About the talk
Dr. Matthew S. Huber’s talk to the Overberg Geoscientists Group of the Geological Society of South Africa on 2 November 2023, followed by questions from the room and from online. It looks at how the Vredefort impact, about two billion years ago, still shapes South Africa’s economy and landscape.
What the talk covers
- Impacts, big and small. Rocks from space hit the Earth all the time. The talk climbs the scale: the Cape of Good Hope meteorite found in 1793, part of which was forged into a sword for Tsar Alexander I in 1814; the huge Hoba meteorite in Namibia; the 2013 Chelyabinsk airburst, whose shock wave damaged around 3,000 buildings; and the bowl-shaped Tswaing crater near Pretoria. Then comes an impactor on the scale of several Table Mountains.
- How a giant impact works. A computer simulation shows a crater opening about 40 km deep in under a minute, rebounding to some 30 km above the old surface, then collapsing into a crater with a central peak ring and a sheet of melt. The Moon’s Schrödinger crater and the dinosaur-killing Chicxulub impact are used as comparisons.
- The evidence at Vredefort. The original crater was about 300 km across, and around 10 km of rock has since eroded away, leaving a deep cross-section. Impact melt dikes, pseudotachylite, shatter cones and shocked zircon all show it was an impact, and tiny droplets of ejected molten rock have been found in Greenland and Russia.
- Why it matters today. The impact brought the Witwatersrand gold-bearing rocks up from deep underground, so they could be found; about a third of all the gold ever mined came from that basin. The fractured granite beneath the Karoo traps helium. The impact breccia in the Maremane Dome, 500 km away, hosts the iron deposits at places like Sishen. Vredefort’s granite is decorative stone, a training ground for geologists and a tourist destination, and the area is a UNESCO World Heritage Site with rock carvings up to 3,000 years old.
- Questions. The discussion covers geoheritage and education at Vredefort, the Bushveld Complex (which is about 40 million years older), where the helium comes from, a virtual museum of South African geology, and how material blasted off Earth could end up on the Moon or Mars.
Vredefort shows why planetary science belongs in South Africa. The largest impact structure on Earth is in learners’ own backyard, and the same processes that shaped it have shaped the Moon and Mars. That is the planetary-science half of SAPIENT’s story: help South Africans see how rocks from space made their landscape and its wealth, and give them the technology to go on exploring.