The comet impact had been relatively minor, on the cosmic scale of such events. But it had been sufficient to silence Earth; nobody on the Moon knew who, or what, had survived on its surface. Xenia wondered if even those Trees could survive the greater and more frequent impacts that many had predicted were the inevitable outcome of the conflict in the Oort cloud, as the Crackers threatened to break through the Gaijin cordon, as warring ETs hurled giant rogue objects into the system’s crowded heart, century after century.

Such musing failed to distract her from thoughts of Berge’s illness, which advanced without pity. She was touched when he chose to come stay with her, to “see it out,” as he put it.

Her fondness for Berge was not hard to understand. Her daughter had died in childbirth. This was not uncommon, as pelvises evolved in heavy Earth gravity struggled to release the great fragile skulls of Moon-born children — and Xenia’s genes, of course, came direct from Earth, from the deep past.

So she had rejoiced when Berge was born, sired by her son of a lunar native; at least her genes, she consoled herself, which had emanated from primeval oceans now lost in the sky, would travel on to the farthest future. But now, it seemed, she would lose even that consolation.

But she was not important, nor the future, nor her complex past. All that mattered was Berge, here in the present, and on him she lavished all her strength, her love.

Berge spent his dwindling energies in feverish activities. Still his obsession with Leonardo clung about him. He showed her pictures of impossible machines, far beyond the technology of Leonardo’s time: shafts and cogwheels for generating enormous heat, a diving apparatus, an “easy-moving wagon” capable of independent locomotion. The famous helicopter intrigued Berge particularly. He built many spiral-shaped models of bamboo and paper; they soared into the thick air, easily defying the Moon’s gravity, catching the reddening light.

She wasn’t sure if he knew he was dying.

In her gloomier hours — when she sat with her grandson as he struggled to sleep, or as she lay listening to the ominous, mysterious rumbles of her own failing body, cumulatively poisoned, racked by the strange distortions of lunar gravity — she wondered how much farther humans must descend.

The heavy molecules of the thick atmosphere were too fast-moving to be contained by the Moon’s gravity. The air would be thinned in a few thousand years: a long time, but not beyond comprehension. Long before then people would have to reconquer this world they had built, or they would die.

So they gathered metals, molecule by molecule.

And, besides that, they would need knowledge.

The Moon had become a world of patient monks, endlessly transcribing the great texts of the past, pounding the eroding wisdom of the millennia into the brains of the wretched young. It seemed essential to Xenia they did not lose their concentration as a people, their memory. But she feared it was impossible. Technologically they had already descended to the level of Neolithic farmers, and the young were broken by toil even as they learned.

She had lived long enough to realize that they were, fragment by fragment, losing what they once knew.

If she had one simple message to transmit to the future generations, one thing they should remember lest they descend into savagery, it would be this: People came from Earth. There: cosmology and the history of the species and the promise of the future, wrapped up in one baffling, enigmatic, heroic sentence. She repeated it to everyone she met. Perhaps those future thinkers would decode its meaning, and would understand what they must do.

Berge’s decline quickened as the Sun slid down the sky, the clockwork of the universe mirroring his condition with a clumsy, if mindless, irony. In the last hours, she sat with him, quietly reading and talking, responding to his near-adolescent philosophizing with her customary brusqueness, which she was careful not to modify in this last hour.

“But have you ever wondered why we are here and now?” He was whispering, the sickly gold of his face picked out by the dwindling Sun. “What are we, a few million, scattered in our towns and farms around the Moon? What do we compare to the billions who swarmed over Earth in the great years? Why do I find myself alive now rather than then? It is so unlikely…” He turned his great lunar head. “Do you ever feel you have been born out of your time, as if you are stranded in the wrong era, an unconscious time traveler?”

She would have confessed she often did, but he whispered on.

“Suppose a modern human — or someone of the great ages of Earth — was stranded in the sixteenth century, Leonardo’s time. Suppose he forgot everything of his culture, all its science and learning—”

“Why? How?”

“I don’t know… But if it were true — and if his unconscious mind retained the slightest trace of the learning he had discarded — wouldn’t he do exactly what Leonardo did? Study obsessively, try to fit awkward facts into the prevailing, unsatisfactory paradigms, grope for the deeper truths he had lost? Don’t you see? Leonardo behaved exactly as a stranded time traveler would.”

“Ah.”

She thought she understood; of course, she didn’t. And in her unthinking way she launched into a long and pompous discourse on feelings of dislocation: on how every adolescent felt stranded in a body, an adult culture, unprepared…

Berge wasn’t listening. He turned away, to look again at the bloated Sun.

“I think,” she said, “you should drink more soup.”

But he had no more need of soup.

It seemed too soon when the Day was done, and the cold started to settle on the land once more, with great pancakes of new ice clustering around the rim of the Tycho sea.

Xenia summoned Berge’s friends, teachers, those who had loved him.

She clung to the greater goal: that the atoms of gold and nickel and zinc that had coursed in Berge’s blood and bones, killing him like the mustard plants of Maginus — killing them all, in fact, at one rate or another — would now gather in even greater concentrations in the bodies of those who would follow. Perhaps the pathetic scrap of gold or nickel that had cost poor Berge his life would at last, mined, close the circuit that would lift the first ceramic-hulled ships beyond the thick, deadening atmosphere of the Moon.

Perhaps. It was cold comfort.

But still they ate the soup, of Berge’s dissolved bones and flesh, in solemn silence. They took his life’s sole gift, further concentrating the metal traces to the far future, shortening their own lives as he had.

She had never been a skillful host. As soon as they could, the young people dispersed. She talked with Berge’s teachers, but they had little to say to each other; she was merely his grandmother, after all. She wasn’t sorry to be left alone.

Before she slept again, even before the Sun’s bloated hull had slid below the toothed horizon, the winds had turned. The warmer air was treacherously fleeing after the sinking Sun. Soon the first flurries of snow came pattering on the black, swelling surface of the Tycho sea.

Her seals slid back into the water, to seek out whatever riches or dangers awaited them under Moon core ice.