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Stratigraphic sequences of sedimentary rocks reflect cyclical changes in deposition rate and environment due to relative sea-level variations -- which, in turn, are commonly assumed to reflect global (eustatic) sea-level changes. However, in a computer simulation, Petersen et al. show that small-scale mantle convection can also cause development of stratigraphic sequences, which suggests that previous sequence-based analyses may draw the wrong conclusions regarding global sea-level changes in the geologic past. In the simulation, the lower panel depicts a cross section of the lithosphere (crust in dark blue, mantle in light blue) and the underlying mantle convection (yellow). Lead author Kenni Petersen explains how this mantle convection creates repeated patterns of deposition and erosion and shapes the evolution of the (vertically exaggerated) sedimentary basin (upper panel).