Stochastic accretion of the Earth

Abstract

Earth is depleted in volatile elements relative to chondritic meteorites, its possible building blocks. The extent of this depletion increases with decreasing condensation temperature, and is approximated by a cumulative normal distribution, unlike that in any chondrite. However, moderately volatile elements, occupying the mid-range of the distribution, have chondritic isotope ratios, contrary to that expected from loss by partial vaporisation/condensation. Here we reconcile these observations by showing, using N-body simulations, that Earth accreted stochastically from many precursor bodies whose variable compositions reflect the temperatures at which they formed. Impact-induced atmospheric loss was efficient only when the proto-Earth was small, and elements that accreted thereafter retain near-chondritic isotope ratios. Earth's composition is reproduced when initial temperatures of planetesimal- to embryo-sized bodies are set by disk accretion rates of (1.08 $\pm$ 0.17) $\times$ 10${}^{-7}$ solar masses/yr, although they may be perturbed by ${}^{26}$Al heating on bodies formed at different times. The model implies a heliocentric gradient in composition and rapid planetesimal formation within $\sim$ 1 Myr, in accord with radiometric volatile depletion ages of Earth.

13 pages, 4 figures. Nat Astron (2022)

References in corpus (9)

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Cited by in corpus (5)

• Terrestrial planet formation from a ring
• Interior Controls on the Habitability of Rocky Planets
• Modification of the radioactive heat budget of Earth-like exoplanets by the loss of primordial atmospheres
• Sublimation of refractory minerals in the gas envelopes of accreting rocky planets
• Outgassing Composition of the Murchison Meteorite: Implications for Volatile Depletion of Planetesimals and Interior-atmosphere Connections for Terrestrial Exoplanets