They are open to the public from February to December each year, six days a week. Tours are conducted every half-hour.
Next to the caves is the Robert Broom site museum, housing exhibits of immensely ancient animal and bird life.
Bones and breccia in cavesSolution and roof collapses create entrances to the caves in the form of vertical shafts. Soil, rocks, bones and vegetation fell in from the surface – the animals and plants from which fossils formed did not actually live in the cave.
The bones which found their way into these shafts were often just fragments left by the activities of predators and scavengers around the shaft entrances. But sometimes – far less often – a whole animal would fall down a cavity to be fossilized in the infill. The famous australopithecine skeleton “Little Foot”, which was found deep inside a Sterkfontein grotto, is an example of this.
Over time, the material that fell into the shafts built up to form talus cones, which look like giant inverted ice-cream cones, on the cave floor. These formations were cemented by lime-charged water to form concrete-like breccia a type of rock. Bones within these talus cones were mineralized by calcium carbonate and stained with manganese and iron from the dolomite soil.
Sometimes floor collapses into lower caves or erosion by surface water disrupted the stratified layers, mixing deposits. This means that even if some deposits are deeper than others, they are not necessarily older than those nearer the surface.
The bulk of the Sterkfontein cave deposits were not disrupted in this way. The University of the Witwatersrand geologist Professor Tim Partridge classified the deposits from oldest to youngest as geological Members 1-6 from the Sterkfontein formation. The infills span a period from 4.2 million years ago to less than 200,000 years ago. The different infills have characteristic fossil and/or artifact (stone tool) content. 