The second period of the Mercurial geologic timescale, lasting from 3900–3850 Ma ago, during which the late heavy bombardment continued and many of the smaller basins on the surface of Mercury formed.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。