Walking Through Time - First season

On the leap day of the 29th of February 2016,

a bright light and a strange noise

filled the skies over northern Scotland.

It was later identified as a meteor breaking up

as it entered the Earth's atmosphere.

But not all extraterrestrial bodies break up

before they hit the ground.

Brand-new research in this part of Scotland suggests that something

extraordinary and unbelievably powerful happened here

to shape the landscape.

Could north-western Scotland have suffered an asteroid strike

almost as catastrophic as the impact

that may have wiped out the dinosaurs?

Scattered all along this coast is evidence of a major event of

extraterrestrial origin.

I'm headed out into this spectacular landscape to find out what happened.

As a palaeontologist, I'm fascinated by the sometimes violent

geological events that have shaped our planet.

Oh, my goodness, they're everywhere.

Loads and loads of them. Oh, look.

My asteroid hunt will take me along the finest beaches,

up the most epic mountains and craggiest,

most remote sections of coastline...

It speaks to you. It tells you about where you are.

...in search of evidence for an ancient asteroid crater

that might not only be the first to be found on mainland Britain...

Smash, smash, smash!

Raining down over everywhere in the vicinity! <span

...it could be amongst the biggest on the face of the Earth.

This is utter catastrophe in a matter of minutes.

This coastline is a lovely place for a walk.

You've got sea, in the distance views of epic-looking mountains,

but of course it's more than just beautiful.

And despite the fact that people have come here in their thousands to

study the rocks in these parts,

there are still secrets to be uncovered.

And a new discovery along this coast in these very,

very cliffs is pointing towards something remarkable.

Something explosive.

My geological mystery trail begins a mere two hours' drive

north-west of Britain's most northern city, Inverness.

At the North West Highlands Geopark.

Within the park is a magical landscape

of three-billion-year-old rocks,

majestic mountains, lochs, castles and beautiful white-sand beaches,

complete with turquoise water.

My extraterrestrial investigation

takes me from Clachtoll Beach to Enard Bay,

inland up the mountain of Stac Pollaidh,

along Loch Assynt and to the caves of Inchnadamph.

Finally, further inland, I'll hear the latest evidence in the search

for the asteroid's long-lost crater.

Before I start my walk,

I want to get a feel for how the ancient landscape would've looked

before and after that asteroid landed.

The best place to do that

is on the astonishing white sands of Clachtoll Beach.

It's not just the beauty here that is stunning.

The rocks hereabouts, well,

the ages of them are absolutely mind-blowing.

Joining me on the beach is Dr Laura Hamlet.

This is possibly one of the most spectacular beaches I think I've ever been to.

Yeah, it has that effect.

As a geo-archaeologist for the Geopark,

she has a handle on the awe-inspiring rocks

that make up her own back yard.

Can you talk me through the stunning landscape that I've got around me here?

OK. So, around the beach here you've got the two different rock types.

You can see up on the hill there you've got the Lewisian gneiss,

three billion years old.

It's one of the oldest rocks in Western Europe,

and it's the oldest rock in the British Isles, that's for sure.

And then the outcrops around the beach,

these are the Torridonian sandstone.

Probably about a billion years old.

So a little bit younger!

'The phenomenally old Lewisian gneiss underpins the landscape here,

'but sitting on top of it is this very different purplish rock,

'Torridonian sandstone.'

You've got the Lewisian gneiss. I mean, how did that form?

It probably started life out as maybe volcanic,

deep underground for many, many years,

almost liquid at points, it was so hot, and then eventually,

it popped up to the crust surface again and became the landscape.

And it's into that landscape

that we get the Torridonian sandstone forming?

That's right. Now, how did that come to be laid down?

So, the material that makes it up was basically weathered and eroded from

a vast mountain chain, which was off to what's now the west.

And at Clachtoll just here we've got some very fine sediments,

which shows us this was a lake bed, and it's been wetting and drying,

which causes these desiccation cracks.

Locally we actually refer to these ones as Frankenstein stitches,

so a much better description.

That is a much better description, that's brilliant!

It really does look like a stitch!

So, we've got, you know, this incredible geology.

Has it influenced the life of people locally?

Absolutely. The sand here is actually made up of fragments of Torridonian,

fragments of Lewisian,

but there's also quite a bit of shell in it as well.

So the shell creates an alkaline soil essentially,

so you get around areas like this

a very fertile soil, so excellent for farming.

You can see the little crofters' farms hereabouts

and that's just lovely,

and that's all partly due to the geology.

Yeah, the geology creates this lovely fertile soil.

This beautiful landscape is the ultimate in low population density.

Vast open spaces interspersed with

little crofters' cottages and fishing villages.

But to get on the trail of the mysterious asteroid,

I have to leave the present day and head way back into the past

to a time long, long before humans came onto the scene.

I'm heading to Enard Bay.

It's here that I'm meeting up with an old friend.

Spectacular coastline. It is.

It's pretty idyllic, isn't it?

Dr Mike Simms is the Curator of Palaeontology at the Ulster Museum.

But there's something a bit further along which is really very unusual.

And that's the thing that actually tempted me here.

For the past five years he's been investigating clues on this coast.

And he's recently discovered something completely new.

Mike's been analysing this rocky outcrop called the Stac Fada Member.

It looks just like more sandstone, doesn't it? Yeah!

And in fact for decades it was thought to be sandstone,

until about 50 years ago when people actually realised that this is

something a little bit different.

1.2 billion years old and 12 metres thick in places,

it contains clues that have long proved puzzling to geologists.

There's a lot of sand in there, but in amongst it

there's these little green blobs. Yeah.

There's one there, there, there.

There's a little piece there. And those were pieces of molten rock.

That's not like a river sandstone at all.

That something quite, quite different,

so what sort of environment do you find molten rocks in, generally?

The obvious one being, say, lava, for example, being molten rock.

Yeah, and this isn't a lava flow cos it's got all that sand mixed in it.

It was thought to be a volcanic mudflow, a lahar,

but it would still have been pretty hot, you're talking 200,

300 degrees centigrade.

And it stretches for about 50km along the coast to north and south.

A lahar, a debris-laden slurry of ash, mud and water,

is a truly devastating natural disaster.

The idea that this was all caused by a volcano

continued until around 2008,

when various researchers started suggesting that perhaps something

even more dramatic was responsible.

So what are we looking for? We're looking for little pea-like things

sticking out of the... Oh, I can see some. Oh, goodness, they're everywhere.

Yes, there's loads and loads of them. Yeah, they're everywhere. Wow.

These are actually what's called accretionary lapilli.

Right. Bit of a mouthful. It is a bit of a mouthful, yes!

And the reason they're called accretionary is because they've actually got layers,

when you cut one through they're almost like an onion.

'These little balls can be formed in

'the roiling dust clouds that accompany volcanic eruptions.'

They're produced in very hot clouds of dust.

Dust particles stick to an original little rock fragment or crystal

that's being carried up by the heat,

and perhaps it'll sink down a bit

and then more turbulence will lift it back up,

and another layer will go on it,

and it'll get bigger and bigger and bigger.

But of course eventually it's going to get too heavy,

and then they sort of will rain down out of the sky.

So accretionary lapilli are very characteristic

of some types of volcanic eruptions.

It all fits in with the notion that this was an absolutely massive

volcanic eruption.

So, what's the mystery, then?

There's no evidence of any other volcanic activity at all,

and that puzzled the geologists for decades.

With the absence of volcanic activity in this place at that time,

there had to be a different explanation.

Mike is part of a growing group of scientists who are putting forward

a totally different theory.

Back in 2008, a team of geologists led from Oxford University,

they looked in detail

at various aspects of this deposit and they said,

"No, this isn't a volcanic deposit,

"this has been caused by a meteorite impact." Ha-ha!

And that is just... Wow!

You think, oh, my goodness.

Once you know that, suddenly things become a lot clearer.

You can explain why it's so thick and why it is so extensive.

This was a really, really big impact.

The evidence on these shores points to a massive asteroid impact

somewhere here 1.2 billion years ago.

Over a pint in a pub, just to the south of Enard Bay,

Mike presents two more tiny but conclusive pieces of evidence.

To prove that it really is a meteorite, you...

you know, extraordinary claims require extraordinary evidence,

and there are two key bits of evidence that you actually find

in the Stac Fada impact deposit here.

One of them is an element called iridium,

and I've actually got a little nugget with me.

'This nugget is from Mike's museum.'

It's the rarest nonradioactive element on Earth.