Tool-Marked Bones Prior to the Oldowan Change the Paradigm

Domínguez-Rodrigo et al. (1) critiqued our paper (2), which provided the earliest evidence for stone tool use and animal tissue consumption as evidenced by bones bearing tool-induced marks found at DIK-55 (Dikika, Ethiopia) and dated to 3.39 Ma. Applying a configurational approach, they questioned the bones’ context and without examining or conducting new analysis on the original fossils, argued that all of the Dikika marks resulted from trampling, because a small subset of these marks superficially resembled a small subset of experimentally trampled specimens. Furthermore, they argued (1) that stone tool use and meat consumption before the current consensus dates requires finding manufactured stone tools in situ at the same or similarly dated localities as the tool-marked bones. Also, in their view, the modified bones should be found in situ and completely without additional marks that could fall within the variation of non-stone tool-inflicted marks. If these conditions are not met, they argued that marks that would otherwise be interpreted as stone tool-inflicted (e.g., DIK-55—two marks, A1 and A2) must also be rejected

Direct nanoscale observations of CO2 sequestration during brucite [Mg(OH)2] dissolution

The dissolution and carbonation of brucite on (001) cleavage surfaces was investigated in a series of in situ and ex situ atomic force microscopy (AFM) experiments at varying pH (2-12), temperature (23-40 °C), aqueous NaHCO 3 concentration (10-5-1 M), and PCO2 (0-1 atm). Dissolution rates increased with decreasing pH and increasing NaHCO3 concentration. Simultaneously with dissolution of brucite, the growth of a Mg-carbonate phase (probably dypingite) was directly observed. In NaHCO 3 solutions (pH 7.2-9.3,), precipitation of Mg-carbonates was limited. Enhanced precipitation was, however, observed in acidified NaHCO 3 solutions (pH 5, DIC ˜ 25.5 mM) and in solutions that were equilibrated under a CO2 atmosphere (pH 4, DIC ˜ 25.2 mM). Nucleation predominantly occurred in areas of high dissolution such as deep step edges suggesting that the carbonation reaction is locally diffusion-transport controlled. More extensive particle growth was also observed after ex situ experiments lasting for several hours. This AFM study contributes to an improved understanding of the mechanism of aqueous brucite carbonation at low temperature and pressure conditions and has implications for carbonation reactions in general. © 2012 American Chemical Society

Effect of secondary phase formation on the carbonation of olivine

Large-scale olivine carbonation has been proposed as a potential method for sequestering CO2 emissions. For in situ carbonation techniques, understanding the relationship between the formation of carbonate and other phases is important to predict the impact of possible passivating layers on the reaction. Therefore, we have conducted reactions of olivine with carbonated saline solutions in unstirred batch reactors. Altering the reaction conditions changed the Mg-carbonate morphology. We propose that this corresponded to changes in the ability of the system to precipitate hydromagnesite or magnesite. During high-temperature reactions (200 °C), an amorphous silicaenriched phase was precipitated that was transformed to lizardite as the reaction progressed. Hematite was also precipitated in the initial stages of these reactions but dissolved as the reaction proceeded. Comparison of the experimental observations with reaction models indicates that the reactions are governed by the interfacial fluid composition. The presence of a new Mgsilicate phase and the formation of secondary products at the olivine surface are likely to limit the extent of olivine to carbonate conversion. © 2010 American Chemical Society