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dc.contributor.authorStüeken, Eva E.
dc.contributor.authorBoocock, Toby
dc.contributor.authorSzilas, Kristoffer
dc.contributor.authorMikhail, Sami
dc.contributor.authorGardiner, Nicholas J.
dc.identifier.citationStüeken , E E , Boocock , T , Szilas , K , Mikhail , S & Gardiner , N J 2021 , ' Reconstructing nitrogen sources to Earth’s earliest biosphere at 3.7 Ga ' , Frontiers in Earth Science , vol. 9 , 675726 .
dc.identifier.otherPURE: 274172680
dc.identifier.otherPURE UUID: f00a9251-5510-4ee9-8636-a395d1a49718
dc.identifier.otherBibtex: 10.3389/feart.2021.675726
dc.identifier.otherORCID: /0000-0001-5276-0229/work/93894399
dc.identifier.otherORCID: /0000-0001-6861-2490/work/93894746
dc.identifier.otherORCID: /0000-0003-3465-9295/work/93894958
dc.identifier.otherScopus: 85105947537
dc.identifier.otherWOS: 000649945800001
dc.descriptionES acknowledges support from the School of Earth and Environmental Sciences at St Andrews. TB was funded by a NERC IAPETUS Doctoral Training Program (NE/R012253/1) studentship. Fieldwork at Isua was supported by the Carlsberg Foundation through grant CF18-0090 to KS.en
dc.description.abstractEarth’s sedimentary record has preserved evidence of life in rocks of low metamorphic grade back to about 3.2–3.5 billion years ago (Ga). These lines of evidence include information about specific biological metabolisms, permitting the reconstruction of global biogeochemical cycles in the early Archean. Prior to 3.5 Ga, the geological record is severely compromised by pervasive physical and chemical alteration, such as amphibolite-granulite facies metamorphic overprinting. Despite this alteration, evidence of biogenic organic matter is preserved in rare localities, including meta-turbidites from the 3.8 to 3.7 Ga Isua Supracrustal Belt, Western Greenland. But detailed insights into metabolic strategies and nutrient sources during the time of deposition of these Eoarchean meta-sedimentary rocks are lacking. Here we revisit the Isua meta-turbidites and provide new data for metal abundances as well as organic carbon and nitrogen isotope values. Our results reveal mixing between authigenic and detrital nitrogen phases with the authigenic phase likely fractionated by metamorphic degassing. Rayleigh fractionation models of these 3.7 Ga samples indicate pre-metamorphic δ15N values of between −1 and −10‰. The most plausible initial values are below −5‰, in agreement with a prior study. While the upper endmember of −1‰ could indicate biological N2 fixation at 3.7 Ga, the more plausible lighter values may point toward a distinct biogeochemical nitrogen cycle at that time, relative to the rest of Earth’s history. In light of recent experimental and phylogenetic data aligned with observations from the modern atmosphere, we tentatively conclude that lightning and/or high-energy photochemical reactions in the early atmosphere may have contributed isotopically light nitrogen to surface environment(s) preserved in the Isua turbidites. In this case, recycling of Eoarchean sediments may have led to the isotopically light composition of the Earth’s upper mantle dating back to at least 3.2 Ga.
dc.relation.ispartofFrontiers in Earth Scienceen
dc.rightsCopyright © 2021 Stüeken, Boocock, Szilas, Mikhail and Gardiner. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.en
dc.subjectNitrogen isotopesen
dc.subjectGB Physical geographyen
dc.titleReconstructing nitrogen sources to Earth’s earliest biosphere at 3.7 Gaen
dc.typeJournal articleen
dc.description.versionPublisher PDFen
dc.contributor.institutionUniversity of St Andrews.School of Earth & Environmental Sciencesen
dc.contributor.institutionUniversity of St Andrews.St Andrews Centre for Exoplanet Scienceen
dc.contributor.institutionUniversity of St Andrews.St Andrews Isotope Geochemistryen
dc.description.statusPeer revieweden

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