Boulders on Iceland's Surtsey Island may look old, but they are actually as young as the island itself, which was born after volcanic eruptions on November 14, 1963. Iceland constitutes the largest above-sea section of the 10,000-mile (16,093-kilometer) Mid-Atlantic Ridge, a mostly underwater mountain range that zigzags vertically through the Atlantic Ocean.

(Text adapted from "Surtsey: Island Born of Fire," May 1965, National Geographic magazine; photograph shot on assignment for, but not published in, National Geographic Books)