26 Cenozoic crater ages and geologic stages. [From data of but I have substituted Chicxulub.) This chart tacitly assumes cause and effect, which may be incorrect. It really asks this question: Does the age of each of the well-dated Cenozoic impact craters match that of a geologic stage boundary? Stothers concluded that the answer is yes, and at a confidence level of 98 percent to 99 percent.

A fruitful line of research to confirm his conclusion would be to select a significant number of craters whose ages appear to lie close to the 28-million- to 32-million-year periodicity, but where the age measurement errors are too large for certainty, and to launch an intensive dating program so as to determine the ages of those craters more precisely. Grieve estimates that in order to conduct a fair test, the age uncertainties would have to come down to no more than 10 percent of the age itself. In other words, for a 30-million-year-old crater, the uncertainty would have to be no worse than ± 3 million years, well within the reach of today's technology.21

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