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Oldest known asteroid strike may have ended Snowball Earth

More than 2 billion years ago, an asteroid slammed into Earth and created a 43-mile wide crater in Western Australia’s outback. Now, researchers believe it is the oldest known impact crater, predating others by 200 million years. And it’s possible that the impact led to a great thaw as Earth exited a global frozen state.

Unlike the moon, Earth’s surface is geologically active and constantly changing. This makes it difficult to determine the oldest impact craters because erosion and active tectonic plates bury the evidence.

To determine that Australia’s Yarrabubba crater is the oldest, researchers conducted an isotopic analysis of minerals within the crater. Zircon and monazite, both minerals found at the site, had undergone “shock” recrystallization caused by an asteroid strike. They published their findings Tuesday in the journal Nature Communications.

Given its age, the crater has eroded to a remnant of what it once was, making it hard to determine its original size. That’s true of other craters researchers have tried to identify across Africa and Australia before. In those cases, they dated material created by the asteroid strikes, but couldn’t find the impact craters.

Snowball earth

The new age of the Yarrabubba crater, created by dating the minerals, is more precise than previous estimates, at 2.229 billion years old.

“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,” said Chris Kirkland, study co-author and professor at Curtin University’s School of Earth and Planetary Sciences in Perth, Australia.

This determination allowed the researchers to match by the timing of the asteroid strike with what they know of Earth’s history.

“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” said Nicholas Timms, study co-author and associate professor at Curtin University’s School of Earth and Planetary Sciences.

“This twist of fate suggests that the large meteorite impact may have influenced global climate.”

The researchers ran different simulations to understand the ways the asteroid strike may have impacted Earth and its climate. Until now, “the impact cratering record was absent when significant changes in the Earths hydrosphere and atmosphere occurred” between 2.1 billion to 2.5 billion years ago, according the study.

They simulated what might have happened if the asteroid struck a continental ice sheet, given the state of “Snowball Earth” at the time.

“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 whether this impact may have tipped the scales enough to end glacial conditions.”

Water vapor is an effective, and the most abundant, greenhouse gas that can absorb radiation and send it back to Earth’s surface, contributing to warming.

That’s between 87 trillion and 5,000 trillion kilograms of water vapor hurtling into the atmosphere which would have had a warming effect. The researchers believe that the potential effects of this on the global climate warrant more research. The asteroid strike that led to the mass extinction of the dinosaurs 66 million years ago also led to global ocean cooling and widespread acid rain — which we know because it’s been widely studied.

“Our findings highlight that acquiring precise ages of known craters is important – this one sat in plain sight for nearly two decades before its significance was realized,” said Aaron Cavosie, study co-author and Senior Research Fellow at Curtin University’s School of Earth and Planetary Sciences.

“Yarrabubba is about half the age of the Earth, and it raises the question of whether all older impact craters have been eroded or if they are still out there waiting to be discovered.”

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