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A major interdisciplinary debate has been in progress over the last few years regarding the cause for the mass extinction of a large number of species, including the dinosaurs, at the end of the Cretaceous Period of geologic history (∼ 65 million years ago). One important theory under discussion is that the event was triggered by the collision with Earth of an extraterrestrial object, such as an asteroid or comet of ∼10-km diameter.