Aerial view of crater (courtesy Department of Geology, University of the Witwatersrand)

The Controversy

Two genetic hypotheses were proposed: a volcanic, and a meteorite impact origin. The traveller-writer F Jeppe first described the Tswaing Crater as a unique feature of volcanic origin in 1868. Percy Wagner was the first geologist who studied the crater in detail and published a book about it in 1922. He concluded that the crater must be the result of a volcanic event of some sort, a finding that was based mainly on the presence of various volcanic rocks occurring along the crater rim. In contrast, the German geologist Rohleder, in 1933, was the first to suggest an impact origin for the crater, comparing it to the Steinheim Basin in southern Germany, which since then has also been confirmed as a meteorite impact crater. In 1946 the eminent meteorite researcher, F C Leonard, published the first-ever list of possible meteorite craters on Earth and included Tswaing. 

After that, individual researchers repeatedly discussed this possibility, but never produced unambiguous evidence in support of the impact hypothesis.