Fossils of early human ancestors found in a South African cave system may be 1 million years older than first thought, according to a study published Monday..
The findings published in the Proceedings of the National Academy of Sciences journal suggest that they are between 3.4 million to 3.6 million years old - older than Ethiopia's renowned Lucy or Dinkinesh fossil that was discovered in 1974 and dated back to 3.2 million years.
The ancient hominin fossils were discovered in the Sterkfontein Caves, 30 miles northwest of Johannesburg, that form part of a UNESCO World Heritage Site known as the Cradle of Humankind. Hominins include humans and our ancestral relatives, but not the other great apes.
"Because Sterkfontein has the largest concentration of Australopithecus fossils from an individual site in Africa, it has been a critical part of the research and debates on our ancestry," professor Kathleen Kuman, who was part of the research team led by Purdue University, told NBC News on Wednesday.
Kuman, a professor emeritus at the University of the Witwatersrand, added that the new dates "show that these South African hominid fossils were largely contemporary with species in East Africa such as Australopithecus afarensis and are unlikely to be their descendants, better revealing the more complex nature of how species evolved in the past."
Lucy or Dinkinesh and her species, Australopithecus africanus, hail back to about 3.9 million years old, according to a news release by Purdue University. It added that the research team used new technology developed at the university to date the South African fossils, which scientists had previously theorized were between 2 million and 2.5 million years old,
So the debate on the origins of modern humans has been reignited by this study.
"The new dates now help us to place such evolutionary developments more accurately in time," Kuman said.
Study lead Darryl Granger's team used accelerator mass spectrometry to measure radioactive nuclides in the rocks, as well as geologic mapping to help date the Australopithecus-bearing sediments at Sterkfontein, Purdue University said in the news release.
While the Sterkfontein cave system has preserved a long history of hominin occupation in the area, dating the fossils can be difficult as rocks and bones tumbled to the bottom of a deep hole in the ground, it said.
In East Africa, dating fossils is easier because researchers can use layers of ash from volcanoes to estimate how old they are, it added.
"What our data does is resolve these controversies. It shows that these fossils are old - much older than we originally thought," Granger said in a statement.