A 30,000 year slumber
In 2014, a team of French scientists led by Jean-Michel Claverie and Chantal Abergel announced a startling discovery from a 30-meter-deep sample of Siberian permafrost. They had found and revived a virus that had been dormant for 30,000 years, an era when Neanderthals still walked the Earth. The virus, named Pithovirus sibericum, is a "giant virus," a category of viruses so large they are visible under a standard light microscope. Measuring about 1.5 micrometers in length, it is larger than some bacteria.
The researchers used amoebas as bait to see if any viable viruses were present in the ancient ice core. When the single-celled organisms began to die, the team isolated the culprit: P. sibericum. The ancient virus was still infectious, readily invading and replicating within the amoeba hosts. This specific virus is harmless to humans, but its revival showed that viable, infectious pathogens can survive for geological timescales in the frozen earth.
The zombie virus record
Subsequent research has uncovered even older infectious agents. A 2022 study detailed the revival of 13 ancient viruses from several Siberian permafrost samples. The record-holder from this group is Pandoravirus yedoma, dated to 48,500 years old. It was found in a sample taken from under a lake in Yakutia, Russia. Like Pithovirus, Pandoravirus is a giant virus that only infects amoebas. Other viruses from the study were isolated from the 27,000-year-old remains of a woolly mammoth and the frozen intestines of a Siberian wolf.
These discoveries raise serious questions as the Arctic warms at a rate four times faster than the rest of the planet. Permafrost covers nearly a quarter of the land in the Northern Hemisphere and acts as a vast frozen reservoir of ancient microbes. While the revived amoeba-infecting viruses pose no direct threat, scientists are concerned that other pathogens, potentially harmful to humans or animals, could re-emerge as the ground thaws due to climate change and increased industrial activity in the Arctic. A 2016 anthrax outbreak in Siberia, linked to a thawed reindeer carcass, killed one child and thousands of reindeer, showing that the risk is not theoretical.