The Environmental Context of the Earliest Acheulean at Olduvai Gorge, Tanzania

Abstract

Water, vegetation, and human habitats are tightly coupled, and Olduvai Gorge, Tanzania is an exceptional locality for examining evolutionary events that associate with water availability and environmental stability or change. This project investigates interactions between and among paleo-hydrology, habitat type, and the human response to changing environmental settings. The objective is to interpret the climate and environmental context of the oldest Acheulean stone tool industry at Olduvai Gorge using plant leaf wax lipid marker molecules, or biomarkers, as a source for carbon and hydrogen isotopes. The emphasis is on a roughly 200,000-year period (1.83 to 1.66 Ma), a timeframe that includes a key transition in stone tool technology from the Oldowan to the Acheulean, and the widespread distribution of the genus Homo.To investigate the human-environment interactions for Olduvai’s earliest Acheulean, terrestrial sediments from Beds I and II were systematically sampled and processed for normal (n-) alkanes and n-alkanoic acids. The focus is on the Frida Leakey Korongo North (FLK-N) and West (FLK-W) archaeological sites, which contain Oldowan and Acheulean tools, respectively, the geologic feature known as the Castle, and multiple landscape geological samples. From a methodological perspective, the innovation lies in the detailed environmental analyses using leaf wax biomarkers as a proxy record for paleo- hydrology and vegetation, and for the assessment of changes in precipitation, temperature, atmospheric CO2, aridity/humidity and plant type.The results indicate that both Oldowan and Acheulean assemblages were predominantly used within woodland settings with abundant freshwater nearby. The archaeological sites were situated within a mosaic environment of open grassland, closed riparian and groundwater-fed woodlands, lacustrine habitats, and ecotones. Both technological types were most likely used to process plant material such as hard-shelled nuts and fruits, but the Acheulean was also utilized for exploiting underground tubers as well as meat obtained in open settings.

Leaf Wax Lipid Extraction for Archaeological Applications

“…Plant wax lipid extraction and analysis is now being applied in archaeology contexts to investigate human‐environment interactions (Brittingham et al., 2019; Colcord et al., 2018; Collins et al, 2017; Connolly et al., 2019; Lupien et al., 2018; Magill, Ashley, & Freeman, 2013a, 2013b; Magill, Ashley, Domínguez‐Rodrigo, & Freeman, 2015; Patalano, 2019; Uno et al., 2016). Because n ‐alkanes and n ‐alkanoic acids record ancient environmental conditions through δ 13 C and δD ratios, they can track variations in hydroclimate, vegetation community and structure, and habitat type and be used to investigate human biological and cultural adaptive responses to ecological changes.…”

“…Typically, microbial reworking of leaf waxes results in UCM distributions with chromatographic outputs between C 16 and C 22 (Grimalt et al., 1988). Fortunately, this does not overlap with the retention window for higher‐chain n ‐alkanes, and many samples will have slight evidence for microbial activity that does not interfere with GC‐MS/IRMS analyses; in fact, even relatively modern topsoils can exhibit UCMs (Patalano, 2019). In extensively reworked samples, on the other hand, the severity of the UCM may completely obscure the n ‐alkanes, making it impossible to obtain any reliable data.…”

Enacting Maasai and Palaeoanthropological Versions of Drought in Oldupai Gorge, Tanzania

“…Engaging in what palaeoanthropologists called a 'multi-proxy approach' , researchers examined an amalgamation of various traces of past environments that they had excavated -such as biomarkers and phytoliths -in order to clarify the environmental conditions that may have influenced hominins to change their patterns of behaviour and to develop the Acheulean stone tool industry roughly a million and a half years ago. Lipid 'biomarkers' , such as normal (n-) alkanes, are chemically inert organic compounds that resist biodegradation throughout extremely large stretches of time, and analysing the isotopic values of biomarkers that are found in the sediments that surround buried stone tools can reveal changes in past plant composition and availability of water (Eglinton and Eglinton, 2008;Patalano, 2019). Biomarker research that SDS scientists conducted confirmed a drying and warming trend at an Oldupai Gorge site in the deep past, and demonstrated that the site was likely a riverine forest surrounded by a mosaic-like landscape that featured both heavily treed areas and more open environments (Patalano et al, 2017).…”

“…Lipid 'biomarkers' , such as normal (n-) alkanes, are chemically inert organic compounds that resist biodegradation throughout extremely large stretches of time, and analysing the isotopic values of biomarkers that are found in the sediments that surround buried stone tools can reveal changes in past plant composition and availability of water (Eglinton and Eglinton, 2008;Patalano, 2019). Biomarker research that SDS scientists conducted confirmed a drying and warming trend at an Oldupai Gorge site in the deep past, and demonstrated that the site was likely a riverine forest surrounded by a mosaic-like landscape that featured both heavily treed areas and more open environments (Patalano et al, 2017). Another trace of the past are 'phytoliths' , which begin to form when live plants absorb silica and the silica subsequently fills cell spaces.…”

Plant wax biomarkers in human evolutionary studies

“…While climatic and environmental variability have been prominently discussed in influencing the broad patterns of human evolution, 1–5 linking ecosystem changes to technological and behavioral responses remains challenging. To address such research challenges, the analysis of plant wax lipids from ocean and lake cores, 6–8 paleo‐lake drilling projects, 9–13 archeological and geological outcrops, 14–18 cave deposits, 19–21 and hominin‐bearing sediments 22 have the potential to provide well‐integrated, high‐resolution data on past plant ecology and environmental stresses in regions where hominins evolved.…”