A skull of Australopithecus africanus specimen known as "Mrs. Ples" (via Wikimedia Commons)

The Maropeng and Sterkfontein Caves in South Africa are hailed as the “Cradle of Humankind,” yielding fossils that reveal evidence of our early ancestors who lived a geological age ago. While Homo sapiens — the contemporary evolution of humans who walk (and trample) the planet today — have only been around for about 200,000 years, famous examples of Australopithecus, including Lucy (also known as Dinkinesh in Ethiopia, where she was discovered in the Awash Valley in 1974) indicate a lineage of early human civilizations stretching back millions of years.

But our scientific understanding of just how many millions of years has undergone a recent revolution, as a new technique for analyzing and dating sediment and rock related to fossils in the Sterkfontein Caves site has pushed the age of those remains back a million years than previously thought. Purdue University professor and researcher Darryl Granger, whose doctoral thesis work included developing a method for dating cave sediments that is now used internationally, is part of a coalition of researchers who now believe that fossils in Sterkfontein Cave date from about 3.4 to 3.7 million years ago, rather than 2 to 2.5 million, as previously thought. This means that the South African trove of Australopithecus remains, including “Mrs. Ples” (who is apparently actually a Mr., but who’s counting?) and “Little Foot” contains the oldest known hominin remains — stealing the title away from Lucy, who is dated from about 3.2 million years ago.

Stratigraphic sections and associated photos showing previously dated flowstone (image courtesy PNAS)

“Sterkfontein has more Australopithecus fossils than anywhere else in the world,” Granger said, in a press release from Purdue. “But it’s hard to get a good date on them. People have looked at the animal fossils found near them and compared the ages of cave features like flowstones and gotten a range of different dates. What our data does is resolve these controversies. It shows that these fossils are old – much older than we originally thought.”

Granger and a team that includes scientists from the University of the Witwatersrand in Johannesburg, South Africa, and the University Toulouse Jean Jaurès in France have published a paper on their findings, which utilize “cosmogenic nuclides” — extremely rare isotopes produced when high-energy cosmic rays hit rocks — to date remains. It also challenged notions of evolutionary descent between proto-humans, finding evidence of coexistence between two types of hominins.

“Our dates demonstrate the limitations of the widely accepted concept that Australopithecus africanus, which is well represented at Sterkfontein, descended from A. afarensis,” the study asserts. “The contemporaneity of the two species now suggests that a more complex family tree prevailed early in the human evolutionary process.”

While the particulars and particulates might be best left to scientists, the takeaways are revolutionary to contemporary thinking about how humans evolved, and what life was like for our ancient ancestors.

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Sarah Rose Sharp

Sarah Rose Sharp is a Detroit-based writer, activist, and multimedia artist. She has shown work in New York, Seattle, Columbus and Toledo, OH, and Detroit —...