Loess is a homogeneous, fine yellow soil that has been deposited across 1 million square miles (2.6 million sq. km) of land that covers several areas of the world: Asia, Europe, and North America. It ranges in thickness from area to area and can be as thick as 10 feet (3 m) in some locations. Loess (rhymes with us) originated from glacial processes. As the massive weight of the glacial ice moved across the Earth's surface, the ice ground along the rock slowly and abraded and pulverized it into a powderlike substance. Later, as the climate warmed and the ice melted, running water washed the flourlike deposits from under the glaciers and into streams along the edges of the ice. As the area dried out, winds carried loess across the land. Its texture was so fine that it was carried great distances. This spread the deposits across wide areas and left rich, easily recognizable, homogeneous soil.

Loess is a proxy because climatologists can use it to map the past existence of glaciers. In the United States, for example, scientists have been able to determine through the mapping of both loess and rock debris deposits that ice sheets once existed in the area where the Great

This is the upper part of a section of loess near Baoji in southern China's Central Loess Plateau. Climatologists have determined that these soils represent interglacial periods when climates were wet enough to sustain vegetation development. During glacial periods, climates were colder, drier, and windier, leading to sparse vegetation cover and extensive mineral dust (loess) accumulation. (Nat Rutter, Department of Geology, University of Alberta, Edmonton, Canada, NOAA Paleoclimatology Program)

Lakes are located today. Ice sheets also covered the British Isles and Scandinavia in Europe during this period, as evidenced by loess deposits there.

Loess deposits have also been found in mountain (alpine) environments, indicating the existence of glaciers in the past. Evidence has also been uncovered of multiple glaciations using loess as a proxy tool, as some loess deposits are much older. Currently, climatologists believe there have been at least three or four individual ice events that generated loess.

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