The Vredefort impact structure is the largest verified impact structure on Earth. The crater, which has since been eroded away, was around across when it was formed. 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, which is near its centre. The structure's central uplift is known as the Vredefort Dome. The impact structure was formed during the Paleoproterozoic Era, 2.023 billion years (± 4 million years) ago. It is the second-oldest known impact structure on Earth, after Yarrabubba. In 2005, the Vredefort Dome was added to the list of UNESCO World Heritage Sites for its geologic interest. Formation and structure The asteroid that hit Vredefort is estimated to have been one of the largest ever to strike Earth since the Hadean Eon some four billion years ago, originally thought to have been approximately in diameter. The bolide that created the Sudbury Basin was larger. As of 2022, the bolide was estimated at between in diameter and to have impacted with a vertical velocity of . The original impact structure is estimated to have had a diameter of roughly , but that has been eroded. It would have been larger than the Sudbury Basin and the Chicxulub crater. The remaining structure, the "Vredefort Dome", consists of a partial ring of hills in diameter, and is the remains of a dome created by the rebound of rock below the impact site after the collision. The impact structure's age is estimated to be 2.023 billion years (± 4 million years), which places it in the Orosirian Period of the Paleoproterozoic Era. It is the second oldest universally accepted impact structure on Earth. In comparison, it is about 10% older than the Sudbury Basin impact (at 1.849 billion years) and the Yarrabubba impact crater is older than the Vredefort impact structure by about 0.2 billion years. Other purported older impact structures have either poorly constrained ages (Dhala impact structure, India) or highly contentious impact evidence in case of the circa 3.023 billion year old Maniitsoq structure, West Greenland and the circa 2.4 billion year old Suavjärvi structure, Russia. Their classification as impact structures remain controversial and unsettled. The dome in the centre of the impact structure was originally thought to have been formed by a volcanic explosion, but in the mid-1990s, evidence revealed it was the