The proponents of this hypothesis claim that cyclic variations in bed compositions are astronomically tuned, and the beds' magnitude can be calibrated to show they were contemporaneous—a strong argument. In order to refute it, it is necessary to propose an alternative mechanism for generating these cyclic bands, or for erosion to have coincidentally removed just the right amount of sediment everywhere before the gypsum was deposited. The proponents claim that the gypsum was deposited directly above the correlated marl layers, and slumped into them, giving the appearance of an unconformable contact. However, their opponents seize upon this apparent inconformity, and claim that the Sorbas Basin was exposed—therefore eroding—while the Mediterranean sea was depositing evaporites. This would result in the Sorbas Basin being filled with evaporites at 5.5 million years ago (Ma), compared to the main basin at 5.96 Ma.).