Evidence from crater ages for periodic impacts on the Earth

Recent evidence has indicated that the impact of a comet or asteroid may have been responsible for mass extinction at the ends of both the Cretaceous and the Eocene. Quantitative analysis by Raup and Sepkoski showed that mass extinctions occur with a 26-Myr period, similar to the period seen in qualitative pelagic records by Fischer and Arthur. To account for the possibility of periodic comet showers, Davis et al. proposed that such showers could be triggered by an unseen solar companion star as it passes through perihelion on a moderately eccentric orbit. To test a prediction implicit in this model we examined records of large impact craters on the Earth. We report here that most of the craters occur in a 28.4-Myr cycle. Within measurement errors, this period and its phase are the same as those found in the fossil mass extinctions. The probability that such agreement is accidental is 1 in 10