Various suggestions of a geological periodicity of 2–7 m.y. have been made in the literature. If such periods exist, they fall between the earth' orbital (Milankovitch) periods and the solar system's galactic (Oort) periods and have no known internal or external source. To study the period range 1–10 m.y., four types of Cenozoic marine data were subjected to formal time series analysis. No significant periodicities were found, and only a mean interval between global marine episodes (∼5 ± 2 m.y.) could be defined. Possible causes of the variability are discussed.
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