“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.”
“You mean,” Yuri said, “these little guys are feeding.”
“I’ve observed the adults, too, spending time on lichen beds like this. But the youngsters are presumably more in need of nutrients; their stems need to grow. So the youngsters spend more of their time plugged in, so to speak. Other Arduan creatures, like the kites, must have similar rooting sites. If we look hard enough we’ll find them. Certainly these creatures, which are a mixed-up compound of what we call animals and plants, are never more plant-like than at such moments. Perhaps their animal-like consciousness, a sense of self-awareness and identity, briefly dissolves into a deeper green…”
Mardina wasn’t listening, Yuri saw. All her attention was on the young builders.
He said to her, “You like these little guys, don’t you?”
She looked defensive. He knew she didn’t like having her feelings questioned, any more than he did himself. But she admitted, “Look, I’m no noble savage. But I grew up with the old stories—you know? Of the gengas, the spirits of my ancestors infusing the land. Well, I have no ancestors here, there are no gengas for me. But these builders—this is their world. They honour their dead, we know that. Maybe their gengas will look after me. I know it makes no sense—”
The ColU said, “Careful.”
There was a clatter, like a bag of chopsticks being shaken. Yuri, standing over Mardina and the infants, turned to see a pair of older builders bearing down on them, spinning, limb stems clattering.
“Hey, take it easy, you guys.” Mardina stood up. She whirled around in her orange jumpsuit, shaking out her arms and legs. “We’re just looking, we won’t harm these little fellas.”
The ColU abruptly rolled back a half-metre, a sure sign in Yuri’s experience that it was surprised, and raised its sensor pod on its arm high in the air. “Lieutenant… what are you doing?”
“What does it look like? Can’t you see these blokes are warning us off?”
Yuri said, “You mean they’re talking to us? What, with the dance?”
“In the dance, in the way they clatter their limbs—I don’t know, I don’t speak builder. I’m just trying to reassure them, that’s all.”