Permafrost is soil or sediment that remains frozen for most of the year. In the scientific world, permafrost is known for how well it can preserve bodies -- like that of Yuka, a baby wooly mammoth who was found with a remarkably well --preserved brain.

Unfortunately, permafrost does not only preserve harmless and informative things, as we can see from the recent anthrax outbreak in the Yamalo-Nenerts region this summer.

This past July was the hottest on record in Russia, meaning more of Siberia’s permafrost melted than usual. Permafrost normally only thaws between 30 and 60 centimeters deep. This year, permafrost thawed up to a full meter into the ground. As a result, carcasses that had once remained under the permafrost are beginning to come closer to the surface, and with them, any infections or illnesses they may have carried before freezing over.

This includes “zombie anthrax”, so called because it was found in the thawing body of a dead reindeer. Although it has not been seen in the region for 75 years, studies have shown that anthrax spores can remain viable for up to 105 years in the permafrost. This means that the anthrax in the reindeer carcass had not “died” yet when the corpse thawed. As a result, 40 people were infected, and a 12-year-old boy and at least 2,300 reindeer have died. The bodies of the infected animals will be incinerated to prevent further spread of the disease.

“Zombie anthrax” is not the only deadly disease potentially lurking under the ice. Smallpox victims of the 18th and 19th centuries are also buried in permafrost-covered cemeteries, and there is a possibility that even older diseases, even ones that potentially affected Neanderthals, may still remain viable in the region today.

Although researchers have already examined one smallpox graveyard along the Kolyma River and found no viable traces of disease, smallpox DNA "fragments" were present, so researchers agree that further examination is advisable to prevent another possible outbreak.