Collaborative Research: Development and Application of Cryptotephra Studies to Resolve Debates over Chronology in Modern Human Origins Research in South Africa

Arizona State University, Scottsdale AZ

Investigators

Abstract

Dr. Eugene Smith of the University of Nevada Las Vegas and Dr. Curtis Marean of Arizona State University along with an international team of scientists will apply a new dating method to determine when a suite of uniquely human features first appeared in evolutionary history and thus help to understand when, where and why the human lineage evolved. South African Middle Stone Age (MSA) sites have figured prominently in this work, revolutionizing knowledge of modern human origins by pushing back and enriching knowledge of the timing of key features science considers definitive of humans. Modern dating techniques and their application to archaeological sites provide the basis for determining when key events in early human history occurred. These techniques use complex models that produce age estimates and not absolute dates. In the past, different laboratories have used different models that may result in different ages for the same geologic unit. This has created a dating controversy that reduces confidence in the timing of key events in early human prehistory. There is general agreement that the best way of producing robust age estimates is to use several independent dating techniques. Recently, the research team identified volcanic ash in a rock shelter occupied by early humans at Pinnacle Point, South Africa, and the best fit of the chemistry of this ash is to the 75,000 year old eruption of the Toba volcano in Indonesia. This discovery provides an independent dating tool that can be used along with traditional dating methods to resolve the dating controversy and tie the record of human origins preserved at Pinnacle Point and other areas of southern Africa to the global record of modern human origins. Drs. Smith and Marean and their research team will collect and process samples from four archaeological sites in southern Africa to identify and determine the distribution of ash from the Toba eruption. This work will, for the first time, tie early human history recorded at each of these sites to a single dating model and remove any debate about the timing of key events in early human development. Correlation of volcanic ash to source volcanoes will be done using the chemistry of the ash. The ash is in the form of very small (micron sized) glass grains known as shards. These grains are analyzed by instruments that focus a small-diameter electron or laser beam on the shard to determine their chemical makeup. The chemistry is then compared to a database of known chemistry to identify the source and age of the ash. This project will not only provide a new independent dating tool for archaeological sites, but also help train students and early career scientists in the techniques of archaeology and geology.