But Alia went further: by manipulating events in her present, she was able to change the information in the past — to project herself here, into what was to her history. It was as if you could tinker with a few dug-up dinosaur bones and change the lives of the creatures of which they were relics.

Something like that.

I was struck, though, by a resonance with something I’d read in uncle George’s manuscript: If time is circular, if future is joined to past, is it possible that messages, or even influences, could be passed around its great orbit? By reaching into the furthest future, would you at last touch the past?… George, or anyhow his strange friends, had intuited something of the truth, perhaps.

Tom laughed, an explosive giggle. “Sorry,” he said. “Every so often I just lose it. I mean, it’s just,” he waved a hand, “you’re asking me to accept that this is a superhuman being from the far future. This ape. Where’s the disembodied brain in a jar? I mean, what can she do but swing on tires?”

I think we all knew how he felt.

We talked on. It was a difficult dialogue. We were the ignorant talking to the uneducated. I got the impression Alia really didn’t know much about all this, and cared less — as a modern teenager wouldn’t know anything about the implants in her body, as long as they worked. And we knew too little to make much sense of what she said anyhow; we had to translate it into terms we understood, interpret the information she gave us in terms of our own modern theories, which might have been as partial, falsely based or just plain wrong as notions of planet-bearing crystal spheres.

And every so often, as we worked our way through these miasmas of interpretation and guesswork, we were confronted by vast conceptual gulfs.

“Our time must be strange to you,” Rosa said. “If you were born on a ship, among the stars. The way we live must seem very alien.”

“Oh, but I prepared,” Alia said. “In the course of my Witnessing. You don’t have to visit Earth to know what it must have been like!”

“I don’t understand,” Tom said.

Alia spread her arms wide, and her long hairs dangled like curtains. “There are things I like, and things I don’t like, that have got nothing to do with being born on a ship. I like open spaces, long prospects. I don’t like enclosed spaces or running water, or rats or spiders, or blood. I grew up in zero gravity, but I can be scared of heights! All these are responses ingrained deep into my system, and the systems of my ancestors, long before they left Earth. So, you see, even if I knew nothing of Earth, I could reconstruct it just from my own responses. In fact, that has been done a number of times, by cultures cut off from their origins — people who forgot where they came from. Even they can deduce something of Earth…”

“Astounding,” Rosa said. “You left Earth behind half a million years ago. You traveled across the stars. And yet you took the savannah with you, didn’t you?”

Sonia said, “You mentioned rats. Are there animals where you came from?”

“Animals? There are rats everywhere. They don’t all sing. There are bugs and birds.” Birds flocked on her starship, she said; I couldn’t think of a more exotic, charming image. “Earth’s biosphere shows more diversity than any other human world in the Galaxy, however. That’s one reason we know it really is Earth, the original.”

“Like Africa,” Rosa said. “There is more genetic variation there, too. As Africa is for us, the home of mankind, so Earth is for these future people.”

Sonia prompted, “And there are still animals on Earth?”

“Birds. Snakes. Insects. Bugs. That’s all, really.”

“They are the supertaxa,” Gea said. “Taxa have different evolutionary rates. Some speciate more rapidly than others; some lineages last longer than others; and some taxa — the birds, snakes, rats and mice, various weeds — have both a high speciation rate and a high longevity. And so when an extinction event strikes, the supertaxa provide the great survivors. What Alia describes is exactly what I would have expected to find on an Earth of the future, after our extinction event is done. Snakes and rats and birds.”

“But no big animals?” Sonia asked wistfully.

Gea said, “I want to show you something.” She produced a VR image of a lumpy-looking animal: a rhino, but covered in shaggy brown fur.

Alia gaped. “Megafauna!”

Tom said, “That’s a Sumatran rhino, isn’t it?”

“Yes,” Gea said. “An unusual form, adapted for living in hilly rainforests. It went extinct, earlier this year. The last of them died in a zoo in Germany.”

“I’ve never seen anything like it.” Alia sounded as if this creature was as exotic as a dinosaur, to her. She glanced at me. “Michael, have you?”

“I’m not a wildlife buff,” I said. “If you followed me around all my life you’ll know that.”

Gea said, “The Sumatran rhino was a living fossil. It is the least changed of all large-mammal lineages since the Oligocene, thirty million years ago, halfway back to the dinosaurs. We live in extraordinary times. That species endured for thirty million years. Even the people in this room had the opportunity to meet it, to touch it, just months ago. And now it has vanished, a geological instant after its encounter with humanity. Just like that. As all the megafauna which survived the Ice Age have gone, one by one.”

Sonia said wistfully, “And they never came back, according to Alia. You’d think they could have been brought back from the DNA.”

“Perhaps there was never room,” Rosa said. “Not if the world remained owned by humans. For we would not allow anything bigger and hungrier than us to survive.”

“Besides, evolution goes forward, not backward,” Gea said. “The mega-mammals, once gone, will never return.”

Alia was watching us. “You all sound so guilty!”

Tom said, “Do people in the future look back on our time?”

“Oh, yes.”

“And do they judge us?”

“Judge you?” Alia laughed, a strange whooping sound, but then bit it off. “I’m sorry. I know this concerns you, in this age. If not, if you didn’t have this awareness, I guess you wouldn’t be attempting the hydrate stabilization project.”

“You know about that?” I asked.

“Of course. I Witness you, Michael Poole. But why should you be judged? Look — if one species of bird out-competes another, are you going to talk about morals? Of course not. It’s just a question of competition for space in an ecology.”

“And is that how you see us?” John asked bitterly. “Are we just animals in an ecology to you?”

Alia seemed genuinely puzzled by this line of questioning. “How else would you want to be thought of?”

I said, “There is much debate about geoengineering projects. You must know that. We aren’t sure if we have the right to meddle on a planetary scale.”

Alia seemed baffled by this. “But you are already, umm, meddling.” She paused, as if accessing more data. “Consider the Earth. Twenty percent of the land and a good proportion of the sea is covered by artificial ecosystems, each containing a small number of species, selected and bred for one consumer—”

“Farms,” Sonia said.

“Yes. You have changed the very geomorphology of the planet: you have carved vast chunks out of mountains and landscapes, you have built new lakes, and reclaimed other lands from the sea, and you have created entirely artificial land forms of a type never seen before.”

Gea interrupted, “But all this must be trivial compared to the great transformation of your time, an age when mankind has covered a Galaxy.”

“Oh, of course. In the future we do it bigger and better. But planet-shaping, geoengineering, meddling, is what people do. Human history has always been a tangle of environmental changes, human responses, accidents… Human will is only one component. Just accept it!”