This photo taken Tuesday, Oct. 23, 2012 and released by the National Geographic Society on Thursday, Jan. 10, 2013, shows a series of cairns left by people crossing the desert flats, to help others navigate during dust storms, in Djibouti. Two-time Pulitzer Prize-winning reporter Paul Salopek has taken the first steps of an unimaginably long walk - a 21,000-mile (34,000-kilometer) journey from Ethiopia to Argentina expected to last seven years. (AP Photo/National Geographic, Paul Salopek) NO SALES, ONE TIME USE ONLY, NO ARCHIVE