'Yes, well...'

'Oh, yes, there are some nice quiet periods, everything settles down, and then, whammo!'

'There's no need to get so excited...'

'I've been here!' said Rincewind. 'This is how this place works! And now, please, you tell me how, I mean how, can anything living on this world possibly mess it up? I mean, compared to what hap­pens anyway?' He paused, and gulped air. 'I mean, don't get me wrong, if you pick the right time, yes, sure, it's a great world for a holiday, ten thousand years, even a few million if you're lucky with the weather but, good grief, it's just not a serious proposition for anything long term. It's a great place to grow up on, but you would­n't want to live here. If any thing's got off, the best of luck to them.'

He waved a finger at the rat, who was watching them suspi­ciously. Underneath them, the ground trembled again.

'See him?' he said. 'We know what's going to happen. In a mil­lion years or so his kids are going to be saying, wow, what a great world the Big Rat made for us. Or it'll be the turn of the jellyfish, or something that's still bobbing around under the sea that we don't even know about yet! There's no future here! No, that's wrong ... I mean there's always a future, but it belongs to someone else. You know what chalk's made of here? Dead animals! The actual rock is made of dead animals! There were some ...'

Even in his overheated state, he paused. It probably wasn't a good idea to remind people about the apes. A vague, suspicious guilt was nudging him.

'There were these creatures,' he said, 'and they were using lime­stone caves. Limestone's made from ancient blobs, I saw it being made, like snow in the water ... and these creatures are living in the bones of their ancestors! Really! This place ... this place is a kalei­doscope. You smash it up, wait a moment, and there's another pretty pattern. And another one. And another o ...'He stopped. And sagged. 'Could I have a glass of water, please?'

'That was a very ... interesting speech,' said Ponder.

'A point of view, certainly,' said Ridcully.

The other wizards had, however, lost interest. They usually did, if the speeches were not given by them.

'Shall I tell you something else?' said Rincewind, a little more calmly. 'This world is an anvil. Everything here is between a rock and a hard place. Every single thing on it is the descendant of crea­tures that have survived everything the world could throw at them. I just hope they never get angry ...'

The Senior Wrangler and the Dean had ambled towards a huge cylinder. The word 'MAETNANS' was painted in large black let­ters on the side.

'Hey, you chaps!' the Dean shouted. 'There's something talking inhere ...'

The inside of the cylinder reminded the wizards of a lighthouse. There was a spiral staircase; shaped cupboards lined the walls. Lights glowed dimly, whole constellations of them. Certainly the builders of this thing had discovered magic.

The 'A-L-A-A-M' word still blinked on and off in the air.

'I wish that wretched thing would stop,' said the Senior Wrangler.

The light vanished. The sound stopped.

'They've probably invented demons,' said the Dean airily. 'Listen ... hello.'

A pleasant female voice said, 'Elevator Unstable.'

'Oh, magic,'said Ridcully flatly. 'Well, we know how to deal with magic. We want to go up in the magic box, voice.'

'Do we?' said Ponder

'Anything better than staying in this gloomy place,' said Ridcully. 'It'd be quite an interestin' experience, too. We'll take one last look the world and then, well ... frankly, that's it.'

'Instability Rising', said the voice. It did not sound worried by the news.

'What did it say?' said the Dean. 'Sounded like name of a place,'

'Very good, very good,' said Ridcully 'Now let's be going shall we?'

The pattern of lights moved. Then the voice said, as if it'd been thinking it over, 'Emerjansi Override.'

The door slid shut. The cylinder jerked. Shortly afterwards, some pleasant music started, and didn't really get on anyone's nerves for several minutes.

The rat watched the thing rise up the cables in the centre of the pyramid.

The ground shook again.

Slowly, the web around the world came apart.

Ice walls had attacked some of the cable moorings on the ground, but instability was already there, working inexorably as it had done for the past few weeks, turning little movements into big movements.

Slowly, one cable broke free from its pyramid, glowing red-hot as it was jerked through the atmosphere, flailing across the sky.

Around the curve of the world, the others danced and groaned...

When the end finally came, it took only a day. The lines folded around the centre of the world, writhing incandescently across hundreds of miles of snow. The necklace tore apart far above. Some bits drifted away. Others spun gently towards the surface, to impact hours later.

A ring of fire burned for a while around the equator.

And then the cold returned.

As the wizards said, it would all be the same in a hundred million years' time. But it would be different tomorrow.

In the deserted High Energy Building, HEX turned the omniscope outwards, homing in on signs of the strange new life.

It found comet cores, strung on cables thousands of miles long. There were dozens of these trains, many millions of miles from the frozen world, accelerating into the abyss between the stars.

Lights twinkled on their surfaces. The extelligence inside appeared to be travelling hopefully.

A yellow cylinder tumbled gently across the darkness. It was empty.

WAYS TO LEAVE OUR PLANET

RINCEWIND'S IMPASSIONED SPEECH HAS A POINT. If you think he's overstating his case, and that the Earth is really an idyllic place to live, bear in mind that he's been on our planet a lot longer than we have, and he's seen a lot that we've missed, because we experience the world on a much shorter timescale than the wizards have done. We think the planet's a great place. We grew up here. We were made for it, and it's just right for us ... at the moment. Tell that to the dinosaurs. You can't, can you. That's the point.

We're not suggesting that you sell up everything and start build­ing a lifeboat. But even the United States congress is beginning to wonder just how safe our planet really is, and politicians are not usually known for taking long-term views. The sight of Shoemaker-Levy 9 smashing into Jupiter raised a few political eyebrows. Tentative schemes are afoot to set up a defence system against incoming comets and asteroids. Spotting them early enough is the trick. Find them quickly, and a modest little rocket motor can save our planetary bacon.

It is in many ways amazing that life on Earth has survived every­thing that the universe has so far thrown at it. Evolution runs on Deep Time, less than a hundred million years hardly counts. Life is extremely resilient, but individual species are not. They last a few million years and then they become obsolete. Life persists by changing, by being a series of opening chapters. But, being human, we'd like to see our own story turn into at least a block­buster dekalogy.

We can take small comfort in one thing. Although right now we don't worry enough about incoming disaster from Up There, we do worry a lot about home-grown disaster Down Here: nuclear warfare, biological warfare, global warming, pollution, overpopulation, destruction of habitat, burning of the rainforests, and so on. However, there's no danger that human actions will wipe out the planet. Compared to what nature has already done, and will do again, our activities barely show up. One large meteorite packs more explosive power than all human wars put together, a hypothetical World War III included. One Ice Age changes the climate more than a civilization's worth of carbon dioxide from car exhausts. As for something like the Deccan Traps ... you wouldn't want to know how nasty the atmosphere could become.