How did humans evolve? To answer that, we need to look at when and where our early ancestors lived. This journey through human evolution has always been complex, but recent volcanic activity in East Africa might hold crucial clues.
A new study published in the Proceedings of the National Academy of Sciences sheds light on volcanic ash layers in Kenya’s Turkana Basin. This area has been a rich source of early human fossils, helping us to piece together our distant past.
For years, pinpointing a timeline for early human evolution has been a challenge. The Great Rift Valley in East Africa, where Turkana is located, features many significant fossil sites. Here, volcanic eruptions over millions of years have left layers of ash that help us date fossils.
These volcanic events act like natural clocks. When magma erupts, it cools quickly, forming ash layers and pumice rocks. These rocks often contain minerals that can be dated using a technique called radiometric dating. This means we can determine the age of the fossils by dating the ash layers surrounding them.
Even when we can’t find datable crystals, we can match ash layers based on their unique chemical signatures. This allows researchers to trace ash from one site to another, even across large distances. For example, an ash layer in Ethiopia might match one in Kenya, confirming that they erupted around the same time. This approach has been invaluable for decades.
However, slight differences in age (just a few thousand years) among eruptions make it challenging to distinguish some ash layers. Many have similar chemical signatures, complicating the dating process.
In our recent study, we used modern dating tools that improve precision significantly. This allows us to differentiate ash layers that erupted only 1,000 to 2,000 years apart. Through this method, we identified three distinct volcanic events linked to the Nariokotome tuffs.
While age estimates help, they don’t tell the whole story. The layers have very similar chemical “fingerprints.” That’s where trace elements come into play. These elements, though found in tiny amounts, offer unique signatures that help us distinguish between the layers.
By employing laser-based mass spectrometry, we analyzed these trace elements, uncovering unique profiles for each layer.
Once we had precise ages and distinct chemical profiles, we could trace these ash layers to important archaeological sites. For example, the Nadung’a site in West Turkana, known for its ancient stone tools, now appears to be around 30,000 years older than previously thought.
This research is significant not only for Kenya but also for the wider region. We traced equivalent ash layers to Ethiopia, confirming that three separate eruptions spread material across vast distances. The methods we developed offer a new way to study human evolution.
As we apply our techniques to more ash layers, we aim to better understand key questions about early humans. Did tool technology develop gradually or suddenly? Were multiple hominin species living at the same time? How did volcanic activity and changing climates impact early human life?
This new approach brings us closer to answering these essential questions about our origins.
Special thanks to David Phillips and Janet Hergt for their contributions to this article.
