Paris (AFP)

It is half the age of Earth: the oldest asteroid impact crater, located in western Australia, is 2.2 billion years old and could be the source of major climate change, according to a study published Tuesday.

The Yarrabubba impact crater, about 70 km in diameter, difficult to identify due to the erosion of its original structure, is considered to be one of the oldest on Earth. However, it had so far been impossible to date it accurately.

Using an ultra-precise dating method (the sensitive high-resolution ion microprobe), researchers at Curtin University in Perth, Australia, have succeeded in targeting the grains of minerals that have "recorded" the shock of the impact , through a recrystallization process, details their study published in Nature Communications.

"There is geological evidence (separate from the study, editor's note), based on the presence of deposits, of the existence of glaciers on Earth between 2.4 and 2.2 billion years ago. And the deposit the youngest, found in South Africa, corresponds to the age of the impact of Yarrabubba ", explains to AFP Timmons Erickson, of the Johnson center of Nasa, principal author of the study.

If nothing proves the existence of a glacier on the impact zone, "it is interesting to note that at this place, the ice deposits are absent from the memory of the minerals during approximately 400 million years after shock, "said Christopher Kirkland, also an author.

The researchers therefore suggested, on the basis of numerical modeling, the scenario of a meteorite which would have struck a frozen landscape, piercing a layer of ice 5 km thick, then projected into the atmosphere a phenomenal amount of water vapor - up to 500 billion tonnes.

This ejection of water vapor, "a greenhouse gas even more powerful than CO2", would have led to warming helping the planet to emerge from this ice age.

An unusual scenario, with most meteor impacts being associated with general cooling - the best known example being that of the asteroid which struck the Yucatan in Mexico and would have ended the reign of the dinosaurs around 66 million d years.

"Our simulations are unique over a period of glaciation," argues Timmons Erickson, conceding that it is at this stage a "hypothesis". "We hope it will inspire other researchers to investigate the climatic consequences of an impact" during this ice age.

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