{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"6ac73fcf1772751b6ed5504ad444a57262c69c4de7d73a2880802f8d19b6e4d5","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["42f002b66520f7698177d5eac7b296b8f522b1043e236bc90ff8792599f07739","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"19995014ad8369b9e3285665a1c6de534e07f3dd00ab2675f5991fd2dc20156e","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"earth.geodynamo.early-dynamo-power","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Rocks show Earth had a magnetic field at least 3.4 billion years ago, long before the solid inner core probably formed. If the core conducts heat as well as recent calculations say, ordinary heat-driven stirring may have been too weak to run the dynamo (the self-sustaining generator that turns flowing liquid iron into a magnetic field).","posed_since":"","precise":"Paleointensity data indicate a dynamo since at least about $3.4 \\text{ to } 3.5\\,\\mathrm{Ga}$, with possible records to about $3.7\\,\\mathrm{Ga}$ from Isua, Greenland (Nichols and coauthors, JGR Solid Earth 2024, https://doi.org/10.1029/2023JB027706). With core thermal conductivity $k$ of order $10^{7}\\,\\mathrm{erg}/(\\mathrm{s}\\,\\mathrm{cm}\\,\\mathrm{K})$ or higher, the adiabatic heat flow can exceed $Q_{\\mathrm{cmb}}$ before inner-core nucleation (the new core paradox). Identify which source supplied the needed entropy: precipitation of MgO, $\\mathrm{SiO_2}$ or FeO, a basal magma-ocean dynamo, tidal or precessional forcing, or a lower $k$. An answer is a thermal and chemical core history that satisfies the paleointensity record and mineral-physics constraints.","problem_ref":"42f002b66520f7698177d5eac7b296b8f522b1043e236bc90ff8792599f07739","references":"","settled_by":"Experimental precipitation rates of light-element oxides at core conditions combined with a resolved core conductivity and a consistent core thermal history.","status_note":"Vidal and Cebron 2025 (arXiv:2506.19039) find lunar tidal forcing alone insufficient before 3.25 Ga, while Kiernan and coauthors 2026 (arXiv:2606.16340) propose resonant tidal coupling enhanced by a basal magma ocean; no consensus.","title":"What powered the geodynamo before the inner core 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