Carbon isotope evidence for the stepwise oxidation of the Proterozoic environment

Article Abstract:

A new analysis of carbon isotope levels in sedimentary rocks from the Proterozoic eon show that the organic carbon reservoir increased in size relative to the carbonate reservoir. This increase and the associated oxidation of the global environment during Proterozoic times coincided with geological events such as rifting and orogeny rather than with the organic release of oxygen through photosynthesis. This finding controverts the generally accepted theory that biological rather than geological evolution was decisive in boosting the amount of oxygen in the atmosphere.

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A latitudinal gradient in carbon turnover times in forest soils

Article Abstract:

A latitudinal gradient in 13C and 14C activity exists in soils, and low-altitude soils are undergoing depletion in the 13C signature. The 13C and 14C activity of particulate organic carbon from soils of C3 biomes in a global distribution of low-altitude locations is measured. The soil organic carbon (SOC) value increases by nearly 1% on moving from low to high altitude. Low altitude soils respond rapidly to alterations in the carbon level. The long residence time of soils from high altitudes indicates that these soils act as a sink for anthropogenic CO2.

Soils, Forest ecology, Soil carbon

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Expansion of C4 ecosystems as an indicator of global ecological change in the late Miocene

Article Abstract:

Plants using the C4 photosynthetic pathway proliferated markedly during the Miocene between seven and five million years ago. C4, also called the Hatch-Slack cycle, differs from the C3 and CAM pathways by causing carbon dioxide (CO2) to produce four-carbon acids. Evidence from fossil soil and fossil tooth enamel suggests that C4 plants spread quickly during this period, probably because lower atmospheric CO2 concentrations fostered their growth.

Environmental aspects, Miocene Epoch, Photosynthesis, Paleobotany

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