{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"5166efdcea94d0d452db10cb01497d913a8963dda11263b55caee311314c55d5","created":"2026-10-03T07:18:02Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"84a6764582f1d69e252293d094ff006a52ae16898b8a3b8cf8da7cb60a49311f","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"earth.geodynamo.top-core-stratification","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Some seismic and magnetic data suggest the outermost few hundred kilometers of the liquid core form a calm layer that does not churn. Other analyses find no such layer, and its presence changes how the field is generated and how fast the core cools.","posed_since":"","precise":"Some SmKS seismic phases (waves reflected several times beneath the core-mantle boundary) show reduced P velocity in the top few hundred km of the outer core, and Buffett (Nature 2014, https://doi.org/10.1038/nature13122) interpreted a 60-yr geomagnetic fluctuation as magnetic-Archimedes-Coriolis waves requiring a stratified layer about $140\\,\\mathrm{km}$ thick; other studies fit the data without a layer. Determine whether a stable layer exists, its thickness and buoyancy frequency $N$, and whether its origin is thermal (subadiabatic heat flow) or chemical. An answer is thickness and $N$, or an upper bound, consistent with seismology, secular variation and core thermal history.","problem_ref":null,"references":"","settled_by":"Joint inversion of mantle-corrected SmKS travel times and geomagnetic secular variation for wave modes that exist only in a stratified layer.","status_note":"","title":"Is the top of Earth's liquid core stably 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