Sir David Attenborough goes in search of the very first animals. His journey begins in a forest near his childhood home in Leicester.
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I'm on a fantastic journey to look for the origins of life.
I shall be travelling not only around the world, but back in time,
to try and build a picture
of what life was like in that very early period.
It will be a journey full of wonders.
Parts of it were unknown until only a few years ago.
In 50 years of programme-making, I've been lucky enough to explore
the living world in all its splendour and complexity.
The blue whale! The biggest creature that exists on the planet!
Now, I'm off to explore the origins of all this.
To look for the very first living creatures that appeared on the planet.
In recent years, scientists have unearthed dramatic evidence of what those first creatures were like.
We can also find clues in living animals.
And this enchanting little creature
is what we were looking for.
Using the latest technology, it's possible to bring those first animals to life
for the first time in half a billion years.
From the moment they appeared
to the time that they took their pioneering steps on land,
we can deduce how animals acquired bodies that move,
eyes that saw and mouths that ate.
And we can understand how those first organisms
laid the foundations for modern animals as we know them today.
Hello, old boy. How are you?
'Including you and me.'
My 40,000 mile journey begins very close to home, in Britain.
This is the Charnwood Forest in Leicestershire in the middle of England.
As a schoolboy, I grew up near here.
And in these rocks, a discovery was made
that transformed our understanding
of that mystery of mysteries, the origin of life.
The history of life can be thought of as a many-branched tree,
with all the species alive today
related to common ancestors down near the base.
The five kingdoms of life, the main branches, were established early on.
Protists - amoeba-like creatures.
And animals. That for me is the most fascinating question of all.
How and when did they first appear?
The answers are only now beginning to emerge -
and some of the first clues came from here in Charnwood Forest.
I was a passionate fossil collector.
But I never came to look for them in this part of Charnwood,
because the rocks here are among the most ancient in the world.
Around 600 million years old, in fact.
And every geologist knew or at least was convinced that rocks of
such extreme age couldn't possibly contain fossils of any kind.
And then a boy from my very own school, just a few years after I left it,
made an astounding discovery.
Against all the predictions of scientific know-alls,
he found a fossil in these ancient Leicestershire rocks.
And this is it.
It's called and is known around the world as Charnia,
after the forest in which it was discovered.
But what is it?
Is it animal or plant?
The fact is it comes from such a remote period
that the distinction between those two forms of life was not yet clear.
But one thing is certain.
It clearly was alive.
Charnia was a marine organism, part of an ancient community
of living things that lived in darkness at the bottom of an ocean.
That much we do know.
But what was this strange creature?
When did it first appear?
And how is it related to modern animals?
The answers to these questions are only now beginning to emerge.
There were further finds in Charnwood forest, like this disk,
which was probably the holdfast
which secured the frond of Charnia to the sea floor.
And then people began to look in rocks of this great age
all around the world.
And lo and behold they discovered a whole range of fossils
that enable us now to put together in extraordinary detail
the first chapters in the history of life.
That all happened a very long time ago.
Imagine travelling back through time.
Humans have been around for two million years.
The dinosaurs were wiped out 65 million years ago.
Charnia is more than eight times older than the oldest dinosaur.
It lived about 560 million years ago.
But compared with the age of life itself, that's nothing.
Before Charnia and other complex organisms existed,
the only living things were microscopic single cells.
They first appeared about three and a half billion years ago
when the Earth was a very different place.
The early continents were still forming.
The days were a mere six hours long, because at that time
the Earth was spinning much faster on its axis than it does today.
The land was dominated by volcanoes -
hostile and lifeless.
But deep in the oceans, life had begun.
The latest theory is that chemicals spewing from underwater volcanic vents
solidified and created towers like these,
and this produced the conditions needed for the first cells to form.
Some of these began to harness the energy of sunlight, just as plants do today, and formed colonies.
These rocky stromatolites in western Australia
have been constructed by very similar photosynthesising bacteria.
Others managed to survive by extracting nourishment directly
from the environment, like the fungi and animals that would later evolve.
This state of affairs continued for a vast period of time.
For some three billion years, simple microscopic organisms
were the most advanced form of life on the planet.
That's way over half the entire history of life on Earth.
And then suddenly, within the space of a few million years, a mere
blink of the eye in evolutionary terms, advanced organisms appeared.
Why is a mystery,
but we may find some clues to it on the coastline down here.
On the Eastern coast of Canada, there is evidence of an event that
may well have been the spark that started the evolution of animals.
These rocks have been dated by radioactivity
to just before the moment that life became very complex.
So if we can understand the circumstances under which these rocks were formed,
we may get a clue as to why it was that life suddenly became more complex.
Fragments of red stone are embedded in the darker rock.
They look out of place.
And, in fact, they are.
Geologists call them drop stones.
They were transported here by glaciers.
As the ice moved off the land,
it floated out over the sea in a great shelf,
carrying with it stones that it had gathered on the continents.
And when the ice eventually melted,
the stones fell into the sediments on the sea floor.
This wasn't the only place covered by ice.
Drop stones of the same age have been found in deposits all over the world.
The evidence points to a global spread of glaciation.
Just before complex life appeared, the world was in the grip
of the biggest ice age in its entire history.
It's been called Snowball Earth.
The Earth was plunged into a deep freeze
so severe it probably extended
from pole to pole.
The surface of the seas were frozen over.
On the continents, ice caps and glaciers developed.
In places, the ice was probably a kilometre or so thick.
We still don't know enough about the details, but it's likely that
those conditions lasted for millions of years.
Stromatolites and similar bacterial colonies that dominated the Earth
were crushed under the advancing glaciers.
Life was nearly annihilated before it had truly begun.
It's difficult to imagine how life managed to survive in those circumstances.
But survive it did.
Microbiologist Dr Hazel Barton
believes that modern glaciers can tell us how it did so.
She has come to the Columbia Icefield in the Rocky Mountains
in search of organisms that are still able to endure such extremes today.
The thing about being here
is it looks like everything's been wiped clean,
the glacier's come through and it's destroyed all life,
there's nothing living.
But to a microbiologist this looks a bit like a rainforest.
From here you can see discolouration on the surface of the ice,
but that's not dirt -
that is photosynthetic bacteria that are surviving there
and that creates an ecosystem where you have plants
and you have predators come in and feed on those organisms.
So even though it looks dead, it's actually wildly alive with life.
The kind of life you can see here is pretty ancient.
They've had to adapt to a lot of global catastrophes.
They had to adapt to Snowball Earth.
Microorganisms that live in these harsh environments we call extremophiles.
They have an amazing amount of adaptability that's hardwired in their genomes.
You can freeze them, you can bury them a mile down in ice
and its not much of a hindrance because of their adaptable nature.
We owe our existence to ice-dwelling extremophiles.
Snowball Earth almost extinguished life,
but tiny organisms like these hung on for millions of years.
I think what you had is
organisms that could withstand extreme environments
conditioning themselves to this changing ecosystem.
You had a skin of microbes on the surface of the planet,
and you had these organisms living between where the, the glaciers contacted the rock,
and that was enough life trickling over so that
when those conditions retreated, and it became more favourable,
then it was like, pff, and everything took off again.
Finally, Snowball Earth began to warm.
There is evidence that around this time,
there was a global surge in volcanic activity.
Eruptions punched through the ice, spewing carbon dioxide into the air.
As it spread through the atmosphere, it produced a greenhouse effect,
trapping heat so that the earth warmed and the ice melted.
We still have a lot to discover about what happened next,
but it seems likely that it was the melting of Snowball Earth
that led to the next great development of life.
As the glaciers retreated,
so nutrient-rich meltwater flooded into the oceans.
For the surviving cells, this flood of ground-up rock was a bonanza.
For the microbes that could photosynthesise,
the pulverised rock was a potent fertiliser.
And their growth would have a direct influence on early animal cells.
Cyanobacteria and other oxygen-producing microbes
began to bloom across the globe.
These flourished in colonies of plant-like microbes
that pumped out enormous volumes of oxygen.
And it was this increase in oxygen
that was the key to the rise of the animal kingdom.
Now, simple microscopic life
had the fuel it needed to develop into something bigger.
After billions of years of single-celled life,
something amazing happened in the deep sea.
Up to this moment, living cells that had been produced by division
simply drifted away from one another.
But now, with the aid of increased oxygen,
some cells were sticking together.
Some of these clumps ultimately evolved into animals.
To find out how oxygen drove this process,
I have come to Australia's Barrier Reef,
to look at one of the most primitive of animals alive today -
one that can truly be called a living fossil.
It is one of the simplest multi-celled organisms that we know,
but its basic body structure has nonetheless enabled it
to survive virtually unchanged for around 600 million years.
It's a sponge.
Sponges are just collections of simple cells
that have clumped together and got stuck together.
They don't have a digestive system or a nervous system
or a blood circulatory system,
and they get their food and their oxygen
by just pumping seawater through channels in the body.
But they can give us an indication of how it was that cells
first clumped together to form bodies of any real size.
At the microscopic level, sponge cells are bound together
by a tangle of hairy, stringy protein molecules called collagen.
This collagen glue is found only animals, and nowhere else.
Collagen is sometimes called the sticky tape of the animal world.
It's the commonest protein in our body.
It forms the framework of our skins.
Plastic surgeons use it to pump up our lips.
You need oxygen to manufacture collagen
and with the rising amount of oxygen in the atmosphere
at the end of Snowball Earth, cells were able to manufacture it.
At the Research Station on Heron Island on the Great Barrier Reef,
scientists are working to understand
how it was that multi-celled organisms
began to colonise the earth.
To find the answer, marine biologist Professor Bernard Degnan
is studying sponges.
The things that connect sponges to the rest of the animal kingdom
we can find at the level of the cell and the gene.
When we look at its genes, it's clearly an animal.
We look for the things that bind all animals together,
so what does a human share not only with a chimpanzee
and for that matter a tiger but what it shares with a sponge.
If we can find any common threads,
we're getting really to the heart of the matter of multicellularity
in the animal kingdom, so that's the key.
A classic experiment gives us some insight.
First, a sponge is cut into small pieces.
Then it is pushed through a sieve on the end of a syringe.
This breaks the animal down into its individual cells.
This may seem a brutal thing to do to a living organism,
but to a sponge this is of no consequence.
In response, it does something quite astonishing.
The cells begin to move...
and then they form clumps.
Soon the clumps form bigger clumps,
until three weeks later, a miniature sponge has formed.
Sponges have this amazing capacity to regenerate themselves.
And what we can do is actually rebuild a sponge
from the cell level up.
From this experiment, we can maybe infer a few things
that happened 600 million years ago with the very first animals.
We can infer that there were cells coming together,
they could adhere to each other, they used extracellular proteins
like collagen to glue themselves together.
They had the ability to communicate with each other
and a certain amount of flexibility that allowed them to interact
to give rise to something that's bigger and greater,
a large macroscopic multicellular animal.
The advantages of being multi-celled were many.
Colonies of cells could collect more food,
control their internal environment
and act efficiently by working as a team.
It was just the beginning.
In Canada, there is an extraordinary place
that reveals what happened next.
Here you can see how just a few million years after the melting of Snowball Earth,
the earliest multi-celled organisms became much more sophisticated...
and much bigger.
This is Mistaken Point in Newfoundland.
It got that name because in years gone by sailors coming up the eastern coast of North America
but lost in the fogs that are so frequent here
would head north for the open ocean
but be wrecked on these savage rocks.
But today Mistaken Point has a completely different reputation.
Today it is recognized as one of
the most important fossil-bearing sites in all the world.
For here you can see fossils
of the very first animals that evolved on this planet.
The fossils in these rocks are both wonderful and bizarre.
When the sun is low in the sky,
the slanting light shows up their structure in great detail.
Organisms were no longer
just clumps of undifferentiated cells, like sponges.
They were organized into defined shapes.
And among them are some that look exactly like Charnia
that had been first recognised in Charnwood Forest.
Here, there are not only hundreds of examples of Charnia,
but a whole community of other strange creatures.
Everywhere you look there are complex markings and indentations
of one kind or another -
it's almost as though children have been playing in wet sand.
It's like walking through a carpet of ancient creatures.
It's difficult to imagine that 565 million years ago
this was the bottom of the ocean
and these were some of the first animals to live on this planet.
Here at Mistaken Point,
exceptional conditions have preserved these delicate life forms.
Each one of these layers of rock
was once mud lying at the bottom of an ocean.
An ocean so deep it was very cold,
and very poor in oxygen,
so any organism that died here took a very long time to decay.
But those that did have been preserved
with an astonishing degree of perfection.
What makes this place so different?
There was a volcano rising from the sea floor close by,
and it spewed out millions of tons of ash.
The ash sank to the bottom,
blanketing everything like a sub-marine Pompeii.
Over millions of years, the ash itself was buried by muddy sediments
and then all was turned into rock.
And then, over hundreds of millions of years,
mountain-building forces thrust the whole sea-floor upwards
to its present position on the coast of Canada.
Dr Guy Narbonne is a world expert on the fossils of Mistaken Point.
What you can see on this surface
is the grey is the muddy sea bottom
and this is where the creatures all lived.
And they were knocked down and covered by a bed of volcanic ash.
And you can see it here and all of this pink and white
speckled stuff is volcanic ash.
The volcanic ash cast every part of them,
like putting plaster around your arm if you break it,
and that led to a perfect preservation
of every detail of the outside.
Radioactivity in this light-coloured ash layer
allows Guy Narbonne to date precisely the eruptions,
and therefore the fossils.
Some are as old as 579 million years.
Here we can see one of the best of the fossils on the surface.
It consists of disks, and they all have these pustules
on them and that's why we rather affectionately call them pizza disks.
And they were very simple in form,
but the first truly large creatures in Earth evolution.
The pizza discs are only one of the species found here.
Most are fern-like fronds, like this enormous species of Charnia.
This is a two-metre-long frond.
-And this is not the biggest.
We have about 200 specimens of this here.
The frond of Charnia found in Charnwood was isolated.
But here at Mistaken Point, a whole community of organisms has been preserved together...
and that could give us new information.
You're calling this an animal but is it justified to call it an animal?
-It's rather plant-like.
Well, "What is it?" is a big question.
We know for a fact it can't be a plant
because we're in water thousands of metres deep,
there wouldn't have been enough light to read a newspaper.
We're several orders of magnitude too little light for photosynthesis.
OK, so it's not photosynthesising because it's too deep
and therefore it's not a plant. What's it living on?
What we believe they're living on is dissolved carbon and other nutrients in the deep oceans.
So it's absorbing these nutrients through its entire body.
Very thin. Probably not much thicker than your thumbnail.
These organisms were very simple animals.
Beyond the reach of light, they had to survive by absorbing chemical sustenance.
But most animals we know today are able to move about.
Even sponges and corals have swimming larvae.
But there's no evidence of that here.
The creatures were all immobile.
Nothing could move.
Nothing had a mouth,
nothing had muscles.
Probably none of them had colour,
probably an eerie whiteish colour to everything.
These are the oldest large multi-cellular creatures on Earth,
the oldest things that might be called proto-animals.
This is not like anything that exists on earth today.
Even though they're not directly related to us,
like some distant relative, they provide us with a view of our own beginnings.
One of the most peculiar things about these wonderful proto-animals
is the way they constructed their bodies.
Unlike modern creatures, they had a very simple pattern of branching.
Despite their size, these are still very simple animals.
They can be put together with just six to eight genetic commands,
as against some 25,000 such commands that were needed to construct a mammal like me.
You can see this if you look at them in detail.
You see that they are made up of a series of very small modules
which are attached to one another in a number of different ways.
Their modular or fractal way of building their bodies is one of Guy Narbonne's main areas of research.
His study is centred on one particular species.
This is Fractofusus.
It's the most common fossil in the Mistaken Point assemblage.
We have literally thousands of specimens.
And it would have lain on the sea bottom like you see there.
A spindle-shaped mass, very thin.
It consists of these elements.
And there are 20 of them on either side.
And if you look at an individual element,
it's remarkably finely-branched.
It's a style we called fractal or self-similar.
These fractal organisms grew by repetitive branching,
with each branch exactly the same as its predecessor
from the microscopic level upwards.
It was a simple, yet extremely, effective way of building a body.
Such finely-divided branches gave the organism a huge surface area,
and this allowed them to absorb nutrients directly without mouths and without guts.
This simple fractal body plan proved very successful.
So animals using it grew large for the first time in the history of life on Earth.
Fractal design was perfect for getting these earliest creatures off and running
and its easy to see why.
It takes a minimum of genetic programming in order to make one.
You could probably do it with six or eight codes in your PC
to make something that was fractally branching.
And then combining them to make up larger elements is literally child's play,
like a toddler might take Lego blocks and put them all together in order to make up a larger structure.
The fossils of Mistaken Point provide a detailed record of fractal animals.
But the absence of anything like them in more recent rocks is very significant.
Just a few million years after they first evolved, they vanished.
They have no living descendents.
They were an evolutionary dead end.
And the reason?
The very simplicity of their fractal way of growing.
They utterly dominate about the first 20 million years of the evolution of complex multi-cellular proto-animals.
However, this fast start was also their demise.
Because they were incapable of evolving things like
guts and brains and muscles and teeth that later animals did.
If animals were to acquire these things,
they would have to build their bodies in a completely different way.
And eventually, animals appeared that did exactly that.
To see them, I'm travelling south from Newfoundland across the equator
to South Australia.
The Ediacara Hills.
Here lie animals whose body plans are fundamentally the same as those of almost all animals alive today...
The creatures that are preserved here lived just after fractal animals began to die out.
And about 550 million years ago, their differently-organised bodies gave them something quite new...
But how and why did animals first begin to move?
Scientists are beginning to find answers to those fascinating questions.
And much of the detail comes from these extraordinary fossils behind me.
A team of scientists, led by palaeontologist Dr Jim Gehling
is uncovering the evidence in great detail.
When you have these beds covered in red clay
you have a good chance of the beds having well-preserved fossils.
This is the original sea floor.
And this sea-floor was very different from that in the deep waters of Mistaken Point.
This was once a shallow reef.
It is 550 million years old.
The surface of the ocean floor was covered with organic ooze.
It may have even been green or orange. We don't know the colour.
But there was a lot of organic material made up by bacteria and all sorts of microorganisms.
But sitting in and amongst that garden of slime, we would have seen these strange creatures.
Jim Gehling's team is working to decipher the fossils.
But it is not easy because these creatures still lacked any hard parts to their bodies.
If I was working on dinosaurs, I'd go to a spot,
find the bones and carefully dig them up, take them back into the lab, reconstruct the dinosaur.
But I'm not dealing with bones. I'm dealing with soft-bodied creatures.
All you've got are imprints of squishy things living flat on the seafloor.
Despite the challenges, Jim has discovered compelling evidence here
that these animals had begun to move.
On this fossil bed, we find something very interesting.
It's a series of faint, but very definite circles.
They are almost identical in size and they overlap quite often.
And then when you go to the end of the series of discs,
you find a hollow with the imprint of a very distinct fossil,
that of Dickinsonia.
Dickinsonia was a cushion-like creature
that lay flat on the seafloor.
It ranged from the size of a penny to that of a bath mat.
These imprints represent something very important.
They are the first evidence
of a kind of mobility of animals on the seafloor.
The first animal movements were undoubtedly slow, but perhaps even too slow to notice.
To see them in action, you have to speed them up.
Dickinsonia crept from one feeding place to the next,
absorbing the organic matter beneath it and then moving on once again.
Perhaps it moved with the help of hundreds of tiny tubular feet, as starfish do today.
The excavations at Ediacara reveal that Dickinsonia wasn't the only mobile creature around.
Animals everywhere were on the move, actively seeking food.
This shape here is a resting place of a slug-like animal called Kimberella.
And these here, marks, are showing how it fed.
It had a proboscis, a snout,
and it fed by sifting through the mud, making these scratch marks.
But it tells us more than how this animal fed.
It also tells us how it moved because if you look back this way,
this is where is started feeding
and then it moved along here with more feeding marks and grooves,
and then it settled down here
into the mud where its final resting place was.
So this shows that the animal not only fed like that,
it actually moved like that.
Kimberella was a very early ancestor of today's molluscs.
It probably had a single muscular foot,
just as snails and slugs have today
with which it pulled itself along the sea bottom.
Our speeded-up view of the Ediacaran seafloor
gives an idea of what a busy place the oceans had now become.
Whether that movement is by creeping or crawling over the seafloor,
it doesn't matter because that animal
has advantages over an animal that is fixed to the seafloor.
It can move away from danger.
It can move towards richer sources of food.
It can move away from places which are over-colonised by its neighbours.
That gives it an enormous advantage in the history of life.
This new mobility was only made possible by a major change in the layout of animals' bodies.
When we get to Ediacara, we still have some of those beautiful fractal-like forms
that you see at Mistaken Point but in the Ediacara Hills we see something very different
and that is, for the first time,
you see a blueprint for all animals from then on, including ourselves.
'The modern animal body plan is called bilateral symmetry.'
What we see here is Spriggina.
Let's make a cast of the fossil.
Spriggina represents the first ever animal
which had clear bilateral symmetry.
It had a body with a head at one end, a tail at the other.
And almost identical halves, if you split it down the middle.
We see these together with other creatures
which have this kind of body form.
Spriggina is just one of countless kinds of fossils
in the Ediacara Hills that had developed in this way.
It had a head and a tail, and so it moved in a particular direction.
It's quite likely that they had sensory organs concentrated in the head.
Now why does my nose occur near my mouth?
It's a very good reason. I want to smell the food before I ingest it.
Why are my eyes above my mouth?
So I can see what I'm eating.
This head demonstrates that sensory capacity had evolved.
It was able to sense where food was likely to be on the seafloor.
And, therefore, clearly had a mechanism for actually moving towards that food.
Bilateral animals like Spriggina had another advantage.
Between the head and the tail, there are numerous segments.
So these animals could increase in size by simply adding more segments.
What is more, each segment could do a particular job.
Once you start to move,
you develop a front end and that becomes your head.
And you also, by definition, have a back end.
And in between, segments on which you can add appendages.
On that basic pattern, you can add further features.
On the front end, that's where you need sense organs, eyes, feelers.
On the appendages, you can modify them to be hooks and claws
that would help you to catch things.
And at the back end, there will be a pore from which you excrete the waste products.
And that is the basic body plan of almost all the animals that are alive on Earth today.
It had taken 3,000 million years for multi-celled organisms to appear for the first time.
But now, less than 100 million years later, an evolutionary blink of an eye,
animals had appeared that had the same basic body plan as most that live today.
They had heads and tails and segmented bodies.
And they were able to move to find food.
How was it that animals had suddenly become so complex?
The Ediacara Hills may hold the evidence for an answer to that question.
Living organisms don't live forever.
If a species is to survive it has to reproduce and the first simple animals did that very simply,
by straightforwardly dividing.
But if a species is to survive it also has to have the ability to change with a changing environment.
And to do that involves reproducing in a rather different way.
Evidence of how that happened can also be seen is these very ancient Australian rocks.
In 2007, palaeontologist Dr Mary Droser
discovered in these 550-million-year-old deposits
evidence that animals had started to reproduce sexually.
The animal concerned is called Funisia.
If Droser's theory is right, this wormlike creature produced offspring
by exchanging genetic material with other individuals.
This gene-swapping, or sex,
shuffles the genetic pack, greatly accelerating variation and therefore evolution.
Sexual reproduction is absolutely one of the most fundamental steps
in the history of life.
It is why we have the diversity that we have.
It's the birds and the bees.
As far as we know, this is the first evidence of animals' sexual reproduction,
and we're not catching the animal in the act of it,
we're looking at the product of what we conclude was sexual reproduction.
This fossil is key to Mary Droser's argument.
The small circles show where the animals were anchored to the ground.
You can see that these attachment structures are basically all the same size.
They're all about a couple of millimetres in diameter.
And you could go to another bed, and all the Funisia are half a centimetre in diameter.
So the same size are all occurring together.
This uniformity of size in a particular place is, Mary Droser believes,
strong evidence that a new way of reproducing had arrived.
We link this to sexual reproduction
because if you look in modern environments, when you have this kind of size groupings,
that is 99.9% of the time a product of sexual reproduction.
To understand why, I'm travelling 2,000 miles northeast of Ediacara to the Great Barrier Reef.
Here, there are modern creatures that reproduce in the way that Funisia is thought to have done.
Corals, like Funisia, are anchored to the seabed.
They feed by filtering food from the water.
And the way they breed creates one of nature's greatest annual spectacles.
Once a year, there's an important event among the corals.
We're not sure how it's coordinated.
It probably has something to do with the moon.
But it gives us a hint as to how sexual reproduction might have first appeared.
At exactly the same time,
the corals release countless millions of sperm and eggs all at once.
The event is precisely timed to maximise the chances
Millions of offspring are simultaneously conceived.
So, as the coral grows, the individuals that make up
the colonies are all of exactly the same age and size,
just like Funisia.
It's unlikely that Funisia was the first animal to reproduce sexually.
But its discovery suggests that many other animals are also reproducing by mixing their genes.
And that might explain how complex animals evolved so quickly.
The arrival of sexual reproduction speeded evolution.
Here was a mechanism that produced greater genetic variation more quickly.
So, over many generations, species were able to adapt to their changing environments.
550 million years ago, animal life was on the verge of a major advance.
In an environment where animals were becoming more mobile, they would have to adapt fast.
Movement requires a lot of energy.
Simply absorbing nutrients through the surface of the body
as Dickinsonia did was much too slow a process.
Mobile animals would need to consume huge quantities of food.
And they would do that by evolving the very first stomachs, mouths and teeth.
You can see how they might have done so in Switzerland...
..where a new kind of technology provides a window into the past.
This stadium-sized building houses one of the world's most powerful microscopes.
It's called the synchrotron.
Professor Philip Donoghue is preparing the tiniest of fossils for the synchrotron.
These miniscule balls were excavated from a quarry in South China.
Each and every one of them is the fossilised embryo of an ancient creature.
If we really want to understand these fossils,
what we need to do is not just to look at the surface
which we can do with an electron microscope.
We need to look inside.
We have to use some form of X-ray tomography, a bit like CAT scanners in hospitals.
But we have to use one that allows us to look at the very tiniest details down to a thousandth of a millimetre.
The synchrotron is the only X-ray type machine that provides
the kinds of resolution that we need to see all the tiny details within the fossilised embryos.
It was astonishing, I mean it was a real eureka moment
that you could get to the very finest levels of fossilisation,
the very finest detail that the fossil record could ever give up using this technology.
Powerful generators fire high-energy electrons around a circular tube at close to the speed of light.
After one million orbits, the electrons emit X-rays so powerful, they can penetrate solid rock
or these tiny fossils.
Donoghue uses data from the synchrotron
to build a three-dimensional picture of the fossils.
We know it's a fossil embryo because it's surrounded by a preserved egg sac.
And using tomography we can see inside to the developing animal.
This fossil is the embryo of a tiny marine worm called Markuelia.
It lived just twenty million years after the animals of Ediacara.
Using his 3D model, Donoghue is able to see inside it
and there he found evidence of something new.
These fossils provide the first clear evidence for a gut within animals.
We can clearly see that there's a mouth right at one end
surrounded by rings of teeth that extend inside the mouth.
And then there's a gut that extends all the way through to an anus at the other end.
Internal digestion enabled Markuelia to extract energy from its food in a very efficient way.
And the fact that it had teeth suggests that it had a new diet -
The fact that it's got rings of teeth arranged by its mouth, that it would have averted out
or it would have ejected out of its mouth to grasp prey items, tells us that this thing was a predator.
For the first time, there were hunters in the oceans.
And that had enormous evolutionary implications.
There was about to be an explosion of life that would lay the foundations for modern animals.
In another wave of evolution,
the animal basic body plan became more and more elaborate.
Fearsome predators appeared in the seas,
great monsters on the land and animals became masters of the Earth.
Next time I continue my journey in the Rocky Mountains of Canada,
the deserts of North Africa
and the tropical rainforests of Australia.
I will discover how and why animals evolved skeletons and shells.
How they developed true, picture-forming eyes.
How others went to extraordinary lengths
to protect themselves from attack.
And I shall discover the first animals that moved out of the sea to conquer the land and the air.
Subtitles by Red Bee Media Ltd
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In fifty years of broadcasting, Sir David Attenborough has travelled the globe to document the living world in all its wonder. Now, in the landmark series, David Attenborough's First Life, he completes his journey by going back in time to the roots of the tree of life, in search of the very first animals. Attenborough's journey begins in a forest near his childhood home in Leicester, where a fossil discovery transformed our understanding of the evolution of complex life. Travelling to the fog bound coastline of Newfoundland and the Australian outback, Attenborough unearths the earliest forms of animal life to exist on Earth.
These bizarre and wonderful creatures are brought to life with the help of cutting edge scientific technology and photorealistic visual effects. From the first animal forms that moved to the first mouths that ate, these were creatures that evolved the traits and tools that allow all animals, including ourselves, to survive to this day.