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

Plastic response of circular footings on sand under general planar loading

Data from a set of tests of model circular footings on dense sand are presented. The footings were subjected to a variety of combinations of vertical, horizontal and moment loading. The tests were designed to provide the information necessary to construct a complete model of the footing behaviour, based on the concepts of plasticity theory. In particular, the tests provide detailed information about the shape of the yield surface, and so allow generalization of bearing capacity calculations to cases other than purely vertical loading. Information is also obtained about the hardening law and flow rule appropriate for a plasticity model, and the elastic response within the yield surface