Abstract
Tides and Earth‐Moon system evolution are coupled over geological time. Tidal energy dissipation on Earth slows Earth′s rotation rate, increases obliquity, lunar orbit semi‐major axis and eccentricity, and decreases lunar inclination. Tidal and core‐mantle boundary dissipation within the Moon decrease inclination, eccentricity and semi‐major axis. Here we integrate the Earth‐Moon system backwards for 4.5 Ga with orbital dynamics and explicit ocean tide models that are “high‐level” (i.e., not idealized). To account for uncertain plate tectonic histories, we employ Monte Carlo simulations, with tidal energy dissipation rates (normalized relative to astronomical forcing parameters) randomly selected from ocean tide simulations with modern ocean basin geometry and with 55, 116, and 252 Ma reconstructed basin paleogeometries. The normalized dissipation rates depend upon basin geometry and Earth′s rotation rate. Faster Earth rotation generally yields lower normalized dissipation rates. The Monte Carlo results provide a spread of possible early values for the Earth‐Moon system parameters. Of consequence for ocean circulation and climate, absolute (un‐normalized) ocean tidal energy dissipation rates on the early Earth may have exceeded today′s rate due to a closer Moon. Prior to ∼3Ga, evolution of inclination and eccentricity is dominated by tidal and core‐mantle boundary dissipation within the Moon, which yield high lunar orbit inclinations in the early Earth‐Moon system. A drawback for our results is that the semi‐major axis does not collapse to near‐zero values at 4.5 Ga, as indicated by most lunar formation models. Additional processes, missing from our current efforts, are discussed as topics for future investigation.
Highlights
At the present day, the Moon passes over the same terrestrial longitude every 24.8 hours, on average
Part of the extracted energy is dissipated by tides, and part goes into expanding the semi-major axis of the geocentric lunar orbit
Energy dissipated by tides and core-mantle boundary (CMB) interactions within the Moon comes from the orbit and contracts the semi-major axis
Summary
The Moon passes over the same terrestrial longitude every 24.8 hours, on average. The second largest diurnal tidal constituent, O1, has a period of 25.8 hours Energy dissipation from these tides and other semi-diurnal and diurnal constituents, in both the ocean and the solid Earth, cause the semi-major axis (a) of the lunar orbit around Earth to increase, and Earth s sidereal rotation rate (ωE) to decrease G. Williams & Boggs, 2016), which includes effects of tides and core-mantle boundary dissipation within the Moon G. Williams & Boggs, 2015), is used in conjunction with the ocean tide model results to simulate Earth-Moon history. The orbital dynamics model begins at the present-day and is run backwards over 4.5 billion years (4.5 Ga), the approximate age of the Earth-Moon system.
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