Sand and Soil
Sand defines the Gobi Desert, the dried-out remains of soils that once sustained life during the ice ages. Unlike soil, sand lacks the organic material to nurture plant life. Experts still puzzle over the source of the great, hypnotic fields of massive sand dunes that dominate hundreds of square miles of the nearly rainless desert. Some insist that the sand dunes are fed by sediments deposited thousands of years ago in great lakes that accumulated in the great basins and depressions that became the Gobi Desert. They maintain that the sand came from soil washed out of the nearby mountains plus the limestone skeletons of microscopic creatures that lived in those ancient inland seas.
However, other experts have found evidence that the great, planetary wind patterns blew much of the sand and soil into the enclosed basins from across much of Asia. They point to the worn, blasted chains of hills and mountains that lie scattered throughout the uplands and tablelands of the Gobi plus the great windstorms that blow across northern China and the Russian steppes and into the region. Viewed from space, the desert's great chains of sand dunes align with prevailing wind patterns and the great, seasonal shifts in wind directions. Measurements of individual sand dunes in wind-plagued areas like Takla Makan have recorded movements of as much as 150 feet (50 m) in a single year.
The dust-covered plains of the Gobi and northern China constitute one of the planet's greatest expanses of loess, which is made of fine dust transported long distances by the wind. In the Gobi, the loess layers are 30 or 40 feet (10–12 m) thick, deposited by the wind and composed of a fine dust of limestone made from the skeletons of sea creatures. Most of the layer formed during the ice ages, after the inexorable movement of glaciers ground limestone layers into fine powder. When the glaciers retreated and released the pulverized limestone soil, the fierce winds picked it up and blew it into the Gobi. Here, it formed layers of sandstone soft enough for the people living in the area to dig cavelike houses out of the cliffs and hills.
The fine, dry soils of the Gobi still affect the rest of the planet. For instance, one recent study tracked a dust storm in the Gobi Desert that grew so fierce that it rose high into the atmosphere. There, high-altitude wind currents dispersed the dust throughout the world. All across Asia, airports shut down for lack of visibility. Studies show that the distinctive limestone dust of the Gobi can cross the ocean and waft to Earth in the United States and elsewhere.