The mountaineer, who reached Everest's summit for the sixth time on May 16, also posted a photograph of what remains of the step.
Named after Sir Edmund - the first person along with Tenzing Norgay to scale it on the way to the summit - the face is believed to have been damaged by the 7.8-magnitude natural disaster which struck in Nepal in 2015.
Another climber, Pasang Tenzing Sherpa, said confusion might have come about because mountaineers marking a new route to the summit had approached it from another side, "from where the Hillary Step can not be seen". "Hillary Step" stood on the mountain's southeast ridge, and was the last great challenge before reaching the top.
"It was mentioned last year, and I really climbed last year, but we were not sure it had collapsed because the area was full of snow".
Yearwood's death is the third on Everest this month and comes one day after Indian climber Ravi Kumar went missing in the same area during his descent from the peak.
The destruction of the Hillary Step could make the ascent easier since climbers will no longer face a vertical rock climb.
Snowfall in 2016 made it hard to confirm whether the Step had disappeared.
Navin Trital of Expedition Himalaya, the company that helped coordinate that climb, tells the news service that Marchetti "died while being brought down to a lower camp". Planet Mountain, a website devoted to climbing news, writes that the Hillary Step "probably" collapsed due to the devastating 2015 quake in Nepal.
In May 2016 there were pictures by the American Himalayan Foundation which showed that Hillary Step had changed its shape.
"Today there might be as many at 150 climbers reaching the top from the Nepal side, but it isn't a record number", Ang Tsering Sherpa, head of the Nepal Mountaineering Association, told AFP. "The Hillary Step often formed a bottleneck but some years they fixed an up and a down rope", he said.
The climbing season begins in March and runs through the end of May to take advantage of the best weather conditions on Everest.