Smith Lecture: Earth-Moon Dynamics Recorded in a >3.7 Billion Year Old Tidalite, Isua Supracrustal Belt, Greenland
Earth-Moon dynamics force tidal ebb and flood currents in the oceans that leave their mark as rhythmically layered "tidalites" in the sedimentary record. Studies have shown that tidalites occur from the Archean Eon to today, and point to a slowly decreasing rotation rate of the Earth and progressive lunar retreat. Recently a tidalite was found in Earth’s oldest sedimentary rocks preserved in the >3.7 billion year old Isua Supracrustal Belt, Greenland. Within this belt, a meta-sandstone succession displays hierarchical layering that can be associated with semi-diurnal, fortnightly, and monthly tidal forcing. Spectral analysis of multiple transects through the sedimentary layering indicates 31.1 days per synodic month, an Earth-Moon distance of 45 Earth radii, and a 14.3-hour day. To now, the oldest known tidalite that has allowed reconstruction of ancient Earth-Moon dynamics is from a 2.45 billion year old rock succession. This discovery extends our knowledge of ancient tides back in time by more than a billion years, and provides data pertaining to Earth formation, differentiation and tidal dissipation, and the origin and orbital evolution of the Moon.