A probabilistic assessment of the rapidity of PETM onset

Single-foraminifera measurements of the PETM carbon isotope excursion from Maud Rise have been interpreted as indicating geologically instantaneous carbon release. Here, the authors explain these records using an Earth system model and a sediment-mixing model and extract the likely PETM onset duration

Biogeochemical controls on photic-zone euxinia during the end-Permian mass extinction

Geochemical, biomarker, and isotopic evidence suggests that the end-Permian was characterized by extreme oceanic anoxia that may have led to hydrogen sulfide buildup and mass extinction. We use an earth system model to quantify the biogeochemical and physical conditions necessary for widespread oceanic euxinia and hydrogen sulfide release to the atmosphere. Greater than threefold increases in ocean nutrient content combined with nutrient-trapping ocean circulation cause surface-water H2S accumulation in the paleo–Tethys Ocean and in areas of strong upwelling. Accounting for the presence of sulfide-oxidizing phototrophs in the model suppresses but does not prevent widespread release of H2S to the atmosphere. Evidence from the geologic record is consistent with modeled geochemical distributions of widespread nutrient-induced euxinia during the end-Permian, suggesting H2S toxicity and hypercapnia may have provided the kill mechanism for extinction

FAR-DEEP core archive and database

The collection of FAR-DEEP (Fennoscandian Arctic Russia Drilling Early Earth Project) cores includes material from 15 drill holes through 2,500–2,000 Ma sedimentary and volcanic successions in Russian Fennoscandia. Amounting to a total core length of 3,650 m, the recovered material provides one of the best available rock records for studying the major environmental upheavals during the early Palaeoproterozoic, and for assessing timing, causes and effects of the rise of atmospheric oxygen (Melezhik et al. 2010). The great scientific promise that the FAR-DEEP material holds for current and future studies of the Palaeoproterozoic Earth calls for a dedicated cataloguing system that facilitates an easy capture of generated technical, geological and geochemical data on the cores, and provides means for effective sharing of information among researchers. In order to make the unique material available for future studies, all cores and related documentation have been thoroughly archived in the core repository and the database, respectively. This archive is linked tightly to the user-friendly and Web-accessible database system serving as an essential gateway for exploring the full potential of the material

Emergence of the aerobic biosphere during the Archean-Proterozoic transition: challenges of future research

The earth system experienced a series of fundamental upheavals throughout the Archean-Paleoproterozoic transition (ca. 2500–2000 Ma). Most important were the establishment of an oxygen-rich atmosphere and the emergence of an aerobic biosphere. Fennoscandia provides a fairly complete record of the hallmark events of that transition: widespread igneous activity, its association with a possible upper-mantle oxidizing event, the global Huronian glaciation, a rise in atmospheric oxygen, the protracted and large-magnitude Lomagundi-Jatuli carbon isotope excursion, a substantial increase in the seawater sulfate reservoir, changes in the sulfur and phosphorus cycles, a radical modification in recycling of organic matter, and the Shunga Event—the accumulation of unprecedented organic-matter–rich sediments and the oldest known inferred generation of significant petroleum. Current research efforts are focused on providing an accurate temporal framework for these events and linking them into a coherent story of earth system evolution

Isotopic evidence for massive oxidation of organic matter following the great oxidation event

The stable isotope record of marine carbon indicates that the Proterozoic Eon began and ended with extreme fluctuations in the carbon cycle. In both the Paleoproterozoic [2500 to 1600 million years ago (Ma)] and Neoproterozoic (1000 to 542 Ma), extended intervals of anomalously high carbon isotope ratios (δ<sup>13</sup>C) indicate high rates of organic matter burial and release of oxygen to the atmosphere; in the Neoproterozoic, the high δ<sup>13</sup>C interval was punctuated by abrupt swings to low δ<sup>13</sup>C, indicating massive oxidation of organic matter. We report a Paleoproterozoic negative δ<sup>13</sup>C excursion that is similar in magnitude and apparent duration to the Neoproterozoic anomaly. This Shunga-Francevillian anomaly may reflect intense oxidative weathering of rocks as the result of the initial establishment of an oxygen-rich atmosphere

Evolution of the global carbon cycle and climate regulation on Earth

The existence of stabilizing feedbacks within Earth's climate system is generally thought to be necessary for the persistence of liquid water and life. Over the course of Earth's history, Earth's atmospheric composition appears to have adjusted to the gradual increase in solar luminosity, resulting in persistently habitable surface temperatures. With limited exceptions, the Earth system has been observed to recover rapidly from pulsed climatic perturbations. Carbon dioxide (CO₂) regulation via negative feedbacks within the coupled global carbon‐silica cycles are classically viewed as the main processes giving rise to climate stability on Earth. Here we review the long‐term global carbon cycle budget, and how the processes modulating Earth's climate system have evolved over time. Specifically, we focus on the relative roles that shifts in carbon sources and sinks have played in driving long‐term changes in atmospheric pCO₂. We make the case that marine processes are an important component of the canonical silicate weathering feedback, and have played a much more important role in CO₂ regulation than traditionally imagined. Notably, geochemical evidence indicate that the weathering of marine sediments and off‐axis basalt alteration act as major carbon sinks. However, this sink was potentially dampened during Earth's early history when oceans had higher levels of dissolved silicon (Si), iron (Fe), and magnesium (Mg), and instead likely fostered more extensive carbon recycling within the ocean‐atmosphere system via reverse weathering—that in turn acted to elevate ocean‐atmosphere CO₂ levels