A VENUS ORBIT--LUNAR ORBIT RESONANCE MODEL AS A POSSIBLE EXPLANATION FOR THE EARLY PROTEROZOIC "GREAT OXIDATION EVENT"

The main question is: CAN THE “GREAT OXIDATION EVENT” (Reinhard et al., 2009, Science, 326, p. 713) BE SOMEHOW ASSOCIATED WITH THE EVOLUTION OF THE EARTH-MOON SYSTEM? An answer is “YES, MAYBE”, if the perigean cycle (the prograde progression of the perigee point of the lunar orbit) is in resonance with the orbit of Venus.

Since Earth and Venus are in an approximate 5:8 orbital resonance (Chapman, 1986, J. Roy. Astron. Soc. Can., 80, p. 336), the critical numbers for the perigean cycle would be multiples of 5. The perigean cycle at present is 8.85 yr with the lunar orbital radius (LOR) at 60.3 earth radii (ER) and the length of the perigean cycle increases as the LOR decreases. The perigean cycle is 15 yr when the LOR is at ~47 ER. The essential condition for an effective resonance is for the apogee (the far distance) of the lunar orbit to be pointing toward Venus every 15 Earth yr (24 Venus yr). Using an orbital traceback of the Earth-Moon system similar to that of Hansen (1982, Rev. Geophys. Sp. Phys., 20, p. 457), the Moon would be ~47 ER and Earth rotation rate ~15.4 hr/d about 2.7-2.5 Ga ago.

The main effect when moving forward in time from ~43 ER to 47 ER is a slow, but unidirectional, forced eccentricity (ECC) of the lunar orbit from a nominal value of 0.055 to perhaps 0.3 or higher. In this scenario the semi-major axis (SMA) of the lunar orbit is gradually increased to the resonance value but the angular momentum (AM) of the lunar orbit lags behind. The highest rock (and ocean) tides occur at the end of this forced ECC scenario (i. e., rock tidal amplitudes increase from 0.8 m at 0.055 ECC to 2.5 m at 0.358 ECC). After the SMA of the lunar orbit reaches the resonance value (47 ER), the period of the perigean cycle remains constant for several 100 Ma. The tidal amplitudes gradually decrease as the AM of the lunar orbit increases, via tidal friction processes, and the ECC of the lunar orbit decreases as the lunar orbit returns to a circular morphology with ECC ~0.055.

Current speculation is that rapid plate movement, increased carbon dioxide emissions, and cyanobacteria were involved in the “GREAT OXIDATION EVENT” (Reinhard et al., 2009). If rock tides have some influence on plate tectonics at present (Scoppola et al., 2006, GSA Bull., 118, p. 199), then such an increase in rock tides in the Early Proterozoic should have had an effect on “plate tectonics” in that era.