Episode 1 Wonders of Life

Every living thing that we know to exist is found on this one rock.

In this programme, I want to show you how almost four billion years ago,

this rock became a home to life...

..which has since flourished, diversified

and evolved into the extraordinarily varied natural world we see today.

I want to show you why our world is the only habitable planet

we know of, anywhere in the universe.

Now, the answer depends on the presence of a handful

of precious ingredients that make our world a home.

One of the most important of which is a substance vital to all

known forms of life.

Water.

Our planet is the only one we know with a surface

still drenched in liquid water.

The story of how each drop ended up here has been hard to fathom.

Largely because it happened

so long ago, there's very little direct evidence.

But in the Yucatan jungle in Mexico,

clues to how it turned up can still be found.

The landscape here is peppered with deep wells of water, called cenotes.

Every civilisation on the Yucatan, be it the modern Mexicans

or the Mayans, had to get their water from the cenotes.

And I've got a map, a completely unbiased map, of the larger

cenotes here, which I'm going to overlay on the Yucatan.

And look at that - they lie in a perfect arc,

centred around a very particular village,

which is there,

and it's called Chicxulub.

Now, to a geologist, there are very few natural events that can

create a structure, such a perfect arc as that.

All the evidence points to just one explanation.

We're looking at what's left of a gigantic asteroid strike.

One that wiped out three-quarters of all plant and animal species

when it hit the earth 65 million years ago.

You may think that impacts from space are a thing of the past,

a thing that only happened to the dinosaurs,

but that's not true either.

About 55 million kilograms of rock hits the earth every year,

and around two per cent of that is water.

This hints that at least some of earth's water arrived from space.

Late in 2010, these glimpses of comet Hartley 2 arrived

back on earth.

They were sent by NASA's Deep Impact probe.

From the comet's surface dust and ice spray into space.

Analysis of this water showed that it has a very similar

chemical composition to the water in our oceans.

This was the first firm evidence that icy comets must have

contributed to the formation of our world's oceans.

Earth began life as a molten hell.

Its internal heat drove off any trace of moisture.

But soon the planet cooled and it's thought that water brought

by comets condensed, contributing to the creation of the first clouds.

Then, 4.2 billion years ago, a deluge, the like of which

the solar system has never seen before or since, rained down...

..forming our oceans.

As a liquid, water molecules are held together by hydrogen bonds.

And breaking these bonds

and turning liquid into gas takes a lot of energy.

In other words,

hydrogen bonds are what makes water's boiling point high.

High enough to have allowed it to remain on the surface

of the earth as a liquid to the present day.

So from quite early in its history,

our home has been able to hang on to this most vital of ingredients.

Water is an essential part of all metabolic processes within the body.

It's fundamental to photosynthesis and respiration,

and is the critical solvent in each and every one of our cells.

But water isn't the only thing that makes our planet home.

Complex life relies on another precious chemical.

Oxygen.

Understanding how earth developed an atmosphere rich in oxygen has taken

centuries, and now we know that the secret lies with ancient bacteria.

In 1676, a Dutchman called Anton Leeuwenhoek was trying to

find out why pepper is spicy.

See, they thought that there were little spikes on peppercorns

that dug into your tongue.

He was using the microscope,

which had been discovered about 50 or 60 years before,

but inexplicably had never been used for anything useful before.

He put the peppercorns on there

and he looked down and he couldn't see anything.

So he thought, "OK, I'll grind them up, dissolve them in water

"and have a look."

When he did that, he didn't see anything interesting in the

peppercorns, but he found that there were little animals swimming around.

And he said that he estimated he could

line about 100 of the "wee little creatures" -

those were his words -

up along the length of a single coarse sand grain.

What Leeuwenhoek thought were animals,

were, in all probability, not animals at all.

Although he didn't know it at the time,

he'd discovered a whole new domain of life.

Bacteria.

They are by far the most numerous organisms on the earth.

In fact, there are more bacteria on our planet than

there are stars in the observable universe.

And there is one kind of bacteria more numerous than all the rest.

One of the most striking structures I can see on this slide is

a kind of a blue-green filament, which is a little

colony of a type of bacteria called cyanobacteria.

These things are incredibly important organisms.

Fossilised cyanobacteria have been found as far back

as 3.5 billion years ago.

And at some point, around 2.4 billion years ago,

they became the first living things to use pigments to split

water apart and use it to make food.

This evolutionary invention was incredibly complex.

Even its name is a mouthful -

oxygenic photosynthesis.

It starts with a photon from the sun hitting that green pigment,

chlorophyll.

Chlorophyll takes that energy

and uses it to boost electrons up a hill, if you like.

And when they get to the top, they cascade down a molecular

waterfall, and the energy is used to make something called ATP,

which is essentially the energy currency of life.

This little molecular machine is called Photosystem 2,

and it makes energy for the cell, from sunlight.

But when the electrons reach the bottom of that waterfall,

they enter Photosystem One, they meet some more chlorophyll which

is hit by another photon from the sun, and that energy raises

the electrons up again and forces them onto carbon dioxide, turning

that carbon dioxide eventually into sugars, into food for the cell.

Now, why all this complexity?

You know, why do you need these two photosystems joined

together in this way, just to get some electrons and make sugar

and a bit of energy out of it?

It's because only when life coupled these two biological machines

together, that it could split water apart and turn it into food.

But it wasn't easy.

The thing is that water is extremely difficult to split.

So for a leaf to do it, for a blade of grass to do it,

just using a trickle of light from the sun is extremely difficult.

In fact, the task is so complex, that unlike flight or vision,

which evolved separately many times during our history,

oxygenic photosynthesis has only evolved once.

In other words, the descendants of one cyanobacterium that

worked out, for some reason, how to couple those complex

molecular machines together in some primordial ocean,

billions of years ago, are still present on the earth today.

The cyanobaceria changed the world, turning it green.

And that had a wonderful consequence.

With this new way of living, life released

oxygen into the atmosphere of our planet for the first time.

And in doing so, over hundreds of millions of years,

it eventually completely transformed the face of our home.

Organisms started using oxygen to respire,

yielding a lot more energy which allowed

the development of more complex life, like plants and animals.

With these two ingredients, oxygen and water,

our planet has provided a home to life for billions of years.

But how can we define what life actually is?

The answer lies in the way that living things process

one of the universe's most elusive properties energy.

Energy is a concept that's central to physics,

but because it's a word we use every day,

its meaning has got a bit woolly.

I mean, it's easy to say what it is, in a sense.

Obviously this river has got energy because over the decades

and centuries, it's cut this valley through solid rock.

But while this description sounds simple,

in reality, things are a little more complicated.

Over the years,

the nature of energy has proved notoriously difficult to pin down,

not least because it has the seemingly magical property that it never runs out.

It only ever changes from one form to another.

Take the water in that waterfall.

At the top of the waterfall, it's got something called gravitational

potential energy, which is the energy it possesses due to

its height above the earth's surface.

See, if I scoop some water out of the river into this beaker,

then I'd have to do work to carry it up to the top of the waterfall.

I'd have to expend energy to get it up there.

So it would have that energy as gravitational potential.

I can even do the sums for you.

Half a litre of water has a mass of half a kilogram.

Multiply by the height, that's about five metres, and

the acceleration due to gravity is about ten metres per second squared.

So that's half, times five, times ten, is 25 joules.

So I'd have to put in 25 joules to carry this water to

the top of the waterfall.

Then if I emptied it over the top of the waterfall,

then all that gravitational potential energy would be

transformed into other types of energy.

Sound, which is pressure waves in the air.

There's the energy of the waves in the river. And there's heat.

So it'll be a bit hotter down there because the water's

cascading into the pool at the bottom of the waterfall.

But a key thing is, energy is conserved,

it's not created or destroyed.

So because energy is conserved, if I were to add up all the energy in the

water waves, all the energy in the sound waves, all the heat energy at

the bottom of the pool, then I would find that it would be precisely

equal to the gravitational potential energy at the top of the falls.

What's true for the waterfall is true for everything in the universe.

It's a fundamental law of nature,

known as the First Law of Thermodynamics.

And the fact that energy is neither created nor destroyed has

a profound implication.

It means energy is eternal.

Every single joule of energy in the universe today was

present at the Big Bang 13.7 billion years ago.

Potential energy held in primordial clouds of gas and dust

was transformed into kinetic energy, as they collapsed

to form stars and planetary systems just like our own solar system.

That primordial energy was trapped deep inside new planets.

And it's the slow release of the energy found in the earth's core

that is thought to have kick-started life.

Although no-one knows for sure how life began,

it's certain that it had to have an energy source.

One theory says that it started under extreme conditions

almost four billion years ago,

when the earth's energy was churning up the ocean floor.

These are pictures from deep below the surface

of the Atlantic Ocean, somewhere between Bermuda and the Canaries.

And it's a place known as the Lost City.

You can see why.

Look at these huge towers of rock, some of them 50-60 metres high,

reaching up from the floor of the Atlantic and into the ocean.

It's what's known as a hydrothermal vent system.

So these things are formed by hot water and minerals

and gases rising up from deep within the earth.

But the reason it's thought that life on earth may have

begun in such structures is because these are a very unique

kind of hydrothermal vent called an alkaline vent.

And about four billion years ago, when life on earth began,

sea water would have been mildly acidic.

There was a difference in the chemical

make-up of the water INSIDE the vent and that outside it.

One was alkaline, the other acidic.

And just like a battery, this difference acted as an energy store.

When such a difference is equalised, energy is released.

And that energy can be used to do things.

And the vents don't just provide an energy source,

they're also rich in the raw materials life needs.

Hydrogen gas, carbon dioxide and minerals containing iron,

nickel and sulphur.

But more than that.

See, these vents are porous, there are little chambers inside them,

and they can act to concentrate organic molecules.

You've got everything inside these vents.

You've got concentrated building blocks of life

trapped inside the rock.

So this could be where your distant ancestors come from.

And places like these could be the places where life on earth began.

In these four billion years, that spark has grown into a flame.

And a few simple organisms clustered around a hydrothermal vent

have evolved to produce new and complex creatures.

Today, life no longer depends on energy from the earth.

Instead, almost all life is fuelled

by the transformation of the sun's energy.

As sunlight bathes our planet, it's harnessed

and passed on from one life form to another.

And there is one creature that embodies, more than most,

just how that happens.

This is the golden jellyfish.

A unique sub-species only found in this one lake on this

one island, in the tiny Micronesian republic of Palau.

Golden jellyfish have evolved to do something that very few other

animals can do.

It really is incredible.

As far as you can see,

all the way down till the light vanishes, there are jellyfish.

And you can see they've congregated in the sun.

If you go over there to where the lake's in shade,

there are just none.

They're in this pool of light, beneath the sun.

There are millions of them.

Beautiful elegant things just floating around.

This lake is home to over 20 million jellyfish,

whose success comes down to a remarkable adaptation.

Their bodies play host to thousands of other organisms.

Photosynthetic algae that harvest energy directly from sunlight.

And once harvested, is passed on to the jellyfish to use.

The energy flows from sun to algae, to jellyfish.

The ones at the surface are gently turning.

The reason they do that is to give all their algae an equal

dose of sunlight.

And it's not just their anatomy that's adapted to harvest

solar energy.

Every morning as the sun rises,

the jellyfish begin to swim towards the east.

And as the sun tracks across the sky, they move back again towards

the west, where they spend their night.

So the jellyfish have this beautiful, intimate

and complex relationship with the position of the sun in the sky.

As sunlight is captured by their algae,

it's converted into chemical energy.

Energy they use to combine simple molecules,

water and carbon dioxide, to produce a far more complex one...

glucose.

Once absorbed by the jellyfish, glucose

and other molecules not only power their daily voyage

across the lake, they provide the basic building blocks the jellyfish

use to grow the elegant and complex structures of their bodies.

So the jellyfish, through their symbiotic algae,

absorb the light, the energy from the sun,

and they use it to live, to power their processes of life.

And that's true, directly or indirectly,

for every form of life on the surface of our planet.

Although all life uses energy in the same way, what I find

remarkable is how spectacularly diverse our natural world is.

From the tiniest bacteria to the tallest trees

and the most obscure-looking animals.

So how has life become so varied?

We know that every living thing on the planet today,

so every piece of food you eat, every animal you've seen,

everyone you've ever known, or will know, in fact, every living thing

that will ever exist on this planet,

was descended from one speck.

We call it the last universal common ancestor, or LUCA.

So just as the universe had its origin in a big bang,

all life on this planet had its origin in that one moment.

Now, we don't know what LUCA looked like.

We don't know precisely where it lived or how it lived.

But we do know this - if you start to trace my ancestral line back

to my parents, to their parents, to their parents,

to their parents, all the way back through geological timescales

over hundreds of thousands and millions and billions of years,

there will be an unbroken line from me all the way back to LUCA.

We know that, because every living thing on the planet today

shares the same biochemistry.

We all have DNA. It's made of the same bases - A, C, T and G.

They code for the same amino acids.

Those amino acids build the same proteins which do very similar jobs,

whether you're a plant, a bacterium or a bipedal hominid like me.

So all life uses the same fundamental biology.

Those four bases, A, C, G and T, which code for just 20 amino acids,

which in turn build each and every one of life's proteins.

Be you bacteria, plant, bug or beast,

your design comes from your DNA.

So it's this molecule that must hold the key to understanding why

life today is so diverse.

We now know that the answer to why life on earth is so varied

is actually the answer to why the DNA molecule itself is so varied.

What are the natural processes

that cause the structure of DNA to change?

Well, part of the answer actually doesn't lie on earth at all.

It lies up there amongst the stars.

And I can show you what I mean using this, which is a cloud chamber,

a piece of apparatus that has a unique place

in the history of physics.

I'm going to cool it down using dry ice, frozen carbon dioxide,

just below minus 70 degrees Celsius.

Put the top on...

HIGH-PITCHED WHISTLING

Hear that?

That's the metal at the bottom of the tank,

cooling down very rapidly to minus 70.

The cloud chamber works by having a super-saturated

vapour of alcohol inside the chamber.

There's plenty on there.

Now, I want to get that alcohol,

I want to boil it off to get the vapour into the chamber.

So I'm going to put a hot water bottle on top.

And this is the first genuine particle physics detector.

It's the piece of apparatus that first saw antimatter,

and it really does consist only of a fish tank, some alcohol,

a bit of paper and a hot water bottle.

There, look at that. You see that cloud, that vapour trail?

That's a cosmic ray.

That was initiated by a particle, probably a proton,

that hit the earth's atmosphere.

Now imagine if one of those hits the DNA of a living thing.

What that will do is cause a mutation.

That mutation may be detrimental or,

very, very occasionally, it might be beneficial.

Mutations are an inevitable part of living on a planet like earth.

They're the first hint of how DNA and the genes that code for

every living thing change from generation to generation.

Mutations are the spring

from which innovation in the living world flows.

But cosmic rays are not the only way in which DNA can be altered.

There's natural background radiation from the rocks,

there's the action of chemicals and free radicals.

There can be errors when the code is copied.

And then all those changes can be shuffled by sex, and indeed

whole pieces of the code can be transferred from species to species.

So bit by bit, in tiny steps from generation to generation,

the code is constantly randomly changing.

Now, whilst there's no doubt that random mutation does alter DNA,

evolution is anything but random.

Evolution is driven by a process called natural selection.

And there's no better place to see how it works

than in the forests of Madagascar.

HOOTING CRY

There, at the top of the tree,

is an indri, which is the largest lemur in Madagascar.

And the reason it's thought that we find lemurs here

in Madagascar and Madagascar alone is because there are no simians.

There are no chimpanzees, none of my ancestral family dating back

tens of millions of years to out-compete them.

So what's thought happened is that around 65 million years ago,

one of the lemurs' ancestors managed to sail across

the Mozambique Channel and landed here.

There were none of those competitors here,

and so the lemurs have flourished ever since.

There are now over 90 species of lemur and sub-species in Madagascar.

No species of my lineage, the simians.

Over a vast sweep of time,

the lemurs have diversified to fill all manner of different habitats.

From the arid spiny forests of the south,

to the rocky canyons in the north.

There is something about this island that is allowing the lemurs'

DNA to change in the most amazing ways.

We're on the hunt for an aye-aye, the most closely

related of all the surviving lemurs to their common ancestor.

-Right there.

-Oh, yeah! Here.

Yes.

The team want to attach radio collars onto the aye-ayes

so they can track their movements.

But first they need to find and sedate them,

which is an incredibly tricky business.

I mean, how you get a clean shot in this, I've no idea.

Well, here is the aye-aye that was tranquillised last night.

They finally got her about half an hour after we left.

I think it was probably because we were disturbing her.

Apparently, as soon as we'd gone, she came down the tree

and she was tranquillised.

And as you can see, she's pretty well sedated now,

which is fortunate for me

because she has certain adaptations that I wouldn't like to be deployed.

You can see, there, her teeth.

The teeth are very unusual for a primate. In fact, unique,

because they carry on growing.

So she's much more like a rodent in that respect.

And that's so she can gnaw into wood.

You see, aye-ayes have filled a unique niche on Madagascar.

It's a niche that's filled by woodpeckers in many other

areas of the world.

What she does is she feeds on grubs and bugs inside trees.

And to do that, she has several unique adaptations,

of which her teeth are one.

The most startling is this central finger here. It's bizarre.

It's got a ball and socket joint for a start,

so it has complete 360-degree movement.

It feels to me almost as if it's broken,

but it isn't, it's just you can move it around in any direction.

And she uses that finger initially to tap on the trunk of the tree,

and then listening to the echo from that tapping with these huge ears,

she can detect where the grubs are.

And then she gnaws through the wood with those rodent-like teeth,

and then uses this finger again to reach inside the hole

and get the bugs out.

So the question is, why?

How could an animal be so precisely adapted to a particular lifestyle?

She's waking up now.

And the answer is natural selection.

See, what must have happened is, way back,

when the ancestors of the lemurs, the lemuriforms,

arrived in Madagascar, there must have been a mutation that

lengthened the middle finger ever so slightly in one of those lemurs.

And that must have given it an advantage.

That must have allowed it, perhaps, to reach into little holes

and search for grubs.

There's some reason why that lengthened middle finger

meant that that gene was more likely to be passed to the next

generation, and then down to the next generation.

So that landscape of possibilities is narrowed.

It's narrowed because that gene persists.

And it's persisted now for at least 40 million years,

because this species has been on one branch of the tree of life

now for over 40 million years.

And so over those years that middle finger has got

more and more specialised.

Natural selection has allowed the aye-aye's wonderfully mutated

finger to spread through the population.

And this same law applies to all life.

If you have a mutation that helps you in the struggle to survive,

you are more likely to leave more offspring,

and in the next generation, that mutation is more likely to survive.

So this animal is a beautiful example, probably one

of the best in the world, of how the sieve of natural selection produces

animals that are perfectly adapted to live in their environment.

This process of evolution has led to the diversity of living things

we see on the planet today.

Seen against the blackness of space, the earth is a fragile world.

But seen by science, it's a world that's been crafted

and shaped by life over almost four billion years.

Life that could have started at the bottom of the oceans

in hydrothermal vents,

life that today taps into the flow of energy from the sun,

adapting...

changing...

and evolving...

to create the magnificently diverse natural world we see today.

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