The breakup in space of a comet or asteroid prior to impact could produce a surface or oceanic impact by the largest object, and hundreds of smaller fragments could create air-bursts affecting an entire hemisphere (Bunch et al. 2012). Approximately 90% of all ejecta from the main impact would fall within five crater radii, although [...]
But why not France, Bos!?
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Independent investigators have failed to confirm the reports of enhanced concentrations of spherules and platinum-group elements in YD boundary sediments.
Boslough, Surovell et al., January 30, 2013, Arguments and Evidence Against a Younger Dryas Impact Event
Interhemispheric evidence of a cosmic impact [...]