The sharp dip shortly after 1000 A.D. is due to
The sharp dip shortly after 1000 A.D. is due to Black Death. The Black Death was one of the most destructive diseases in human history, resulting in the deaths of an estimated 75 to 200 million people and peaking in Europe in the years 1346–53. It was an epidemic plague which is caused by a bacterium (Yersinia pestis) transmitted to humans from infected rats by the oriental rat flea.