Rivers and Seas Collide 2 Coast

This is Coast.

Tide and traffic on the Thames flow two ways.

In deep waters at the estuary mouth,

ships from around the world come to unburden themselves

on the docks at Sheerness.

But back in the 19th century,

a group of foreign stowaways snuck off a ship and never left.

They set up a secret community within the harbour walls.

This is the des res of Britain's only colony of scorpions.

But not the monster kind.

European yellowtail scorpions arrived here from Italy

on a masonry ship some 200 years ago.

Now the offspring of those Italian scorpions

have found a British admirer.

Hi, I'm Becks, and I'm a scorpaholic.

I've been fascinated by scorpions since I was a teenager,

and been hooked ever since.

I'm here to see Britain's only colony of scorpions.

I've got to wait for the sun to go down.

Properly dark now, so I'm going to see if I can find some.

I'm using a UV torch

because scorpions glow under ultraviolet light.

I think I've just spotted one.

Definitely an adult.

Probably out looking for something to eat.

It is pretty cool, though, having scorpions in the UK.

They are a member of the spider family.

They've got eight legs, not six.

They eat woodlouse,

they're ambush predators so they will just sit and wait,

and then something will come past and they'll jump out and grab it

and subdue it with their claws, rather than stinging it.

They don't generally use their stings, these ones.

# That's amore! #

Very happy that we found some.

This is a tiny little incy one.

So cute. With tinyness comes speed.

It's been a great night.

We've seen loads of scorpions,

but I think I'll put this one back before it legs it.

Bye, little fella.

Yeah, I think I'll leg it now, too!

I'm exploring the Firth of Forth on Scotland's east coast,

where canny folk profited from their prime location,

ideal for seaborne business.

And with rich seams of coal for power, the population boomed.

With more mouths to feed,

getting enough fresh food was tricky

so they looked to the sea to preserve their provisions.

You'll find the evidence at St Monans.

Here, food-processing created a curious landscape.

The shore is lined with lots and lots

of very strange grass-covered humps.

What seems to be a ruined building over there,

and up there a stone windmill.

The ruins of industrial activity reveal themselves the more you look.

This land was remodelled

by people making the most of one bounty from the sea

that isn't in short supply - salt.

Before refrigeration, salt was a valuable commodity,

preserving herring landed along the east coast.

Scottish salt was also exported to England,

turning a tasty profit to the saltworks.

Those strange hummocks come in sets.

Each set of hummocks is the ruins of a pan house.

Inside each of those pan houses

there was an iron pan about six metres by three metres

with coal fires beneath it.

Sea water was pumped,

probably using this windmill from the sea, in pipes,

up to each pan house.

Once it had been boiled off in the pans, you had salt.

A rare film brings the enterprise back to life.

Saltworks once flourished along Scotland's east coast.

The last operation at Prestonpans

didn't close its doors until 1974.

It was the abundance of coal along this estuary

that made it a good site

for boiling up sea water.

A sample of sea water stirs up a mystery

right at the heart of this forgotten industry.

Out there is the sea full of salt.

And I can certainly taste it.

This little brook running into the sea...

..doesn't taste salty at all,

so why is fresh water fresh and why is sea water salty?

It's one of those brilliantly simple, infuriating questions

that kids ask.

Why is the sea salty?

I'm enlisting the help of a grown-up.

Simon Boxall's from the National Oceanography Centre.

He should be able to work it out.

We've all swum in the sea, we know it doesn't taste like fresh water,

Simon, but why is it salty?

You have to go right back to the beginning stage of the Earth,

back several billion years.

If you go back that far, the Earth was a completely different place.

It was full of volcanic eruptions,

there was lots of steam around.

But also there was a lot of sodium in the rocks,

and that sodium was being hit by the hydrochloric acid

that was given off by these volcanic vents.

And then we take these two very harmful chemicals.

On the one hand you've, got the element of sodium - very reactive.

On the other hand, you've got chlorine -

very dangerous and very reactive.

You put the two together

and you create something, sodium chloride,

which is the sort of thing you sprinkle on your chips

and certainly isn't harmful at all.

So you've got this hydrochloric acid

pouring out of the volcanic vents,

meeting the sodium hydroxide which is already lying around

-in the rocks on the seabed...

-That's right.

-..creating this stuff called sodium chloride, which is salt.

-Yeah.

These ancient chemical reactions

gave birth to our salty seas.

We can create those sort of primordial days.

We can actually take some hydrochloric acid,

the sort of stuff that came out of the vents of the volcanoes.

We've got some dilute sodium hydroxide,

which represents the stuff that was in the rocks.

And between us, if you want to, we can make some salt,

we can take these two quite nasty chemicals

and we can produce something that's really vital to life in many ways.

This is hydrochloric acid. It's very dilute.

We're going to pop it into this vessel here.

OK. We're going to then add our sodium hydroxide.

Now, at the moment,

basically the sodium and the chlorine are combining

and that's giving off heat.

-Can you feel that?

-It's warm, really warm.

-Wow!

-We've effectively neutralised that acid,

that sodium hydroxide,

and what we have in there now is basically water...

-Yes.

-And salt.

We've compressed billions of years of the Earth's evolution

to make a miniature ocean.

Boiling off our DIY sea water leaves the prize ingredient.

So here it is, our very own home-made salt.

White crystals that washed wealth in from the sea

to help feed an estuary.