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!”