Harmonic analysis of the sandstone foreset-laminae thickness series from the Chaibasa tidal rhythmite, India, clearly shows that a normal semidiurnal tidal system with synodic month of ∼32 lunar days was in effect during the late Paleoproterozoic (2100–1600 Ma). The minimum number of solar days in a lunar sidereal month was ∼31. Published quantitative tidal-rhythmite data of others in combination with data derived from the Chaibasa tidal rhythmite indicate long-term stability of the lunar orbit and progressive increase in the Earth-Moon distance during the Proterozoic.

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