Percorrer por autor "Mackay, Alex"
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- Early human impacts and ecosystem reorganization in southern-central AfricaPublication . Thompson, Jessica C.; Wright, David K.; Ivory, Sarah J.; Choi, Jeong-Heon; Nightingale, Sheila; Mackay, Alex; Schilt, Flora; Otárola-Castillo, Erik; Mercader, Julio; Forman, Steven L.; Pietsch, Timothy; Cohen, Andrew S.; Arrowsmith, J. Ramón; Welling, Menno; Davis, Jacob; Schiery, Benjamin; Kaliba, Potiphar; Malijani, Oris; Blome, Margaret W.; O’Driscoll, Corey A.; Mentzer, Susan M.; Miller, Christopher; Heo, Seoyoung; Choi, Jungyu; Tembo, Joseph; Mapemba, Fredrick; Simengwa, Davie; Gomani-Chindebvu, ElizabethModern Homo sapiens engage in substantial ecosystem modification, but it is difficult to detect the origins or early consequences of these behaviors. Archaeological, geochronological, geomorphological, and paleoenvironmental data from northern Malawi document a changing relationship between forager presence, ecosystem organization, and alluvial fan formation in the Late Pleistocene. Dense concentrations of Middle Stone Age artifacts and alluvial fan systems formed after ca. 92 thousand years ago, within a paleoecological context with no analog in the preceding half-million-year record. Archaeological data and principal coordinates analysis indicate that early anthropogenic fire relaxed seasonal constraints on ignitions, influencing vegetation composition and erosion. This operated in tandem with climate-driven changes in precipitation to culminate in an ecological transition to an early, pre-agricultural anthropogenic landscape.
- Quantifying the effect of heating temperature on silcrete blank productionPublication . Watson, Sara; Li, Li; Mackay, AlexIn southern Africa, heat treatment of silcrete is documented by ~164 ka and is considered an important technological innovation, allowing knappers to improve the flaking properties of rocks for lithic blank production. Previous research has explored structural, mechanical, and geochemical changes in silcrete during heat treatment, but most studies have not explored the implications of those transformations for the blanks produced. Experiments that have examined the effects of heat treatment on blank production tend to rely on replicative flintknapping, where small changes in the way a blank is removed can create “noise.” In this study, we provide quantitative data to understand the effects of silcrete source and heating temperature on blank production using a flaking machine to isolate the effects of heat treatment on blank morphol ogy. Our results show changes in absolute blank dimensions, and in the frequency of abrupt terminations as a result of heat treatment. However, the benefits of heat treatment may only occur within a limited temperature range and are heavily source dependent. This suggests that we should reconsider broad generalizations about the role of heat treatment in lithic technology and its supposed benefits and focus more on silcrete source and source-based effects on blank production.