0:00:25 > 0:00:2815 miles beyond Liverpool,
0:00:28 > 0:00:32Alice Roberts is crossing Sefton Sands,
0:00:32 > 0:00:35one of the UK's most extensive stretches of dunes.
0:00:35 > 0:00:40Nearly there. I must say, this is a pretty exciting journey to work.
0:00:43 > 0:00:48The Sefton Sands are over 4,000-years-old.
0:00:48 > 0:00:53And there's a mystery, not in the dunes, but buried on the beach.
0:00:53 > 0:00:59Beneath the sand lie layers of clay which bear ancient human footprints
0:00:59 > 0:01:03left here over 5,000 years ago.
0:01:03 > 0:01:09But once exposed by the tide, they last a few days before vanishing.
0:01:09 > 0:01:15So I'm meeting specialists to work out who these people were and what they were doing.
0:01:15 > 0:01:20- John, how far has this arm actually got to go up?- To the pin.
0:01:20 > 0:01:25Dr Annie Worsley is a physical geographer from Edgehill College,
0:01:25 > 0:01:28and Professor Michael Day
0:01:28 > 0:01:35of London's Natural History Museum is one of the world's leading experts in fossil footprints.
0:01:41 > 0:01:49Gordon Roberts discovered the prints by chance, 15 years ago when he was walking his dog.
0:01:49 > 0:01:54The tides wash away the sand lying on layers of clay underneath,
0:01:54 > 0:01:59revealing footprints running in trails across the surface.
0:01:59 > 0:02:04- A right foot, a left foot, a right. This one looks...- That looks lovely.
0:02:04 > 0:02:08It's less distorted, so if we sponge it out...
0:02:08 > 0:02:14- That's been compacted by the weight of the person.- That's lovely.
0:02:14 > 0:02:19It looks like an adult-size foot to me, Gordon.
0:02:19 > 0:02:23You can feel how compacted it is.
0:02:23 > 0:02:27It's been baked in mud in the sun.
0:02:27 > 0:02:30That's really hard.
0:02:30 > 0:02:35Originally formed in mud, the prints were baked solid by the sun
0:02:35 > 0:02:37and preserved with layers of sand.
0:02:37 > 0:02:44Successive investigations have confirmed them to be at least 5,000 years old.
0:02:44 > 0:02:49This is somebody that's walked up the beach, and you can see
0:02:49 > 0:02:53the footprints disappearing underneath here.
0:02:53 > 0:02:58That's how we know for sure that they weren't made yesterday.
0:02:58 > 0:03:01That's right.
0:03:01 > 0:03:06The fact that the trails continue underneath a datable layer of clay
0:03:06 > 0:03:10proves that the footprints were not formed yesterday.
0:03:10 > 0:03:15The prints are recorded before being washed away by the tides.
0:03:15 > 0:03:19In 15 years, Gordon has painstakingly catalogued
0:03:19 > 0:03:23273 trails before they were lost forever.
0:03:23 > 0:03:28One of the first to interpret this kind of ephemeral archaeology
0:03:28 > 0:03:31was Professor Michael Day.
0:03:31 > 0:03:38He deciphered the earliest human footprints discovered in Tanzania - over three million years old.
0:03:38 > 0:03:42I want to know what they can tell us
0:03:42 > 0:03:45about the people that made them.
0:03:45 > 0:03:49There's more information than you might expect.
0:03:49 > 0:03:55You can find out about them. You can tell their height from the length of the foot.
0:03:55 > 0:03:59You can find what he or she was doing.
0:03:59 > 0:04:04You also get information from the environment.
0:04:04 > 0:04:09Your height is approximately seven times the length of your foot.
0:04:09 > 0:04:12I make that about 260 millimetres.
0:04:12 > 0:04:17So it's a simple calculation to work out how tall this person was.
0:04:17 > 0:04:23And that's about 1.7 metres, which is about 5'7", 5'8".
0:04:23 > 0:04:26Oh, that's exactly the same as me!
0:04:26 > 0:04:31Yeah, so this is a Mesolithic person, same height as me.
0:04:31 > 0:04:34- Not an ancestor?- Maybe!
0:04:34 > 0:04:41What do you think the lifestyle of these people 5,000 years ago would have been?
0:04:41 > 0:04:45Remember, there was no farming, they could not produce food easily.
0:04:45 > 0:04:51The reason for them being on this beach must be to do with food.
0:04:51 > 0:04:55- Yeah.- They were scavengers, hunters, getting whatever they could find.
0:04:55 > 0:04:59So this is the end of hunter-gathering.
0:04:59 > 0:05:06- It's just before farming.- Just the beginning of farming, when food production became a big revolution.
0:05:06 > 0:05:10Of course, dress them up as we're dressed up now,
0:05:10 > 0:05:15and they'd be passed on the beach without any hesitation.
0:05:27 > 0:05:33We've got the sample now, and it's nicely coloured up with saffron and glycerol.
0:05:33 > 0:05:37Annie Worsley is examining organic material
0:05:37 > 0:05:43from close to the footprints to find clues about what kind of environment
0:05:43 > 0:05:47these people called home five millennia ago.
0:05:47 > 0:05:52We've got spheroidal carbonaceous particles.
0:05:52 > 0:05:58- Oh!- In other words, they're round, they're made of carbon, instead of angular black fragments.
0:05:58 > 0:06:05- Surely that's just more charcoal. - That's from a big bonfire of some sort.- Really?
0:06:05 > 0:06:11It could be they are getting pottery kilns going, or metal.
0:06:11 > 0:06:16The fragments of charcoal and plant material
0:06:16 > 0:06:20are all that remain of the world our ancestors inhabited.
0:06:20 > 0:06:26But they contain vital clues about why these people were here.
0:06:26 > 0:06:30It didn't look exactly like it does today. There may have been sandhills
0:06:30 > 0:06:36several kilometres west, in other words, out under the sea.
0:06:36 > 0:06:39But in-between here and those sand ridges,
0:06:39 > 0:06:45would have been a complex landscape made up of lagoons, tidal creeks.
0:06:45 > 0:06:49There would have been salt marshes, and there would have been scrubland
0:06:49 > 0:06:52a little way east from where we're sitting now.
0:06:52 > 0:06:55Between 5,000 - 7,000 years ago,
0:06:55 > 0:06:59we're looking at an average July temperature
0:06:59 > 0:07:02a degree or two warmer than today.
0:07:02 > 0:07:07Which might be why the animals came here and the people came here.
0:07:07 > 0:07:13After the last ice age, our island became densely covered
0:07:13 > 0:07:20in primeval forest, so prehistoric people sought out the resources they needed along the coast.
0:07:35 > 0:07:40With the tide fast approaching and light fading,
0:07:40 > 0:07:45Gordon's found a huge set of prints belonging to an aurochs, the ancestor to the modern cow.
0:07:45 > 0:07:49They could be a clue to what these people were doing here.
0:07:49 > 0:07:55- Wow! They're huge!- Yes, indeed, this perhaps is the best.
0:07:55 > 0:07:58You can see a sort of cloven hoof.
0:07:58 > 0:08:03I wouldn't like to come face to face with the thing that made these.
0:08:03 > 0:08:06Bull aurochs were fast and ferocious,
0:08:06 > 0:08:11and of course large - six foot high to the shoulder blades.
0:08:11 > 0:08:15- 11 foot from the muzzle to the rump. - Huge.
0:08:15 > 0:08:18This is a modern cow's foot,
0:08:18 > 0:08:22and you can see the cloven-hoof down here.
0:08:22 > 0:08:26But you can see how much smaller...
0:08:26 > 0:08:31This is a full-grown cow, not a calf. A full-sized cow.
0:08:31 > 0:08:35I wouldn't like to meet it on the beach.
0:08:35 > 0:08:41So following the last ice age, our coast was not at the margins of human life,
0:08:41 > 0:08:44it was at its centre.
0:08:44 > 0:08:47It was here that our ancestors experienced
0:08:47 > 0:08:49one of the greatest revolutions,
0:08:49 > 0:08:54away from subsistence by hunting and gathering towards farming.
0:08:55 > 0:08:59Deep beneath the Sefton sand, we see more than mere footprints -
0:08:59 > 0:09:04we get to see the marks of one of humanity's greatest leaps forward.