Vredefort impact structure

The Vredefort impact structure is one of the largest impact structures on Earth. The crater, which has since been worn away, has been estimated at 170–300 kilometres (110–190 mi) across when it was formed, the latter estimate suggesting the initial crater was larger than Chicxulub crater, the largest mostly intact impact crater on Earth. The remaining structure, comprising the deformed underlying bedrock, is located in present-day Free State province of South Africa. It is named after the town of Vredefort, near its centre. The structure's central uplift is known as the Vredefort Dome, which is around 100–120 kilometres (62–75 mi) in diameter. The impact structure was formed during the Paleoproterozoic Era, 2.023 billion (± 4 million) years ago. It is among the oldest known impact structures on Earth, after Yarrabubba (2.23 billion years old) and possibly Miralga. The structure's extraterrestrial origin was established in 1961 after the location of shatter cones by American geologists Robert S. Dietz and Robert B. Hargraves, though an impact was proposed as early as 1937 by Claude C. Albritton and John D. Boon. In 2005, the Vredefort Dome was added to the list of UNESCO World Heritage Sites for its geologic interest.