Sefton Sands Coast

15 miles beyond Liverpool,

Alice Roberts is crossing Sefton Sands,

one of the UK's most extensive stretches of dunes.

Nearly there. I must say, this is a pretty exciting journey to work.

The Sefton Sands are over 4,000-years-old.

And there's a mystery, not in the dunes, but buried on the beach.

Beneath the sand lie layers of clay which bear ancient human footprints

left here over 5,000 years ago.

But once exposed by the tide, they last a few days before vanishing.

So I'm meeting specialists to work out who these people were and what they were doing.

-John, how far has this arm actually got to go up?

-To the pin.

Dr Annie Worsley is a physical geographer from Edgehill College,

and Professor Michael Day

of London's Natural History Museum is one of the world's leading experts in fossil footprints.

Gordon Roberts discovered the prints by chance, 15 years ago when he was walking his dog.

The tides wash away the sand lying on layers of clay underneath,

revealing footprints running in trails across the surface.

-A right foot, a left foot, a right. This one looks...

-That looks lovely.

It's less distorted, so if we sponge it out...

-That's been compacted by the weight of the person.

-That's lovely.

It looks like an adult-size foot to me, Gordon.

You can feel how compacted it is.

It's been baked in mud in the sun.

That's really hard.

Originally formed in mud, the prints were baked solid by the sun

and preserved with layers of sand.

Successive investigations have confirmed them to be at least 5,000 years old.

This is somebody that's walked up the beach, and you can see

the footprints disappearing underneath here.

That's how we know for sure that they weren't made yesterday.

That's right.

The fact that the trails continue underneath a datable layer of clay

proves that the footprints were not formed yesterday.

The prints are recorded before being washed away by the tides.

In 15 years, Gordon has painstakingly catalogued

273 trails before they were lost forever.

One of the first to interpret this kind of ephemeral archaeology

was Professor Michael Day.

He deciphered the earliest human footprints discovered in Tanzania - over three million years old.

I want to know what they can tell us

about the people that made them.

There's more information than you might expect.

You can find out about them. You can tell their height from the length of the foot.

You can find what he or she was doing.

You also get information from the environment.

Your height is approximately seven times the length of your foot.

I make that about 260 millimetres.

So it's a simple calculation to work out how tall this person was.

And that's about 1.7 metres, which is about 5'7", 5'8".

Oh, that's exactly the same as me!

Yeah, so this is a Mesolithic person, same height as me.

-Not an ancestor?

-Maybe!

What do you think the lifestyle of these people 5,000 years ago would have been?

Remember, there was no farming, they could not produce food easily.

The reason for them being on this beach must be to do with food.

-Yeah.

-They were scavengers, hunters, getting whatever they could find.

So this is the end of hunter-gathering.

-It's just before farming.

-Just the beginning of farming, when food production became a big revolution.

Of course, dress them up as we're dressed up now,

and they'd be passed on the beach without any hesitation.

We've got the sample now, and it's nicely coloured up with saffron and glycerol.

Annie Worsley is examining organic material

from close to the footprints to find clues about what kind of environment

these people called home five millennia ago.

We've got spheroidal carbonaceous particles.

-Oh!

-In other words, they're round, they're made of carbon, instead of angular black fragments.

-Surely that's just more charcoal.

-That's from a big bonfire of some sort.

-Really?

It could be they are getting pottery kilns going, or metal.

The fragments of charcoal and plant material

are all that remain of the world our ancestors inhabited.

But they contain vital clues about why these people were here.

It didn't look exactly like it does today. There may have been sandhills

several kilometres west, in other words, out under the sea.

But in-between here and those sand ridges,

would have been a complex landscape made up of lagoons, tidal creeks.

There would have been salt marshes, and there would have been scrubland

a little way east from where we're sitting now.

Between 5,000 - 7,000 years ago,

we're looking at an average July temperature

a degree or two warmer than today.

Which might be why the animals came here and the people came here.

After the last ice age, our island became densely covered

in primeval forest, so prehistoric people sought out the resources they needed along the coast.

With the tide fast approaching and light fading,

Gordon's found a huge set of prints belonging to an aurochs, the ancestor to the modern cow.

They could be a clue to what these people were doing here.

-Wow! They're huge!

-Yes, indeed, this perhaps is the best.

You can see a sort of cloven hoof.

I wouldn't like to come face to face with the thing that made these.

Bull aurochs were fast and ferocious,

and of course large - six foot high to the shoulder blades.

-11 foot from the muzzle to the rump.

-Huge.

This is a modern cow's foot,

and you can see the cloven-hoof down here.

But you can see how much smaller...

This is a full-grown cow, not a calf. A full-sized cow.

I wouldn't like to meet it on the beach.

So following the last ice age, our coast was not at the margins of human life,

it was at its centre.

It was here that our ancestors experienced

one of the greatest revolutions,

away from subsistence by hunting and gathering towards farming.

Deep beneath the Sefton sand, we see more than mere footprints -

we get to see the marks of one of humanity's greatest leaps forward.