Yuri laughed. ‘I’ll carve you a statue.’

The ColU didn’t seem offended. ‘In any event my studies are of their very nature long term. I am endeavouring to establish the story of life on this world. Its origin and its relationship, if any, to Sol life; the key stages of its development such as the emergence of photosynthesis, of multicellular life—’

‘A big statue, then. Anyhow you’re too curious, about the Arduan life. Too theoretical. You’re only supposed to be helping us exploit it.’

‘Artificial sentience, all sentience, is untidy, blurred at the edges; it is difficult to constrain curiosity, once imbued. That’s one of the reasons the big AIs constructed in the age of the Heroic Generation would now be considered illegal. Indeed, to equip ColUs like myself for this expedition, the ISF and other off-world agencies were given special dispensation by the sentience-law regulators. And besides, Yuri Eden, I was programmed to support a minimum of fourteen colonists, soon growing in number as the births began. I have the time to wonder.’

‘Oh, we aren’t stimulating enough for you?’

‘It is as if my mind expands to populate the emptiness. Is this a common property of sapience?’

Yuri said brutally, ‘You only ever had twenty-five years, and the clock’s ticking, right? Then you’ll shut down and rust. And all the plans and dreams you’re cooking up under that plastic dome and in your expanding mind will just be lost for ever, forgotten.’

‘All mortal creatures must face termination. Yuri Eden, I’m surprised you speak to me this way. Is it because I am a made thing? I mean, made by humans. A golem, of sorts. In myth, such creatures are always less than human, because they are one step further from God. Is that how you see me, Yuri Eden?’

‘I see you as a symbol of the blind, stupid powers who thought it was a good idea to dump me and Mardina on this alien world.’

‘But I, too, am a victim of that blind stupidity, as you put it. As for myself, I can assure you that—’

‘Shut up. I only talk to you about this stuff because I’m bored.’ That much, at least, was true.

‘Enough, Yuri,’ Mardina said. ‘You can talk to me if you like, ColU. So how are you progressing with this great project of yours?’

‘With difficulty. The geology of this world is singularly unhelpful. None of it is old, Mardina Jones. And by “old” I mean in excess of a few hundred million years. At least in the local geological unit.

‘Take this bit of sandstone in my grabber claw.’ It held out the sample. ‘You can see strata, laid down in some vanished ocean over a few million years. Then came the tectonic spasms that uplifted it, breaking the strata. There was an age of erosion as the strata were exposed to the weather. Then more geological turbulence resulted in the injection of molten granite into the weaker strata; you can see intrusions here and here. But even the rock from which the original sandstone formed, eroded relics of volcanic products from a still earlier era, was comparatively young, as a dating from traces of radioactive elements establishes.’

Yuri’s head spun with this mishmash of geological events. ‘I can’t get all that in order. What you’re saying is—’

Mardina said, ‘That the surface of the planet is recent, geologically speaking. Like Venus. Isn’t that right?’

‘Yes,’ said the ColU. ‘Venus appears to undergo a global resurfacing event every few hundred million years. The crater record shows this clearly. Here the resurfacing may be region by region, rather than the entire surface at once. Per Ardua is evidently geologically active; we’ve seen active regions ourselves, the mud pools, the evidence of uplift to the north. But it is an older world than the Earth, or Venus; Proxima is older than the sun. Maybe this localised activity, this geological bubbling, is something to do with that greater age. A given region may wait tens, hundreds of millions of years for such an event. But when it comes it is enough to wipe out much of any fossil record I might have found.’

‘Frustrating,’ Mardina murmured.

‘But there are ways forward,’ said the ColU. ‘Mostly through study of the extant biology.’

‘The DNA.’

‘The Arduan creatures do not have DNA. But yes. A comparative study of their genetic material reveals deep relationships. I can already draw up a family tree based on the Arduan genetic record. With estimates of mutation rates I should soon be able to come up with a skeleton chronology. It is already clear, for instance, that the Arduan stromatolites, or their ancestors, must predate the stem forms. When did multicellular life begin here? When did the first multi-stem-architecture creatures emerge, and what were they like? Do they have any analogous survivors today? And—’

Yuri said, ‘I still say you’ve got big dreams for a bit of farm machinery.’

Mardina suppressed a laugh.

‘It is in the nature of sentience,’ the ColU said, ‘to dream. My work is done here, at this bluff. Are you ready to go on?’

They walked on, pausing once to eat, coming at last to the western shore of the lake.

This was the domain of the builders, on the fringe of the great stem beds that extended far out into the water where the birds flocked. Mardina had labelled this part of the shore the ‘nursery’, because there was a concentration of families with their young. If you could call them families. Certainly the area was studded with the low, nest-like constructions that the ColU now believed, based on Yuri’s clumsy explorations, were Proxima storm shelters for the young.

And here, today, on patches of the native analogues of mosses and lichen, young builders were basking in Proxima light. They gathered in clusters of a couple of dozen or more, each basically a tripod leaning on one rear leg and tilting back so it faced the star hanging in the sky. Their triple main stems were rooted in the lichen patches, and Yuri saw masses of fibres, tendrils, reaching down from the stems into the lichen – or maybe vice versa.

While the ColU plucked samples with a fine manipulator arm and scanned around with its sensor units, Mardina got down on her knees before the cluster of little builders, being careful not to block the light. ‘You know, I’ve seen them being born,’ she said. ‘ “Born”, I suppose you’d call it that. The three parents – and there are always three of them – get together in a cluster, upright, and they kind of pull bits out of each other. Stems, especially the fine ones from the dense core sections. Then they put them together, like they’re assembling a kit-part model. But it stops being methodical after a while. They start to move, whirling around, the three of them joined together around the newborn.’ She rocked, her kneeling body swaying in a gentle circle, imitating the movement she’d seen. ‘A dance of conception, of birth. Some deep biology going on. And when they separate, there’s a new little guy.’

‘Wow,’ Yuri said. Mardina had never told him about these observations before. ‘Builder sex, huh?’

‘If you can meaningfully call it sex,’ the ColU said, rolling back. ‘There would presumably have to be three sexes, not two. I’ve seen no evidence of the sexual differentiation observed in many species on Earth. But the peculiar sexual congress you describe is clearly a way for genetic material from the parents to be mixed up in the infants, at the level of the stems, at least.

‘And there’s more. Notice how they make junctions between their bodies and the lichen bed. I think these builders are something like some of the earliest plants on Earth. Such plants hadn’t yet evolved proper root systems, but instead formed a symbiotic relationship with fungi. The fungi would feed nutrients and water to the plant, in return for sugars manufactured by the plant. I think what we’re seeing here is a complex symbiosis between the builders and the photosynthesising bacteria and fungi of the lichen.’