Inference to the Only Explanation: The Case of the Cretaceous/Paleogene Extinction Controversies

In the sciences of the deep past, it is taken for granted that the hypothesis that offers the best explanation is the best confirmed. I examine in detail the debate over the K/Pg mass extinctions that began in 1980 with the publication of the paper by Alvarez et al. that proposed the impact extinction hypothesis. I summarize this debate and show how the impact hypothesis eventually achieved consensus as the best explanation. I then consider the relevance of that case study to an evaluation of the employment of inference to the best explanation (IBE) in the earth sciences. I first reject a number of the standard objections to IBE and then strongly endorse John Norton’s claim that no form of ampliative inference can receive a priori justification. Nevertheless, drawing on the case study and other instances, we may identify four “abductive virtues” that characterize many of the most successful instances of IBE, making them attractive and even compelling.