Evaluating the Potential of Cryptotephra in Refining the Chronology and Climatic Context of Human Evolution in the Levant

Introduction

The initial dispersal patterns of early modern humans (EMH) out of Africa, and the eventual replacement by EMH of other hominin species, is a fundamental area of research within evolutionary anthropology, archaeology and climate science. The Levant plays a key role within this process as it is thought to be the main corridor for the movement of hominins from Africa to Europe and the rest of the world, and it is also a region subject to periods of significant climatic fluctuation through time. Reconstructing accurate chronological models for interpreting and comparing archaeological records in this area, which represent more than one phase of hominin dispersal (Fig. 1a), and linking these with regional paleoclimate archives is critical to establishing the potential relationships between major biological and cultural changes and coeval environmental transitions, and thus our understanding of some of the principal driving forces behind key events in recent human evolution.

Fig. 1. a) Key palaeoclimatic and volcanic ash records and potential migration pathways during glacial and interglacial conditions signified by Marine Isotope Stages (MIS); b) Locations of the Levantine archaeological sequences to be studied in this project.

Set within this scientific context, the aim of this pilot project is to establish the methodological and logistical framework for a new interdisciplinary research programme which utilizes inherent properties of cryptotephra (distally transported microscopic volcanic ash) as a novel dating and synchronization technique to enhance our knowledge of the links between long-term climate change and human evolution in the Levant. The RESET Project (2008–2013; http://c14.arch.ox.ac.uk/reset/) was the first programme to establish the potential use of cryptotephra in constraining the chronology of hominin dispersal patterns, adaptation and climate change in Eastern Europe and North Africa over the last ∼130 000 years. Along with identifying cryptotephra layers preserved in key Palaeolithic cave sites, RESET also determined that eastern Mediterranean marine and lake sediment cores contain numerous discrete tephra deposits (Fig. 1a). These investigations offered an innovative perspective to Neanderthal and EMH research, both as a site dating tool and as a means to directly correlate archaeological and palaeoclimate records across widely-spaced areas through tephrostratigraphic marker horizons of precisely the same age and geochemical provenance. Based on this evidence, we inferred that cryptotephra techniques may also be successfully applied to the adjacent Levant region, which up to now had never been investigated utilizing this approach.

Thus, in 2013 we began to explore the potential of this area by collecting and working on samples from the key archaeological site of Kebara Cave (Israel), in collaboration with Ofer Bar-Yosef, to test for the presence of cryptotephra in the important time window from ∼40 to 75 000 years ago. Initial results from this preliminary study of Kebara demonstrate several cryptotephra layers present in the sequence sampled, which is an excellent success rate compared to many of the European sites studied within RESET. From these findings we are confident that our research in the Levant is at the beginning of a very important ‘proof of concept’ phase. Through seed-funding from the Council for British Research in the Levant (CBRL) we have been able to expand this work to include a new field survey of key Palaeolithic sites within Israel in advance preparation for a major grant application to the Leverhulme Trust.

Pilot Project

CBRL funding for this project enabled a 12-day reconnaissance trip to Israel from 25 April–6 May 2015 to meet collaborating project partners and discuss the proposed research in more detail (Table 1). In a series of small group meetings, we identified the potential of key Middle and early Upper Palaeolithic sequences available for cryptotephra study, as well as any logistical and administrativeissuesrelevanttotheproposedresearchand the expected scholarly outputs. I also had the opportunity to visit selected archaeological sites with respective project partners to assess sampling requirements specific to each of the localities to be investigated under the proposed study (Fig. 1b), including: (1) site access and relevant site preparation issues, (2) current condition of sampling profiles and sections, (3) depths of stratigraphic sequences and archaeological contexts, (4) approximate time needed and sample numbers per site to forecast budgetary requirements, and (5) estimated 2017–2019 fieldwork schedules. All collaborating research teams have formally confirmed both their participation in the proposed project and their ability to secure necessary permission to access and study the sites under their respective jurisdictions. The scholarly network building and first-hand site knowledge gained through the CBRL pilot project was thus critical for development of the research design and academic and logistical infrastructure needed to generate a highly innovative and competitive grant proposal for larger-scale project funding.

Table 1. Key international collaborators and archaeological sites to be investigated in the Levant (LP = Lower Palaeolithic, MP = Middle Palaeolithic, UP = Upper Palaeolithic).

Outcomes and Future Research

The proposed research project represents an important scientific collaboration between numerous international institutions and academic colleagues. Project meetings and on-site discussions in 2015 allowed our teams to formulate well-defined objectives and goals, as well as a comprehensive multi-year research plan, including a detailed estimate of costs and timelines for completion of fieldwork, laboratory analyses and collaborative outreach and publication of this interdisciplinary research programme. The key outcome derived from our CBRL funded pilot project was the submission in December 2016 of a major grant application to the Leverhulme Trust for the project ‘Unravelling the pattern, impacts and drivers of early modern human dispersals from Africa ‘(PI S. Blockley). Leverhulme project funding was successful (Grant Number RPG-2017-087) and this 3-year research programme commenced in July 2017.

Other important outcomes of this pilot project have been the development of new academic partnerships and the potential application of an important new scientific dating and correlation technique to several key archaeological sites of global significance. Tabun Cave, in particular, is virtually unique in that it has not only provided the reference archaeological sequences for the Levantine Lower and Middle Palaeolithic, including crucial human and faunal remains, but the site still contains significant in situ sediments ideal for the study proposed here. The rest of the localities which are being made available for sampling form a catalogue of nearly every key site in the Middle–Early Upper Palaeolithic record of Israel, providing what must be a unique opportunity to examine, compare and potentially correlate them, using this novel tephrostratigraphic approach. With larger-scale funding, this project should make a significant contribution towards refining the succession of hominin dispersals into and through the Levant, including any potential temporal overlap between Neanderthal and EMH populations in this region, and correlating these processes with local and regional palaeoclimatic and palaeoenvironmental records. With an improved and more robust chronological framework, achieved through the successful integration of cryptotephra data with other dating and archaeological methods, a clearer picture of Levantine prehistory is sure to emerge.