Fossils discovered in ‘cradle of mankind’ may be a million years older than previously thought

(ORDO NEWS) — Numerous ancient hominin remains from the caves of South Africa may be much, much older than previously thought.

The Sterkfontein limestone cave system near Johannesburg has yielded so many ancient Australopithecus hominin bones over the past century that its location has been dubbed the “Cradle of Humankind,” which is very important for the study of human evolution.

Now, new dating methods suggest the remains date back nearly 4 million years – making them even older than Dinkinesh’s famous Australopithecus afarensis, nicknamed Lucy.

“There are more Australopithecus fossils in Sterkfontein than anywhere else in the world,” said geologist and geophysicist Darryl Granger of Purdue University.

“But it’s difficult to date them. People have looked at animal fossils found near them, compared the ages of cave objects such as rocks, and come up with a whole range of different dates. Our data resolves these contradictions. They show that these fossils are ancient – much older, than we originally thought.

Dating ancient remains is not easy, especially in caves. Dinkinesh has been dated to 3.2 million years ago based on radiometric dating of volcanic ash in the deposits where it was found, but caves are more pristine environments where volcanic ash does not fall.

Previous estimates for the complex Sterkfontein system were based on the age of the calcite stone found in the cave infill. It was formed approximately 2-2.5 million years ago.

However, colored stone can form over older deposits, and this appears to have been the case at Sterkfontein.

Most of the Sterkfontein australopithecine was recovered from a cave infill called Member 4. That’s exactly what it looks like: a material that filled what used to be a cavity, resulting in a sedimentary layer that, in this case, hid but preserved the remains of ancient hominins.

The famous skull of Mrs. Ples was previously found in Member 4, the most complete specimen of its kind ever discovered.

Previous work examining another famous Australopithecus skeleton from Sterkfontein, a human skeleton called Little Foot excavated from Aggregate 2, has shown an age of 3.67 million years.

Granger’s methods played an important role in this dating. Since the age of the other deposits is still the subject of heated debate, he and his colleagues turned to methods for determining the age of the 4th deposit.

Instead of examining a stone or other bones found nearby (which may not be contemporary with the remains in question), the team examined the rock in which the Australopithecus remains were embedded. In particular, they investigated the radioactive decay of two rare isotopes in quartz: aluminum-26 and beryllium-10.

“These radioactive isotopes, known as cosmogenic nuclides, are produced by reactions of high-energy cosmic rays near the earth’s surface, and their radioactive decay dates back to the time the rocks were buried in the cave when they fell into the entrance along with the fossils,” Granger explained.

From these isotopes, the team determined that all deposits containing Australopithecus date back to between 3.4 and 3.7 million years ago. This means that all the remains found at the deposit belong to the beginning of the Australopithecus era, and not to its end, as previously thought.

This has important implications for our understanding of human evolution and Sterkfontein’s place in it, the researchers say.

“Younger hominins, including Paranthropus and our genus Homo, appeared between about 2.8 and 2 million years ago,” says archaeologist Dominic Stratford of the University of the Witwatersrand in South Africa, coordinator of the Sterkfontein study.

“Based on previously proposed dates, the South African Australopithecus was too young to be their ancestor, so it was considered more likely that Homo and Paranthropus evolved in East Africa.”

The new result, consistent with the Little Foot dating, suggests that Homo and Paranthropus – also found in the Cradle of Humankind – appeared nearly a million years after Member 4 lived, meaning the order of events and where they occurred could be reconsidered.

“The re-dating of the Australopithecus infills in the Sterkfontein caves will no doubt re-ignite debate about the diverse characteristics of the Australopithecus from Sterkfontein and whether there could have been South African ancestors of later hominins,” Grainger said.

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