Sandy clues to ancient climate.
The orientation of these dunes in north-central Nebraska provide a clue that the climate there a millennium ago was much different than it is today. The Nebraska Sand Hills have been frozen in place by vegetation for 800 to 1,000 years, says David B. Loope, a geologist at the University of Nebraska in Lincoln. The 12-to-15-meter-tall dunes, which run from west-northwest to east-south-east, couldn't have been formed by modern wind patterns, which bring plant-nurturing moisture to the region from the Gulf of Mexico in the springtime. Loope and his colleagues report in the July 21 Science that to build the dunes 1,000 years ago at the beginning of the so-called Medieval Warm Period, much drier spring winds must have blown in from the southwest.