220,000 years ago, the plains of what would become South Africa's Gauteng Province looked very similar to today's African woody grasslands. Herbivores like the Sable or Roan antelope (Hippotragus sp.)   and Equus capensis(a large zebra - now extinct), could have been found chewing the leaves of small Acacia trees or grazing in the tall grasses. Lions, leopards, and hyena waited for their next meal. African elephants, giraffes and the now extinct giant Wildebeest, Megalotragus priscus, rounded out the grassland megafauna.
Anatomically modern humans, or their hominid relatives may have also lived in the region.  These humans might have even witnessed (or been victim to) the tremendous energy released when a large asteroid, traveling many times the speed of sound, crashed into the grasslands outside an area now covered by the modern city of Pretoria.
(Right) The hypersaline lake on the floor of the Tswaing Impact Crater. The hills in the background delineate the crater rim. (Photo by David Kring)
The asteroid would have passed through the atmosphere in a matter of seconds, causing an explosion nearly a hundred times more powerful than the Hiroshima atomic bomb blast as it smashed into the Earth. The stony projectile, 30-50 meters in diameter, was vaporized by the blast which excavated a crater more than 100 meters deep and over a kilometer in diameter. Bedrock from near the impact would have been ejected and overturned out to a distance of several hundred meters (Click here to learn about Tswaing's geology).

The damage inflicted by the impact was similar to a nuclear bomb blast, but without
ionizing radiation damage. The asteroid, bedrock, and any fauna or flora at ground
zero would have been vaporized.   Based of comparisons to the calculated effects of the Barringer Meteorite Crater impact (a crater of nearly equal size), the explosive shockwave would have produced winds in excess of 1000 km/hr within 3 to 5 km of the impact (see effects map). These winds would have stripped away grass near the crater and flattened acacia and bush willow trees out to a radial distance of ~14 to 19 km.

    The impact shock wave would also have had severe effects on animals in the region. Dramatic differences in the internal vs. external pressure exerted on animal bodies within the shock wave would have caused hemorrhaging (internal bleeding) and edema. Animals would also have been injured by displacement, their bodies propelled a short distance by the high velocity winds.

      Branches, rocks, and other debris were also accelerated by the blast, causing shrapnel-type wounds out to a distance of 10 to 13 km.  Vegetation and animals may also have been subject to the thermal emission from the blast, causing burn damage out to a maximum range of ~10km. This intense heat may have started range fires, although no evidence of fire has been reported.

    The probable sum of these effects is the destruction of vegetation over an area 800 to 1500 km2. Damage to vegetation would have extended over an additional 200 to 600km2. Animals within 3 to 4 km of the impact site would probably been killed, with maiming injuries extending out to distances of ~16 to 24 km. While these effects are severe, they were confined to the immediate region and did not cause extinctions.

The newly formed bowl-shaped depression soon filled with water. However, the lake's hypersaline characteristics made it undesirable for acquatic plants and animals.Today, only algae and one species of salt-tolerant sedge live in the lake. Plants and animals likely recolonized the surrounding area within a few to ~100 years.

While these effects are severe on a regional scale, the Tswaing impact event had none of the global environmental consequences that a very large mass-extinction-causing impact like Chicxulub would have had. Nevertheless, an impact of this magnitude would have devastating consequences if it occurred in a populated area such as modern day Pretoria, only forty kilometers south of the Tswaing Crater.

Note: The Tswaing Crater was previously known as the Pretoria Saltpan or Zoutpan crater.