Earth Story

Today, we are in the midst of a scientific revolution

in our understanding of the Earth

and our relationship to it.

Recently, scientists have begun to

think of the Earth in a new way -

almost as a living organism.

Like a living thing it is forever on the move,

driven by the restless energy

locked up in its interior.

And as the planet has evolved,

so has life,

shaped by the same forces

that move continents and change climates.

In Earth Story we shall explore this new vision

of a living planet

and the essence of this vision

is an understanding of time.

The most profound question

any scientist can ask about the earth

is also a simple one -

how old is it?

It's a question geologists have been striving

to answer for 200 years.

At the turn of the century

one such geologist came to a remote corner

of Southern Africa

called the Barberton Mountain Land.

His name was Alan Hall

and he had a commission from the South African government

to map this area looking for gold.

The Barberton Mountain Land

is several thousand square kilometers of rugged terrain,

cut through by rivers.

Rocky outcrops dot the hills,

signs of the bedrock hidden beneath the landscape.

Hall's aim was to criss-cross the region,

recording these outcrops,

and so build up a picture

of the rocks below the surface.

It was an immense task.

But as he worked his way across the landscape

Hall slowly realized that something was missing.

However hard he looked,

he could find in the rocks

none of the usual signs of fossilized life.

Could Barberton be a fragment of the Earth

from a time before life began?

Just how old was this place?

Hall's question came at a critical moment.

For a hundred years scientists had been arguing

about the age of the Earth

They were struggling to overcome ideas

which had held sway for centuries.

Ideas sanctioned by the full authority

of religious doctrine.

The book of Genesis relates how God created the earth

and everything in it, including ourselves,

in just 6 days.

The implication was that earth history and human history

had begun at the same moment

and this provided 17th century scholars

with a way to determine the age of the earth.

By simply adding up the ages

of Adam's descendants as listed in the Bible,

they concluded that the planet

must have been created in 4004 BC,

which meant it was less than 6,000 years old.

But it didn't look that way to geologists.

when they studied places like Barberton

they saw evidence that the landscape

had changed over time -

that it had a long history.

Hall's modern-day successor is Maarten de wit.

He too is fascinated

by the question of Barberton's antiquity.

I really got interested in this part

of the world many years ago,

but the opportunity to come here didn't arise

until much later.

At the end of the 70s

I came down here to Barberton

and it turned out to be one of the best moves of my life.

It's one of these areas

that has something extremely special

to tell about the story of the earth.

Maarten, like Hall before him,

has mapped the rocks of Barberton in detail.

when you do this,

a striking pattern quickly emerges.

well once you start mapping the hills here,

you'll notice that the landscape

is dominated by stripes -

stripes of rocks -

like that one there.

And if you get your eye in,

after a while you'll see, in fact, all these rock layers,

all are visible.

In this case this huge mass here

has finer vertical rock layers.

Everywhere in Barberton

the landscape seems to be made of layers.

By the nineteenth century,

geologists had begun to realize

that the process that created these layers

was still at work all around them.

Hall and his contemporaries knew that water

can be a powerful agent of change,

eroding rock, but also creating it... over time.

well take this river, for example,

like many rivers,

cutting through the rocks,

moving material downstream -

sand and silt -

and as it moves down

that material will deposit somewhere

in a quiet spot layer upon layer,

and as these layers get deposited on top of one another

they turn into rock slowly.

well here you have a slab of rock.

Now this slab represents a river bed.

There you can even see the sand grains.

These would have been the sand grains in the river.

These ridges that you see here,

they are ripples.

I can tell that it would have flowed

from my hand here downwards in that direction.

Now you can see if you look downwards

that in fact there are several of these

slabs stacked on top of one another.

Here's one,

there you see another one over here,

and another one,

and another one still, and more.

These are dozens of slabs

and they're all tilted right now,

but originally they would have been horizontal

and they represent all history of rivers.

A long history of deposition.

To nineteenth-century scientists

a world made up of layers

didn't look as if it had been created

all in one go as the Bible says.

It must have been built up overtime.

But how much time?

The first person to realise

the profound importance of this question

was a Scotsman, James Mutton.

At Siccar Point on the east coast of Scotland

exposed in the cliff side

there's a small patch of rock

which made a deep impression on Hunt.

Chris Nicholas is a geologist

who has made a special study of his work.

So here we are at one of the most

famous geological localities in the world.

This is Hutton's Unconformity

and what Hutton noticed here

in this cliff

is that at the bottom of the cliff you have these

vertical strata,

overlain by horizontal strata

and between the two

there was an undulating erosional surface.

And what Hutton recognised

was that well if all rocks

were deposited horizontally on the sea-bed,

what on earth was this grey rock doing being vertical

at the base of the cliff there was something wrong here.

And he started to look at rocks in more detail

and he came up with this idea

that what must have happened

is that the grey rock must have been twisted and turned

so that it was vertical,

uplifted out of the sea,

eroded off and then drowned again,

so that the red rock could be deposited on top.

And more than that, it was then uplifted again

to form the cliff we now see.

So there were at least 2 cycles of deposition,

uplift and then erosion

that he could see in this cliff.

And he went on to say "well, these cycles must have taken

an immense amount of time to complete"

because when he looked around him and saw rivers

and the sea eroding today

it doesn't really erode very quickly.

And also he said "well how many cycles

could have taken place before these

and how many will come after this,

we just don't know".

And it led him on to this idea

of the immensity

of geological time

and he came out with a very famous quote of,

well, he could see no vestige

of a beginning and no prospect of an end.

For Hutton the earth was infinitely old.

Siccar Point represents the discovery of geological time

and it's shaped the way

that geologists think and work ever since.