Two special isotopes found in quartz, created by high-energy cosmic ray interactions near the Earth’s surface, have revealed the age of fossils that may be older than the famous Australopithecus afarensis Lucy.
A research team including geologist and geophysicist Darryl Granger from Purdue University in the United States and archaeologist Dominic Stratford from the University of Witwatersrand in South Africa analyzed the rare isotopes in quartz: aluminium-26 and beryllium-10.
“These radioactive isotopes, known as ‘cosmogenic nuclides’, are produced by high-energy cosmic ray interactions near the Earth’s surface, and their radioactive decay reveals their age,” Dr. Granger explained.
2 skulls found from Sterkfontein – (Photo: PNAS)
According to Science Alert, the rock layers containing quartz with these two rare isotopes also housed the remains of several Australopithecus, encapsulating events that occurred almost simultaneously: cosmic rays altering the rocks, human remains being buried, and large boulders falling into the cave entrance.
The mysterious rock belongs to the Sterkfontein limestone cave system in South Africa, dubbed the ‘cradle of humankind’ due to its wealth of ancient Australopithecus fossils.
Previously, the record for the oldest known human ancestor fossil was held by Lucy, a 3.2 million-year-old specimen consisting of 47 fragments that represent 40% of an Australopithecus skeleton excavated in Ethiopia.
The new analysis of aluminium-26 and beryllium-10 has revealed startling findings, indicating that the fossils in Member 4 of the Sterkfontein cave system date back to between 3.4 and 3.7 million years, including the famous Mrs. Ples skull. In Member 2, there are also 3.67 million-year-old remains known as Little Foot.
Thus, the Sterkfontein fossils are older than Lucy, further confirming its status as a ‘cradle of humankind’ that warrants further study. Additionally, this area contains numerous fossils that may reflect the diversity of Australopithecus lineages as well as later species.
The research was recently published in PNAS.
