<p>In 1924 Mount Everest remained unclimbed. Two British expeditions had already tackled what was known to be the highest mountain on Earth. The first, in 1921, found a route to the base. The second, in 1922, attempted the summit, reaching a record height of 27,320 feet before retreating. Two years later, a team that included Colonel E.F. Norton, George Mallory and Andrew Irvine returned to the Himalaya. Armed with greater knowledge and experienc...