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. 2025 Aug;11(31):eadw1280.
doi: 10.1126/sciadv.adw1280. Epub 2025 Aug 1.

Time of proto-Earth reservoir formation and volatile element depletion from 53Mn-53Cr chronometry

Pascal M Kruttasch  1 , Klaus Mezger  1
Affiliations

Time of proto-Earth reservoir formation and volatile element depletion from 53Mn-53Cr chronometry

Pascal M Kruttasch et al. Sci Adv. 2025 Aug.

Abstract

The 53Mn-53Cr chronometry of Solar System materials constrains the early chemical evolution of the protoplanetary disk, which is critical for planet formation. Mn/Cr ratios in carbonaceous chondrites and the bulk silicate Earth indicate that meteorite parent bodies and Earth have variable depletions in volatile elements compared to the bulk Solar composition. This depletion is a consequence of the local temperature decreasing as a function of heliocentric distance before planetesimal accretion. Back-tracking the present-day ε53Cr composition of the hypothetical proto-Earth fraction shows that the cessation of Mn-Cr fractionation from the bulk Solar composition occurred no later than ~3 Ma after CAI formation, similar to disk regions of carbonaceous chondrites at greater heliocentric distances. The timing of limited solid-gas interaction due to the dissipation of gas from the protoplanetary disk caused the cessation of Mn-Cr fractionation and provides a lower limit on its lifetime.

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Figures

Fig. 1.
Fig. 1.. ε53Cr evolution of CCs and their intersection ages (model ages) with the bulk Solar System.
(A) Average ε53Cr evolution curves of CC groups. (B) Kernel density distribution of reservoir formation (RF) ages of CC groups using individual CC meteorites shown in (C). (C) CI normalized 55Mn/52Cr ratios of individual chondrite samples as a function of RF ages. The ages are relative to CAI formation at 4568.54 Ma. Carbonaceous chondrite data are from Zhu et al. (12). The meteorite Maribo (CM2) is excluded due to an exceptionally high present-day ε53Cr of 0.29 ± 0.04 (12).
Fig. 2.
Fig. 2.. Three hypothetical mixing scenarios between the PE and Theia.
Mixing of Mn/Cr between PEM and Theia (mantle) in all cases results in the present-day composition of the BSE. Model I assumes mixing of PEM and Theia with identical Mn/Cr (similar to BSE), independent of size; model II assumes mixing of 90% PEM:10% Theia (± 5%), where Theia’s Mn/Cr is CI chondrite-like; model III assumes mixing of 60% PEM:40% Theia (± 5%), where Theia’s Mn/Cr is CI chondrite-like. Note that in models II and III (Mn/Cr of Theia similar to CI chondrite), Theia was probably too oxidized to form a core. In contrast, under more reduced conditions (model I), Theia likely underwent core formation resulting in Theia mantle (TM) and Theia core (TC). (A) 55Mn/52Cr as a function of the bulk mass fraction of Theia (ΧT), and (B) ε53Cr as a function of Cr mass fraction of Theia (χT) for PEM, PEC, and PE, respectively. The mass fractions of Theia for models II and III are shown as gray areas or on the ordinate for model I.
Fig. 3.
Fig. 3.. ε53Cr evolution of PE-PEM for the three different mixing scenarios.
The ε53Cr evolution is modeled using 10,000 Monte Carlo simulations with variable 55Mn/52Cr of PE and PEM and present-day ε53Cr of PE, and Mn-Cr fractionation of PE into PEM at time t1 (core formation) between 0 and 70 Ma after CAI formation. (A to C) Reservoir formation (RF; PE-CI intersection) ages as a function of core formation (CF; PE-PEM fractionation) ages for the three different mixing models [(A) model I; (B) model II; (C) model III). Dark colors indicate simulations between ε53Cr evolution of PE-PEM resulting in the present-day ε53Cr of PEM; light colors indicate simulations that do not reproduce the present-day ε53Cr of PEM. (D) ε53Cr time evolution of filtered Monte Carlo simulations of PE-PEM resulting in the constrained range of the present-day ε53Cr of PEM. The ε53Cr compositions of chromite grains (with 55Mn/52Cr near zero) from iron meteorites, ordinary chondrites, and Erg Chech 002 (36, 38, 39) are plotted on the bulk Solar System evolution curve for comparison. (E) Kernel density distribution of PE reservoir formation ages resulting in present-day ε53Cr of PEM. ΔTCAI-RF and ΔTCAI-CF are the times of RF and CF relative to CAI formation at 4568.54 Ma.
Fig. 4.
Fig. 4.. Evolution of bulk Solar System 53Mn/55Mn and ε53Cr with time.
The evolution paths are modeled for different estimates for the half-life of 53Mn (5, 60). (A) 53Mn/55Mn evolution lines are anchored to the D’Orbigny angrite with 53Mn/55Mn from (62) and a U-corrected Pb-Pb age from (61). Meteorite data of achondrites compiled in (5) are shown for comparison. (B) ε53Cr evolution curves are modeled by back-calculation from the present-day 55Mn/52Cr and ε53Cr of CI chondrite from (12).
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