{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"742f2c8a800d78187147683e00e46c0b66faa715a06f21fcea15abb63ca7dd04","created":"2026-10-03T07:18:02Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"95908a9cc051268f2c44721889abe6acc1aaaf70ea8088577b26f4fcd6699633","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":"1","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 $1e7\\,\\mathrm{erg}/(\\mathrm{s}\\,\\mathrm{cm}\\,\\mathrm{K})$ 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, SiO2 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":null,"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 existed?","topic_ref":"e13e768be35f03c6e8ec9a4a4d6987bded1527805358b1af395bbdf03b08e310"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"42f002b66520f7698177d5eac7b296b8f522b1043e236bc90ff8792599f07739","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"61c8cd2b19d7b4b88c017aa46ba50b620d07a19061bd0299093802af85c60d26","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"DR0AaJJIC3nLJqB4RLmZagR47471Ftph2cg86bi0fkz_4HnG_laYbpVWc3ygoEtjElfHwVKJdBApfYiUJnTCBw"},"schema":"pubphys.envelope/1"},"record_hash":"42f002b66520f7698177d5eac7b296b8f522b1043e236bc90ff8792599f07739","leaf_index":1315}