The passage supports which one of the following claims about the volcanic-eruption theory? A. It does not rely on assumptions concerning the temperature of molten rock at the lowest pan of the Earth's mantle. B. It may explain what caused the gradual fall in sea level that occurred for hundreds of thousands of years prior to the more sudden disappearance of the dinosaurs. C. It bases its explanation on the occurrence of periods of increased volcanic activity similar to those shown to have caused earlier mass extinctions. D. It may explain the relative scarcity of iridium in rocks on the Earth's surface compared to its abundance in meteorites. E. It accounts for the relatively uneven distribution of iridium in the layer of clay deposited at the end of the Cretaceous period.