Space: Asteroid: the oldest impact is 2.2 billion years old – World



It is half the age of Earth: the oldest asteroid impact crater, located in western Australia, is 2.2 billion years old. It could be the cause 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.

Verdict: the crater of Yarrabubba was formed 2.229 billion years ago. This date coincides with the end of a period of glaciation called “Snowball Earth”.

Water vapour

“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 youngest deposit, 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, ice deposits are absent from the memory of minerals for about 400 million years after the shock ”, underlines Christopher Kirkland, also 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.

Unusual scenario

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 this is at this stage a “hypothesis”. “We hope it will encourage other researchers to investigate the climatic consequences of an impact” during this ice age. (Ps / nxp)

Created: 21.01.2020, 6:26 p.m.

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