1. Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, Colorado 80302, USA
2. Institute of Astronomy, Charles University, V Holeovikách 2, 18000 Prague 8, Czech Republic

Correspondence to: William F. Bottke¹ Correspondence and requests for materials should be addressed to W.F.B. (Email: bottke@boulder.swri.edu).

Abstract

The terrestrial and lunar cratering rate is often assumed to have been nearly constant over the past 3 Gyr. Different lines of evidence, however, suggest that the impact flux from kilometre-sized bodies increased by at least a factor of two over the long-term average during the past 100 Myr. Here we argue that this apparent surge was triggered by the catastrophic disruption of the parent body of the asteroid Baptistina, which we infer was a 170-km-diameter body (carbonaceous-chondrite-like) that broke up Myr ago in the inner main asteroid belt. Fragments produced by the collision were slowly delivered by dynamical processes to orbits where they could strike the terrestrial planets. We find that this asteroid shower is the most likely source (>90 per cent probability) of the Chicxulub impactor that produced the Cretaceous/Tertiary (K/T) mass extinction event 65 Myr ago.

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