SUMMARY The timing of inner core nucleation is a hugely significant event in Earth's evolution and has been the subject of intense debate. Some of the most recent theoretical estimates for the age of nucleation fall throughout the Neoproterozoic era; much younger than previously thought. A young inner core requires faster recent core cooling rates and a likely hotter early core; knowledge of its age would be invaluable in understanding Earth's thermal history and total energy budget. Predictions generated by numerical dynamo models need to be tested against such data, but records are currently much too sparse to constrain the event to a precise period of time. Here, we present results from 720 Ma dolerite dykes (and one sill) from the Franklin Large Igneous Province, which fall within a crucial 300 Myr gap in palaeointensity records. This study uses three independent techniques on whole rocks from 11 sites spread across High Arctic Canada and Greenland to produce virtual dipole moments ranging from 5 to 20 ZAm2 (mean 11 ZAm2); almost one order of magnitude lower than the present-day field. These weak-field results agree with recent ultralow palaeointensity data obtained from Ediacaran rocks formed ∼150 Myr later and may support that the dynamo was on the brink of collapse in the Neoproterozoic prior to a young inner core formation date.

中文翻译：

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来自低温纪的第一个古强度数据及其对内核成核年龄的潜在影响

总结 内核成核的时间是地球演化过程中一个非常重要的事件，并且一直是激烈争论的主题。一些关于成核年龄的最新理论估计贯穿于整个新元古代。比以前想象的要年轻得多。一个年轻的内核需要更快的近期内核冷却速度和一个可能更热的早期内核；了解其年龄对于了解地球的热历史和总能量预算将是无价的。数字发电机模型生成的预测需要针对此类数据进行测试，但目前记录太稀少，无法将事件限制在精确的时间段内。在这里，我们展示了来自富兰克林大火成岩省的 720 Ma 辉绿岩岩脉（和一个岩床）的结果，这些岩脉在古强度记录中处于 300 Myr 的关键差距内。这项研究使用三种独立的技术对来自加拿大北极高地和格陵兰岛的 11 个地点的整块岩石进行分析，以产生从 5 到 20 ZAm2（平均 11 ZAm2）的虚拟偶极矩；几乎比现在的领域低一个数量级。这些弱场结果与最近从约 150 Myr 后形成的埃迪卡拉纪岩石获得的超低古强度数据一致，并且可能支持在年轻内核形成日期之前的新元古代，发电机处于崩溃的边缘。