- A meteorite hit Western Australia 2.2 billion years ago, leaving a 40-mile-wide crater.
- In a study, scientists determined that crater was the oldest on record.
- Researchers think that when the meteorite hit Earth, it released more than 100 billion tons of water vapour into the sky.
- The infusion of water helped warm the Earth, ending a planetwide ice age.
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There are 70,000 meteorites – pieces of debris from space objects that hit Earth – known to scientists. But only 190 of them left behind impact craters scientists could identify.
According to a study published in the journal Nature Communications, the oldest such impact site ever found is in Western Australia, about 500 miles northeast of Perth. About 2.2 billion years ago, a massive meteorite left a crater there 43 miles wide.
Today, the dusty red-hued site called Yarrabubba lacks a defined crater – it disappeared because of erosion and shifting tectonic plates.
“There is very little rock that outcrops at Yarrabubba, and most of it is stained red,” Timmons Erickson, a scientist at NASA’s Johnson Space Centre and the lead author of the study, told Business Insider.
But the rocks created by the cataclysmic event remain. A small hill in the middle of the site, called Barlangi Rock, is made entirely of rocks that formed under the intense heat and pressure of the meteorite’s impact.
By dating those rocks, Erickson and his coauthors were able to pinpoint the exact age of the Yarrabubba crater. Their results showed it was more than 200 million years older than any other crater scientists have found on Earth.
The oldest impact crater ever found
The Yarrabubba site is in the outback of Western Australia; the closest town, Meekatharra, is about 40 miles away by gravel track. Erickson travelled there in 2014 and collected 200 pounds of rocks to study.
To determine the age of those rocks, his team immersed the samples in water at their lab, then supercharged the liquid with 120,000 volts of electrical energy. The electricity split the rocks into microscopic grains of zircon and monazite. These minerals imbibe radioactive material like uranium, which allows scientists to date them.
The analysis showed that the Yarrabubba rocks were 2.229 billion years old, plus or minus 5 million years.
The next oldest impact-crater site on the planet is the giant Vredefort Dome in South Africa, which is 2.02 billion years old. After that is Ontario’s Sudbury impact structure, which is 1.85 billion years old.
The end of a global ice age
But the Yarrabubba crater’s age isn’t the only surprising part of the story, Erickson said: The impact “also occurred during a very dramatic time in Earth’s history, when the planet was transitioning towards something more comparable to today.”
According to the study, when the Yarrabubba meteor hit, it likely smacked into a giant ice sheet. That’s because 2.2 billion years ago, the planet was at the end of an era of glaciation called a “snowball Earth.”
Erickson’s team simulated the effect a massive meteorite hitting an ice sheet and found that such an impact could have released up to 100 billion tons of water vapour into the upper atmosphere.
That infusion of water might have led Earth’s atmosphere to trap more heat, warming the planet and ending the ice age, Erickson said.
“Water is a very efficient greenhouse gas, much more so than carbon dioxide,” he added.
Meteor impacts have changed Earth’s climate multiple times
The Yarrabubba meteor wasn’t the only space rock that changed Earth’s climate. The 6-mile-wide asteroid that struck Chicxulub, Mexico, 66 million years ago sparked wildfires that stretched for hundreds of miles, triggered a mile-high tsunami, and released billions of tons of sulphur into the atmosphere.
That gaseous haze blocked the sun, cooling the Earth and dooming the dinosaurs. Acid rain and fallout from the impact also acidified the world’s oceans in a flash, causing a mass marine extinction.
The authors of the study wrote that such “extraterrestrial bombardment” likely had major consequences for Earth’s development throughout history – if the meteors hit certain parts of the planet.
“Oftentimes it seems that the impact has to hit the Earth in a spot that is fairly unique for it to dramatically modify Earth’s climate,” Erickson said. “For example, the spot on the Yucatan peninsula where the Chicxulub impact occurred happened to have large salt and gypsum deposits, which released huge amounts of sulphur into the atmosphere, creating terrible acid rains.”