As he hiked through the frigid air he spotted many different species of snow algae and lichen. The glacier-facing slopes of the two lateral ridges were especially well populated, flecked by small patches of green, gold, olive, black, rust, and many other colors— perhaps thirty or forty all told. Sax strolled over these pseudo-moraines carefully, as unwilling to step on the plant life as he would be to step on any experiment in the lab. Although truthfully it looked as though most of the lichens would not notice. They were tough; bare rock and water were all they required, plus light— though not much of that appeared necessary— they grew under ice, inside ice, and even inside porous chunks of translucent rock. In something as hospitable as a crack in the moraine, they positively flourished. Every crack Sax looked in sported knobs of Iceland lichen, yellow and bronze, which under the glass revealed tiny forking stalks, fringed by spines. On flat rocks he found the crustose lichens: button lichen, stud lichen, shield lichen, candellaria, apple-green map lichen, and the red-orange jewel lichen that indicated a concentration of sodium nitrate in the regolith. Clumped under the ice flowers were growths of pale gray-green snow lichen, which under magnification proved to have stalks like the Iceland lichen, great masses of them looking delicate as lace. Worm lichen was dark gray, and under magnification revealed weathered antlers that appeared extremely delicate. And yet if pieces broke off, the algal cells enclosed in their fungal threads would simply keep growing, and develop into more lichen, attaching wherever they came to rest. Reproduction by fragmentation; useful indeed in such an environment.

So the lichen were prospering, and along with the species that Sax could identify, with the help of photos on his wristpad’s little display screen, were many more that seemed not to correspond to any listed species. He was curious enough about these nondescripts to pluck a few samples, to take back and show to Claire and Jessica.

But lichen was only the beginning. On Earth, regions of broken rock newly exposed by retreating ice, or by the growth of young mountains, were called boulder fields, or talus. On Mars the equivalent zone was the regolith— thus effectively the greater part of the surface of the planet. Talus world. On Earth these regions were first colonized by microbacteria and lichen, which, along with chemical weathering, began to break the rock down into a thin immature soil; slowly filling the cracks between rocks. In time there was enough organic material in this matrix to support other kinds of flora, and areas at this stage were called fellfields, fell being Gaelic for stone. It was an accurate name, for stone fields they were, the ground surface studded with rocks, the soil between and under them less than three centimeters thick, supporting a community of small ground-hugging plants.