April 14, 2023

Purdue research: Fossils in ‘Cradle of Humankind’ may be more than a million years older than previously thought

The earth doesn’t give up its secrets easily – not even in the “Cradle of Humankind” in South Africa, where a wealth of fossils relating to human evolution have been found. For decades, scientists have studied these fossils of early human ancestors and their long-lost relatives. A dating method developed by Purdue geologist Darryl Granger just pushed the age of some of these fossils found at the site of Sterkfontein Caves back more than a million years. 

Article Title

“What Do Cosmic Rays, Caves in South Africa, and Purdue’s PRIME Lab Tell Us About Our Ancestors?” 


Darryl Granger, professor, Department of Earth, Atmospheric, and Planetary Sciences 


Proceedings of the National Academy of Sciences

Full Article


Article Summary

It is well-known that early humans evolved in Africa, but debates around when and where this occurred are being reignited after recent work at Purdue showed that early human fossils in South Africa are a million years older than previously thought.

Since the discovery of Lucy’s species in East Africa in the 1960s and ’70s, it has been thought that early humans evolved in the East African Rift Valley, with younger species migrating to South Africa much later. This idea has been based on comparative ages of fossils in the two regions, but the South African sites, which are found in caves, have been very difficult to date. 

Professor Darryl Granger, a geologist in the Department of Earth, Atmospheric, and Planetary Sciences who specializes in dating sediment deposits, developed a method for determining the age of the fossils in the cave based on cosmogenic nuclides — extremely rare radioactive particles produced in rocks by cosmic rays. These rare particles can only be measured by extraordinarily sensitive accelerator mass spectrometers, such as Purdue’s PRIME Lab, located two stories beneath the Engineering Mall.  

Using Purdue’s PRIME Lab, Dr. Granger showed that early human fossils found at Sterkfontein Caves in South Africa, part of the Cradle of Humankind World Heritage Site, date to between 3.4 million and 3.7 million years ago, over a million years older than previously supposed. This discovery shows that the South African fossils are just as old as Lucy’s species in East Africa and cannot be a descendant. This shakes up the evolutionary family tree and points to an even older common ancestor.

This new, older age shows us that early humans rapidly diversified and spread across the African continent as they moved from trees to the ground, and it is reopening questions about which species might be the possible ancestor to our genus, Homo, as well as to other branches that eventually went extinct. 

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