Blue Mars(126)

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



meaning that any soil property S 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 oxyhydroxides, 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.

In the greenhouse farms, on the other hand, the soils used had been heavily amended by nutrients and fertilizers and inoculants of all kinds; the result was something like what these scientists were trying for, but the quantity of soil in greenhouses was minuscule compared to what they wanted to put out on the surface. Mass producing soil was their goal. But they had gotten into something deeper than they had expected, Nadia could tell; they had the vexed absorbed air of a dog gnawing on a bone too big for its mouth.

The biology, chemistry, biochemistry, and ecology involved in these problems were far beyond Nadia’s expertise, and there was nothing she could do to make suggestions there. In many cases she couldn’t even understand the processes involved. It was not construction, nor even an analog of construction.

But they did have to incorporate some construction into whatever production methods they tried, and there Nadia was at least able to understand the issues. She began to concentrate on that aspect of things, looking at the mechanical design of the pedons, and also the holding tanks for the living constituents of the soil. She also studied the molecular structure of the parent clays, to see if it suggested anything to her about working with them. Martian smectites were aluminosilicates, she found, meaning each unit of the clay had a sheet of aluminum octahedrals sandwiched between two sheets of silicon tetrahedrals; the different kinds of smectites had different amounts of variation in this general pattern, and the more variation there was, the easier it was for water to seep into the interlayer surfaces. The most common smectite clay on Mars, montmorillonite, had a lot of variety, and so was very open to water, expanding when wet, and shrinking when dry to the point of cracking.