GREENLAND: Norse settlers once thrived in Greenland before vanishing in the 15th century. A new theory suggests that a decline in the medieval walrus-ivory market may have sent them packing. DNA analysis of walrus bones from sites around western Europe shows that during the 13th and 14th centuries, most of the ivory entering the continent belonged to walrus populations found around Greenland, and may have been exclusively supplied by Norse Greenlanders. When the demand for walrus ivory diminished, these settlers may have been forced to abandon the island.