I want just to think what would happen if ice, instead of floating on the surface of water, sank to the bottom.

Imagine, in the winter when you're pond in your garden or in the park, froze the ice when it formed would go to the bottom.

And then as more and more ice built up, the layer of ace at the bottom would get thicker and thicker.

Until, in the end, the pond would be nearly totally frozen and all the fish would be four.

Step onto the surface on would be squirming around on the surface till birds at them or fishermen just picked them up.

Or if you were at sea with a nuclear submarine.

If the sea started freezing, it would be most embarrassing.

Your submarine could appear on the surface of the ice, and you'd be the mercy of whoever you wanted.

How is that different from the other way?

It is now, except the fish gradually gets squashed to the bottom as it gets thicker and thicker.

Now the ice forms on the surface on when it forms.

On the surface, it formed quite a good insulating layer, and eventually if you're really unlucky.

The ice could form all the way down and squash the fish at the bottom.

But that doesn't usually happen because ice is a really very good insulator on DSO most places, unless it's really cold, like in there and dark tickle somewhere like that, there will be liquid water at the bottom.

Even in the Antarctic, there are underground lakes that have recently been discovered where there's liquid water right at the bottom.

As you go deeper, the pressure goes up, and when you go down that low depths, the pressure is higher on the melting point of water actually goes down as the pressure increases.

Now the question is, Why does it happen?

Why does ice float on the surface of the water?

And the answer is that the water molecules in ice are actually joined together by so called hydrogen bombs thes the bonds of oxygen, hydrogen oxygen.

I'm they are in a very regular crystal structure.

When you melt eyes, thes bonds break not all of them, but quite a few of them.

So you still have some of the water molecules join together, but in a very random and haphazard way.

So instead of having a very regular crystal structure.

With the bonds between oxygen, hydrogen and oxygen, they collapse, and so the density gets higher.

So ice is not very much lighter than water, but it's light enough to float.

That's why just the tip of an iceberg sticks out.

If Isis was denser than water, icebergs were just full to the bottom of the sea.

You wouldn't have the film Titanic.

It would have enormous effects on our planet if ice did not float, because ice is your nose white, and so it reflects sunlight.

So when the sea freezes and forms sea ice, this reflects back a lot of the radiation from the sun on dhe, particularly in areas like the Arctic in summer, where it's daylight 24 hours a day, The reflection of the sun's radiation by sea ice is really quite significant.

Sea ice floats particularly well because it is pure ice, but it is floating on salty water, which is denser than ordinary water, and therefore it is particularly buoyant if you stop reflecting so much the sunlight that has implications for the whole of the Earth's climate.

Because more radiation is absorbed by the Earth, it will get warmer and therefore more ice will melt and so on.

So if I didn't float, our planet would probably be a considerably warmer place than it is now.

Of course, the place where most people see floating ice are in their drinks now.

It's quite important when you drink at least, particularly the beginning.

You drink from the top of your glass, so you want the first part of your drinks to be really nice and cold.

And as you checked away and tell stories and so on, the glass goes down, and so you're always drinking from the surface.

So if you put ice cubes into a drink and they sink to the bottom, you'd end up with a warm drink, and that would be a social disaster.

Alcohol.

Pure alcohol is much less dense than water, and I just have a feeling that if you take ordinary ice and put it into pure alcohol, it would sink to the bottom.

We'll have to try the experiment.

We're in the vault, the bullion vaults of the Bank of England, and I'm really excited.

I've never seen so much gold.