Australia is home to the largest asteroid impact crater on Earth. The 400km-wide crater is more than twice the size of the Chicxulub crater in Mexico, which is often attributed with wiping out the dinosaurs.
The new find in the Warburton Basin in Central Australia is a stunning 400km-wide impact zone from a huge asteroid that broke into two pieces just before it hit.
So big was the impact that it fractured the Earth's crust to a depth of around 20km, according to a paper published in Tectonophysics.
The Australian National University says it's the largest impact crater ever discovered – the Chicxulub crater measures 180 km across.
The ANU's Dr Andrew Gilkson explains that a layer of glass showed up in drill core samples during a geothermal research project.
Follow-up modelling of the deep crust identified bulges, rich in iron and magnesium, which Dr Gilkson explained: “There are two huge deep domes in the crust, formed by the Earth’s crust rebounding after the huge impacts, and bringing up rock from the mantle below”.
From the scale of the impact zone, Gilkson reckons each of the two chunks of asteroid to hit was around 10 km across – a real planet-killer – and therein lies a problem: there doesn't seem to be a corresponding extinction event to go with the strike.
The extinction event associated with Chicxulub is easy to see in the fossil record, since that impact aligns closely with the end of the dinosaur era. Not so with Warburton Basin.
As the university notes, “exact date of the impacts remains unclear”, because while the surrounding rocks are between 300 and 600 million years old, there's no layer of sedimentary ash corresponding to the impact; Chucxulub, on the other hand, left an ash layer all over the world 66 million years ago that helped date the event.
“It’s a mystery – we can’t find an extinction event that matches these collisions. I have a suspicion the impact could be older than 300 million years,” Dr Gilkson says. ®