The fossils found in Sterkfontein cavesin South Africa, could be up to a million years older than previously thought and reveal nearly four million years of hominin evolution.
The place, which since the discovery of the first adult hominid of the genus Australopithecus in 1936 is known as the “Cradle of Humankind”, is a UNESCO World Heritage Site in South Africa and is considered the richest deposit of fossils of Australopithecus in the world. Hominid remains found there – some as famous as the «Mrs Ples” Y “Small foot» – include humans and our ancient relatives and offer unique insights into human evolution.
During the last 56 years of research the dating of the site has remained in dispute, particularly that of an area of the cave known as “Member 4” (Member 4) with age estimates ranging from about 2 million years ago, younger than the appearance of our genus Homo up to about 3 million years.
Now, new research presented in an article published this Monday in PNAS magazine reassess the age of Australopithecus from Member 4 at Sterkfontein along with Jacovec Cavern, which contains some additional hominin fossils in a deeper cave chamber and places them at the same age as the oldest remains of this specieslike those of the well-known Lucy.
“The new ages range between 3.4 and 3.6 million years for Member 4, indicating that hominin Sterkfontein were contemporaries of other species of primitive Australopithecus, such as Australopithecus afarensis, in East Africa»ensures Dominic Stratford, director of research on the caves, and one of the authors of the article.
Fossils and cosmic rays
For work, the team Darryl E Granger calculated the ages of the Sterkfontein rocks in which the fossils are found by measuring the amounts of aluminum-26 and beryllium-10 isotopes in quartz-bearing rocks. The rare isotopes were formed by high-energy cosmic rays while the rocks were on the surface and were broken down after they were buried in the cave with the fossils. Cosmogenic isotopes gave an age of about 3.4-3.7 million years, older than the previously determined age of 2.1-2.6 million years.
“These radioactive isotopes, known as cosmogenic nuclides, are produced by high-energy cosmic ray reactions near the Earth’s surface, and their radioactive decay dates back to when the rocks were buried in the cave when they fell into the entrance along with the fossils.”Granger explains.
age of fossils
Previous dating of Member 4 has been based on dating calcite lava deposits found within the cave fill, but careful observations show that the lava flow is actually younger than the cave fill, and therefore Therefore, it underestimates the age of the fossils.
In addition to the new dates at Sterkfontein based on cosmogenic nuclides, the research team carefully mapped the cave deposits and showed how animal fossils of different ages would have mixed together during excavations in the 1930s and 1940s, which led to decades of confusion with previous ages. “What I hope is that this will convince people that this dating method gives reliable results”says Granger. “Using this method, we can more accurately place ancient humans and their relatives in the correct time periods, in Africa and in other parts of the world.”.
Reconsidering the evolution of Homo
“This Reassessment”adds Stratford, “It has important implications for the role of South Africa in the evolutionary stage of hominins. The youngest hominids, including Paranthropus and our genus Homo, appear between 2.8 and 2 million years ago. Based on the dates suggested above, 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.”he points out.
The new dates show that Australopithecus existed in Sterkfontein almost a million years before the appearance of Paranthropus Y Homogiving them more time to evolve here, in the “Cradle of Humankind,” and putting hominins from this site front and center in the story of early human evolution.
Mrs. Ples equals Lucy
“This important new dating work pushes back a million years the age of some of the most exciting fossils in human evolution research, and one of the most iconic fossils from South Africa, Mrs. Ples, to a time when that, in East Africa, we find other iconic fossils of early hominids like Lucy”Stratford points out.
“The dating of the Australopithecus-containing fills in the Sterkfontein caves will undoubtedly revive the debate about the various characteristics of Australopithecus at Sterkfontein, and whether there might be South African ancestors of later hominids.”Granger adds.
The age of the fossils is important because it influences scientists’ understanding of the living landscape of the time. How and where humans evolved, how they fit into the ecosystem, and who their closest relatives are and were are pressing and complex questions. Putting the Sterkfontein fossils in their proper context is one step in solving the whole puzzle.
Font: Vozpopuli
Reference article: https://www.vozpopuli.com/next/fosiles-australopithecos-sudafrica-ancients.html
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