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The Earth's surface It is continually changing due to tectonic activity and erosion, making it very difficult to date very old impact craters (or astroblems). This is what happened to him yarrabubba crater, 70 km wide, in Western Australia, which lacked a precise age but was considered one of the oldest on our planet.
Although material from impact ejecta - material ejected from the crater and deposited around it - more than two billion years old was previously dated in Australia and Africa, the corresponding craters could not be dated.
Now the crater ofYarrabubbahas been accurately dated and the results, which are published inNature Communications,reveal an age of 2,229 million years (Proterozoic), making it the oldest known impact on Earth.
"Yarrabubba, which is located between Sandstone and Meekatharra (small towns in central Western Australia), was recognized as an impact structure for many years, but its age was not well determined," confirms the professor at Curtin University,Christopher L. Kirkland.
He and his colleagues analyzed the minerals crystallized by the shock in the Yarrabubba crater. They did an isotopic analysis - to understand the chemical reactions - of the minerals zircon and monazite in order to obtain the precise age. Thus, they found out that it is 200 million years older than the next oldest recognized impact, theVredefort crater in South Africa.
The impact changed the climate
The team deduced that the impact could have occurred during theglobal glaciation, when the landscapes were covered with ice. The researchers ran a series of models to see what the possible effects of an asteroid impact on an ice sheet could be and how that could change Earth's climate, says the professor. Timmons Erickson, a member of NASA's Johnson Space Center.
“In an impact scenario during glacial conditions, significant water vapor could be released into the atmosphere. Because it is a greenhouse gas, even more efficient than CO2This could lead to the warming of the Earth's atmosphere ”, Erickson emphasizes.
"We now know that the Yarrabubba crater formed right at the end of what is commonly known as the global ice age," Kirkland notes. According to the expert, the chronology raises the possibility that the impact of the oldest asteroid on Earth could have helped to remove the planet from this freezer.
"Yarrabubba is about half the age of Earth and raises the question of whether all the oldest impact craters have been eroded or are they still out there waiting to be discovered," concludes geologist Aaron Cavosie, co-author of the work and researcher at the Australian university.
Timmons M. Erickson et al. “Precise radiometric age establishments Yarrabubba, Western Australia, as Earth’s oldest recognized meteorite impact structure”.Nature communications. January 21, 2020.