Progressive crystallization of Earth’s inner core drives convection in the outer core and magnetic field generation. Determining the rate and pattern of inner-core growth is thus crucial to understanding the evolution of the geodynamo. The growth history of the inner core is probably recorded in the distribution and strength of its seismic anisotropy, which arises from deformation texturing constrained by conditions at the inner-core solid–fluid boundary. Here we show from analysis of seismic body wave travel times that the strength of seismic anisotropy increases with depth within the inner core, and the strongest anisotropy is offset from Earth’s rotation axis. Then, using geodynamic growth models and mineral physics calculations, we simulate the development of inner-core anisotropy in a self-consistent manner. From this we find that an inner core composed of hexagonally close-packed iron–nickel alloy, deformed by a combination of preferential equatorial growth and slow translation, can match the seismic observations without requiring hemispheres with sharp boundaries. Our model of inner-core growth history is compatible with external constraints from outer-core dynamics, and supports arguments for a relatively young inner core (~0.5–1.5 Ga) and a viscosity >10¹⁸ Pa s.

地球内核的逐步结晶驱动外核的对流和磁场的产生。因此，确定内核增长的速率和模式对于理解地球发电机的演变至关重要。内核的生长历史可能记录在其地震各向异性的分布和强度中，这是由内核固流体边界条件约束的变形织构产生的。在这里，我们通过地震体波传播时间分析表明，地震各向异性的强度随着内核内部深度的增加而增加，并且最强的各向异性偏离地球自转轴。然后，使用地球动力学生长模型和矿物物理计算，我们以自洽的方式模拟内核各向异性的发展。由此我们发现，由六方密排铁镍合金组成的内核，通过优先赤道生长和缓慢平移的组合而变形，可以匹配地震观测，而不需要具有尖锐边界的半球。我们的内核增长历史模型与外核动力学的外部约束兼容，并支持相对年轻的内核（~0.5-1.5 Ga）和粘度> 10的论点¹⁸ 帕秒。