Sterkfontein
Located around thirty kilometres to the north-west of Johannesburg, in the Gauteng province, Sterkfontein is the most prolific paleontological site in the world. Thousands of animal and pre-human fossils have been found there, providing essential information on the first members of our lineage. This exceptional concentration of remains is partly due to the geomorphological evolution of the site.
Trees toupees
Landscape of the Bloubank Valley in the Gauteng province of South Africa© Laurent Bruxelles, Inrap
The 1,500-metre-high plateau on the north-west edge of Johannesburg is covered by an immense, sparsely vegetated savannah where gnus, baboons, antelopes, hyenas and ostriches evolve. Numerous small hills topped with toupees of trees are scattered across the landscape. These trees are most often located at the entrance to a cave or a natural sink-hole, reminding us that the other dimension of the Bloubank Valley landscape is found underground.
A karstic gruyère
Lapies of Bloubank Valley in the Gauteng province of South Africa
© Laurent Bruxelles, Inrap
The dolomite bedrock reacts to water in almost the same manner as limestone, and thus dissolves, resulting in the numerous caves have that have been carved out in this area. Sterkfontein is composed of an immense system of cave galleries extending along 10 km. It is complex, three-dimensional labyrinth that has been filled with sediments over time.
Dynamiting
The appearance of the Sterkfontein caves today is largely due to the mining activities.
© Laurent Bruxelles, Inrap
In the early 20th century, miners observed that Sterkfontein and other nearby caves contained calcite concretions (stalagmites, stalactites, flowstones) trapped within tightly cemented gravels, called breccia. They rapidly emptied the caves using dynamite in order to extract the calcite, which was used to lower the melting point of gold. In the leftover spoil, the miners often found fossils trapped in the breccia, which they showed to researchers at the University of Johannesburg, who immediately recognized their importance. In 1920, the gold mining industry invented a substitute for calcite, ending the need to extract it from caves. The miners then abandoned the caves and palaeontologists were free to pursue their research, and were rewarded with hundreds of discoveries !
A key period
The fossils found at Sterkfontein and other nearby sites provide clues on a key period in the history of humankind, between 4 and 1 million years ago. Over millions of years, the bones of the animals and hominids that lived in the valley were swept into caves by flowing water. They were gradually covered with gravels and dirt from the surface and were then fossilized under dozens of meters of sediments. Monkeys, carnivores, Australopithecines, Paranthropus, Homo habilis and Homo ergaster… the Sterkfontein caves contain precious remains of the early stages of the human genus.