The leading theory amongst those supporting the summit push has Mallory overcoming the difficulty of the sheer face of the Second Step by standing on Irvine's shoulders. Armed with Irvine's remaining 3/4-full oxygen tank he could conceivably have reached the summit late in the day, but this would have meant that Irvine would have had to descend by himself. However, rope-jerk injuries around Mallory's waist must mean the two were roped when they fell from below the First Step. 1960s Chinese Everest climber Xu Jing told Eric Simonson and Jochen Hemmleb in 2001 that he recalled spotting a corpse somewhere in the Yellow Band. Despite numerous searches of the north face, no sign of Irvine has turned up so far. One researcher claims to have finally spotted Irvine's body using microscopic examination of aerial photographs. This possible discovery set off a new round of search expeditions in 2010 and 2011.