World's oldest crater found in Australia is 2.229 billion years old, may have ended ice age, say scientists
The Earth’s oldest asteroid strike occurred at Yarrabubba, southeast of the town of Meekatharra in Western Australia. According to the discovery made by researchers from Curtin University and the NASA Johnson Space Center, among others, the crater formed 2.229 billion years ago.
The researchers used isotopic analysis of minerals to calculate the precise age of the Yarrabubba crater for the first time, establishing it as the oldest recognized impact structure on Earth. It is some 200 million years older than the next oldest, the Vredefort impact in South Africa, says the team. “This result establishes Yarrabubba as the oldest recognized meteorite impact structure on Earth, extending the terrestrial cratering record back >200 million years,” says the study published in Nature.
According to scientists, the asteroid strike could have triggered a global thaw. They found that the cataclysmic impact coincided with the end of a global deep freeze known as a Snowball Earth.
The team inferred that the impact may have occurred into an ice-covered landscape, vaporized a large volume of ice into the atmosphere, and produced a 70-km diameter crater in the rocks beneath.
“Yarrabubba, which sits between Sandstone and Meekatharra, had been recognized as an impact structure for many years, but its age wasn’t well determined. Now, we know the Yarrabubba crater was made right at the end of what’s commonly referred to as the early Snowball Earth – a time when the atmosphere and oceans were evolving and becoming more oxygenated and when rocks deposited on many continents recorded glacial conditions,” says Professor Chris Kirkland in the analysis.
What experts found at Yarrabubba
An asteroid strike is one of the most violent geologic events. The researchers write in The Conversation that the Yarrabubba impact occurred during a period in Earth’s history called the Proterozoic eon. “Long before plants, fish, or dinosaurs, life at this time consisted of simple, multicellular organisms,” adds the team.
The researchers explain that asteroid strikes raise the temperature in rocks they hit, causing minerals to lose their accumulated lead, which resets the clock. After impact, the isotopic clocks start ticking again as new lead accumulates. “So by measuring the isotopes of uranium and lead in these minerals, we can calculate how much time has passed since the impact,” say experts.
The research team identified tiny crystals of zircon and monazite at Yarrabubba – each about the width of a human hair – with textures that show they had been heated by a massive impact.
“We analyzed the amounts of lead and uranium isotopes in these crystals using mass spectrometry and found their clocks had been reset 2.229 billion years ago (give or take five million years). That’s when we realized Yarrabubba coincided with a major change in Earth’s climate,” explain the authors.
Curtin University Associate Professor Nicholas Timms notes the precise coincidence between the Yarrabubba impact and the disappearance of glacial deposits.
“The age of the Yarrabubba impact matches the demise of a series of ancient glaciations. After the impact, glacial deposits are absent in the rock record for 400 million years. This twist of fate suggests that the large meteorite impact may have influenced the global climate,” says Timms in the study.
“Numerical modeling further supports the connection between the effects of large impacts into ice and global climate change. Calculations indicated that an impact into an ice-covered continent could have sent half a trillion tons of water vapor – an important greenhouse gas – into the atmosphere. This finding raises the question of whether this impact may have tipped the scales enough to end glacial conditions,” he says.
The study has significant implications for the discovery of future impact craters. It highlights the importance of finding out the precise ages of known craters, adds the research team.