A recent research by NASA has managed to date the autralian crater Yarrabubba in 2 billion 229 million years; it would be about 200 million years older than the South African crater of Vrederfort Dome, which until today held the record.
About 190 impact craters have been identified and only a few of them know the precise age.
Determining when these formations originated is fundamental to understanding the Earth’s history.
Large meteoric impacts have certainly played an important role in the climate history of our planet and its effects on the biosphere.
The most famous case is surely the one that generated the cratere of Chicxulub, Mexico which caused the mass extinction of dinosaurs.
The Paleo-Proterozoic Ice Age
According to the study, the meteorite that formed the Yarrabubba crater arrived on our planet during the Uruguayan Ice Age.
As a result of the impact, huge amounts of ice would have melted and released water vapour into the atmosphere.
The impact could also be related to the end of the Paleo-Proterozoic Ice Age.
According to the simulation, if the Australian ice was between 2 and 5 kilometres thick, an impact capable of giving rise to a crater 70 kilometres long could have generated the emission into the atmosphere of more than 200 trillion kilos of water vapour.
Some of this water would immediately re-propelled to the ground without affecting the global climate in any way.
Another part, on the other hand, could have remained in the atmosphere for a long time and contributed to a warming of the climate due to the greenhouse effect, and therefore at the end of the Uruguayan ice age.
The Yarrabubba Crater
Discovered in 2003, its diameter is quite small (about twenty kilometres), but experts believe that it was once much larger, measuring at least seventy kilometres.
At first sight it is not easy to recognise it: its edges are completely eroded by atmospheric agents and tectonic movements have modified the geological conformation of the region, making the classic circular depression disappear.
However, the presence of a crater can also be detected in other, less direct ways: such as the presence of certain types of fractures in the rocks or impacts, rocks modified or altered by the energy of the meteoric impact.
To determine the age of Yarrabubba, researchers at the Australian University of Curtin and NASA’s Johnson Space Center took rock samples from around the site which, according to experts, would have melted after the shock of the impact and then recrystallised over time.
Two minerals were found inside the rocks: zirconium and monazite.
The recrystallised ores contain a small percentage of uranium which decays over time to lead. Determining the precise amount of uranium decayed into lead allowed scientists to determine the exact age of the ores and, consequently, the age of the impact.
The results of the study were published in Nature Communications.