On the possibility of plate tectonics on Venus

Several arguments have been put forward suggesting that Venus has no place tectonics. We examine some of these arguments and suggest that because conditions on the surface of Venus are very different from those on Earth, the arguments should be reconsidered. We show that in the absence of an ocean, the differential hypsographic curve of Earth would probably have only one mode, like that for Venus. We show that the atmosphere of Venus is quite capable of erosion, provided that near-surface velocities are about 1 m · sec −1 or more, and that therefore the “oceanic” areas on Venus, should they exist, are probably covered with some thickness of sediment. If sedimentation on Venus is at all rapid, it is likely that subduction zones could be filled up and made unrecognizable topographically. Because Venus does not have an ocean, and because its surface temperature is much greater than that on Earth, ridge crests on Venus have a much smaller topographic expression than those on Earth. If significant sedimentation occurs they would be completely unrecognizable topographically

A model of global and basin-scale anoxia

AbstractA simple steady-state 1-D model of the oceanic particulate organic carbon, dissolved oxygen and dissolved phosphate system has been developed to study global and basin-scale anoxia. The model has been calibrated with present-day data and yields estimates of the present-day new-carbon flux (0.65 mol C/yr m2) and riverine phosphate flux (0.43 × 10-4 mol P/yr m2). The model requires substantial departures from present-day conditions for the existence of global steady-state anoxia. Fertility well above present-day values is required (for present-day continental configurations) even with a substantial reduction in thermohaline circulation rates or ventilation. It is shown that small basins, such as the mid-Cretaceous North and South Atlantic, may attain steady-state anoxia with global fertility no greater than present-day values. Finally, it is suggested that large-scale anoxic events may be instrinsically transient phenomena and that modeling of the anoxic events recorded in the geologic record requires a 2-D time-dependent model