Scientists pulled a microscopic animal they dubbed a “zombie worm” from Siberian permafrost, thawed it, and watched it wake up and reproduce. The organism had been frozen since the Late Pleistocene, back when woolly mammoths were still a thing. It took a nap for 24,000 years and came back as if nothing had happened.

The creature is a bdelloid rotifer, a tiny multicellular animal about half a millimeter long, usually found in freshwater environments. They’re already known among scientists for being nearly indestructible—surviving radiation, dehydration, extreme cold, and low oxygen. Researchers from Russia’s Soil Cryology Laboratory drilled down about 11.5 feet into the Alazeya River region of northeastern Siberia, pulled a core sample, and carbon-dated it to between 23,960 and 24,485 years old. Then they thawed it.

The rotifer not only moved but also reproduced asexually, creating more just like it. The thing freaking cloned itself. Scientists barely had time to track which organisms were ancient and which were new offspring before the population expanded.

A Tiny Frozen ‘Zombie Worm’ Woke Up After 24,000 Years and Started Having Babies

The survival mechanism is called cryptobiosis, a state where metabolic activity drops to nearly zero. The organism goes into a kind of biological suspension—not dead, not alive in any meaningful way, just waiting. They suspend their metabolism and accumulate certain compounds, such as chaperone proteins, that help them recover from cryptobiosis when conditions improve, lead researcher Stas Malavin said in a statement.

“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,” Malavin said.

What makes this a real breakthrough is the organism’s sophistication. Single-celled life and simpler structures have been revived from ice before. A multicellular animal with a digestive tract and a rudimentary nervous system that has survived 24 millennia frozen solid is a different matter entirely. The previously known limit for bdelloid rotifers in a cryptobiotic state was around six to ten years. This extends that window by a factor of roughly 2,400.

There’s a less thrilling detail in all of this. As permafrost melts at an accelerating rate, ancient microbes, bacteria, and viruses locked in that ice for thousands of years are getting out. None of the thawed viruses studied so far has been linked to human illness, but scientists are watching the situation carefully. A 24,000-year-old rotifer waking up in a controlled lab is a fascinating result. The same process happening across thousands of miles of thawing arctic ground is a different conversation.

As for whether this brings us closer to human cryopreservation, researchers aren’t sure. Rotifers are relatively simple. Humans are not. The cellular damage involved in freezing and reviving a mammal remains a problem nowhere near solved. The gap between a half-millimeter freshwater invertebrate and a person is, scientifically speaking, enormous.

Still, a creature born during the Ice Age just had babies in a Russian laboratory. That’s pretty wild.