Early tides: Response to Varga et al

Richard Lathe*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Tidal cycling has been causally implicated at the origin of life, but the speed of early tides has not been established. The rotation period of the Earth is the dominant parameter, and a length of day (LOD) of under 6 h at 3.9 Ga was inferred by regression from present values [Lathe, R. 2004. Icarus 168, 18-22]. However, this would imply critical lunar proximity at that time; in their commentary Varga et al. instead argue for a more distant Moon, proposing LOD = 16.8 h . The debate is accentuated because regression from current values requires an Earth-Moon juxtaposition at around 2 Ga, for which there is no evidence. A smooth retreat from a Moon-forming impact at 4.5 Ga is also irreconcilable with the weight of paleotidal evidence. An inflection in the lunar recession curve is required to reconcile current and recent Earth-Moon values with a 4.5 Ga origin, requiring a change in tidal friction during the evolution of the Earth-Moon system. Depending on whether this took place at ∼2-2.5 Ga before present, or more recently (∼ 0.8-0.2 Ga), LOD values are estimated at between 12 and 16 h, suggesting a compromise figure of LOD = ∼14 h, with tides every ∼7 h, at 3.9 Ga.

Original languageEnglish
Pages (from-to)277-280
Number of pages4
Issue number1
Publication statusPublished - Jan 2006


  • Cycling
  • Earth
  • Moon
  • Origin of life
  • Tide


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