Since several karst caves northwest of the South African metropolis of Johannesburg in 1999 were declared the "world heritage of humanity", this region has been happy to advertise with the term "Cradle of Humankind" - "cradle mankind". The reason: In the area of just 25,000 hectares, there were many fossils of pre- and early people in 15 caves. With Australopithecus, Paranthropus and Homo, three different hominean genera lived there practically simultaneously two million years ago. Almost a third of all known finds of pre -people come from this comparatively small region, which is about twelve times as large as the Frankfurt airport.
However, there is one problem. The bones and skulls of Australopithecus specimens do not quite fit into the classical picture of human history. According to this, the genus Homo and thus also anatomically modern humans have evolved from the australopithecines. So, in the cradle of mankind, Australopithecus should have lived significantly before his descendants. However, as a new dating revealed, this was apparently exactly the case, Darryl Granger from Purdue University in the US state of Indiana and his team explain in the journal "PNAS".
The working group examined the finds from the Sterkfontein cave that holds the volume record for Australopithecus fossils in one place. In detail, the five researchers and a researcher looked at the shift in which most of the pre -senses came to light. Traditionally, the dating of the found layer is 2.1 to 2.6 million years due to sinter deposits. The finds should therefore have the same age. In any case, this was the assumption so far. Darryl Granger and his team wanted to know more precisely and now analyzed the breccate rock in which the fossils were embedded.
Dating with the help of the radioactive decay
Particles with very high energy from the radiation, which is constantly raining down on the Earth's atmosphere from space, repeatedly hit boulders lying on the surface. Natural radioactive isotopes such as aluminum-26 and beryllium-10 are constantly being formed during this process. "If the rock is later in a cave underground, for example, much less cosmic radiation arrives there and fewer of these isotopes are formed," explains archaeologist and dating specialist Daniel Richter from the University of Mainz, who was not involved in the study in "PNAS". Then the radioactive clock starts ticking: beryllium-10 and aluminum-26 decay very evenly over the course of millions of years to boron-10 and magnesium–26. From the amount of isotopes, Granger and his team now calculated when the breccias around the fossils actually went underground: in their opinion, the rock had not been in the open air for 3.4 to 3.7 million years - and thus a good million years longer than previously assumed.
"Since the remains of dead organisms are quickly decomposed on the surface, the Australopithecus fossils in the Sterkfontein cave should have been deposited at around the same time as the dated components of the BRECZIE," explains Richter. The pre -people should have lived about 3.5 million years ago.
An age difference of a million years!
But where does the huge difference of around one million years between old and new dating? Why did the Sinter turn out to be so much younger compared to the Brekzie, in which the Australopithecus remains? A look into the history of the fossils in the Sterkfontein cave gives an important note: there, there fell millions of millions ago with the remains of the pre-people through a hole to deep down into the cave. Such karst caves often flows from water from which lime separates and forms sintering layers. Such deposits may have only formed long after the fossil falls. Darryl Granger and his team have now collected indications for a late formation of the sintering layers. "Unfortunately, some details in this chain of argument are not shown in detail in the study," criticizes Daniel Richter. "However, this does not change the basic statement that the fossils should be around 3.5 million years old there," the archaeologist continues.
Accordingly, the Australopithecines lived in this area about a million years before the first early people of Art Homo erectus. So you can certainly belong to the ancestors of the genus Homo. The term "cradle of mankind" for the small area near Johannesburg should nevertheless be misleading. Finally, there were around the same time in the same time as genre comrades that were located in the Afar triangle of today's Ethiopia. There excavated fossils, including the famous Lucy, are counted into a different line: Australopithecus afarensis, which could also have been ancestor of the genus Homo.
"Genetic analyses have recently shown that Neanderthals, Denisovans and early modern humans had common descendants whose traces are still detectable in the genetic material of people living today." Daniel Richter thus points to studies of recent years. "It is not far from the consideration that something similar has also happened with the Australopithecus lineages," says the archaeologist. But then the cradle of humanity would not have stood only in a small region in today's South Africa. Rather, large parts of the continent could claim this title for themselves.
