“We could see them under the microscope, inside the lungs,” Zimmerman says.

But were these “zombie” bacteria? Could they come back to life and infect other people? Zimmerman tried to revive the bacteria. He took a smidge of tissue from the lungs. Warmed it up. Fed it.

“But nothing grew,” Zimmerman says. “Not a single cell.”

Zimmerman says he wasn’t surprised the bacteria were dead. Pneumonia bacteria have evolved to live in people at body temperature, not cold soil.

“We’re dealing with organisms that have been frozen for hundreds of years,” he says. “So I don’t think they would come back to life.”

But what about viruses — like smallpox or the 1918 flu? “I think it’s extremely unlikely,” Zimmerman says.