^a,bYogita Kadlag, ^c,dAryavart Anand, ^eMario Fischer-Gödde, ^dKlaus Mezger, ^fKristoffer Szilas, ^gSteven Goderis, ^bIngo Leya
Icarus (in Press) Open Access
Link to Article [https://doi.org/10.1016/j.icarus.2024.116143]
^aGeosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad, Gujarat 380009, India
^bSpace Science and Planetology, Physics Institute, Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
^cMax-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
^dInstitut für Geologie, Universität Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
^eInstitut für Geologie und Mineralogie, University of Cologne, Zülpicher Straße 49b, 50674 Köln, Germany
^fDepartment of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark
^gArchaeology, Environmental Changes, and Geo-Chemistry (AMGC) Research Group, Department of Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium

The late addition of extra-terrestrial material may represent an important source of Earth’s volatiles. The composition of impactors can be reconstructed using ⁵⁴Cr abundances in impact related rocks preserved in the terrestrial record. The average ε⁵³Cr and ε⁵⁴Cr of Earth’s mantle determined from mantle rocks of 3.8 Ga to present are 0.03 ± 0.02 and 0.08 ± 0.04, respectively. Impact melt rocks and spherule beds linked to impact structures larger than 50 km that formed between 3.4 Ga and 66 Ma have ε⁵³Cr ranging from −0.04 to 0.17, and ε⁵⁴Cr ranging from −0.64 to 1.41. A carbonaceous chondrite-like impactor contribution dominated the Meso- to Paleoarchean spherule layers (> 3.0 Ga), whereas a mixed chondrite flux composed of carbonaceous and non‑carbonaceous chondrites, with a possible contribution of differentiated meteorites is observed in the younger spherule layers (2.5 Ga to 66 Ma). This likely reflects the break-up of distinct asteroid families through time. Although available impact materials are limited, the Cr isotope signatures of materials related to large impacts suggest a change in the composition of crater-forming impactors on Earth, from predominantly carbonaceous chondrite-like more oxidized material during the Archean to predominantly non‑carbonaceous -like more reduced and volatile poor material in recent times. Chromium isotopes suggest that not >0.01 wt% of CC-like material added to the Earth’s mantle after Archean. Thus, it is inferred that the mass accreted after 3.0 Ga contributed insignificantly to the water and other volatile element budget of the Earth.