The ice spread from the poles towards the equator. In the high mountains, the boundary of perpetual snow has moved lower. Vast body of seawater froze and sea levels dropped significantly. Continents and islands were joined together, seabeds became landmasses. A few hundred thousand years later, during rapid warming, the fast melting of the ice brought water back into the cycle. This caused sea levels to rise by more than 100 metres, and land was again submerged.
During the glaciations, the appearance of ice sheets and the decrease in temperature formed climate zones, which led to the formation of vegetation belts and the related characteristic animal communities. The characteristic vegetation of the glaciations resembled the tundra or cold steppe of today.
The expansion and retreat of the ice sheet has continuously transformed the various vegetation belts, sometimes fragmenting and separating previously coherent habitats. Some plant and animal species have survived these periods in refugia, from which they have been able to spread again under more favourable climatic conditions.