Tardigrades have competition in the realm of microscopic and incredibly sturdy beasties. Like tardigrades, Bdelloid rotifers can also survive drying, freezing, starving, and even low-oxygen conditions. Now, scientists report that they revived some of these rotifers after having been frozen in Siberian permafrost for at least 24,000 years.

The incredible observations are reported in the journal Current Biology. The researchers took samples of permafrost about 3.5 meters (11.5 feet) deep and slowly warmed the sample, which led to the resurrection of several microscopic organisms including these tiny little animals.

"Our report is the hardest proof as of today that multicellular animals could withstand tens of thousands of years in cryptobiosis, the state of almost completely arrested metabolism," co-author Stas Malavin of the Soil Cryology Laboratory at the Institute of Physicochemical and Biological Problems in Soil Science in Pushchino, Russia, said in a statement.

The team specializes in studying frozen organisms in the permafrost and was very careful in extracting this sample. Given the resilience of these animals, it was important to make sure that the sample was not contaminated with more recent layers. The age of the permafrost, and the creatures frozen within it, was also determined with other independent means such as radiocarbon dating.

Rotifers have been reported in scientific literature to be able to survive for up to 10 years when frozen. Clearly, the mechanism that allows them to withstand such conditions is even better than previously thought possible.

Scientists are not sure how the critter and other similar organisms can protect their cells and organs from the ice crystals that form during the freezing process. The creatures should be ripped apart, but they are not. Something extremely peculiar must be happening in these tiny animals as they are slowly frozen.

Rotifer recovering from week-long cryptobiosis in the lab. Video credit: Lyubov Shmakova. 

"The takeaway is that a multicellular organism can be frozen and stored as such for thousands of years and then return back to life – a dream of many fiction writers," Malavin added. "Of course, the more complex the organism, the trickier it is to preserve it alive frozen and, for mammals, it's not currently possible. Yet, moving from a single-celled organism to an organism with a gut and brain, though microscopic, is a big step forward."

The rotifers discovered not only came back to the land of the living but were also able to reproduce asexually via parthenogenesis. The team will continue to study the permafrost to see if more animals with these skills exist and to discover what mechanism comes into play to let an organism survive frozen for thousands of years.