Of course two billion years is a lot of time for a landscape to wear away, so estimating the original size of the crater with accuracy isn't straightforward.

If the new modeling is correct, the asteroid that hit two billion years ago would have been bigger than the one that created the Chicxulub crater and killed off the dinosaurs some 66 million years back in time.

"Unlike the Chicxulub impact, the Vredefort impact did not leave a record of mass extinction or forest fires, given that there were only single-cell lifeforms and no trees existed two billion years ago," says planetary scientist Miki Nakajima, from the University of Rochester in New York State.

Material from the Vredefort impact has been spotted as far away as what is modern-day Russia, but the researchers think this location would have been much closer to the impact crater two billion years ago.