The earth does not reveal its deeply buried secrets easily – not even in South Africa’s “Cradle of Humankind,” where many fossils of human ancestors have been found. These ancient fossilized remains of early humans and their extinct relatives have been researched by experts for many years. An innovative fossil dating technique created by Darryl Granger, a professor of earth, atmospheric, and planetary sciences in the College of Science at Purdue University, was used to examine bones in the Sterkfontein Caves, an important fossil site in northern South Africa known as the “Cradle of Humankind.” The results of the new study were released in the Proceedings of the National Academy of Sciences.
“The Cradle of Humankind”
A variety of fossil-bearing cave deposits can be found at the Cradle of Humankind. It is a UNESCO world heritage site in South Africa comprising a variety of fossil-bearing cave deposits. The Sterkfontein is a complex and deep network of cave systems that have been home to hominins for years. It gained popularity after the first adult Australopithecus, an ancient hominid found in 1936. “Hominins” is a term used to describe us and our ancestors; and not the other great apes. Since then, other Australopithecus fossils have been discovered there, including the famous Mrs. Ples and the almost complete skeleton referred to as “Little Foot.”
Cradle of civilization
Sterkfontein and other cave sites in the Cradle of Humanity have been the subject of decades-long research as paleoanthropologists, and other scientists wanted to throw light on human and environmental evolution over the last four million years. Professor Raymond Dart of the University of the Witwatersrand in Johannesburg received two boxes of fossils in 1924 from Professor Robert Burns Young of Buxton Limeworks in the Taung region of South Africa’s North West Province.
Dart understood the significance of a small fossil skull that belonged to a creature, which was neither a man nor an ape. “Australopithecus africanus, which translates to ‘southern ape of Africa,’ was one of our ancestors and was an extinct hominid closely linked to humans,” Dart explained.
The fossils of our ancestors are older than we first believed
The research showed that fossil remains of early human ancestors found at the Sterkfontein site were much older than previously believed. The new dates would make the Sterkfontein Cave fossils older than the well-known Australopithecus Lucy fossil, also known as Dinkinesh from Ethiopia. It’s a 3.2 million-year-old Ethiopian fossil found in I979, and her species, Australopithecus Africanus, dates back to roughly 3.9 million years. The recently discovered fossils are also from the genus Australopithecus, a hominid that was once believed to have lived between 2 million and 2.6 million years ago.
“Sterkfontein holds more Australopithecus fossils than anywhere else in the globe,” Granger said in a press release. “It is kind of challenging and difficult to get a reliable date. People have compared the ages of cave features like flowstones and the animal fossils found nearby to arrive at a variety of dates. These disagreements are settled by our data. It demonstrates that these fossils are far older than previously believed.”
A new look at the ancient ancestors
Granger and a team of scientists, including researchers from the University of the Witwatersrand in Johannesburg, South Africa, and the University Toulouse Jean Jaurès in France, have found that not only Little Foot but all of the Australopithecus-bearing cave sediments are 3.4 million to 3.7 million years old. This makes these fossils of human ancestors a million years older than earlier thought and changes how scientists think about human ancestors and evolution. Due to their age, the fossils are closer to the start of the Australopithecus epoch than the end.
A large portion of the Sterkfontein fossils was discovered in Member 4, the world’s richest Australopithecus fossil deposit. Previous studies had suggested the deposit could have been formed as recently as 2 million years ago – earlier than when the genus Homo, to which we (Homo sapiens) belong, initially appeared roughly 3 million years ago.
Those dates proposed that Australopithecines coexisted alongside Paranthropus, a large-toothed hominid, and members of the Homo genus. Based on the hypothesis, experts have previously acknowledged that East African species like Lucy and other Australopithecus afarensis members were possibly the ancestors of South African Australopiths.
Dating cave sediments
Cave sediments can be dated in different methods. The Great Rift Valley volcanoes in East Africa, where numerous fossils of hominid ancestors have been discovered, deposit layers of ash that can be used to date the ash. Since the South African caves lack this “luxury,” scientists utilize these strata to determine how ancient a fossil is. They typically use nearby animal fossils or cave-deposited calcite flowstone to determine the age of the bones.
The flaw in the procedure is that it could be inaccurate since young flowstone could be deposited in ancient silt, and bones could shift in the cave. Dating the actual rocks where the fossils were found would be a more precise procedure.
Granger and his team examined “Breccia,” the concrete-like matrix that embeds the fossil. Granger employed a technique he first created in the middle of the 1990s and is now widely used by many scientists in the field. To determine the age of the Australopithecus-bearing sediments at Sterkfontein, Granger and the team employed accelerator mass spectrometry to analyze radioactive nuclides in the rocks, perform geologic mapping, and gain a better understanding of how cave sediments build.
The dating technique produces ‘reliable’ results
The team also made comprehensive maps of the cave deposits and explained how animal fossils from different ages would have been mixed during the 1930s and 1940s excavations, which is likely what caused decades of misunderstanding about earlier periods.
Granger stated, “I’m hoping this will convince people that this dating method yields reliable findings. Using this strategy, we may more precisely place early humans and their ancestors in Africa and other parts of the world throughout the appropriate times.”
The age of the fossils is important because it affects how scientists interpret the prehistoric landscape. It might be able to shed light on many important and challenging issues, including how and where humans evolved, how they fit into the ecosystem, and who their closest ancestors are. One way to solve the puzzle is to put the Sterkfontein fossils in their proper perspective.
Feature image credit: australopithecus afarensis by Sailko under CC BY 3.0