Abstract: Contrasting the curve derived from the theory of the evolution of the earth-moon system with the ones based on the analysis of the shelly fossils distributed over the period from Ordovician to modern time reveals great discrepancy. Two turning points exist in the curves based on data analysis. The times of these two points coincident with the occurrence of the largest two extinctions in Permian-Triassic and Cretaceous-Tertiary, which is extensively believed to be results of the extraterrestrial impact. Further analysis on the sedimentary facies of these two boundaries throughout the world, which are previously thought of as a world-wide regression provide us more eloquent records. The mutation of interaction and the phase lag between the earth and the moon caused by extraterrestrial impact, from which the obvious mutation of the torque of the tidal force resulted, give us a reasonable interpretation on these two turning points.

Key words: paleontological clock, earth-moon system, extraterrestrial impact, tidal force torque

摘要： 通过对比地球自转速率变化的理论曲线与由古生物钟得到的实际曲线，发现实际曲线上存在的两个转折点正好与地质历史时期中的两次生物大绝灭事件基本一致，结合对事件层上下地层沉积相突变的研究，得出的结论是：由古生物钟得到的地球自转速率变化曲线中的两个转折点是由小行星撞击事件造成的。

关键词: 古生物钟, 地月系统, 撞击事件, 引潮力力矩