The evolution of the lunar dynamo is essential for deciphering the deep interior structure, thermal history, and surface environment of the Moon^1-4. Previous palaeomagnetic investigations on samples returned from the nearside of the Moon have established the general variation of the lunar magnetic field^5-7. However, limited spatial and temporal palaeomagnetic constraints leave the evolution of the lunar dynamo ambiguous. The Chang'e-6 mission returned the first farside basalts dated at ca. 2.8 billion years ago (Ga)^8,9, offering a unique opportunity to investigate a critical spatiotemporal gap in the evolution of the global lunar dynamo. Here we report palaeointensities (~5–21 μT) recovered from the Chang’e-6 basalts, providing the first constraint on the magnetic field from the lunar farside and a critical anchor within the large gap between 3 and 2 Ga. The new results record a rebound of the field strength after its prior sharp decline around 3.1 Ga, which attests to an active lunar dynamo at ca. 2.8 Ga in the mid-early stage and argues against the suggestion that the lunar dynamo may have remained in a low-energy state after 3 Ga until its demise. The result suggests the lunar dynamo was most likely driven by either a basal magma ocean and/or precession, probably supplemented by other mechanisms such as core crystallisation.

月球发电机的演化对于破译月球^1-4 的深层内部结构、热历史和表面环境至关重要。以前对从月球近侧返回的样本进行的古地磁研究已经确定了月球磁场的一般变化^5-7。然而，有限的空间和时间古地磁限制使月球发电机的演化变得模糊不清。嫦娥六号任务返回了第一批可追溯到大约 28 亿年前 （Ga）^8,9 的远侧玄武岩，为研究全球月球发电机演化中的关键时空差距提供了独特的机会。在这里，我们报告了从嫦娥六号玄武岩中回收的古强度 （~5–21 μT），为月球背面的磁场提供了第一个约束，并在 3 和 2 Ga之间的大间隙内提供了一个临界锚点。新结果记录了场强在之前在 3.1 Ga 左右急剧下降后反弹，这证明了在早期中期活跃的月球发电机约为 2.8 Ga，并反驳了月球发电机在 3 Ga 之后可能一直保持低能量状态直到其消亡的说法。结果表明，月球发电机很可能是由基底岩浆海洋和/或岁差驱动的，可能还辅以其他机制，如岩心结晶。