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MANNING: It's in tropical forests,
as here in Indonesia,
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that you find the richest diversity of life
anywhere on Earth.
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The origins of all this diversity was a mystery
that obsessed Victorian naturalists
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when they returned from their collecting trips
with exotic animals and plants.
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The answer finally came from two great scientists.
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One was Charles Darwin.
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The other, a lesser-known Englishman,
working in these forests in the 1850s,
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Alfred Russel Wallace.
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I've always felt a particular affinity for Wallace.
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He was a professional collector
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but he so obviously took a delight
in the natural world
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and he loved its amazing variety.
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He writes in his journals
of how he trembled with excitement
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as a particularly beautiful butterfly
got into his net.
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And he rhapsodises several times
about the beauties of the birds of paradise.
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It was here he developed his theory,
identical to Darwin's,
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about the origin of species
through natural selection.
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The idea that as individuals compete
for space and resources,
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selection acting over many generations
picks out those
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that are best adapted to live in their environment.
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Although it was Darwin
who developed these ideas most completely,
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Wallace added a significant extra twist
to the theory.
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He noticed that this narrow strait
between the islands of Bali and Lombok
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marked a dramatic changeover
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in the types of animals and plants
he was finding in Indonesia.
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Lombok was inhabited by a species
which were common in Australia.
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But in Bali, there was an unexpected changeover
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to plants and animals much closer
to those found throughout Southeast Asia.
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Wallace was puzzled
because the two islands were only 15 miles apart.
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Then he made a bold intellectual leap.
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In a letter which he wrote to Darwin in 1858,
he said,
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"Facts like these can only be explained
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"by the bold acceptance of enormous changes
in the Earth's surface."
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And we know he was absolutely right.
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He can't have had any idea of the mechanism,
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but we know now that Lombok
and the points to the east
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and Bali and points to the west
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were on separate plates, thousands of miles apart.
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And only by continental drift
have they been brought this close together.
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80 million years ago,
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the Australian region
was much further to the south.
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But the plate carrying Australia
and nearby islands with their distinctive wildlife
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was moving gradually northwards.
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Eventually they were brought
closer and closer to Southeast Asia
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to form the Indonesian Archipelago.
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Perhaps we biologists have tended
to regard the evolution of life
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as very much our own preserve.
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But now that geologists are rethinking
the evolution of the planet itself,
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we're forced to recognise
that this has been one of the major factors
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shaping the history of life.
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So I'm going on a journey
through time and around the world
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to learn how the evolution of the Earth
has moulded the evolution of life.
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And how life in turn has helped shape the Earth.
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My journey starts in
the Barberton Mountain Land in Southern Africa.
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This is where the rocks reveal,
better than any others in the world,
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the secrets of the origin of life.
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The rocks here
are three and a half billion years old.
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And this is where geologist Maarten de Wit
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has recently made a very exciting discovery.
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What is so very special about this place?
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Well, they're not the oldest rocks in the world
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but they are without doubt
the best well-preserved rocks around.
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What things are you looking for in particular?
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We're interested in learning
how the planet operated at that time.
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So we're interested in
reconstructing the processes,
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reconstructing what the environment was like.
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One of the things, for example, we're looking at
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is to see if we can detect any life forms.
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MANNING: Maarten suspected
that hidden in these rocks
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could be the very earliest life forms,
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fossils of primitive bacteria-like organisms.
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He sent some rocks to Frances Westall.
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I want to try and find...
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MANNING: She's a microbiologist
with a particular ambition,
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to find the oldest fossil on Earth.
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So, in this particular image
we have this beautifully dividing bacteria
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caught in the act of division by being frozen.
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Instantaneously frozen and preserved.
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Everybody wants to find
the oldest bacteria on Earth.
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And I think we may actually be lucky here.
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MANNING: So these could be
the oldest fossils in the world.
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This is the actual rock
that we got the bacteria from.
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MANNING: Despite the excitement
of their discovery,
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Maarten is actually more interested
in the environment
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where life on Earth first originated.
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What do we know about the conditions
under which the bacteria formed?
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Well, these rocks allow us
to reconstruct an environment
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that is telling us
hot springs were prolific in this area
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at the time that these bacteria were living.
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When we look at the details of this rock,
we can reconstruct an environment
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a bit like Iceland today,
where hot springs are prolific,
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both just above sea level and below sea level.
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A lot of volcanic activity driving a lot of sea water
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and fresh water
through these hydrothermal springs.
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We speculate back in time
that this is the sort of place
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where life might have started.
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MANNING: It seems likely that these hot springs
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are where the Earth gave birth to life.
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It's here that the Earth's own energy
came bubbling to the surface
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and fed those primitive life forms.
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So from the very beginning,
the Earth and life were closely bound together.
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Three and a half billion years ago,
the Earth was a very different place.
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It was probably covered with water,
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the oceans were very shallow,
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and it seems the continents
were just starting to form.
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Today, there's only one place in the world
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to get a glimpse of what life
must have been like on the ancient Earth.
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This is Shark Bay in Northwest Australia.
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These columns contain vast numbers
of microscopic single-celled organisms.
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So all the ancient Earth, all the shallow seas,
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would have been filled with these things.
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DE WIT: That's the amazing thing.
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It's just like thinking back
two to three billion years ago.
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This is what all the shallow seas
would have been like.
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- They were just covered by this kind of life.
- Yes.
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And it was the only life essentially around
at that time.
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This is just a tiny piece that is preserved
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- of what the Earth looked like then.
- Yes.
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And that, to me, after all these years
of working in these old rocks, is amazing.
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Here I'm walking on it. Live.
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And these things are growing right now.
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- It's quite a romantic thought, isn't it?
- It's really amazing.
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- Ancient landscape...
- It blows my mind, actually. I must tell you that.
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MANNING: The mounds are called stromatolites.
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And today they're extremely rare.
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But they represent a very important stage
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in the evolution of early life.
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These were the very first organisms
to use energy from the sunlight to grow
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and emitting oxygen as a by-product.
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That's right. Of course, we know that today,
that's photosynthesis.
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Fixing carbon dioxide, giving off oxygen.
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And of course, in the early stages
of Earth evolution,
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this was a major event.
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This was the first time that we see
oxygen production on planet Earth.
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A very unexpected event.
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And that event moves the evolution
of planet Earth
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into a totally different mode.
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MANNING: As it spread around the planet,
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life in turn began to influence the evolution
and the geology of the Earth.
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The dramatic effect of the oxygen produced by life
on the Earth's geology
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can be seen in the Hamersley Range
in Northwestern Australia.
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What an absolutely marvellous colour.
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I think of iron, I think of rust.
It looks as if it's covered in rust.
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That's exactly what it is. It's rust.
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There's a very thin coating of rust on these rocks.
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And that tells you these rocks
are just very rich in iron.
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MANNING: And the way
these iron-rich rocks were deposited
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show what was happening to the ancient Earth
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during the early stages of the evolution of life.
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The clue is in what geologists call
"banded iron formations".
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Layers of dark red rock, rich in iron
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alternating with pale layers with no iron.
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MANNING: Where does the iron come from?
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DE WIT: Well, the origin of this iron
that comes out in these dark layers
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is volcanic activity in the deep oceans.
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And yet, the geology tells us
these rocks must have been deposited
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in very quiet, shallow seas.
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So there is this paradox.
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Why did this iron travel so far
before it deposits itself?
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Well, the key to that is that iron
is very soluble in water that has no oxygen.
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As soon as it comes out of the volcano,
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it stays in solution
and it circulates around the planet,
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until it reaches an area
where there is oxygen being produced.
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And that's, of course, around these shallow oceans
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where the stromatolites
are producing that oxygen.
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- Right.
- As soon as it hits that,
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the iron comes out of solution
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and forms the start
of these banded iron formations.
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There must be periodic processes going on here
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to produce these bands of iron
then bands of the white material and so on.
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Some of this banding, maybe,
is sort of growth on an annual basis.
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It's a bit like rings in trees, growth rings in trees.
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Wintertime, very little oxygen produced
by these stromatolites,
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- and so the iron wouldn't come out.
- Yes.
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But in summertime,
when the stromatolites are really going,
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they just produce all this oxygen.
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Iron sucks it up and gets deposited.
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Rocks are polished by the water here.
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MANNING: So, while these banded iron formations
were being laid down,
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any oxygen produced by life
was being used up by the iron.
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As a result, there was virtually no free oxygen
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in the early oceans and atmosphere.
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This went on for an incredibly long period of time.
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Vast deposits of banded iron formations
continued to be formed
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for over a billion years.
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And then, about two billion years ago,
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the huge banded iron formations
just stopped forming.
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By now, life was producing so much oxygen
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that the iron was immediately deposited
where it was produced
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and never reached the shallow waters.
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At last, the amount of oxygen
in the oceans and the atmosphere
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started to rise.
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One might say, then, that this is the first time
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that we have evidence of life affecting
the structure of the planet.
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Yes, you're right.
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And I find that an intriguing and wonderful idea.
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For the first time in Earth history
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life is influencing geological processes.
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MANNING: The oxygen in the atmosphere
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also changed the course
of the evolution of life forever.
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Oxygen molecules in the upper atmosphere
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was transformed by the sun's rays into ozone.
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This created a shield protecting the Earth and life
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from the sun's harmful radiation
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and allowed more complex life forms to survive.
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The Earth itself was also changing.
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By one billion years ago, large continents existed.
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And life had evolved into a variety
of different single-celled organisms
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which thrived in the shallow waters
on the edges of these continents.
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Life began on Earth really very early in its history.
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By about 3.6 billion years ago, it was established.
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What I find so remarkable
is that for the next three billion years,
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it stayed as single-celled,
very microscopic organisms.
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And then about 600 or 700 million years ago,
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something amazing happened.
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And it's here on the rocky coast
of Newfoundland in eastern Canada
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that scientists like Ed Landing
have found evidence
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of a major change in the evolution of life on Earth.
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LANDING: We're on a surface here
that is just covered
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with all sorts of fossils.
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Hundreds and hundreds of soft-bodied organisms,
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some of them look like feathers,
almost like little ferns.
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And some of these guys will be
up to a half metre in size.
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A holdfast and something
that almost looks like a feather that comes up.
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Now, what are these things?
Are they plants or animals?
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Well, if you look at this rock section,
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you can interpret the ancient environments.
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The ancient environment was one
that was very deep.
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It was on a continental slope or rise setting.
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We're dealing with something
that is probably thousands of metres of water.
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And that's important here because
light penetrates ocean water
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only a couple of 100 metres.
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And below that it's completely dark.
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These things are living in darkness.
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So these are not plants, these are animals.
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These are the oldest soft-bodied
multicellular animals that are known on Earth.
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MANNING: These fossils
are nearly 600 million years old.
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So why did single-celled life evolve
into multicellular animals?
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Evidence along the coast suggests that, yet again,
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the Earth may have played a major role.
241
00:18:51,687 --> 00:18:55,600
This is a rock unit we can trace around
this part of Newfoundland.
242
00:18:55,687 --> 00:18:56,961
It's very distinctive.
243
00:18:57,047 --> 00:19:00,960
It consists of pebbles, boulders up to great sizes,
244
00:19:01,087 --> 00:19:04,124
of volcanic rocks and sedimentary rocks
245
00:19:04,207 --> 00:19:06,323
surrounded by mud and sand.
246
00:19:06,647 --> 00:19:09,844
This can't be laid down by flowing water.
247
00:19:09,967 --> 00:19:13,926
And the interpretation
is that this is an ice deposit.
248
00:19:15,367 --> 00:19:18,916
MANNING: The rocks and pebbles
were carried here by glaciers.
249
00:19:23,087 --> 00:19:26,238
This was one of the coldest periods
in Earth's history.
250
00:19:26,567 --> 00:19:28,922
The planet practically froze up.
251
00:19:30,887 --> 00:19:33,879
And some glaciers had nearly reached the equator.
252
00:19:35,367 --> 00:19:39,724
This massive ice age probably occurred
because of a combination of events.
253
00:19:44,367 --> 00:19:46,722
About 600 million years ago,
254
00:19:46,847 --> 00:19:50,237
the continents formed a vast region
in the Southern Hemisphere,
255
00:19:50,327 --> 00:19:51,885
near the South Pole.
256
00:19:52,487 --> 00:19:55,718
This reduced the circulation of oceanic waters
257
00:19:55,807 --> 00:19:59,686
and stopped warm air and warm water
reaching the poles.
258
00:20:05,007 --> 00:20:08,283
Huge sheets of ice developed across the planet.
259
00:20:12,847 --> 00:20:15,919
The effect of all this on life was devastating.
260
00:20:16,287 --> 00:20:18,323
70 percent was killed.
261
00:20:22,767 --> 00:20:27,887
The single-celled organisms were the victims
of the first mass extinction of life on Earth.
262
00:20:30,167 --> 00:20:33,682
The Earth which had given birth to life
had nearly destroyed it.
263
00:20:36,087 --> 00:20:38,999
And then the massive continents broke apart.
264
00:20:39,247 --> 00:20:42,603
The increased circulation in the oceans
warmed the Earth.
265
00:20:43,127 --> 00:20:45,357
The big freeze was over.
266
00:20:47,607 --> 00:20:50,679
This worldwide event
which actually brought glaciers
267
00:20:50,767 --> 00:20:53,679
down to sea level in the tropics is thought to be...
268
00:20:53,767 --> 00:20:56,281
It's a change in Earth history.
269
00:20:56,407 --> 00:21:00,685
And what we end up having at this time
is, well, two things.
270
00:21:00,767 --> 00:21:03,998
One is cold, glacial waters sink
271
00:21:04,247 --> 00:21:06,920
and the deep oceans became oxygenated.
272
00:21:07,247 --> 00:21:10,205
When the ice melted, sea level rose
273
00:21:10,287 --> 00:21:13,085
and you had shallow seas covering the continents.
274
00:21:13,247 --> 00:21:16,045
And this was a time of evolutionary radiation
275
00:21:16,127 --> 00:21:18,163
of soft-bodied animals.
276
00:21:20,287 --> 00:21:23,085
MANNING: The end of the Ice Age
created the right conditions
277
00:21:23,167 --> 00:21:27,718
for more complex, multicellular life forms
to flourish and evolve.
278
00:21:28,287 --> 00:21:30,164
LANDING: Before the glaciation,
279
00:21:30,247 --> 00:21:33,080
we're starting to see very enigmatic,
280
00:21:33,167 --> 00:21:36,762
multicellular things that might be animals.
281
00:21:36,847 --> 00:21:39,566
But after the glaciation, we're seeing
282
00:21:39,647 --> 00:21:44,004
quite complex
soft-bodied organisms living attached
283
00:21:44,087 --> 00:21:46,521
and perhaps crawling around on the bottom.
284
00:22:05,647 --> 00:22:09,162
MANNING: It seems that
once multicellular life had evolved,
285
00:22:09,247 --> 00:22:11,920
there was an explosion of new life forms.
286
00:22:12,767 --> 00:22:14,439
And the best place to see this
287
00:22:14,527 --> 00:22:18,156
is in a remote area
of the Canadian Rocky Mountains.
288
00:22:29,247 --> 00:22:31,044
I'm coming very close now
289
00:22:31,527 --> 00:22:34,803
to a place which is holy ground for zoologists.
290
00:22:35,847 --> 00:22:38,042
One day in August 1909,
291
00:22:38,407 --> 00:22:41,763
the famous American palaeontologist
Charles Walcott
292
00:22:42,047 --> 00:22:44,197
was riding along here on horseback.
293
00:22:44,807 --> 00:22:46,684
He knew this area quite well.
294
00:22:47,087 --> 00:22:50,079
There was a slab lying across the trail.
295
00:22:50,527 --> 00:22:53,803
And he was afraid that his horse would stumble.
296
00:22:54,127 --> 00:22:57,915
So he dismounted and tried to shift it.
297
00:22:58,007 --> 00:22:59,520
But it was too heavy.
298
00:22:59,607 --> 00:23:01,837
So he took his hammer and struck it.
299
00:23:02,167 --> 00:23:07,525
And it split open to reveal
a miraculously preserved little fossil.
300
00:23:08,047 --> 00:23:11,084
And Walcott saw immediately
that it was an animal
301
00:23:11,167 --> 00:23:13,886
of a type that he'd never seen before.
302
00:23:13,967 --> 00:23:16,800
So he knew he simply had to find
303
00:23:16,927 --> 00:23:19,964
the place from which that rock had slid.
304
00:23:20,527 --> 00:23:22,438
And that's where I'm going now.
305
00:23:58,887 --> 00:24:03,244
Every year, Des Collins and his team
spend the summer collecting fossils
306
00:24:03,327 --> 00:24:06,080
from the most famous fossil quarry in the world,
307
00:24:06,207 --> 00:24:07,686
the Burgess Shale.
308
00:24:09,127 --> 00:24:12,278
There's a little bit of sponge right here
on this side,
309
00:24:12,847 --> 00:24:14,599
an ostracod there.
310
00:24:41,527 --> 00:24:45,042
MANNING: I suppose what strikes me,
coming to this very famous place,
311
00:24:45,127 --> 00:24:46,401
is how small it is.
312
00:24:46,487 --> 00:24:48,523
It's a really very small area.
313
00:24:48,607 --> 00:24:53,078
Sure. Sure. Well, the fossils are really mostly
concentrated in front of the cliff area.
314
00:24:53,167 --> 00:24:54,998
And we've collected something like,
315
00:24:55,087 --> 00:24:58,875
in total, something like 100,000 specimens
have been collected here.
316
00:24:58,967 --> 00:25:01,003
- Over the years. Yeah.
- Quite amazing.
317
00:25:01,087 --> 00:25:05,000
MANNING: The sheer quantity and quality
of fossils from the Burgess Shale
318
00:25:05,087 --> 00:25:06,725
is quite staggering.
319
00:25:07,847 --> 00:25:12,079
But even more surprising is that
all the major categories of modern animals
320
00:25:12,167 --> 00:25:13,964
had already evolved.
321
00:25:14,527 --> 00:25:18,566
I mean, you can see the finest details
of the hairs on... Are these the gills?
322
00:25:18,647 --> 00:25:19,682
The gills there, right.
323
00:25:19,767 --> 00:25:22,804
Well, this is one of the best specimens
of this that we've ever collected.
324
00:25:22,887 --> 00:25:25,560
Well, what you can see
is all the beautiful swimming flaps
325
00:25:25,647 --> 00:25:27,842
with the gills running on the end.
326
00:25:28,287 --> 00:25:30,562
And you can see the gut
running right through the body.
327
00:25:30,647 --> 00:25:34,356
And at the front, you've got these very large
great appendages.
328
00:25:34,847 --> 00:25:35,962
A beautiful arthropod.
329
00:25:36,047 --> 00:25:39,357
Looks very much like the arthropods
and the shrimps that you see in the sea today.
330
00:25:39,447 --> 00:25:42,564
It's the soft body parts that you get so well here.
I mean...
331
00:25:42,647 --> 00:25:45,081
- Right.
- What about... I mean, you get jellyfish?
332
00:25:45,167 --> 00:25:47,601
Well, this is a ctenophore, that's a comb jelly...
333
00:25:47,687 --> 00:25:50,599
MANNING: And scientists could see
that for the very first time,
334
00:25:50,687 --> 00:25:54,805
these animals were part
of a complex community of plants and animals
335
00:25:54,967 --> 00:25:58,164
and some of the animals lived by eating others.
336
00:25:58,447 --> 00:26:03,043
This is the claw of Anomalocaris
that belongs to an extinct class of arthropods.
337
00:26:03,127 --> 00:26:05,687
And this is one of the claws that comes out of
the front of the animal?
338
00:26:05,767 --> 00:26:08,964
Right, right, the front of the animal.
And the other extraordinary thing are the jaws.
339
00:26:09,047 --> 00:26:12,323
One guy thought that was a jellyfish.
That's a very strange-looking jellyfish.
340
00:26:12,407 --> 00:26:15,843
We now know it's got 32 teeth, all going in,
they've got points at the end of them.
341
00:26:15,927 --> 00:26:18,395
I've got a model here of the Anomalocaris.
342
00:26:18,527 --> 00:26:20,882
And you can see the jaws.
343
00:26:21,527 --> 00:26:22,642
MANNING: Right.
344
00:26:22,727 --> 00:26:26,163
And if you compare the size of this
to the size of this in this proportion to the body,
345
00:26:26,247 --> 00:26:30,957
then these jaws came from an animal
that was probably about a metre in length.
346
00:26:31,047 --> 00:26:32,526
- That's a really big animal.
- Yeah.
347
00:26:32,607 --> 00:26:35,599
MANNING: The biggest animal
that ever lived at that time.
348
00:26:35,687 --> 00:26:40,158
So 520 million years ago,
both predator and prey had evolved.
349
00:26:40,967 --> 00:26:44,926
They were inextricably bound together
as part of a food chain.
350
00:26:45,607 --> 00:26:47,837
From now on, the evolution of life became
351
00:26:47,927 --> 00:26:50,680
even more vulnerable
to any changes on the planet
352
00:26:50,807 --> 00:26:53,002
which could affect this food chain.
353
00:27:09,367 --> 00:27:12,165
But life was evolving only in the oceans.
354
00:27:12,247 --> 00:27:15,717
The water teemed
with different animals and plants.
355
00:27:23,847 --> 00:27:26,486
The land was barren and lifeless.
356
00:27:31,287 --> 00:27:34,643
Then, about 450 million years ago,
357
00:27:34,807 --> 00:27:38,880
as the numbers and complexity of species
in the sea multiplied,
358
00:27:38,967 --> 00:27:43,358
plants at last made the evolutionary step
which allowed them to leave the water.
359
00:27:45,087 --> 00:27:47,920
Once plants had made the move,
everything changed.
360
00:27:48,607 --> 00:27:53,727
Soil started to build up, trapping water,
transforming the surface of the continents.
361
00:27:58,687 --> 00:28:02,043
But the plants didn't have the land
to themselves for long.
362
00:28:02,127 --> 00:28:05,597
Soon after they invaded, the animals followed.
363
00:28:08,607 --> 00:28:13,203
I'm here on the Scottish island of Arran
with geologist Chris Nicholas.
364
00:28:17,167 --> 00:28:19,556
And this is Carboniferous period.
365
00:28:19,647 --> 00:28:22,207
NICHOLAS: That's right.
These rocks here are Carboniferous in age.
366
00:28:22,287 --> 00:28:26,485
And what we find here is that all of these plants,
367
00:28:27,407 --> 00:28:32,800
when they die, they're being buried
and compressed together
368
00:28:33,247 --> 00:28:36,205
- to form coal.
- And that's coal, all right.
369
00:28:36,287 --> 00:28:41,645
MANNING: This coal is graphic evidence
that the land was covered with dense forests,
370
00:28:42,407 --> 00:28:45,001
forests where strange creatures lurked.
371
00:28:46,407 --> 00:28:49,843
NICHOLAS: So this is a fossil track way.
372
00:28:51,447 --> 00:28:54,120
You can see we've got these two parallel...
373
00:28:54,687 --> 00:28:55,836
Yeah.
374
00:28:55,927 --> 00:28:59,761
...lines of footprints that go round and they curve
375
00:28:59,847 --> 00:29:01,485
and head off under that slab.
376
00:29:01,807 --> 00:29:05,402
MANNING: This, I think, is the first track
of a terrestrial animal.
377
00:29:05,487 --> 00:29:09,162
Yes, we think that we can work out
how many legs it had
378
00:29:09,607 --> 00:29:11,962
from the repetition of these footprints.
379
00:29:12,047 --> 00:29:15,119
- So we reckon this thing had about 23...
- Twenty-three pairs of legs.
380
00:29:15,207 --> 00:29:16,481
Pairs of legs. That's right.
381
00:29:16,567 --> 00:29:20,355
So it really was a relative
of the modern centipedes and millipedes.
382
00:29:20,447 --> 00:29:21,562
Well, we think so, yeah.
383
00:29:21,647 --> 00:29:24,081
But much bigger.
It must have been over a metre long.
384
00:29:24,167 --> 00:29:25,156
That's right...
385
00:29:25,247 --> 00:29:30,321
MANNING: These first fossil footsteps on land
are 350 million years old.
386
00:29:32,687 --> 00:29:35,565
But at the same time, descendants of fishes,
387
00:29:35,647 --> 00:29:39,037
the land vertebrates, had also emerged
from the sea.
388
00:29:39,127 --> 00:29:41,687
There was an explosion of new life on land.
389
00:29:51,887 --> 00:29:53,923
And just 50 million years later,
390
00:29:54,007 --> 00:29:57,317
the land was alive with amphibians and reptiles.
391
00:29:58,847 --> 00:30:02,157
There are more fossils of these early reptiles
here in South Africa
392
00:30:02,247 --> 00:30:04,477
than anywhere else in the world.
393
00:30:04,887 --> 00:30:07,879
Amongst these reptiles was one special group.
394
00:30:07,967 --> 00:30:10,959
They're called the mammal-like reptiles.
395
00:30:14,927 --> 00:30:19,000
Gideon Groenwald has found
hundreds of mammal-like reptile fossils.
396
00:30:22,007 --> 00:30:25,363
If we look at, for instance, the skull of this animal,
397
00:30:25,447 --> 00:30:29,725
we will find a very reptile-like skull.
398
00:30:29,807 --> 00:30:34,642
But if we turn it over and you look at the inside,
you will find a palate in the mouth.
399
00:30:34,887 --> 00:30:36,843
Now, the palate indicates to us
400
00:30:36,927 --> 00:30:40,237
that this animal could chew
and breathe at the same time,
401
00:30:40,327 --> 00:30:41,806
which is very important.
402
00:30:41,887 --> 00:30:45,926
If you look at reptiles today,
they throw the head back
403
00:30:46,047 --> 00:30:49,835
and they chomp off big chunks of food
and they swallow all this food in,
404
00:30:49,927 --> 00:30:52,122
a very inefficient way of eating.
405
00:30:53,727 --> 00:30:56,878
Whereas, if you look at a mammal,
it will breathe while it's chewing.
406
00:30:56,967 --> 00:31:01,643
It actually grinds the food into
much smaller pieces. It's a very efficient feeder.
407
00:31:02,047 --> 00:31:04,641
And for that reason, the mammal-like reptiles
408
00:31:05,247 --> 00:31:10,958
had the ability to survive much worse conditions
than the reptiles of that age.
409
00:31:12,567 --> 00:31:16,276
MANNING: These mammal-like reptiles,
our own very distant relatives,
410
00:31:16,367 --> 00:31:19,165
were the first reptiles to dominate the world.
411
00:31:19,967 --> 00:31:21,639
But they didn't evolve into true mammals
412
00:31:21,727 --> 00:31:26,164
until the planet itself had gone through
some extraordinary upheavals.
413
00:31:26,727 --> 00:31:29,116
250 million years ago,
414
00:31:29,207 --> 00:31:31,960
a series of unrelated changes to the Earth
415
00:31:32,127 --> 00:31:34,721
resulted in a dramatic change to life.
416
00:31:38,807 --> 00:31:41,196
The continents had been moving together
417
00:31:41,287 --> 00:31:44,757
and had formed one huge supercontinent
called Pangaea.
418
00:31:47,967 --> 00:31:51,039
This huge landmass reduced the coastline,
419
00:31:51,127 --> 00:31:53,402
reducing the habitats for marine life.
420
00:31:54,367 --> 00:31:57,279
At the same time, sea levels dropped dramatically,
421
00:31:57,367 --> 00:32:01,406
exposing and killing all those species
living on the continental shelf.
422
00:32:02,087 --> 00:32:05,318
90 percent of marine life was destroyed.
423
00:32:08,967 --> 00:32:12,846
On land, this coincided with a catastrophic event
424
00:32:12,927 --> 00:32:14,883
in what is now Siberia.
425
00:32:32,167 --> 00:32:36,399
COURTILLOT: It's very hard to imagine
what may have happened when this lava erupted.
426
00:32:36,487 --> 00:32:39,718
The volumes, the size, the speeds involved.
427
00:32:41,407 --> 00:32:44,797
This is not something that has been seen
since the human race exists,
428
00:32:44,887 --> 00:32:46,718
since the human species exists.
429
00:32:46,807 --> 00:32:51,198
You should try to imagine a fissure,
a crack in the Earth's crust
430
00:32:51,287 --> 00:32:53,357
possibly 400 kilometres long,
431
00:32:53,647 --> 00:32:55,205
spewing lava,
432
00:32:56,447 --> 00:33:00,281
throwing material, dust
but most importantly gases,
433
00:33:00,367 --> 00:33:05,282
carbon dioxide, sulphur dioxide,
that will eventually lead to acid rain,
434
00:33:05,367 --> 00:33:08,677
darkness, cooling, altering vegetation,
435
00:33:09,287 --> 00:33:11,926
destroying animals
that would need vegetation for support
436
00:33:12,007 --> 00:33:15,363
and eventually killing animals
that would eat animals that ate vegetation.
437
00:33:15,447 --> 00:33:18,280
So the whole life chain being completely changed.
438
00:33:19,247 --> 00:33:22,603
Many teams around the world
have collected samples from this lava
439
00:33:22,687 --> 00:33:24,757
and dated it very accurately
440
00:33:24,847 --> 00:33:29,318
and found that
it was precisely 250 million years old.
441
00:33:30,247 --> 00:33:35,765
MANNING: Massive volcanic outpourings like these
which ruin ecosystems, destroying food chains,
442
00:33:36,087 --> 00:33:39,045
are regular events in the history of the Earth.
443
00:33:39,847 --> 00:33:43,635
COURTILLOT: These volcanic eruptions are part
of a very important rhythm of the Earth.
444
00:33:43,727 --> 00:33:46,480
The planet is essentially trying to cool down
445
00:33:46,767 --> 00:33:51,283
and that heat leaves with that big bubble of rock
which, when coming to the surface,
446
00:33:51,367 --> 00:33:54,803
melts and produces, through cracks
induced in the Earth's crust,
447
00:33:54,887 --> 00:33:57,082
the gigantic lava outpourings.
448
00:33:59,647 --> 00:34:03,162
It shows that the Earth's geology
has a direct influence
449
00:34:03,247 --> 00:34:08,275
in changing the course of evolution
at certain times but in a gigantic way.
450
00:34:09,447 --> 00:34:11,165
Was it not for these catastrophes,
451
00:34:11,247 --> 00:34:13,238
well, life on Earth today
would be completely different,
452
00:34:13,327 --> 00:34:15,795
and most likely, we would not be here.
453
00:34:18,367 --> 00:34:22,406
That combination of events on Earth
250 million years ago
454
00:34:22,767 --> 00:34:27,079
led to the biggest
and most catastrophic mass extinction of life
455
00:34:27,167 --> 00:34:28,680
that's ever occurred.
456
00:34:29,047 --> 00:34:31,515
It probably lasted for several million years.
457
00:34:31,607 --> 00:34:35,077
But whilst it was going on,
the carnage was enormous.
458
00:34:36,167 --> 00:34:39,955
It's hard to comprehend now,
but during that time,
459
00:34:40,047 --> 00:34:45,804
80 to 90 percent of life, on land
and especially in the sea, disappeared.
460
00:34:47,447 --> 00:34:52,362
So our modern understanding
of how the Earth works, how it operates,
461
00:34:52,927 --> 00:34:56,078
has given us a new view
on the processes of evolution.
462
00:34:56,487 --> 00:35:00,560
Yes, because it does seem that there have been
these marked events,
463
00:35:00,647 --> 00:35:04,401
these punctuations in the history of life
caused by whatever reasons,
464
00:35:04,487 --> 00:35:07,843
which have caused massive extinctions
465
00:35:08,127 --> 00:35:11,597
and therefore provided opportunities
for other groups to evolve.
466
00:35:11,687 --> 00:35:13,757
So rather than being just a steady
467
00:35:13,847 --> 00:35:17,396
and almost ineluctable change
from simple to more complex,
468
00:35:17,567 --> 00:35:20,127
life has these punctuation marks across it.
469
00:35:20,407 --> 00:35:22,045
And each punctuation mark
470
00:35:22,167 --> 00:35:26,285
provides a period of opportunity for new
and perhaps slightly unpredictable groups
471
00:35:26,367 --> 00:35:27,959
to evolve and diversify.
472
00:35:28,047 --> 00:35:33,246
And therefore the whole of life on Earth has been
affected by these singularly chance events.
473
00:35:33,727 --> 00:35:39,404
It's difficult to know who will be the beneficiaries
of these events and who will actually lose out.
474
00:35:40,007 --> 00:35:41,645
I think that's the way you've got to look at life.
475
00:35:41,727 --> 00:35:46,164
There are always winners and losers
in any situation like that.
476
00:35:46,567 --> 00:35:48,285
But it adds that sort of...
477
00:35:49,327 --> 00:35:52,956
spicy sort of unpredictability
to the history of life on Earth.
478
00:35:54,727 --> 00:35:57,241
MANNING: And the winners are the survivors,
479
00:35:57,327 --> 00:36:00,558
those species with the ability
to live through the changes.
480
00:36:01,127 --> 00:36:04,722
And after the mass extinction
of 250 billion years ago,
481
00:36:05,247 --> 00:36:08,398
a few of the mammal-like reptiles
managed to survive.
482
00:36:09,807 --> 00:36:13,595
The mammal-like reptiles
survived these very difficult times
483
00:36:13,927 --> 00:36:15,758
because they were burrowing.
484
00:36:16,087 --> 00:36:22,196
And this is a very good example
of a cast of a burrow that you find in the rocks.
485
00:36:23,767 --> 00:36:26,964
And this is really a unique find.
486
00:36:27,967 --> 00:36:33,439
Where we found the animal inside a burrow.
487
00:36:34,967 --> 00:36:39,677
MANNING: Burrowing allowed these animals
to survive in an increasingly harsh world.
488
00:36:41,007 --> 00:36:44,204
The whole of Pangaea
was gradually moving northwards,
489
00:36:44,447 --> 00:36:47,644
taking this part of Southern Africa
closer to the Equator.
490
00:36:48,287 --> 00:36:52,599
The climate became hotter and hotter,
drier and drier.
491
00:36:53,407 --> 00:36:57,161
And by 200 million years ago,
some of the mammal-like reptiles
492
00:36:57,367 --> 00:37:01,042
had evolved into a new group
of much smaller animals.
493
00:37:02,847 --> 00:37:04,803
Now for the first time
494
00:37:06,207 --> 00:37:10,041
we have the remains of true mammals.
495
00:37:10,367 --> 00:37:15,361
And this here is the skull
of one of these tiny mice-like creatures
496
00:37:15,967 --> 00:37:20,324
that managed to survive
these very difficult living conditions.
497
00:37:21,527 --> 00:37:26,123
By burrowing, they lived in burrows
and they fed only during the night.
498
00:37:28,207 --> 00:37:34,680
They're small, furtive, highly sensitive,
really quite intelligent mammals.
499
00:37:34,927 --> 00:37:38,920
And you'd think they would just,
in an evolutionary sense, explode,
500
00:37:39,007 --> 00:37:43,080
dominate everything around us,
because we're so familiar with mammals today.
501
00:37:43,367 --> 00:37:45,881
But the mammals don't take over the Earth,
do they?
502
00:37:45,967 --> 00:37:50,483
Curiously enough, those hot, dry desert conditions
don't suit mammals.
503
00:37:50,927 --> 00:37:54,602
Reptiles such as dinosaurs
were perfect for those conditions.
504
00:37:54,807 --> 00:37:58,083
Deserts usher in dinosaurs and really from then on
505
00:37:58,167 --> 00:38:04,356
mammals are curiously confined
just to a nocturnal insectivore sort of niche
506
00:38:04,487 --> 00:38:09,641
and scurry around at night,
perhaps around the sleeping bodies of dinosaurs,
507
00:38:09,927 --> 00:38:12,236
while dinosaurs dominate the daytime.
508
00:38:20,927 --> 00:38:24,636
MANNING: The dinosaurs were
the most successful of all the vertebrates
509
00:38:24,727 --> 00:38:27,195
that have ever lived on land.
510
00:38:27,287 --> 00:38:31,485
There were the dominant group
for over 170 million years.
511
00:38:37,607 --> 00:38:40,599
And then, as we all know, they disappeared.
512
00:38:41,367 --> 00:38:45,155
65 million years ago,
there was another mass extinction.
513
00:38:46,007 --> 00:38:49,363
The dinosaurs went, the pterodactyls,
514
00:38:49,447 --> 00:38:51,961
the ichthyosaurs, those marine reptiles,
515
00:38:52,167 --> 00:38:53,646
many other species,
516
00:38:53,727 --> 00:38:56,560
even the beautiful ammonites
were never seen again.
517
00:38:57,207 --> 00:39:00,563
60 to 70 percent of life became extinct.
518
00:39:00,887 --> 00:39:03,276
It disappeared from the fossil record.
519
00:39:08,367 --> 00:39:13,077
Many scientists now believe that
a meteorite from outer space struck the Earth.
520
00:39:21,127 --> 00:39:24,836
They believe that this created a gigantic fireball.
521
00:39:26,407 --> 00:39:30,002
Dense clouds of material and dust
were thrown into the sky,
522
00:39:30,087 --> 00:39:33,363
obliterating the sun for months or even years.
523
00:39:36,887 --> 00:39:40,084
The whole ecostructure would have collapsed.
524
00:39:40,927 --> 00:39:45,876
But some scientists have doubts.
Did a meteorite really destroy the dinosaurs?
525
00:39:49,007 --> 00:39:53,125
A crater caused by the impact of a meteorite
has been found.
526
00:39:54,007 --> 00:39:57,682
The centre is right here,
in the village of Chicxulub in Mexico.
527
00:39:58,647 --> 00:40:01,957
The crater is the right date, 65 million years old.
528
00:40:02,927 --> 00:40:04,679
But is it the right size?
529
00:40:05,047 --> 00:40:09,359
Some scientists think the meteorite
was too small to have wiped out the dinosaurs.
530
00:40:14,767 --> 00:40:19,283
Trying to settle the argument are seismologists
Mike Warner and Jo Morgan.
531
00:40:20,087 --> 00:40:22,601
They're working out the size of the crater.
532
00:40:22,847 --> 00:40:26,965
Using over 100 seismometers
buried in the ground and out at sea,
533
00:40:27,247 --> 00:40:29,238
they can build up a seismograph,
534
00:40:29,327 --> 00:40:34,003
a picture of the crater which is hidden
under 65 million years' worth of sediment.
535
00:40:35,087 --> 00:40:37,203
And their results were surprising.
536
00:40:37,527 --> 00:40:41,315
WARNER: The size of the object that hit the Earth
was about 12 kilometres in diameter.
537
00:40:41,407 --> 00:40:46,117
But it was, relatively speaking, rather small
on the size that people had been guessing.
538
00:40:46,247 --> 00:40:49,717
MANNING: It seemed to be too small
to have killed the dinosaurs.
539
00:40:49,967 --> 00:40:54,483
But their seismograph shows the meteorite
couldn't have landed in a worse place.
540
00:40:55,247 --> 00:40:59,320
A small impact shouldn't be devastating.
It shouldn't mess up the environment.
541
00:40:59,407 --> 00:41:01,682
And maybe the dinosaurs were lucky.
542
00:41:01,847 --> 00:41:03,519
If we look at these rocks here,
543
00:41:03,607 --> 00:41:07,282
they're formed in shallow lagoons
much like we see around Chicxulub.
544
00:41:07,847 --> 00:41:10,236
And they contain a lot of sulphur.
545
00:41:10,727 --> 00:41:13,764
WARNER: Rocks with sulphur in,
if you hit them really hard with an impact,
546
00:41:13,847 --> 00:41:15,519
then they generate sulphur dioxide.
547
00:41:15,607 --> 00:41:17,199
And if you put sulphur dioxide in the atmosphere
548
00:41:17,287 --> 00:41:19,198
it combines with water
and it makes sulphuric acid.
549
00:41:19,287 --> 00:41:22,404
Little droplets of sulphuric acid
way up in the stratosphere.
550
00:41:22,487 --> 00:41:23,840
And that's particularly deadly,
551
00:41:23,927 --> 00:41:27,761
it stops sunlight getting to the ground
for 10 years, perhaps 100 years.
552
00:41:28,447 --> 00:41:32,235
So, maybe the dinosaurs were killed
just by these rocks that we're seeing here
553
00:41:32,327 --> 00:41:34,238
because those were hit very, very hard.
554
00:41:37,287 --> 00:41:40,245
MANNING: But maybe the dinosaurs
were doubly unlucky.
555
00:41:41,407 --> 00:41:45,082
Because at the same time
on the other side of the world in India,
556
00:41:45,407 --> 00:41:48,205
another catastrophic event was taking place.
557
00:41:48,967 --> 00:41:52,516
Volcanoes were again pouring out
massive amounts of lava.
558
00:41:53,087 --> 00:41:55,123
It was an unimaginable amount,
559
00:41:55,327 --> 00:41:58,683
the like of which had not been seen
for 200 million years.
560
00:42:01,207 --> 00:42:06,042
The volcanoes were also belching out
clouds of dust, turning day into night.
561
00:42:07,327 --> 00:42:12,082
The combination of the meteorite
and the Indian volcanoes was too much.
562
00:42:12,247 --> 00:42:15,956
It turned the Earth's surface
into a dark, burning world
563
00:42:16,207 --> 00:42:19,802
where all the rules
governing survival of the fittest changed.
564
00:42:20,927 --> 00:42:23,441
The dinosaurs never had a chance.
565
00:42:39,687 --> 00:42:42,520
Those events 65 million years ago
566
00:42:42,887 --> 00:42:46,960
resulted in another dramatic turning point
in the evolution of life.
567
00:42:49,047 --> 00:42:52,676
The dinosaurs had all gone,
most of the other reptiles had gone
568
00:42:52,887 --> 00:42:55,196
and there was a void of large animals.
569
00:42:56,607 --> 00:43:00,395
Into that void the mammals
and the birds jumped very quickly.
570
00:43:00,567 --> 00:43:04,560
The mammals in particular
had been held down by the reptiles,
571
00:43:04,647 --> 00:43:07,639
dominance of the reptiles,
for many millions of years.
572
00:43:07,887 --> 00:43:11,357
And they radiated out extensively
all over the Earth.
573
00:43:12,207 --> 00:43:16,439
The primates emerged
and eventually we emerged ourselves.
574
00:43:20,767 --> 00:43:25,079
The last leg of my journey
through the story of life is here in Africa.
575
00:43:25,207 --> 00:43:28,597
Not too far north of where I started
with the origin of life.
576
00:43:30,927 --> 00:43:34,602
I'm in Kenya, in the Great Rift Valley of Africa.
577
00:43:36,287 --> 00:43:38,801
And it's here that scientists are discovering
578
00:43:38,887 --> 00:43:41,720
just how closely the evolution of the Earth
579
00:43:41,807 --> 00:43:44,924
is linked to the evolution of our own ancestors.
580
00:43:50,447 --> 00:43:52,165
Over the last million years,
581
00:43:52,487 --> 00:43:58,244
the Earth has experienced a succession of
ten glaciations interspersed with warm periods.
582
00:44:03,367 --> 00:44:05,927
This waxing and waning of the ice sheets
583
00:44:06,007 --> 00:44:09,204
has had a profound effect
on the rest of the world's climate
584
00:44:09,287 --> 00:44:10,845
and our own evolution.
585
00:44:18,207 --> 00:44:21,119
Rick Potts spends every summer
searching for evidence
586
00:44:21,247 --> 00:44:26,275
to show why modern humans evolved
from our ape-like ancestors.
587
00:44:26,367 --> 00:44:28,927
We're going up through time,
up through time here
588
00:44:29,007 --> 00:44:31,760
and then we reach a point
where the soil disappears
589
00:44:31,847 --> 00:44:34,680
and this white sediment of the lake bed comes in,
590
00:44:34,767 --> 00:44:39,158
which shows that the lake had expanded and
covered the whole area of the southern Kenya Rift,
591
00:44:39,247 --> 00:44:40,646
just in this area.
592
00:44:41,087 --> 00:44:43,442
And again these fluctuations continue
593
00:44:43,527 --> 00:44:46,758
and then the soil comes back
just for a short period of time.
594
00:44:46,847 --> 00:44:48,997
What do you mean by a short period of time here?
595
00:44:49,087 --> 00:44:51,920
Probably, oh, a few hundred years at most.
596
00:44:52,007 --> 00:44:55,602
And then the soil disappears
and it's replaced by the lake up here.
597
00:44:56,807 --> 00:45:00,800
And then the soil comes back in again
for a short period of time.
598
00:45:01,207 --> 00:45:03,721
Lake again and then a very sharp demarcation
599
00:45:03,807 --> 00:45:06,879
where the soil again
goes as far as the eye can see.
600
00:45:06,967 --> 00:45:11,404
And this occurred at a time when the Ice Age
fluctuations in Europe and North America
601
00:45:11,487 --> 00:45:15,480
were just really getting going
and tremendous fluctuations going on.
602
00:45:18,287 --> 00:45:22,075
MANNING: But how can rapid fluctuations
between dry and wet periods
603
00:45:22,167 --> 00:45:25,523
be the driving force of the evolution
of modern humans?
604
00:45:27,647 --> 00:45:31,560
POTTS: This is the species Homo habilis
and it had still a relatively small brain.
605
00:45:31,647 --> 00:45:36,960
This was a clever creature, make no doubt
about it, but it wasn't quite us.
606
00:45:37,287 --> 00:45:40,359
It reminds me very much of the chimpanzee.
607
00:45:40,447 --> 00:45:44,201
I mean, why didn't we stay as upright apes
like chimpanzees?
608
00:45:44,287 --> 00:45:48,565
In my view, we evolved
because of climate fluctuation,
609
00:45:48,647 --> 00:45:51,445
of the tremendous fluctuations
610
00:45:51,527 --> 00:45:55,600
and uncertainty of environments
that we can see here in the geologic record.
611
00:45:55,727 --> 00:45:58,002
This is Homo sapiens, our own species.
612
00:45:58,167 --> 00:46:02,638
And this one evolved during those fantastic
fluctuations of environment
613
00:46:02,847 --> 00:46:06,476
that we see beginning about
600 to 700 thousand years ago.
614
00:46:06,687 --> 00:46:10,475
And you can see the incredibly large size
of the brain case.
615
00:46:10,647 --> 00:46:13,207
So the rate of change began to accelerate?
616
00:46:13,447 --> 00:46:16,359
Yes. Tremendous acceleration
in the rate of brain growth.
617
00:46:16,447 --> 00:46:18,517
And this had to do with I think, with flexibility,
618
00:46:18,607 --> 00:46:22,361
with the ability to adapt
to those tremendous changes in environment.
619
00:46:22,927 --> 00:46:25,043
For example, communication.
620
00:46:26,247 --> 00:46:28,397
Through language we are able to say,
621
00:46:28,607 --> 00:46:31,440
"You know, my grandfather told me that
622
00:46:32,887 --> 00:46:37,403
"the time before him, you could find fruits
to eat on the other side of that mountain
623
00:46:37,567 --> 00:46:38,602
"when there is a drought."
624
00:46:38,687 --> 00:46:40,882
And that's something that no other animal can do.
625
00:46:40,967 --> 00:46:45,483
Being able to refer to places and things
and abstract things that you can't even see.
626
00:46:45,567 --> 00:46:47,842
And yet we can communicate about them.
627
00:46:48,807 --> 00:46:50,445
We're used to the idea
628
00:46:50,687 --> 00:46:53,963
that organisms are adapted
through natural selection
629
00:46:54,087 --> 00:46:57,557
to match the specific environment
in which they live.
630
00:46:57,647 --> 00:47:00,445
But I think there's another process of selection
631
00:47:00,727 --> 00:47:05,403
that is... represents an adaptation to the
variability and the fluctuation of environments.
632
00:47:05,487 --> 00:47:08,559
And this is a process that distances an organism
633
00:47:08,647 --> 00:47:10,638
from any one specific environment.
634
00:47:10,727 --> 00:47:12,683
And I think that we, Homo sapiens,
635
00:47:12,767 --> 00:47:15,520
are the paramount example
of this kind of species.
636
00:47:16,207 --> 00:47:19,836
(HERDSMAN CALLING OUT AND CRACKING WHIP)
637
00:47:22,327 --> 00:47:24,921
MANNING: So we, too, like the rest of life,
638
00:47:25,007 --> 00:47:29,239
are the product of constant physical changes
that have occurred here on Earth.
639
00:47:32,367 --> 00:47:33,880
As a biologist,
640
00:47:34,007 --> 00:47:38,285
I've always concentrated
on the evolution of life in biological terms.
641
00:47:38,967 --> 00:47:41,527
But it adds a completely new dimension
642
00:47:41,607 --> 00:47:44,917
to recognise how closely
the evolution of life is linked
643
00:47:45,007 --> 00:47:47,362
with the inexorable changes of the Earth.
644
00:47:51,087 --> 00:47:55,126
We now know that Earth isn't simply
the place where we happen to live.
645
00:47:55,887 --> 00:47:57,684
We know it's a dynamic planet
646
00:47:57,767 --> 00:48:00,565
and we know the Earth has been
one of the driving forces,
647
00:48:00,647 --> 00:48:03,719
shaping evolution since
the very beginnings of life.
648
00:48:05,127 --> 00:48:08,324
We also know that the way
life has evolved on Earth
649
00:48:08,607 --> 00:48:12,156
makes our planet different
from our neighbouring planets.
650
00:48:13,527 --> 00:48:16,803
But the Earth is also special in its geology.
651
00:48:17,847 --> 00:48:22,159
And in the next programme,
we'll be exploring why we are so different.
652
00:48:23,207 --> 00:48:25,516
What makes the Earth so special?