Sloss (1972) demonstrated approximate synchroneity of Phanerozoic sedimentary sequences of the North American craton and the Russian platform. The sequences are separated by major craton-wide unconformities. Steiner and Grillmair (1973) proposed a galactic model for Phanerozoic and Precambrian glaciation events. Minima of a complex parameter of the galactic model correlate with the ages of the six major unconformities with a standard deviation of ±7.7 to ±14.5 m.y., depending on which Phanerozoic time scale is used. Arbitrary sets of periodic numbers compared with the galactic model yield a mismatch of ±24 to ±30 m.y. The galacto-geologic correlations may thus indicate a causal relationship. Assuming the global validity of approximately synchronous craton-wide unconformities, the galactic model may represent an alternative, external mechanism of crustal deformation whereby most of the energy for crustal movements is presumably of extraterrestrial origin. The reason for this galacto-geologic correlation is not known, but an explanation is not as important at the present time as confirmation of the synchroneity of these major transgressions and regressions on other cratonic blocks, because it may require a fundamental change in attempts to balance the energy budget of the planet Earth throughout geologic time.