December GEOLOGY and GSA TODAY media ...( Boulder CO USA - Topics include: onse...)

Boulder, CO, USA - Topics include: onset of plate tectonics on Earth; Arctic Ocean's role in the global climate system; cause of the end-Permian mass extinction; Olduvai Basin lake cycles and survival of early hominins; an ancient mantle plume and the break-up of Rodinia; relationship between earthquakes and melting glaciers; monitoring Mt. Etna gas composition and eruption forecasting; and cause of the end of the PETM. The GSA TODAY science article examines Colorado citizen involvement in geoscience research.

Subduction origin on early Earth: A hypothesis
Vicki L. Hansen, University of Minnesota, Duluth, Department of Geological Sciences, Duluth, Minnesota 55812-3036, USA. Pages 1059-1062.

How and when plate tectonics began has been enthusiastically debated for decades; since the advent of the plate tectonics theory in the early 1960s. Hansens paper presents a hypothesis for how plate tectonics might have begun on early Earth. According to this hypothesis, spatial and temporal overlap of internal mantle flow (endogenic, or internal process) and a large bolide impact (exogenic, or external) triggered two signature processes of plate tectonics: spreading, which leads to the formation of new crust, and Subduction, which leads to the recycling of crust. The spatial and temporal intersection of the triggering endogenic and exogenic processes could have occurred variably across early Earth; thus, plate tectonic mechanisms could have begun at different places and different times. Hansens hypothesis postulates that the ability of a terrestrial planet to develop plate tectonics results from a balance between the strength of its surface layer and the size of bolide impact it can surviveboth of these factors can be related to planet size. Hansens hypothesis may allow us to predict if other planets could have evolved plate tectonics, and as such, might be Earth-like in character. The tectonic evolution of early Earth likely played key
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