Influence of solidification mechanism on magma ocean dynamics and evolution

During a later stage of Earth's accretion, approximately 4.5 billion years ago, impacts of Mars-sized bodies created a deep terrestrial magma ocean of global extent on proto-Earth. Once core formation is complete, the magma ocean begins to solidify. However, the solidification mechanism and the location where crystallization initiates remain unclear and are subjects of debate. One widely accepted model posits that solidification begins at the bottom of the magma ocean (e.g., [1]). Contrarily, laboratory experiments conducted under high-pressure and temperature conditions suggest two alternate scenarios: Solidification may also commence at the top of the magma ocean (e.g., [2]) or at mid-depth (e.g., [3,4]). The latter might yield a deep molten layer, referred to as a basal magma ocean, at the core-mantle boundary, which could potentially endure chemically and thermally isolated from the remaining mantle for an extended period [5].

We model these three distinct solidification styles (bottom-up, top-down, mid-depth) and examine their impact on the dynamics and temporal evolution of a convecting magma ocean through computational simulations. Determining whether the magma ocean solidifies from the bottom up, top-down, or in a mid-outward manner holds paramount significance for Earth's evolution, influencing factors such as the level of differentiation and the initial conditions governing the advent of plate tectonics. Furthermore, the dominant mechanism and its timing could bear crucial implications for the ensuing evolution of the mantle and the distribution of geochemical trace elements.

References:
[1] Andrault et al. (2011) EPSL, 304(1), 251–259.
[2] Mosenfelder et al. (2007) JGR: Solid Earth, 112(B6).
[3] Stixrude et al. (2009) EPSL, 278(3), 226–232.
[4] Boukaré et al. (2015) JGR: Solid Earth, 120(9), 6085–6101.
[5] Labrosse et al. (2007) Nature, 450(7171), 866–869.