Impact-induced melting, magma ocean evolution and core-mantle differentiation during accretion of the Earth

• Applicant: Professor Dr. David Rubie
• Subject Area: Mineralogy, Petrology and Geochemistry ; Geophysics
• Term: from 2015 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 275826910

During the early history of the Solar System, the Earth differentiated into its metallic core and silicate mantle by a multistage process that was strongly coupled to accretion of the planet. Accretion occurred through numerous collisions with other smaller planetary bodies, each of which delivered both energy and metal to the growing planet. The high energies involved in accretional impacts caused large scale melting of the early Earth and magma ocean formation which facilitated the segregation of iron-rich metal from silicate to produce the core and mantle. Major questions about this early period of Earth's history remain unanswered. For example, was there a single long-lasting deep magma ocean during accretion (as is often assumed) and, if so, how did its depth evolve with time? Alternatively was there a series of short-lived deep magma oceans and, if so, how did their depths evolve with time? Such questions depend on magma ocean cooling/crystallization timescales which, in turn, depend critically on the presence or absence of an insulating atmosphere. Although an insulating atmosphere has been postulated to be present after the Moon-forming giant impact, it has also been shown that accretional impacts cause atmospheric loss. Magma ocean evolution and how it is coupled to insulating atmospheres will be investigated in this project using a novel approach. We have previously integrated a multistage core formation model with numerical simulations of planetary accretion that is based on highly simplified assumptions about magma ocean depths. Employing this integrated approach we propose to actually calculate the depth of melting during each of thousands of accretional impacts based on kinetic energies and impact angles. The depth of melting is of critical importance because it determines the pressure-temperature conditions at which chemical equilibration between liquid metal and liquid silicate occurs, which, in turn, determines the chemical evolution of Earth's mantle and core. Furthermore the cooling/crystallization timescale of resulting global magma oceans will be determined and included in the model for different insulating atmosphere scenarios. The combined accretion/differentiation model will also enable the compositions of Earth's building materials to be determined as a function of their heliocentric distances of origin in the proto-planetary disk.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1833: Building a Habitable Earth
• International Connection: France, USA
• Cooperation Partners: Professor Dr. Daniel J. Frost; Professor Dr. Gregor Johann Golabek; Seth Jacobson, Ph.D.; Professor Dr. Hans Keppler; Professor Dr. Jay Melosh (†); Alessandro Morbidelli, Ph.D.