The Vredefort crater is the largest verified impact crater on Earth. More than 300 kilometres (190 mi) across when it was formed, what remains of it is in the present-day Free State province of South Africa. It is named after the town of Vredefort, which is near its centre. Although the crater itself has long since been worn away, the remaining geological structures at its centre are known as the Vredefort Dome or Vredefort impact structure. The crater is estimated to be 2.023 billion years old (± 4 million years), with impact being in the Paleoproterozoic Era. It is the second-oldest known crater on Earth.
The asteroid that hit Vredefort is estimated to have been one of the largest ever to strike Earth (at least since the Hadean Eon some four billion years ago), thought to have been approximately 10–15 km (6.2–9.3 mi) in diameter.
The original crater was estimated to have a diameter of roughly 300 km (190 mi), but that has been eroded. The remaining structure, the "Vredefort Dome", consists of a partial ring of hills 70 km (43 mi) in diameter, and are the remains of a dome created by the rebound of rock below the impact site after the collision.
The dome in the centre of the crater was originally thought to have been formed by a volcanic explosion, but in the mid-1990s, evidence revealed it was the site of a huge bolide impact, as telltale shatter cones were discovered in the bed of the nearby Vaal River.
According to en.wikipedia