Three devastating outbreaks have previously been linked to the plague by historical records and DNA studies. The First Pandemic began with the Plague of Justinian around A.D. 541 and killed up to 100 million people. The Second Pandemic included the 14th-century Black Death, responsible for killing some 30 to 50 percent of Europeans. And the Third Pandemic, which arose in China during the 1850s, lasted until the mid-20th century.
But when researchers sequenced DNA from the teeth of Bronze Age humans from Eurasia, they found genetic signs of the bacterium that causes plague, Yersinia pestis, in 7 out of 101 individuals tested. That means the plague was infecting people at least 4,800 years ago—some 3,300 years earlier than is known from the historical record.