As Mallory and Irvine struggled into their heavy oxygen apparatus, expedition geologist Noel Odell snapped their picture. Irvine, only 22 years old, stood calmly with his hands in his pockets as he watched Mallory fuss with his oxygen mask. A few minutes later, at 8:40 a.m., the pair set off with eight Tibetan porters up the North Ridge toward Camp V. The next morning, with four porters, they pushed higher, to Camp VI, only some 2,000 feet below the summit. The porters descended, carrying with them two notes from Mallory scribbled in pencil on torn-out pages from a small notebook. One was addressed to expedition cinematographer John Noel: "It won't be too early to start looking for us either crossing the rock band under the pyramid or going up skyline at 8.0 p.m." (Mallory obviously meant 8 a.m.) The other note was addressed to Odell, with a gentlemanly apology for leaving Camp IV a mess and a request to bring up a forgotten compass. "Perfect weather for the job!" he added.

The next morning, June 8, Mallory and Irvine faced a series of daunting hurdles on their way to the summit: a crumbly strip of steep limestone slabs now known as the Yellow Band, a nearly vertical 100-foot wall of harder rock that came to be called the First Step, a dicey and exposed ridge walk, and then another 100-foot Second Step, far more difficult than the first. Above the Second Step, a broad, gently rising plateau led to an easier Third Step and then the snow-covered summit pyramid itself.

Later that morning, Noel Odell left for Camp VI, carrying the forgotten compass. The geologist had become exceptionally well acclimatized to Everest's thin air, and he climbed without supplemental oxygen, looking for fossils along the way. At 12:50 p.m. he looked up and saw something unforgettable. "There was a sudden clearing of the atmosphere," he would later write, "and the entire summit ridge and final peak of Everest were unveiled. My eyes became fixed on one tiny black spot silhouetted on a small snow-crest beneath a rock-step in the ridge; the black spot moved. Another black spot became apparent and moved up the snow to join the other on the crest. The first then approached the great rock-step and shortly emerged at the top; the second did likewise. Then the whole fascinating vision vanished, enveloped in cloud once more. There was but one explanation. It was Mallory and his companion moving, as I could see even at that great distance, with considerable alacrity.... The place on the ridge referred to is the prominent rock-step at a very short distance from the base of the final pyramid."

Concluding that his colleagues were perhaps three hours from the summit, Odell climbed up to Camp VI, hoping that the others would make it back by nightfall. As a snow squall blew up, he ducked into the tiny two-man tent, finding it strewn with clothing, the climbers' sleeping bags, and spare parts of oxygen apparatus.

Concerned that the camp might be difficult to find in the swirling snow, Odell scrambled another 200 feet up the mountain, whistling and yodeling to guide Mallory and Irvine back. But it was still too early, he realized, for the climbers to come back. At 4:30 p.m., leaving the compass and some food, Odell descended to Camp IV to wait.

But Mallory and Irvine never returned.