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.

IMMATURE SOILS have indistinct or weakly developed horizons, generally restricted to surface organic horizons or A horizons resting directly on little-altered parent material or rock.

Inherent disadvantages of cold, aridity, immature soils, snow, permafrost and poor drainage must be amply compensated, for example by relative freedom from interspecific competition, parasites and predators; if there were no such compensations, polar lands would lie barren.