Evidence of gargantuan asteroid strike unearthed in Australia

A close-up of the spherules that led the researchers to suspect an asteroid impact on Earth about 3.5 billion years ago(Credit: A. Glikson)

All it takes is a quick look up at the moon to understand what a violent place the early solar system was. All those craters are the results of asteroids smashing into the lunar surface. The Earth was likewise battered all those billions of years ago, but the evidence of many asteroid strikes has long been erased through topography changes. Researchers at Australian National University (ANU) though, have found clues to a massive asteroid that impacted our planet about 3.5 billion years ago, when the Earth was less than a quarter as old as it is now.

Many early asteroid, or meteorite, strikes are discovered by finding their impact craters, such as the Chicxulub crater in the Gulf of Mexico, which is the site where the asteroid that's believed to have wiped out the dinosaurs landed 66 million years ago. In this case, the researchers found tiny glass beads called spherules buried about 77 meters (253 ft) beneath the Earth's surface in northwestern Australia where they took core samples.

Even though the beads were largely degraded, the scientists were still able to see that they contained levels of chemical elements such as platinum, nickel and chromium consistent with those found in asteroids. The thinking is that when the asteroid struck, the spherules were created from vaporized material and dispersed around the planet. For this reason, the researchers can't be sure where exactly the asteroid impacted the Earth, although they do know it was a doozy, measuring 20 to 30 km (12 to 19 miles) across – which makes it about twice the size of the Chicxulub asteroid.

"The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble," said Andrew Glikson, from the ANU Planetary Institute. Glickson is the lead author on a paper about the finding published in the July issue of the journal Precambrian Research.

The researchers were also able to pinpoint the age of the asteroid, as the spherules were found wedged between two layers of volcanic sediment from about 3.5 billion years ago.

"This is just the tip of the iceberg," says Glickson, who's been researching asteroid impacts for 20 years. "We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds. Asteroid strikes this big result in major tectonic shifts and extensive magma flows. They could have significantly affected the way the Earth evolved."

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