ARI SHAPIRO, HOST:
In the late 1960s archaeologists discovered a set of familiar bones in Ethiopia - a skull bone, a lower jaw, parts of a torso. These were remains of Homo sapiens, early humans. That collection is known as Omo 1.
AILSA CHANG, HOST:
The contents of Omo 1 were initially thought to be around 200,000 years old, already some of the oldest human bones ever unearthed. But scientists have debated their precise age.
TIM WHITE: To understand how humans evolved in Africa, you need a time frame. And to construct that time frame, one needs to have accurate dating techniques. Unfortunately, we are just beyond the range of radiocarbon or C-14 dating. So you have to employ other techniques to determine the true age of these fossils.
CHANG: That's Tim White, professor of integrative biology at UC Berkeley. One of those techniques involves determining the age of the environment where the bones were found - in the case of Oma 1, a layer of volcanic ash.
CELINE VIDAL: There was a bit of controversy because the way Oma 1 was first dated was using an ash layer that was supposedly found just below. But it wasn't found where the fossils were actually found. It was found a bit further away.
SHAPIRO: Celine Vidal is a volcanologist at the University of Cambridge, and she says that the ash layer above Oma 1 was fine like flour. That's hard for scientists to date.
CHANG: But in a new analysis, Vidal and her colleagues found that the volcanic ash had the same chemical fingerprint as a massive volcanic eruption over 233,000 years ago.
VIDAL: That relies on the principle that every eruption has a unique chemical fingerprint, a unique chemical signature. So when it's possible to analyze a signature of an ash layer and if it correlates with the signature of an ash layer somewhere else and we know the age of one of the deposits, then we can guess indirectly the age of the deposits it's correlated with.
CHANG: Since Oma 1 was under that ash, Vidal thinks the bones are at least 33,000 years older than previously thought. The study was published in the journal Nature. Here's Tim White again.
WHITE: At what point did these people expand from Africa? What is their technology? What was the environment that they occupied? What was Africa like in those days? All of that depends on a strong geological framework but especially on a chronological framework. And that is what this new work has provided for one of the more complete skeletons from this time period.
SHAPIRO: In other words, if these human remains are much older than we thought, the story of humanity might be, too.
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