In the evolutionary tree, hominids are what connect modern humans to the great apes (from which they appear to have separated about 6 million years ago). This is why paleoanthropologists have been studying them for almost a century: they represent a crucial turning point in human evolution.
It all began in 1936. In the caves of Sterkfontein, South Africa, the doctor and paleontologist Robert Broom made an incredible discovery: the first adult specimen of the genus australopithecus, a species of primordial hominid from which our genus seems to have emerged, Homo.
Since then, these caves have become a hub for evolutionary research, and called “the cradle of humanity”. The complex network that composes them (over 60 meters deep) has already "given" us hundreds of Australopithecus fossils.
Dating is deceiving
The cave has six areas: those 1 to 3 are underground, while those 4 to 6 are exposed to the air due to erosion in the cave's roof. Most of the fossils of australopithecus It is located in area 4.
The "cradle of humanity" will still have many surprises in store for us, but the discoveries already made have their own load of mysteries. The first: How old are the area 4 fossils REALLY?
The researchers estimated that the fossils of Australopithecus in the lower section of area 2 they are between 2 and 3,7 million years old. And it's a big problem, because it contrasts with the estimated age of the fossils found further away, in area 4. The first estimates said that those were "old" between 2 and 2,4 million years, but the The accuracy of these estimates is totally in question.
Darryl Granger of Purdue University is among the researchers who have questioned the age of the Area 4 fossils. Recently, Granger and a team of French and South African scientists attempted to date the famous fossils using a new method. And they published their results in Proceedings of the National Academy of Sciences (I link them to you here).
The doubts were well founded
The team found that the fossils of australopithecus in the sediments of the caves of area 4 they are between 3,4 million and 3,7 million years old, which makes them of about a million years older than originally thought. With the famous fossils finally placed in the correct timeline, scientists can better imagine the life of these early hominids, including the environmental conditions in which they lived.
The findings also increase the geographic range and diversity of our early ancestors, reigniting debates about the history and timeline of human evolution.
Does evolution need to be rethought?
Dating the fossils in the caves is difficult. Cave sediments do not form in neat layers like surface rocks, due to the presence of large boulders, animal remains, and other factors. Paleontologists may be confused by the presence of huge boulders, animal fossils and debris from different eras that can fall into the cave. In other words, the fossils below are not necessarily more ancient.
For the original estimates, the experts dated the calcite deposits in the cave. Granger and his colleagues point out that several findings show that these deposits may be younger than other deposits within the cave. So the team carefully examined the geological features in Area 4, and concluded that the deposits are in fact much younger than the surrounding rock that contains the fossils. In other words, the dating was correct, but it referred to the calcite, and not to the fossils. Does evolution need to be rethought? Dating methods certainly do.
Help from heaven
To date the fossils, Granger took the finds to his laboratory, the Purdue Rare Isotope Measurement Laboratory, or PRIME Lab, where he and colleagues developed a new technique for determining the age of fossils: it is based on the so-called cosmogenic nuclides.
How does it work?
These nuclides are isotopes created by cosmic rays, energetic particles that can come from the sun, from outside the solar system, and even from other galaxies. Cosmic rays cause reactions within rocks that create specific types of radioactive atoms with a different number of neutrons than the element's stable form. However, underground rocks are safe from these intergalactic particles. Researchers can then use the decay ofaluminum-26 and beryllium-10, isotopes formed by exposure to cosmic rays, to understand when the rocks and the fossils they contain were buried in the cave.
Combining this measurement with an extensive geological survey of the area, the researchers concluded that the fossils are at least a million years older than the original estimate.
What do you do with evolution?
This estimate makes the Area 4 finds the oldest ever recorded. And they force researchers to fit the age of early hominids with our current understanding of human evolution. L'archeology has new blood to explore.
For example, since members of our genus, Homo , appeared between 2 million and 2,8 million years ago, it was thought that fossils of Australopithecus South African were too young to be their ancestors. And now?
As in the best films all we can add is: to be continued.
