These 2,500-year-old petroglyphs, portraying figures with tulip-shaped heads and hourglass bodies, mark an ancient human presence in the Sahara desert’s Aïr Mountains. Despite the extreme temperatures and sparse rainfall characterizing these arid landscapes, more than one billion people eke out a living in desert regions today.

(Photo shot on assignment for, but not published in, "Journey to the Heart of the Sahara," March 1999, National Geographic magazine)

Photograph by George Steinmetz