The authors expressed the view in 1952 that tidal friction between the earth and moon could account for many features such as alterations in biological rhythms, or tectonic effects of unequalled amplitude throughout geological times and the remote past. Tests for this theory are: (a) It is remarkable that the loss of angular momentum by the earth since the "original" state almost exactly matches the amount required to bring the moon from the earth's equator to its present orbit; (b) Recent observations of daily growth increments in fossil organisms show, at least for the last 400 m.y., that the order of magnitude of the time-scale previously adopted by the authors is satisfactory, the scale having only to be somewhat shortened and the values—theoretical and observed—of the month-to-day ratio are in good concordance.

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