About two billion years ago, an asteroid measuring at least 10 kilometres across hurtled toward Earth. The impact occurred southwest of what is now Johannesburg, South Africa, and temporarily made a 40-kilometre-deep and 100-kilometre-wide dent in the surface. Almost immediately after impact, the crater widened and shallowed as the rock below started to rebound and the walls collapsed. The world's oldest and largest known impact structure was formed.
Scientists estimate that when the rebound and collapse ceased, Vredefort Crater measured somewhere between 180 and 300 kilometres wide. But more than 2 billion years of erosion has made the exact size hard to pin down.
The Vredefort Dome, which measures about 90 kilometres across, was observed on 27 June 2018, by the Operational Land Imager (OLI) on Landsat 8.
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Credit: NASA/USGS/Landsat & Kathryn Hansen