TY - JOUR
T1 - Ruthenium isotope vestige of Earth’s pre-late-veneer mantle preserved in Archaean rocks
AU - Fischer-Gödde, Mario
AU - Elfers, Bo Magnus
AU - Münker, Carsten
AU - Szilas, Kristoffer
AU - Maier, Wolfgang D.
AU - Messling, Nils
AU - Morishita, Tomoaki
AU - Van Kranendonk, Martin
AU - Smithies, Hugh
N1 - Funding Information:
Acknowledgements We thank F. Wombacher and A. Katzemich for support in the laboratory and K. Tani and I. Nishio for help during fieldwork. This research was supported through DFG grant number FI 1704/5-1 within the priority programme SPP 1833 ‘Building a Habitable Earth’ to M.F.-G., by the European Commission through ERC grant number 669666 ‘Infant Earth’ to C.M., by the Carlsberg Foundation grant number CF18-0090 to K.S., and by Kanazawa University “SAKIGAKE 2018” to T.M. H.S. publishes with the permission of the Executive Director, Geological Survey of Western Australia.
Publisher Copyright:
© 2020, The Author(s), under exclusive licence to Springer Nature Limited.
PY - 2020/3/12
Y1 - 2020/3/12
N2 - The accretion of volatile-rich material from the outer Solar System represents a crucial prerequisite for Earth to develop oceans and become a habitable planet1–4. However, the timing of this accretion remains controversial5–8. It has been proposed that volatile elements were added to Earth by the late accretion of a late veneer consisting of carbonaceous-chondrite-like material after core formation had ceased6,9,10. This view could not be reconciled with the ruthenium (Ru) isotope composition of carbonaceous chondrites5,11, which is distinct from that of the modern mantle12, or of any known meteorite group5. As a possible solution, Earth’s pre-late-veneer mantle could already have contained a fraction of Ru that was not fully extracted by core formation13. The presence of such pre-late-veneer Ru can only be established if its isotope composition is distinct from that of the modern mantle. Here we report the first high-precision, mass-independent Ru isotope compositions for Eoarchaean ultramafic rocks from southwest Greenland, which display a relative 100Ru excess of 22 parts per million compared with the modern mantle value. This 100Ru excess indicates that the source of the Eoarchaean rocks already contained a substantial fraction of Ru before the accretion of the late veneer. By 3.7 billion years ago, the mantle beneath southwest Greenland had not yet fully equilibrated with late accreted material. Otherwise, no Ru isotopic difference relative to the modern mantle would be observed. If constraints from other highly siderophile elements besides Ru are also considered14, the composition of the modern mantle can only be reconciled if the late veneer contained substantial amounts of carbonaceous-chondrite-like materials with their characteristic 100Ru deficits. These data therefore relax previous constraints on the late veneer and are consistent with volatile-rich material from the outer Solar System being delivered to Earth during late accretion.
AB - The accretion of volatile-rich material from the outer Solar System represents a crucial prerequisite for Earth to develop oceans and become a habitable planet1–4. However, the timing of this accretion remains controversial5–8. It has been proposed that volatile elements were added to Earth by the late accretion of a late veneer consisting of carbonaceous-chondrite-like material after core formation had ceased6,9,10. This view could not be reconciled with the ruthenium (Ru) isotope composition of carbonaceous chondrites5,11, which is distinct from that of the modern mantle12, or of any known meteorite group5. As a possible solution, Earth’s pre-late-veneer mantle could already have contained a fraction of Ru that was not fully extracted by core formation13. The presence of such pre-late-veneer Ru can only be established if its isotope composition is distinct from that of the modern mantle. Here we report the first high-precision, mass-independent Ru isotope compositions for Eoarchaean ultramafic rocks from southwest Greenland, which display a relative 100Ru excess of 22 parts per million compared with the modern mantle value. This 100Ru excess indicates that the source of the Eoarchaean rocks already contained a substantial fraction of Ru before the accretion of the late veneer. By 3.7 billion years ago, the mantle beneath southwest Greenland had not yet fully equilibrated with late accreted material. Otherwise, no Ru isotopic difference relative to the modern mantle would be observed. If constraints from other highly siderophile elements besides Ru are also considered14, the composition of the modern mantle can only be reconciled if the late veneer contained substantial amounts of carbonaceous-chondrite-like materials with their characteristic 100Ru deficits. These data therefore relax previous constraints on the late veneer and are consistent with volatile-rich material from the outer Solar System being delivered to Earth during late accretion.
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UR - http://www.scopus.com/inward/citedby.url?scp=85081729616&partnerID=8YFLogxK
U2 - 10.1038/s41586-020-2069-3
DO - 10.1038/s41586-020-2069-3
M3 - Article
C2 - 32161386
AN - SCOPUS:85081729616
SN - 0028-0836
VL - 579
SP - 240
EP - 244
JO - Nature
JF - Nature
IS - 7798
ER -