Multiple comet impacts around 1500 years ago triggered a "dry fog" that plunged half the world into famine. Historical records tell us that from the beginning of March 536 AD, a fog of dust blanketed the atmosphere for 18 months. During this time, "the sun gave no more light than the moon", global temperatures plummeted and crops failed, says Dallas Abbott of Columbia University's Lamont-Doherty Earth Observatory in New York... Now Abbott and her team have found the first direct evidence that multiple impacts caused the haze. They found tiny balls of condensed rock vapour or "spherules" in debris inside...