Fossils of Earliest Ancestors a Million Years Older Than Previously Thought: Scientists

Fossils of our earliest ancestors in the "cradle of humankind" are a million years older than previously thought, according to new research.

The Sterkfontein Caves in Johannesburg, South Africa, reveal nearly 4 million years of evolution, say scientists, and contain more than a third of the world's early hominid bones - crucial links in the chain to modern humans.

Australopithecus crania from Sterkfontein cave in Africa
Fossils of our earliest ancestors in the "cradle of humankind" are a million years older than previously thought, according to new research. This image shows four different Australopithecus crania that were found in the Sterkfontein caves in South Africa. Jason Heaton, Ronald Clarke/Ditsong Museum of Natural History

The UNESCO World Heritage Site has now been identified as the "global center" of our ancient past.

It was home to "Little Foot," whose almost complete 3.67 million-year-old skeleton was dug up there.

A famous pre-human skull dating back 2.3 million years - affectionately known as "Mrs. Ples" - has also been unearthed.

They belonged to a primitive species known as Australopithecus. Hundreds more individuals have been found within the network of underground tunnels.

The dolomitic hills in which the caves are located are 2.6 billion years old - over half the age of the Earth itself.

Most Australopithecus fossils have been excavated from an ancient cave infill called "Member 4." Its age has been disputed for more than half a century with estimates ranging from 2 million years - younger than our genus Homo - back to about 3 million years.

The study overturns the long-held idea that South African Australopithecus is a younger offshoot of East African Australopithecus afarensis.

Co-author Professor Dominic Stratford, of Wits University, Johannesburg, said: "The new ages range from 3.4-3.6 million years for Member 4 - indicating the Sterkfontein hominins were contemporaries of other early Australopithecus species, like Australopithecus afarensis, in east Africa."

Darryl Granger of Purdue University
Darryl Granger of Purdue University developed the technology that updated the age of an Australopithecus found in Sterkfontein Cave. New data pushes its age back more than a million years, to 3.67 million years old. Purdue University photo/Lena Kovalenko

The study in the journal PNAS is based on the radioactive decay of the rare isotopes aluminum-26 and beryllium-10 in the mineral quartz.

Lead author Professor Darryl Granger, of Purdue University in Indiana, said: "These radioactive isotopes, known as cosmogenic nuclides, are produced by high-energy cosmic ray reactions near the ground surface, and their radioactive decay dates when the rocks were buried in the cave when they fell in the entrance together with the fossils."

Previous methods relied on analysis of calcite flowstone deposits, but observations showed these are younger than the cave fill, underestimating the age of the fossils.

Stratford said: "This reassessment of the age of Sterkfontein Member 4 Australopithecus fossils has important implications for the role of South Africa on the hominin evolution stage.

"Younger hominins, including Paranthropus and our genus Homo, appear between about 2.8 and 2 million years ago.

"Based on previously suggested dates, the South African Australopithecus species were too young to be their ancestors, so it has been considered more likely that Homo and Paranthropus evolved in East Africa."

But Australopithecus existed at Sterkfontein almost a million years prior to the appearance of Paranthropus and Homo, providing more time for them to evolve.

It places the hominins "front and center" in the history of early human evolution, explained the researchers.

Hominid Australopithecus afarensis
A sculptor's rendering of the hominid Australopithecus afarensis is displayed as part of an exhibition that includes the 3.2 million-year-old fossilized remains of "Lucy," the most complete example of the species, at the Houston Museum of Natural Science, August 28, 2007, in Houston, Texas. Dave Einsel/Getty Images

Stratford said: "This important new dating work pushes the age of some of the most interesting fossils in human evolution research, and one of South Africa's most iconic fossils, Mrs. Ples, back a million years to a time when, in east Africa, we find other iconic early hominins like Lucy."

Most species of Australopithecus were diminutive, usually standing 3 feet 11 inches to 4 feet 7 inches tall. Males were bigger than females - like its descendants today.

The most famous Australopithecus was smaller - the 3.5 foot tall "Lucy" discovered in 1974 in Ethiopia. She is an Australopithecus afarensis and lived between 3.85 and 2.95 million years ago.

Granger said: "The redating of the Australopithecus-bearing infills at the Sterkfontein Caves will undoubtedly reignite the debate over the diverse characteristics of Australopithecus at Sterkfontein - and whether there could have been South African ancestors to later hominins.

"Sterkfontein has more Australopithecus fossils than anywhere else in the world. 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."

The findings were published in Proceedings of the National Academy of Sciences.

This story was provided to Newsweek by Zenger News.