Melbourne, Sep 16 (The Conversation) The quest to unravel the mystery of human evolution has always circled around the questions of when, where, and under what conditions our early ancestors lived and evolved. The intricate timeline of this evolution has been notoriously difficult to establish, but recent research highlights a promising clue: ancient volcanic eruptions in East Africa.
Published in the Proceedings of the National Academy of Sciences, our recent study sheds new light on the volcanic ash layers found in Kenya's Turkana Basin—a site of great importance where numerous early human fossils have been discovered. We have achieved high-precision age estimates, marking a significant advancement towards constructing a more detailed timeline of human evolution.
The Great Rift Valley of East Africa, renowned for its fossil sites, is a region where the Turkana Basin stands out as crucial for research into early human origins. This area, positioned along an active tectonic boundary, has witnessed volcanic eruptions spanning millions of years. As early humans and their hominin relatives traversed these landscapes, volcanic eruptions regularly cloaked the terrain in ash, effectively entombing their remains. These ash and fossil layers, now invaluable time stamps for archaeologists, stretch across extensive regions.
Volcanic eruptions, due to their rapid occurrence, act as precise temporal markers. During eruptions, hot magma cools and forms volcanic ash and pumice rocks, which often contain minerals like feldspars—natural stopwatches that can be dated radiometrically. By analyzing ash layers directly surrounding fossil discoveries, scientists can reliably determine fossil ages.
Even in the absence of datable crystals, the unique chemical signatures of different volcanic eruptions provide a distinct geochemical fingerprint, allowing researchers to trace a specific eruption over considerable distances. This method has been employed in the region for decades, enabling the association of geographically disparate ash layers from Ethiopia, Kenya, and beyond, provided their chemical compositions match.
While previous studies have charted Turkana Basin's geology, the frequent eruptions, sometimes only thousands of years apart, pose challenges. Many ash layers have similar chemical signatures, making differentiation challenging. The Nariokotome tuffs, three such volcanic ash layers, illustrate this difficulty. Despite clear separation in the geological records, their chemical and age estimates are strikingly similar. Our study focused on refining these estimates.
Utilizing modern dating tools, which offer a tenfold increase in precision compared to older methods, we successfully distinguished the Nariokotome tuffs as separate volcanic events with precise eruption dates. However, determining ages alone wasn't enough; the tuffs' similar geochemical fingerprints due to their temporal proximity demanded further distinction through trace elements, which offer unique chemical signatures.
Using laser-based mass spectrometry to analyze trace element compositions, we obtained distinct geochemical profiles for each ash layer. These refined profiles allowed us to trace the ash layers to crucial archaeological sites. For example, the Nadung'a site in West Turkana, a significant prehistoric site known for its 7,000 stone tools, is now understood to be approximately 30,000 years older than initially believed, thanks to our updated analysis.
Crucially, our refined methods extend beyond Kenya, as demonstrated by tracing equivalent-aged ash layers to Ethiopia's Konso Formation, confirming their origins from distinct eruptions. The meticulous combination of high-precision dating and detailed geochemical profiling, exemplified by the Nariokotome tuffs, highlights a potent methodology poised to refine our understanding of human evolution.
As we apply these techniques more broadly, both within the Turkana Basin and potentially beyond Kenyan borders, we edge closer to resolving key evolutionary questions: Did technological innovations and new species emerge gradually or abruptly? Did various hominin species coexist? How did environmental shifts and frequent volcanic activity shape early human development? With precise geological timelines, we approach answers to these enduring questions surrounding the dawn of humankind. (The Conversation) GRS GRS
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