A South African cave central to our knowledge of ancient human ancestors is not as old as previous estimates suggest. Sterkfontein Cave, near Johannesburg, has been an important source of fossil ancestors from more than 2 million years ago. But its complex geology has thwarted efforts to accurately date the fossils and artefacts buried there.

Andy Herries at the University of New South Wales in Sydney, Australia, and John Shaw at the University of Liverpool, UK, recorded the geomagnetic orientation of different layers of calcite deposits. Knowing when during history Earth's magnetic field reversed provided a basic chronology. From this, the researchers established that many of the deposits, and hence the cave's human remains, are younger than previously thought.

For instance, an Australopithecus fossil known as Little Foot is less than 2.6 million years old — much younger than the well known 3.2-million-year-old Australopithecus afarensis fossil from Ethiopia named Lucy.

J. Hum. Evol. 60, 523–539 (2011)