Our Smith Lecture speaker this week is Linda A. Hinnov, Research Professor, Department of Earth and Planetary Sciences, Johns Hopkins University. She is speaking on Earth-Moon Dynamics Recorded in a >3.7 Billion Year Old Tidalite, Isua Supracrustal Belt, Greenland. Abstract below.
Smith Lectures are Friday afternoons from 4:00 to 5:00 pm, in Room 1528 C.C. Little Building. A reception is held following the lecture in 2540 C.C. Little. The events are free and open to the public. A full schedule for the term may be found on our website:
Best regards, -Anne
Academic Student Services
Department of Earth and Environmental Sciences
University of Michigan
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.