Researchers have discovered fossils of the first Homo sapiens from East Africa as recently as the 1960s. Initially dated to be 130,000 years old, the remains were at the time some of the oldest of our species. New studies indicate, however, that these fossils may actually be more than 230,000 years old.

It was in Ethiopia in the 1960s that paleoanthropologist Richard Leakey discovered fossils with anatomies very similar to those of modern humans. Undoubtedly, these fossils were some of the earliest Homo sapiens who had characteristics very similar to their descendants (us). The fossilized inhabitants of Ethiopia were then named Omo I, after the Omo River.

It turns out that a string of research has been increasingly stretching the age of the fossils of early Homo sapiens In the years following the first dating (which indicated 130,000 years old), analysis and radioactive dating of the surrounding soil showed that the fossilized remains could be up to 200,000 years old.

Researchers in the field in the Omo Kibish Formation. Image: Céline Vidal

Now, however, new research published in Nature has identified layers of volcanic ash among the fossils that may aid in dating. According to the article, the fossil record was between two layers of ash. The first layer, above the fossils, is at least 230,000 years old.

In other words, our earliest ancestors with more modern features must be even older than these ashes.

"The fossils were found in a sequence, below a thick layer of volcanic ash that no one had been able to date with radiometric techniques because the ash is so grainy and fine," says author Céline Vidal of Cambridge University.

Hunting eruptions and the first Homo sapiens

The area of Ethiopia in which these - and several other - fossils emerged is highly volcanically active. And it has been so for the last few thousand years, which must have left geological records that can assist in dating fossils.

"Each eruption has its own fingerprint - its own evolutionary history below the surface, which is determined by the path the magma followed," Vidal says. "Once you crumble the rock, you release minerals with it, and then you can date them and identify the chemical signature of the volcanic glass that holds the minerals together."

Using this geochemical 'fingerprint', the team was then able to link the ash from the Omo I excavation site to an eruption of the Shala volcano, 400km away. This eruption, therefore, occurred 230,000 years ago and covered the bones of the Omo I. From this comes the conclusion that the fossils were even older than the ash from the Shala volcano.

The research is available in the journal Nature.