“Siberians.”

“No Siberian in his right mind would move here. They know better.”

“Laplanders, then. Inuit. People who like the poles.”

“I suppose.”

As it turned out, no one in Bogdanov Vishniac seemed to mind the winters. They had redistributed their mohole mound in a ring around the mohole itself, creating an immense circular amphitheater facing down into the hole. This terraced amphitheater was to be the surface Vishniac. In the summers it would be a green oasis, and in the dark winters a white oasis; they planned to illuminate it with hundreds of brilliant streetlights, giving themselves a stage set day, in a town contemplating itself across a round gap in things, or from the upper wall looking out at the frosted chaos of the polar highlands. No, they were going to stay, no question of it. It was their place.

Nadia was greeted at the airport as a special guest, as always when she stayed with Bogdanovists. Before joining them this had struck her as ridiculous, and even a bit offensive: girlfriend of The Founder! But now she accepted their offer of a guest suite located on the lip of the mohole, with a slightly overhanging window that gave one a view straight down for eighteen kilometers. The lights on the mohole’s bottom looked like stars seen through the planet.

Art was petrified, not at the sight but at the very thought of the sight, and he would not go near that half of the room. Nadia laughed at him, and then when she was done looking, closed the drapes.

The next day she went out to visit the soil scientists, who were happy at her interest. They wanted to be able to feed themselves, and as more and more settlers moved south, this was going to be impossible without more soil. But they were finding that manufacturing soil was one of the most difficult technical feats they had ever undertaken. Nadia was surprised to hear this — these were the Vishniac labs, after all, world leaders in technologically supported ecologies, having lived for decades hidden in a mohole. And top-soil was, well, soil. Dirt with additives, presumably, and additives one could add.

No doubt she conveyed some of this impression to the soil scientists, and the man named Arne leading her around told her with some exasperation that soil was in fact very complex. About five percent of it by weight was made of living things, and this critical five percent consisted of dense populations of nematodes, worms, mollusks, arthropods, insects, arachnids, small mammals, fungi, protozoa, algae, and bacteria. The bacteria alone included several thousand different species, and could number as high as a hundred million individuals per gram of soil. And the other members of the microcommunity were almost as plentiful, in both number and variety.

Such complex ecologies could not be manufactured in the way Nadia had been imagining, which was basically to grow the ingredients separately and then mix them in a hopper, like a cake. But they didn’t know all the ingredients, and they couldn’t grow some of the ingredients, and some that they could grow died on mixing. “Worms in particular are sensitive. Nematodes have trouble too. The whole system tends to crash, leaving us with minerals and dead organic material. That’s called humus. We’re very good at making humus. Topsoil, however, has to grow.”

“Which is what happens naturally?”

“Right. We can only try to grow it faster than it grows in nature. We can’t assemble it, or manufacture it in bulk. And many of the living components grow best in soil itself, so there’s a problem providing feedstock organisms at any faster rate than natural soil formation would provide them.”

“Hmm,” Nadia said.

Arne took her through their labs and greenhouses, which were filled with hundreds of pedons, tall cylindrical vats or tubes, in racks, all holding soil or its components. This was experimental agronomy, and from her experience with Hi-roko Nadia was prepared to understand very little of it. The esoterica of science could go right off her scale. But she did understand that they were doing factorial trials, altering the conditions in each pedon and tracking what happened. There was a simple formula Arne showed her to describe the most general aspects of the problem:

5 = f(PM,C,R,B,T),

meaning that any soil property 5 was a factor ( f ) of the semi-independent variables, parent material (PM), climate (C), topography or relief (R), biota (B), and time (T).Time, of course, was the factor they were trying to speed up; and the parent material in most of their trials was the ubiquitous Martian surface clay. Climate and topography were altered in some trials, to imitate various field conditions; but mostly they were altering the biotic and organic elements. This meant microecology of the most sophisticated kind, and the more Nadia learned about it the more difficult their task seemed — not so much construction as alchemy. Many elements had to cycle through soil to make it a growth medium for plants, and each element had its own particular cycle, driven by a different collection of agents. There were the macronutrients — carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium — then the micronutrients, including iron, manganese, zinc, copper, molybdenum, boron, and chlorine. None of these nutrient cycles was closed, as there were losses due to leaching, erosion, harvesting, and outgassing; inputs were just as various, including absorption, weathering, microbial action, and application of fertilizers. The conditions that allowed the cycling of all these elements to proceed were varied enough that different soils encouraged or discouraged each cycle to different degrees; each kind of soil had particular pH levels, salinities, compaction, and so forth; thus there were hundreds of named soils in these labs alone, and thousands more back on Earth.

Naturally in the Vishniac labs the Martian parent material formed the basis for most of the experiments. Eons of dust storms had recycled this material all over the planet, until it had everywhere much the same content: the typical Martian soil unit was made up of fine particles of mostly silicon and iron. At its top it was often loose drift. Below that, varying degrees of interparticle cementation had produced crusty cloddy material, becoming blocky the lower one dug.

Clays, in other words; smectite clays, similar to Terra’s montmorillonite and nontronite, with the addition of materials like talc, quartz, hematite, anhydrite, dieserite, clacite, beidellite, rutile, gypsum, maghemite and magnetite. And everything had been coated by amorphous iron oxy-hydroxides, and other more crystallized iron oxides, which accounted for the reddish colors.

So this was their universal parent material: iron-rich smectite clay. Its loosely packed and porous structure meant it would support roots while still giving them room to grow. But there were no living things in it, and too many salts, and too little nitrogen. So in essence their task was to gather parent material, and leach out salt and aluminum, while introducing nitrogen and the biotic community, all as fast as possible. Simple, when put like that; but that phrase biotic community masked a whole world of troubles. “My God, it’s like trying to get this government to work,” Nadia exclaimed to Art one evening. “They’re in big trouble!”

Out in the countryside people were simply introducing bacteria to the clay, and then algae and other microorganisms, then lichen, and then halophyllic plants. Then they had waited for these biocommunities to transform the clay into soils, through many generations of living and dying in it. This worked, and was working even now, all over the planet; but it was very slow. A group in Sabishii had estimated that when averaged over the planet’s surface, about a centimeter of topsoil was being generated every century. And this had been achieved using genetically engineered populations designed to maximize speed.