Sion (Switzerland) (AFP)

The small group trudged up the steep slopes of an Alpine glacier before finding what they were looking for: a vein of rock crystal.

The scene took place some 9,500 years ago, and these Mesolithic men used the precious crystal to make their tools.

So many deductions made by archaeologists, who can excavate this extreme site - and many others -, thanks to the melting of the alpine glaciers which frees artefacts from the ice matrix that protected them from the ravages of time , sometimes for almost 10,000 years.

While they do not rejoice in the devastating effects of global warming, the researchers do admit that it created "an opportunity" to fill the huge gaps in our understanding of life in the mountains several millennia ago.

"We make fascinating finds, which open a window on a part of the archeology to which we normally do not have access", explains to AFP Marcel Cornelissen, who took the expedition to the Mesolithic site at 2,800 meters above sea level, near the Brunifirm glacier in the eastern Swiss canton of Uri.

- "really exceptional" -

Until the 90s, it was commonly accepted that prehistoric men hardly ventured into high mountains.

Everyone remembers "Oetzi", the perfectly preserved body of a 5,300 year old hunter discovered in 1991 in Austria and believed to be an exception.

But discoveries, sometimes spectacular, have revealed that the Alps were on the contrary surveyed and visited for millennia.

"We now know that people climbed mountains up to 3,000 meters to look for crystals and other raw materials", explains an archaeologist from the canton of Uri, Christian auf der Maur.

A quiver made of birch bark, which was made around 3,000 BC, was found on the Schnidejoch pass, in the Bernese Alps, at an altitude of more than 2,700 meters, thus confirming the richness of this site .

Leather pants and shoes, belonging to the same hunter, were later discovered along with hundreds of other objects, some of them 6,500 years old.

"It's very exciting, because we find things that we would not generally find in excavations", because the ice has preserved them, rejoices archaeologist Regula Gubler.

And as proof, in September she discovered knotted raffia, probably 6 millennia old, which looks like a fragile basket woven from the same material discovered last year.

If climate change is a boon to discovering these objects, it is also the reason for their rapid destruction once they are again exposed to the elements.

"The retreat of the glaciers and the melting of the ice fields is already too far advanced. I don't think we will find another Oetzi", regrets Marcel Cornelissen.

- Hikers to help -

Faced with the emergency, archaeologists rely on hikers and other climbers to help them save what can be saved.

Sometimes it takes a lot of time and a lot of luck, says archaeologist Pierre-Yves Nicod, who two years ago organized an exhibition on the archeology of glaciers.

He got wind of a discovery by two Italian hikers, who in 1999 came across a wooden sculpture on the Arolla glacier, at 3,100 meters above sea level.

Picked up, cleaned, the sculpture about a meter high ended up on the wall of their living room.

In fact, it was "a Celtic object dating back to the Iron Age", more than 2,000 years old but whose function remains unexplained to this day.

For Pierre-Yves Nicod, it is urgent "to sensitize the population who could come across this kind of artifact".

"It's an archaeological emergency," he insists.

© 2020 AFP