Professor Mike Baillie believes a large portion of it fell into the Celtic Sea. (It may have been spread out over a large area though) The Dark Ages were worldwide. Astronomers Clube and Napier speak of it in their book Cosmic Winter.
Baillie believes that all the dragon imagry in Beuwolf is about this event.
Always wondered about the red dragon and the white dragon, who hasn't. Perhaps it was alchemical before the Arabs invented alchemy, perhaps it was astronomical, perhaps both. There were dragons elsewhere in the world, too, China had them and still does for one.