Dating tiny globules stuck in volcanic rock in Western Australia, researchers have found what they believe to be the oldest record of a meteorite impact, dating back 3.48 billion years!
In Earth’s earliest moments, the solar system had not yet completed its formation, and meteorite impacts were much more common than today, depending on the time. Researchers are trying to find these traces of ancient impacts: a difficult task because erosion and plate tectonics have overcome most craters and other geological records.
Currently, the oldest preserved impact is 2.23 billion years old and is in Western Australia. But the findings, presented at the 54th Lunar and Planetary Sciences Conference, push that age back by using a different research method that focuses on layers of impact ejection.
“There are two groups of impact rocks,” Chris Yakymchuk, a geologist at the University of Waterloo in Canada, told LiveScience. There is one remaining impact crater in the first group – the oldest known is the 2.23 billion year old Yarrabubba structure in Western Australia. In the second group we have rock fragments and minerals created by an impact that were ejected from the impact crater and are now in the rock.”
Spheres indicating an impact from 3.48 billion years ago
The researchers made their discovery in globules discovered in 2019 in volcanic rocks in Australia’s Pibara craton. They were then dated to 3.48 billion years thanks to their unusual isotopic composition. They also contained tiny bubbles that corresponded to splashes of molten rock after a meteorite impact! Scientists have therefore concluded an extraterrestrial origin, thanks in particular to the presence of platinum or iridium in higher quantities than on Earth.
The oldest globules of this type so far date from the age of 3.47 billion years, also from the Pibara craton. However, reviews are missing, which should arrive soon. “This new research documents ejecta in slightly older rocks that are 3.48 billion years old — about 10 million years older than before,” said Chris Yakymchuk. The results appear robust, but access to the full dataset would be required to confirm their validity.”