I do know that the images the young ones see of Earth are affecting them in ways we didn’t anticipate.

For sure, the kids are evolving away from us, Henry. Already. Oh, Nadezhda doesn’t look much different from me at her age, when I was nagging mum to take me to the McDonald’s on Princes Street; it’s going to take generations even to work through the obvious physiological changes — the low G adaptations, for instance; Nadezhda will have to spend her life on courses of treatment against bone calcium loss and body fluid imbalances.

But her children will be a little taller, and a little more resistant; and her grandchildren a little more so… and so on.

Humans will survive here. I’m sure of that now. What I’m not convinced about is how much they will care about old Earth.

The young ones already have their own agenda. It’s hard for them to have any loyalty for the home planet when they see that now you need spacesuits just to survive down there…

There has already been some trouble at the drop points in Procellarum. Resistance to new immigrants, even to accepting more loads of rocks and frozen bugs from Earth.

I just hope it all holds together long enough to get the best of it away, before the end.

Well, maybe it’s inevitable. We’ve done all we can to equip the kids and educate them. Now, the future is theirs…

As the tectonic events accelerated, predictions were being revised, and it seemed they were approaching the Bottleneck itself, the great, final die-back from which nothing on the surface of Earth, nothing, was going to escape. The laws had gotten harsher. No more children to be born on Earth. Anybody who refused to comply would be refused boarding, for themselves or their children, to the Arks to the Moon.

It was harsh, and not universally accepted by the governments, and had caused revolution, and more than one war. In South America, where the Pope had mounted his last stand against the managed decline of the population, the fallout of thermonuclear destruction had added to Earth’s final woes.

And nevertheless — despite the logic and wisdom, despite the inevitability of the Bottleneck — there were still children being born on the Earth: the animal response of frightened humans to the threat of death, life trying to propagate in the face of hopelessness. But the helpless new kids were only more moths to the flames, Henry thought.

In a way, he was glad Jane wasn’t here to see this.

At least she had lived to see her grandchildren, growing straight and tall in the thin, clean air of the Moon.

But as for Henry, this was his home.

He had been in love with the Earth since the first time he opened a geology book, the first time he picked up a pebble from a beach and wondered how it got there. Now it was burning down around him, but he wasn’t about to abandon it.

He found himself walking on a layer of salt, white and bright in the smoggy twilight, that crunched under his feet.

This ocean had dried once before, though not in human history. And that had been significant. The ocean had ceased to buffer the local climate, feeding land areas with rainfall and reducing temperature swings. Forests had disappeared, to be replaced by dry grasslands, and the arboreal creatures had faced the choice of migrating, adapting, or dying.

One group of tree-dwelling primates was forced out of the branches that had hidden them from predators, and pushed onto the new grasslands of Africa, where they were going to need greater size and better locomotion and, above all, to get smarter.

They had never looked back.

Now, five million years later, a descendant of those frightened primates, dressed in a fragile spacesuit, stalked across the dried-up bed of the Mediterranean, looking for fossils and human artifacts, a few last treasures for the final Arks to the Moon.

And a final ten years…

Henry was standing on the Earth’s oldest rocks, and talking to his granddaughter, on the Moon.

…So here I am, Nadezhda, your honorary grandfather, sixty-five years old and no smarter than I ever was, waiting for the other shoe to fall.

I don’t suppose you know what that means. I can’t even remember how long it takes a shoe to fall on the Moon. Or if you wear shoes in those domes of yours.

Whatever.

I have instruments here, various sensors that show me what is happening inside the planet. I have a whole-Earth image here broadcast from one of your nearside observatories, I think at Kepler. I’m glad you can see the surface, from up there. The giant volcanoes blew off the crud, the Venusian atmosphere that was gathering, and who’d have thought that would be a blessing?…

He was in Isua, in west Greenland. He was standing on supracrustal rock bounded on both sides by granitoid gneisses: three point six billion years old. Babies for the Moon, but these rocks were the old men of Earth, the oldest, most stable place on the planet.

It seemed appropriate, to be here, now.

He was in a concrete, heat-insulated, pressurized bunker, which in turn was protected by what he would have called a force field when he was growing up, a piece of the smart stuff the kids on the Moon had been dreaming up. Technological evolution, force-fed by its environment, filling the niches.

He was here because it was one of the few solid, stable places left on the planet.

Earth, from space, looked like a jigsaw puzzle, or maybe like a pan coming to the boil, black continent pieces outlined by blood red.

It was astonishing how events had accelerated, towards the end. It had been faster than anyone had believed.

He wondered how long he’d last. How much of it he would see.

…Did you know I was alive when Apollo 8 flew by the Moon? The astronauts, Borman, Lovell and Anders, were the first humans to see the Earth whole. They thought it was blue, and fragile, like a Christmas tree ornament. Well, they were right. Fragile.

I know you think I’m crazy to stay.

You know, one of the most beautiful theories of the history of the Earth was published by a guy called the Reverend Thomas Burnet, in England in the seventeenth century. Burnet said the Earth originated from chaos, a fluid mass of particles of matter. The particles grew together to form a perfect sphere with a smooth surface, concentric shells of liquid and air around a solid core. But there was an oily fluid in with the water, and when dust mixed with it, it formed a firm and fertile envelope over the layer of oily water.

But the sun’s heat made the fertile shell dry and crack. The waters below boiled, vaporized and exploded, and the Earth was flooded. When the agitation settled out, the waters drained back to the low places. Fragments of Paradise were left sticking up as continents and islands.

And that’s the world I was born on.

Eventually, though, flames would come to purify the Earth, and it would return to its paradisical state, and finally merge with God by becoming a star.

Well, it was a theory. That’s the way geology used to be, kid, a thing of dreams and fancies unsullied by brute fact. We only got into all that science stuff when the industrialists came along and started asking where they were going to find coal and iron ore and oil, and why the hell is the world so complicated anyhow?

We know the answers now, of course: all those aeons of mountain building and destruction, the rise and fall of the seas, the compaction, pressure, heating, cooling, sedimentation, erosion. The Earth is a rocky labyrinth.

Was, anyhow. It’s getting kind of simpler, even as I stand here.

Strange how Burnet seems to have been right all along, though, doesn’t it?