{"paper_id":"4989ff71-62c9-4a92-b0bf-28ce6b2dc3b2","body_text":"Presence of primordial Mg explains the seismic low-velocity layer in the Earth’s outermost outer core | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Presence of primordial Mg explains the seismic low-velocity layer in the Earth’s outermost outer core Zhicheng Jing, Tao Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6039693/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Jan, 2026 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract The exact composition of Earth’s liquid outer core, which is believed to consist primarily of Fe-Ni alloys with minor light elements such as Si, O, C, S, and H, has long been debated. Available models incorporating these light elements cannot explain the seismically identified low velocity layer in the uppermost few hundred kilometers of the outer core, known as the E¢ layer. Here, we propose that the presence of primordial Mg, a potential light element that could have entered the outermost outer core following the Moon-forming giant impact, may provide a viable explanation for the formation of the E¢ layer. Employing first-principles molecular dynamics simulations, we determine the equation of state (pressure-density-temperature relations) and sound velocity ( V P ) of Fe-Mg alloying liquids under outer core conditions, which were unknown previously. Our results suggest that the presence of Mg can slightly decrease the V P of liquid Fe, in contrast to the enhancing effects of other light elements. Using seismically observed density and V P as constraints, we find that 0.5-1.79 wt% Mg is required to match core properties, depending on core composition and seismic models. The amount of primordial Mg in the outer core constitutes a significant portion of the total Mg budget in the bulk Earth, partly explaining its slight depletion in the bulk silicate Earth relative to chondritic meteorites. Earth and environmental sciences/Solid Earth sciences/Core processes Earth and environmental sciences/Solid Earth sciences/Geophysics Earth and environmental sciences/Solid Earth sciences/Geochemistry Full Text Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryDataset.xlsx Supplementary Dataset Supplementaryinformation.docx Supplementary information Cite Share Download PDF Status: Published Journal Publication published 20 Jan, 2026 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-6039693\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Article\",\"associatedPublications\":[],\"authors\":[{\"id\":461547644,\"identity\":\"42245208-e2e3-421a-ad82-ef33e465a403\",\"order_by\":0,\"name\":\"Zhicheng 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