Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific developments and more.

CNN
—

When a National Geographic documentary team discovered a boot and sock sticking out of a melting glacier on Mount Everest in September, they almost immediately recognized its significance as a clue to an age-old mystery.

A name tag still stitched onto the wool sock reads ‘AC Irvine’, showing that it likely belonged to British climber Andrew ‘Sandy’ Irvine. Irvine’s disappearance on Everest in 1924, along with fellow countryman George Mallory, is one of mountaineering’s greatest mysteries – with a solution that has the potential to change history.

The pair disappeared on June 8, 1924, 800 feet below the summit of Everest, while on their way to complete the first documented ascent of the world’s highest mountain. But whether they reached the summit, becoming the first known people to reach this milestone, before dying is still unknown.

Although Mallory’s body was discovered in 1999, neither Irvine’s body nor the camera the climbers carried, which could reveal whether they reached the summit, have ever been found.

That is, until this latest expedition, when the National Geographic team, including Free Solo co-director Jimmy Chin, discovered a foot in what they believe to be Irvine’s boot. While they await DNA confirmation, comparing samples of the foot with those of members of Irvine’s family, this appears to be the first evidence of his death since his disappearance.

“It’s the first real evidence of where Sandy ended up,” Chin said, according to National Geographic. “Many theories have been put forward.

“When someone disappears and there is no evidence of what happened to them, it can be very challenging for families. And just having some definitive information about where Sandy might have ended up is certainly (helpful), and also a big clue to the climbing community about what happened.

A few days before finding the boot, the team discovered an oxygen cylinder from a 1933 expedition that had also attempted to climb Mount Everest. Although that expedition failed, she had found an Irvine ice ax on the northeast ridge, leading Chin’s team to speculate that they might be close to his body.

Based on that hypothesis, they spent the next few days searching the glacier until filmmaker and climber Erich Roepke spotted the boot.

“I think it literally melted a week before we found it,” Chin said.

Chin and the team removed the boot and base from the mountain into a cooler when they noticed birds disturbing the mountain and gave it to the China-Tibet Mountaineering Association (CTMA).

Shortly after their discovery, the team informed Irvine’s family, including his great-niece Julie Summers, who has written a book about the climber.

Summers was “moved to tears” when she learned of the boot’s existence in an “extraordinary and poignant moment,” she said, according to news agency PA Media.

“I have lived with this story since I was seven years old when my father told us about the mystery of Uncle Sandy on Everest,” she added.

“The story became more real when climbers found George Mallory’s body in 1999, and I wondered if Sandy’s body would be discovered next. A quarter of a century after that discovery, it seemed extremely unlikely that anything new would be found.”