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Deglaciation of the Laurentide Ice Sheet in North America was accompanied by sequestration of organic carbon in newly exposed soils. The greatest rate of land exposure occurred around 12,000 to 8,000 years ago, and the greatest increase in the rate of carbon sequestration by soils occurred from 8,000 to 4,000 years ago. Sequestration of carbon in deglaciated peat lands continues today, and a steady state has not been reached. The natural rate of carbon sequestration in soils, however, is small relative to the rate of anthropogenic carbon dioxide production.

Dolomitization of calcite at 218°C in hydrothermal bombs resulted in a series of unstable precursors to the final product, stoichiometric, ordered dolomite. The first phase formed was high-Mg calcite with approximately$35 mole \\% MgCO_{3}$. This was replaced by Ca-rich, poorly ordered dolomite that was, in turn, replaced by ordered, stoichiometric dolomite. The rate of dolomitization and the rate at which unstable phases transformed to stoichiometric dolomite was related to the$Mg^{2+}/Ca^{2+}$ratio of the solution. There was no simple relationship between the$Mg^{2+}/Ca^{2+}$ratio solution and that of the products. SEM analyses of the products are interpreted to indicate that the unstable to stable transformation occurs by three, possibly simultaneous, mechanisms: (1) The small rhombs in the final products indicate that new crystals continue to nucleate during the reaction. (2) The large rhombs indicate that overgrowths of the more stable phase grew on the less stable phase. (3) The very irregular interiors indicate that the initial unstable products underwent a intercrystalline-scale dissolution and reprecipitation replacement.

An equilibrium assemblage of olivine, Ca-free pyroxene, and PtFe alloy can be used to calculate oxygen fugacity at a known temperature and pressure. This oxygen geobarometer has been tested T = 1300-1450°C, P = 1 bar and 10 kbar. The calculated log$fO_{2}$may be compared with that determined by the$CO_{2}-H_{2}$mixture used to control the furnace atmosphere in the 1 bar experiments and, in the case of the 10 kbar experiments, the log$fO_{2}$determined from the graphite-fluid equilibrium. The average deviation of the calculated log$fO_{2}$and that determined by other means is 0.2; the maximum absolute difference is 0.4. The distribution coefficient ($K_{d}$) for Fe and Mg between coexisting olivine and pyroxene was found to range from 1.14 at$X_{Fe{2}SiO_{4}}^{ol} = 0.164$to$X_{Fe{2}SiO_{4}}^{ol} = 0.655$, and varies systematically with the Fe/(Fe + Mg) of the phases.