I'm about to get my hands on this most precious

'and mysterious of colours.'

It's worth all the secrecy when you get to this.

It's absolutely unmistakable.

There's only one metal that's this colour,

and it's gold.

This is very, very pure gold. It's 99.99% pure

and it's also frighteningly valuable.

At today's prices, it's apparently worth £26,000.

You can see why humans value this so much.

It is stunningly beautiful.

'The secret of gold's mesmerising colour comes from its chemistry.

'Gold atoms reflect yellow and red wavelengths,

'producing a deep, rich yellow,

'that's accentuated by gold's metallic shine.

'This unique combination of factors

'makes it seem like gold is generating a warm light of its own.

'It's this property that's enchanted us since ancient times.

'But it's only due to an accident of history,

'that we're able to get our hands on gold at all.

'The story of this precious colour

'reveals one of the most dramatic events that shaped our planet.

'Gold didn't exist when the universe was first formed.

'To make gold and other heavy metals,

'it took unimaginably powerfully forces

'to fuse the atoms of lighter elements together.

'Perhaps the explosion of a supernova, a dying star.

'Or perhaps, as recent research has suggested,

'the colossal energy of two neutron stars,

'tearing each other apart to form a black hole.

'In the early solar system,

'there was a sprinkling of this newly forged metal

'in the swirling mass of dust that would eventually form the planets.

'But this is where the story of gold becomes really intriguing.'

Most of the time when we pick up gold, a necklace or a bracelet,

it's something small, and so you don't really notice how heavy it is.

But with these, it's really noticeable that they're really,

really heavy.

We've all heard someone say

that a person is worth their weight in gold.

Well, this is the pile of gold that weighs the same as me.

It's worth £1.6 million.

The thing is, it's quite a small pile.

It doesn't take up nearly as much space as I do.

It's been squashed down, so it only fills up a very small space.

Each individual gold atom is very, very big,

but the consequence is that gold is very dense and very heavy.

'But I shouldn't be able to hold this dense metal in my hands

'because gold shouldn't really exist on the surface of the planet at all.

'The early Earth was a ball of molten rock.

'In these furnace temperatures,

'gold and other metals existed as a viscous molten mass.

'Over tens of millions of years,

'this mixture of metals sank,

'dragging gold deep into the Earth's core,

'thousands of miles beyond our reach.

'And yet, in certain places on Earth,

'gold lies tantalisingly close to the surface...

'..just waiting to be plucked from the ground.'

This is Jamestown in California,

and it's a town that's got gold woven through its history.

In the hills about 80 miles north of here,

in 1848,

James W Marshall saw the first glint of gold in California.

As the news spread,

hundreds of thousands of people flooded here,

seeking their fortune,

each desperately hoping to see that same golden glimmer.

It became known as the California Gold Rush.

'But if gold did sink deep into Earth's core,

'where did the gold that fuelled the California Gold Rush come from?

'Steve Mojzsis is Professor of Geology at the University of Colorado

'and he's brought with him a clue that points

'to an exotic and violent origin for the gold we find on Earth...'

This one fell in Siberia in 1947.

'..a fragment of a meteorite.'

A very interesting story emerges.

Meteorites are the leftovers of planet formation.

In a sense they're a chemical museum of the early Solar System.

What's inside a meteorite, then?

What they contain are all of the elements that go into making the Earth,

including abundant gold.

So there were meteorites flying around the solar system

full of precious metals?

That's correct, and occasionally these would have struck the Earth.

So we think it was meteorites that delivered the precious

cargo of gold to Earth's surface early in its history.

'Many scientists think there's only one explanation

'for the presence of gold near the Earth's surface.

'It had to be transported here from outer space

'during an intense period of meteorite

'and comet bombardment nearly four billion years ago.

'This violent event left scars across our Solar System,

'including many of the craters that we can still see on the surface of the Moon.

'The craters left on Earth have long since gone,

'worn away by tectonic movement, weathering and erosion.

'But what the meteorites brought with them remains.'

Here's the Earth, all well-separated

with all of the metals where

they're supposed to be in the core,

and then this planet was salted

with meteorite debris that brought metals with it, including gold.

That's the surprising conclusion of the origin of gold to Earth's surface.

Even though the planet had a new supply of gold,

there wasn't anything to see because it was just too dilute.

The gold that there was, was a tiny fraction of the Earth's crust

and it was spread out around the planet. It was really rare.

And yet, billions of years later,

a human could just pick up a nugget of gold out of the landscape.

To get from one to the other, the planet had one final trick to play.

'With only one gram of gold for every thousand tonnes of the Earth's

'crust, there had to be a way to concentrate the tiny

'particles of gold, into the colour we see today.

'And across the surface of the planet is something that can do just that.

'In the streams around Jamestown,

'prospector Brent Shock relies on the properties of water

'to seek his fortune, just like the original Gold Rush pioneers.

'In doing so, he's mimicking the planetary processes

'that finally brought us gold.'

Just sprinkle a little in here.

So this is just dirt from the side there?

This is it. Yeah.

So it's like a little ladder here

and the stream's bouncing over the ladder?

-It creates a low-pressure area. Water slows, gold drops.

-Yes.

You've got your crevices here.

You've got your low-pressure areas there with the ripples.

And if it's dancing a little bit,

the gold can work its way down

and they will grab hold of the fine gold.

So it's getting caught just behind these ridges?

Exactly.

And then you just look through this and look for the colour?

-Yeah, we look, we don't put our fingers in.

-Oh. really?

THEY LAUGH That's me told, isn't it!

So this looks really simple,

but actually there's a very sophisticated thing going on.

You're the scientist.

-A stream can replicate, naturally, this set-up here?

-Yeah.

Constantly rolling. Constantly rising and settling.

Every time the water rises and then starts,

you can come out here a find gold laying on the bedrock.

Almost a renewable resource.

So we keep shovelling this stuff in.

You want to look at the gold.

Is it coarse, is it smooth?

The smoother it is, the farther it's travelled.

Then you want to triangulate your way up

to find out where the vein is, where the source is.

That's what everybody wants, the source of what's feeding this.

'Over millions of years, water picked up gold,

'transported, sorted,

'and concentrated it,

'and then deposited in a form that made it easier for us to find.

It's a process that's still happening,

'and drives our continued obsession

'with one of Earth's most alluring colours.'

This spectacular colour has been on quite a journey.

These atoms have travelled from a distant star in time to be

there for the birth of the solar system.

And then they hit the Earth in an impact which left a golden

signature on our landscape.

And even then it didn't stop,

because there were sorting processes,

first by geology and then by water,

until humans could pluck nuggets like this from the landscape.

And still it carries on,

because there are atoms from Egyptian jewellery

or Inca trinkets that are almost certainly

part of modern wedding rings or gold bullion.

So the cycling carries on,

but this fantastic colour stays exactly the same.

'It's amazing to think that we would never have seen the colour gold

'if it wasn't for the action of water.

'But water has shaped our planet in more fundamental ways.

'Some of its powers we can witness for ourselves...

'..but others, no less important, are hidden from view.

'And to show you,

'I've come to one of the driest places on Earth

'in search of one particular colour.'

I'm 2km up above the floor of Death Valley,

here in the USA, looking out over this tremendous view.

It looks like an alien landscape, but there's a colour down there

which has a huge amount to tell us about things we see every day.

We think of white as a colour of innocence and purity,

but down there, in this harsh landscape,

those white streaks have two stories to tell.

The first is the story of the tiny,

of how this colour works and why it's so common.

And the second is the story of the gigantic,

because the way that this colour is concentrated here

is a reminder of the scale of the processes that sculpt our planet

and paint vast swathes of it in specific colours.

From that fabulous viewpoint, I'm driving down into the valley,

to a place with a fantastic name. It's called the Badwater Basin

and it's very, very low down.

It's not just the lowest place in this valley,

it's the lowest place in all of North America,

and the bottom of it is 85m below sea level.

This is what I could see from above the valley and it's salt.

There are hundreds of square kilometres of it here.

It's just sodium chloride,

what you'd find on your dinner table,

but this salt, and this colour, has a little bit more to it than meets the eye.

'As far as I can see, and crunching under my boots,

'is what appears to be a solid carpet of brilliant white.

'But look at this salt more closely

'and something strange happens.'

Here it is, a handful of salt,

and it's bright white, just like all the salt around me.

But the salt isn't t really white,

and we can see its true nature if we look at it under a microscope.

And then this little camera

is projecting an image onto the screen here.

And what you can see is that each little crystal is a square

and that's because the salt crystals are cubes.

They've got flat edges. There's an orange card behind

and we can see that orange card through these crystals.

Light is going straight through them and coming straight back out.

And what that tells us is that these crystals aren't white,

they're completely transparent.

'We don't see the colour of the card any differently,

'whether a salt crystal is in the way or not.

'White light from the sun comes in,

'and orange light bounces back from the card to our eyes.'

So if the crystals themselves don't have any colour at all,

why is it that my little pile of salt here, and all of this, looks white?

Well, we can see why

if we start to move the microscope to where there's a big pile of them.

If you've got a stack of crystals all together,

the light comes in and it's bent as it passes through the first

crystal and then bent again as it passes through the second crystal.

And so it zigzags its way through the pile of salt,

and it eventually it finds its way out to our eyes.

'With a pile of salt crystals,

'the sunlight bounces around inside them and never reaches the orange card,

'so its orange colour remains hidden beneath and never gets to our eyes.'

White light went in, bounced around, and white light came out,

and that's why we see salt as white.

'It isn't just salt that's white because of this.

'Many things we see as white on a big scale

'are actually made up of tiny, transparent components.

'Clouds are small particles of colourless water

'suspended in colourless air.

'The white foam of breaking waves

'is just a turbulent mixture of water and air.

'And snow is made up of tiny, colourless ice crystals.

'In fact anything transparent that's small enough

'to bounce sunlight around on a tiny scale,

'like these bubbles,

'will look white on a bigger scale.

'But the secret of the colour white is just the beginning of what

'this landscape can reveal.

'Even the presence of this mass of white salt

'tells us a much bigger story about our planet.

'Geologist Garry Hayes has spent years working in Death Valley

'and studying the process by which these salt flats formed.'

We're in the hottest, driest place in the entire Northern Hemisphere.

-And the windiest, it feels like.

-And the windiest, it feels like.

So, I'm just going to pick a bit up here.

What's quite striking is that this is just mud,

and then there's this layer of salt on top just like icing.

-Exactly.

-This feels wet to me but that's brine.

-It is wet.

-It's very salty.

-It is wet, but it's drying quickly.

SHE LAUGHS

And every two or three years you would be standing in a lake

right now, a foot or two deep of water.

The water evaporates, the salt stays.

This salt has been accumulating in this one low area

for the last couple of million years.

'So even here, in one of the driest places on Earth,

'it's water that has shaped and coloured the landscape.

'Water collects here at Badwater Basin from a vast area all around.

'There's no lower point it can flow to.

'so under the baking sun, there's only one place it can go -

'Up.'

So, water brought the salt here, but where did the water come from?

There is a vast amount of ground water underneath this region,

especially underneath these mountains, so water actually travels

and trickles through the mountains rather than around them.

The mountains around us formed between 300

and 600 million years ago on the bottom of the sea.

And these rocks have been pushed up and they've been eroded,

and there are small amounts of salt in the rocks themselves.

So the salt dissolves into the water as the water's flowing here?

Absolutely, yes.

And when it gets here, the salt has nowhere else to go?

It has nowhere else to go.

-And it's sitting right below us, right now?

-It is.

'Here on Death Valley's salt flats,

'the forces that shaped and painted our planet are still in play.

'Every year, about 5cm of rain falls,

'but the evaporation rate is so high,

'it could remove a lake 4m deep in that time.

'So the salt flats continue to grow.

'Beneath my feet is a staggering 3km of salty sediment.

'The intense sun dries out the surface,

'creating this vivid layer of white.'

Look out at this enormous valley

and imagine the slow geological

processes that have shifted and transformed it over eons.

And in this, the place of extremes,

incredibly hot, incredibly dry,

and way below sea level,

those processes have concentrated one colour.

But the details of that colour come from the tiny shape of the crystals.

So you need both the minuscule and the gigantic to generate this,

the purest of colours.

'Our planet's story is captured in the colours it has forged.

'In blue, we see the sheer power of the forces that heaved within

'the young Earth, creating mountains and continents.

'Gold bears witness to a time when meteorites crashed to Earth

'with a cargo of riches, '

that changed our planet forever.

'The dazzling white of salt crystals reveals water as a hidden force,

'sculpting the face of the Earth in unseen ways.

'But there's one more colour that can reveal our planet's final

'and most vital transformation...

'..the one that led to life

'and, ultimately, to us.'

Deep underground isn't the sort of place you would expect to go

looking for a colour.

This colour has only been present for half of Earth's history,

but once it did appear, it appeared on a massive scale.

Hidden right beneath my feet is a colour that represents

one of the biggest transitions in Earth's history.

'I've come to Clearwell Caves in the Forest of Dean,

'a natural cave system, which extends for 30km

'under the Gloucestershire countryside.

'These caves have been mined for more than 4,000 years,

'since the earliest human societies settled in this part of the world.

'The substance those miners were digging for

'is a clue to a remarkable event that transformed Earth

'more than two billion years ago.'

Thousands of miners have been down here

and some of them were looking for this, and this is iron ore.

It's got tremendous potential for civilisation.

Just think of all the things you can turn this into.

A knife or armour or an ornament,

or, later on, a Spitfire.

Tools for neurosurgery or a steam engine.

But this isn't a particularly colourful rock

and it's not what I've come down here to see.

'Another material has been mined here for far longer than iron ore.

'It comes from the same rock, but whilst iron ore is dull

'metallic grey,

'the same can't be said for its colourful cousin.'

This is it. This is red ochre

and it's a really dramatic colour. You don't expect to see

something this striking down in a dark cave like this.

It's actually quite disconcerting sitting here because,

sitting in this hollow of red is a bit like sitting in the mouth of a monster.

It's no coincidence that the iron ore

and the red ochre are found in the same caves,

because to get vast quantities of this red,

what you need is iron and then one very specific molecule.

'With iron filings

'and some salty water,

'it's a process that's remarkably easy to replicate.'

To get this fabulous red colour from grey iron filings,

the trick is to add oxygen.

I just sped it up a little bit, but, basically, adding the water

and a little bit of salt makes the iron

and the oxygen react together a little bit faster.

Because all this is, is a beaker of rust.

And so the combination of oxygen

and iron has just turned this red very, very quickly.

But it's also, over geological time,

what's turned all of these rocks red.

'Go back three billion years

'and the formation of these rocks would have been impossible.

'That's because the atmosphere lacked one crucial ingredient -

'oxygen.

'The fact that these red rocks are here today

'is a clue to, perhaps, the most fundamental change

'in our planet's history.

'The arrival of oxygen created an atmosphere

'that could sustain complex life.

'With me deep underground is Dr Corinna Abesser.

'She's an expert in the chemistry of Earth's atmosphere

'and water systems, and how they've changed over time.'

The Earth would have been a very different place back then.

The atmosphere would have been mostly carbon dioxide.

And back then, there was iron actually in the water of the ocean?

The ocean would contain a lot of dissolved iron.

So even though this is our own planet, this was a very alien world.

Acidic oceans with dissolved iron

and a horrible atmosphere, by our standards.

'And then something changed,

'that changed all that chemistry.'

So around three billion years ago,

new organisms developed called cyanobacteria.

And they used all the ingredients that

existed in abundance at the time, namely carbon dioxide,

water and sunlight,

to produce energy, food.

And a waste product of that is oxygen.

'Cyanobacteria are microscopically tiny organisms

'that evolved in the early oceans.

'They were the first living things to use the process

'we call photosynthesis.

'That is, they used carbon dioxide, water and sunlight

'to produce food to sustain themselves,

'the same process plants still use today.

'And, crucially, the waste product of that chemical reaction is oxygen.

'The presence of this vital new element had a dramatic effect on the planet's oceans.'

These early organisms, the cyanobacteria,

were producing oxygen as waste,

so suddenly there's oxygen creeping into the ocean environment.

Where did it go?

Initially, that would have been used up by all the free iron that was...

or the dissolved iron that was in the ocean,

to form iron oxides, which is a red mineral.

And then you've got, basically, red dust raining out of the oceans

and just falling to the ocean floor

and building up over a very long period of time.

Covering the oceans in a layer of red.

'So, at first, oxygen combined with the dissolved

'iron in the oceans to form solid iron oxide.

'Eventually, when this iron had been used up,

'oxygen continued to accumulate and made its way into our atmosphere...

'..transforming it gradually into the air we breathe today,

'essential for life as we know it.

'And that oxygen also reacted with other elements in the environment.

'changing the colour of our planet.'

And once you've got free oxygen in the atmosphere,

and that's part of what's generated the ochre around us here?

Yes, iron will react with oxygen to form iron oxide,

and that's what we see here in these caves.

So these tiny organisms changed the colour of the planet?

Yes.

'Even though the combination of iron and oxygen

'has painted swathes of our planet red,

'it's created other colours. too.

'Iron oxide can exist in various forms,

'all of which have their own distinctive colour.'

Ochre isn't just the red colours, the haematite.

There's lots of others as well.

Right here there's yellow, and there are also purples and browns,

so just this one compound has a whole paint box associated with it.

And it's a strange thought that 2.3 billion years ago

in an ancient ocean,

one of the simplest organisms we know of

started producing a waste product, oxygen.

And that heralded the first appearance of these colours.

And then 2.3 billion years after that,

one of the most complicated organisms we know of,

a human being,

walked up to a wall like this

and did what comes naturally. They did this.

'Ochre is so common and so colourful that it's been

'used in art for more than 75,000 years...

'..reflecting the importance our ancestors placed on the colour red.

'It's found in prehistoric cave paintings across Europe,

'the Americas and Australasia.

'Even though these distant civilisations never met,

'the content of their art is remarkably similar.

'And their ubiquitous use of red symbolises the relationship

'between them and the land from which they sourced this colour.'

These are ancient colours, both for our planet and for our species,

but what an accident of history these represent.

A waste product, oxygen, seeped into the early Earth,

ended an era,

and began another.

The raw mineral colours of Earth

were about to become the background for a far richer palette

because the arrival of oxygen made possible

the arrival of complex life.

This new palette would be driven by evolution

and so these colours represent the transition of Earth

from a hostile, young planet to something new.

A home.

'Next time, the colours of life.

'I'll discover the bizarre

'and beautiful ways that the living world has harnessed colour...

The forest here is green and healthy.

'..from basic survival to the strange and sophisticated.'

Deep-down physiological changes, broadcast in colour.

Discover more about the story of the colours of the Earth

with The Open University.

Go to...

..and follow the links to The Open University.