TEMPORAL VARIATION OF GEODYNAMICAL PROPERTIES DUE TO TIDAL FRICTION

Abstract

Fossils and tidal deposits as well as the possibility to compute values of the lunar tidal torque for different geological epochs allow us to model the variations in time of the Earth's figure, assuming that the latter remains, on a global scale, close to a hydrostatic equilibrium figure. On this basis, one can infer the variations of the Earth's most important geodynamic parameters over much of the geological past. Thus, the geometrical flattening has decreased from 5 × 10-3 to 3 × 10-3, the normal gravity on annual average increase at the equator by ~2 nanogal. In present study, first the influence of the tidal friction on the length of day (LOD), geometrical flattening and the Earth-Moon distance during the history of the Earth will be discussed. The different despinning rates during the Phanerozoic (Pz: 0-0.56 Ga BP) and Proterozoic (Ptz: 0.56-2.5 Ga BP) will be also demonstrated. For understanding the development of the dynamics of the early Earth and the Earth-Moon system the length of day during Katarchean (3.00-4.55 Ga BP) shortly after the Earth formation was also estimated. © 2005 Elsevier Ltd. All rights reserved.