Three and a half billion years ago, when Earth was in its infancy, scientists believe our planet was struck by an enormous asteroid that probably helped set the course of life as we know it.

And we’re only just finding out about it now.

This week, researchers reported in the journal Precambrian Research that they’d discovered evidence of the apocalyptic event buried inside an ancient rock formation in Australia. Tiny glass beads called spherules – which form when material that gets vaporized during an impact condenses and falls back to Earth – show that the asteroid that caused them would have been 12 to 18 miles across, at least twice the size of the one that killed the dinosaurs.

“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,” lead author Andrew Glikson, a paleoclimate scientist at the Australian National University’s Planetary Institute, said in a statement.

According to Glikson, the 3.46-billion-year-old impact is the second earliest known to have happened on Earth. The asteroid hit so long ago that the crater it must have left has been erased by eons of earthquakes, erosion and tectonic change. Scientists have no idea where it struck.

Indeed, the only reason they know about it at all is the little spherules, which contain elements, such as platinum, nickel and chromium, that had to have come from an asteroid.

The Pilbara Craton, in Northwestern Australia, the geologic formation where the spherules were found, contains some of the oldest rocks in the world.

The Pilbara is also the same spot where some scientists believe they’ve found the earliest evidence of life from 3.48 billion years ago – just a geological moment before the impact likely changed everything.

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