EARTH
Acid mine drainage coats the hippos at Hippo Dam at the Krugersdorp Game Reserve. PHOTO/©Stephan du Toit, 2011
In 1947, in a dolomite cave 50 kilometers northwest of Johannesburg, South Africa, anthropologist Robert Broom discovered a 2.05-million-year-old adult australopithecine skull, one of the oldest and most important hominid fossils ever found. The caves of the Sterkfontein Valley have since produced a treasure trove of australopithecine fossils along with evidence of the early use of stone tools and fire, prompting UNESCO in 1999 to name it the Cradle of Humankind World Heritage Site. For 2 million years, the site has preserved evidence of human origins and evolution — but the activities of modern humans are now threatening its existence.
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