Early tides: Response to Varga et al. Journal Article uri icon

DCO ID 11121/1135-7204-9551-6563-CC

in language

  • eng

year of publication

  • 2006


  • 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 similar to 2-2.5 Ga before present, or more recently (similar to 0.8-0.2 Ga), LOD values are estimated at between 12 and 16 h, suggesting a compromise figure of LOD = similar to 14 h, with tides every similar to 7 h, at 3.9 Ga. (c) 2005 Elsevier Inc. All rights reserved.


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