Famous Sterkfontein Caves deposit 1 million years older than previously thought
Four different Australopithecus crania that were found in the Sterkfontein caves, South Africa. The Sterkfontein cave fill containing this and other Australopithecus fossils was dated to 3.4 to 3.6 million years ago, far older than previously thought. The new date overturns the long-held concept that South African Australopithecus is a younger offshoot of East African Australopithecus afarensis. Credit: Jason Heaton and Ronald Clarke, in cooperation with the Ditsong Museum of Natural History.

There are a lot of fossils relating to human evolution found in South Africa, but the earth doesn't give them up easily.

Scientists have studied the fossils of early humans. The age of some of the fossils found at the site of Sterkfontein Caves has been pushed back by more than a million years. This would make them older than Lucy.

The "Cradle of Humankind" is a UNESCO World Heritage site in South Africa that contains a number of fossil-bearing caves. The discovery of the first adult hominin in 1936 made the town famous. The other great apes aren't included in hinnins. The well-known Mrs. Ples and the nearly complete skeleton of Little Foot have been found there. Over the past four million years, paleoanthropologists and other scientists have studied the cave sites in the Cradle of Humankind to learn more about the evolution of humans and the environment.

One of those scientists is a professor of earth, atmospheric, and planetary sciences in the college of science. There are deposits in caves. He was a PhD student when he came up with a method for dating buried cave artifacts. The Little Foot skeleton was dated to about 3.8 million years old by his previous work at the site.

In a study published in the Proceedings of the National Academy of Sciences, Granger and a team of scientists including researchers from the University of the Witwatersrand in Johannesburg, South Africa and the University Toulouse Jean Jaurs in France, have discovered that not only Little Foot, but all The fossils are closer to the beginning of the era than the end. Dinkinesh is from Ethiopia and her species is back to about 3.8 million years ago.

Fossils in the 'Cradle of Humankind' may be more than a million years older than previously thought
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. Credit: Purdue University photo/Lena Kovalenko

The area has a long history of hominin occupation. Understanding the dates of the fossils here can be difficult as rocks and bones fall to the bottom of a deep hole in the ground.

There are layers of ash that can be dated in East Africa, where there are hominin fossils. Those layers are used to estimate the age of a fossil. Scientists in South Africa do not have that luxury. The fossils around the bones are used to estimate the age of the cave. Young flowstone can be deposited in old sediment, which could make those methods potentially incorrect. The rocks in which the fossils were found can be dated more accurately. The matrix that embedded the fossil is called breccia.

There are more Australopithecus fossils in South Africa than in any other country. It's difficult to find a date for them. People look at fossils near them and compare the ages of cave features with different dates. Our data resolves these issues. The fossils are much older than we thought.

The team used mass spectrometry to measure radioactive nuclides in the rocks, as well as geologic mapping and an intimate understanding of how cave sediments accumulate.

The study of so-called cosmogenic nuclides and what they can reveal about the history of fossils, geological features and rock is carried out by the research group at thePRIME lab. The high-energy particles that bombard the earth are called genic nuclides. Cosmic rays have enough energy to cause nuclear reactions inside rocks at the ground surface and create new radioactive isotopes. An example of this is aluminum-26, which decays into magnesium over millions of years. Since aluminum-26 is formed when a rock is exposed at the surface, but not after it has been deeply buried in a cave, PRIME lab researchers can date cave sediments.

The research team made careful maps of the cave deposits and showed how animal fossils of different ages would have been mixed together during excavations in the 1930s and 1940s, which led to decades of confusion. The hope is that this will convince people that the dating method works. We can place ancient humans and their relatives in the correct time periods using this method.

Scientists' understanding of the living landscape of the time is influenced by the age of the fossils. How and where humans evolved, how they fit into the environment, and who their closest relatives were are some of the pressing questions. One way to solve the puzzle is to put the fossils in their correct context.

More information: Cosmogenic nuclide dating of at Sterkfontein, South Africa, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2123516119. Journal information: Proceedings of the National Academy of Sciences