Title: The Volcanic Glass Menagerie: Obsidian, Tephra & Modern Human Evolution
Speaker: Nick Blegen, University of Cambridge
Venue and Time: Zoom(Link TBA), 19.05.2020, Tuesday, 16:00 s.t.
My research addresses the biological and behavioral evolution of modern humans (Homo sapiens), as well as the environmental circumstances of our species’ origins. This work uses chemical sourcing of natural glass (obsidian) artifacts to establish the changing scale of human ranging patterns over the last ~500,000 years. This work also employs chemical analysis of microscopic glass and minerals in volcanic ashes (tephras) to correlate and date sites relevant to modern human origins across East Africa.
Knowledge of ranging patterns is important for determining the scale of human interactions with one another as well as with their environments. Geochemical sourcing of obsidian artifacts documents past human ranging patterns and can elucidate mobility strategies, home range sizes and exchange networks. Recent studies of East African sites show that obsidians were transported long distances (>50–150 km), much earlier (300,000–200,000 years ago) than previously thought. My ongoing geochemical work is showing our human ancestors were transporting raw materials distances >50–100 km perhaps as early as ~400,000 years ago, over ~100,000 years older than the currently known age of our species. Additionally, new evidence of long-distance raw material transport poses the question: When in human history does the movement of high-quality raw materials like obsidian represent evidence of trade in addition to increased mobility? Whatever combination of exchange and mobility was employed, the fact that early modern humans were moving raw materials around significantly more than previously thought means their interactions with one another as well as with their past environments was more extensive than previously appreciated. This necessitates a more expansive chronological framework with which to test relevant hypotheses.
To establish a chronology of appropriately vast geographic scale my work employs tephrochronology, the chemical correlation and chronometric dating of tephras, to build a robust framework of dated ash layers which are then traced across ancient landscapes over areas >100,000 km2 preserved in East African Rift basins. This tephra-framework ranges from the slopes of the volcano-sources to distal ash layers encasing open-air archaeological sites preserving evidence of past human behaviors as well as rich fossil beds preserving paleoenvironmentally and biologically informative animal and human fossils. Volcanic ash correlation is sufficiently sensitive that we can accurately correlate and date ash particles found hundreds to thousands of kilometers from their volcanic sources, where only a few (~1-1000) microscopic grains of ash per gram3 are preserved as microscopic particles in sediment. The chronological resolution produced from this tephra-framework allows for geographically widespread and chronologically high-resolution comparisons of archaeological and paleontological sequences with paleoclimate reconstructions of East African lake-core sedimentary reservoirs preserving evidence of regional paleoclimate and its effects on early human behaviors and biology.
Combined with conventional archaeological and paleontological excavations, the combination of obsidian sourcing and tephrochronology provides a uniquely high degree of geographic and chronological resolution to East African sites relevant to modern human evolution and dispersals. As both past human ranging patterns and the dispersal of volcanic ashes did not conform to modern political borders, this research also provides the opportunity for large-scale international and interdisciplinary collaborations in the present-day.