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    Solid earth sciences


    A coupled core-mantle evolution: Review and future prospects

    Takashi Nakagawa

    Geomagnetic field, Earth's core, Deep mantle, Long-term evolution

    (a) Schematic illustration of the coupled core-mantle evolution system; (b) Zoom-up of the thermal structure across the core-mantle boundary; (c) Schematic illustration of the feedback mechanism between core and mantle evolution; (d) An example result on the coupled core-mantle evolution model in parameterized mantle convection computation (Upper left: Thermal structure of the mantle; Upper right; Heat budget in the mantle; Lower left: Size of the inner core as a function of time; Lower right: Magnetic moment). On the magnetic moment, two values of the thermal conductivity of the Earth’s core are assumed (163 W/m/K and 125 W/m/K).

    In this review, I provide the current status and future prospects for the coupled core-mantle evolution and specifically summarize the constraints arising from geomagnetism and paleomagnetism on the long-term secular variations of the geomagnetic field. The heat flow across the core-mantle boundary (CMB) is essential for determining the best-fit scenario that explains the observational data of geomagnetic secular variations (e.g., onset timing of the inner core growth, geomagnetic polarity reversals, and westward drift) and should include the various origins of the heterogeneous structures in the deep mantle that have affected the heat transfer across the core-mantle boundary for billions of years. The coupled core-mantle evolution model can potentially explain the onset timing of the inner core and its influence on the long-term geomagnetic secular variations, but it is still controversial among modeling approaches on the core energetics because the paleomagnetic data contains various uncertainties. Additionally, with the coupled core-mantle evolution model in geodynamo simulations, the frequency of the geomagnetic polarity reversals can be explained with the time variations of the heat flow across the CMB. Additionally, the effects of the stable region in the outermost outer core to the magnetic evolution are also crucial but there would be still uncertain for their feasibility.

    However, despite this progress in understanding the observational data for geomagnetic secular variations, there are several unresolved issues that should be addressed in future investigations: (1) initial conditions—starting with the solidification of the global magma ocean with the onset timing of plate tectonics and geodynamo actions and (2) planetary habitability—how the dynamics of the Earth’s deep interior affects the long-term surface environment change that has been maintained in the Earth’s multisphere coupled system.