As she continued northward, the young woman began to notice a change in the terrain. It was becoming drier and more desolate. She had reached the ill-defined northern limit of the wet, snowy continental steppes. Beyond, all the way to the sheer walls of the immense northern glacier, lay the arid loess steppes, an environment that existed only when glaciers were on the land, during the Ice Age.

Glaciers, massive frozen sheets of ice that spanned the continent, mantled the Northern Hemisphere. Nearly a quarter of the earth's surface was buried under their unmeasurable crushing tons. The water locked within their confines caused the level of the oceans to drop, extending the coastlines and changing the shape of the land. No portion of the globe was exempt from their influence, rains flooded equatorial regions and deserts shrunk, but near the borders of the ice the effect was profound.

The vast ice field chilled the air above it, causing moisture in the atmosphere to condense and fall as snow. But nearer the center high pressure stabilized, creating extreme dry cold and pushing the snowfall out toward the edges. The huge glaciers grew at their margins; the ice was nearly uniform across its full sweeping dimensions, a sheet of ice more than a mile thick.

With most of the snow falling on the ice and nourishing the glacier, the land just south of it was dry – and frozen. The constant high pressure over the center caused an atmospheric chute funneling the cold dry air toward lower pressures; wind, blowing from the north, never stopped on the steppes. It only varied in intensity. Along the way it picked up rock that had been pulverized to flour at the shifting border of the grinding glacier. The airborne particles were sifted to a texture only slightly coarser than clay – loess – and deposited over hundreds of miles to depths of many feet, and became soil.

In winter, howling winds whipped the scant snowfall across the bleak frozen land. But the earth still spun on its tilted axis, and seasons still changed. Average yearly temperatures only a few degrees lower trigger the formation of a glacier; a few hot days have little effect if they don't alter the average.