ESTABLISHING PRIMORDIAL CHEMICAL STRATIFICATION IN PLANETARY MANTLES DUE TO ACCRETION

Earth accreted within the protoplanetary disk about the nascent Sun. Both radiometric chronometers (Hf-W, Lu-Hf, etc.; e.g., Barboni et al., 2017) and a highly siderophile element abundance based clock (Jacobson et al., 2014) conclude that this process took somewhere between 50 and 100 million years after the formation of the first solids in the Solar System. There now exists multiple terrestrial planet formation scenarios that can reproduce the masses, orbits, and timescales of Earth’s accretion. During this accretion process, radial mixing may have occurred within the protoplanetary disk delivering material from even the outermost parts of the disk to the growing Earth, but different planet formation scenarios make distinctly different claims regarding how much radial mixing might have occurred (e.g., Lambrecht et al., 2019; Izidoro et al., 2021). To investigate whether a signal from radial mixing could be recorded in Earth’s mantle, we model the accretion and differentiation of Earth throughout all of accretion according to these different scenarios. We track the delivery of distinct building blocks from different parts of the disk, and we simulate the creation of mantle magma oceans (Nakajima et al., 2021), which would homogenize molten parts of Earth’s mantle. In particular, we examine whether a record of carbonaceous chondrite-like outer disk material would leave behind a stratified record in Earth’s mantle at the start of the Hadean.