Abstract Abundant evidence of impact cratering is found on the surfaces of all solid bodies in the solar system, although on Earth this evidence is more restricted owing to the effects of an active geosphere. Investigating impact structures on Earth is important not only from the perspectives of understanding Earth’s geological history and the economic significance of some impact structures, but also because of the demonstrable threat large impacts pose to life on Earth. Besides the formation of a crater, the transfer of exceptional amounts of energy into Earth’s crust during an impact creates distinctive deformation features and rock types that aid in identifying impact sites, including where the original crater form has been lost through erosion or is deeply buried. South Africa contains a small but diverse sample of impact structures in which impact processes can be investigated. The country´s four confirmed impact structures – Tswaing, Kalkkop, Morokweng and Vredefort − have ages between ~200 000 years and 2023 million years, and diameters that range from 1 km to 250 km. They provide an excellent sample of the size range, different morphological types, and different levels of preservation of Earth’s impact structure inventory. Whereas Tswaing is one of Earth’s best-preserved small impact craters, Morokweng and Vredefort are significantly eroded, thus providing insight into the deep-level processes caused by impact. Vredefort is Earth’s largest and most deeply eroded impact structure, and its formation was integral to preservation of the Witwatersrand gold deposits. Morokweng is one of the few terrestrial impact structures preserving a thick, differentiated, impact melt sheet; it is also the only impact structure in which fragments of the impacting meteorite have been recovered from within a melt sheet. Tswaing and Kalkkop preserve rare long-term palaeoenvironmental records for the interior of South Africa, spanning the last several hundred thousand years. Additionally, the South African Archaean rock record also hosts a number of impact spherule beds within 2.5 to 3.3 Ga sedimentary sequences that constitute parts of the earliest impact record known on our planet.
Gibson et al. (Sun,) studied this question.