Building Earth

Studies of meteorites and samples returned from space missions bear the chemical and physical records of planetary formation processes. Mass-independent isotopic anomalies measured in planetary materials indicate two separate accretion reservoirs corresponding to a more volatile-rich region (carbonaceous) in the outer solar system and a more volatile-depleted one (non-carbonaceous), the inner and terrestrial planet formation region [1].

Unequilibrated enstatite chondrites are within 10 parts per million from the Earth’s mantle 142Nd/144Nd composition [2-4]. This difference between the Earth and chondrites may either have been produced by early Sm/Nd fractionation from chondritic materials or was already present within the disk. The isotopic anomalies in 145Nd and 148Nd measured in non-carbonaceous chondrites and achondrites also indicate that a change of the inner disk composition occurred within the first 1.5 million years of solar system formation [5]. On the other hand, major (e.g. Mg/Si) and siderophile elements suggest that enstatite chondrites can neither be the main component forming Earth nor the late accreted materials [6, 7]. Elemental and isotopic fingerprints indicate that the Earth may be primarily built from unsampled materials formed closer to the Sun (e.g. [5]), while volatiles indicate variable sources. Dynamical modeling provides additional constraints on these complex physical, chemical, and isotopic records of Earth and terrestrial planet formation.

[1] Kruijer et al. (2020). [2] Bouvier et al. (2016). [3] Burkhardt et al. (2016). [4] Boyet et al. (2018). [5] Frossard et al. (2021). [6] Fischer-Gödde et al. (2020). [7] Budde et al. (2019).