Tough Tiny Mice Found Living on Frozen Volcano, Stunning Scientists

Tiny mummified mice have been found in one of the harshest environments on Earth, and scientists have been perplexed.

The presence of dead mice atop Andean volcanoes has been confusing scientists since the 1970s, when they were first discovered. The discovery of live ones has both added to the mystery and shed new light.

The volcanoes surpass 20,000 feet—and the temperatures never rise above freezing. At first, scientists believed they must have been brought up there by the Incas. But now, a new study, published in Current Biology, presents evidence that these tiny mice actually ascended these extremely harsh conditions on their own.

The Incas—who lived across pre-Columbian America from the early 13th century to the 16th—used to make pilgrimages to these Andeans summits, for Capacocha—a sacrificial rite. Scientists believed the mice may have been part of the animal sacrifices offered to the Incan gods—or, they may have hidden in their supplies.

Jay Storz, a Willa Cather Professor of biological sciences at the University of Nebraska–Lincoln said in a press release that you "can't fault" these archaeologists for thinking this, as nothing could be living up there.

"It is difficult to overstate how hostile these environments are. On the summits of >20,000 feet volcanoes, the temperature is never above freezing, gale-force winds are relentless, and each breath of air contains less than half the oxygen available at sea level," Storz told Newsweek.

Storz described the mice in a statement as "freeze-dried, mummified mice."

Living at Such Extreme Elevations

The scientists began to doubt the previous scientist's hypothesis when he found a live, leaf-eared mouse on the summit of Llullaillaco—a volcano that rises 22,000 feet and lies on the border between Chile and Argentina. It is the first mammal to be found living at such an extreme altitude.

More live mice were found, as well as dead bodies, across the neighboring volcanoes of Salín, Púlar and Copiapó. All of the volcanoes rise 4 miles above sea level.

Analysis of the mummies continues to confirm one thing: the mice got up there on their own.

Evidence for this came from measuring concentrations of carbon-14—an atom which decays at a set rate. By doing this with the mice mummies, they found that some of them had only died a few decades ago, while some at most, died 350 years ago, the study reports. This makes it impossible that they could have been carried there by the Incan empire, which died out a full century before the oldest mice were found.

"This particular species of leaf-eared mouse is one of the more common small mammals at high elevations in the Central Andes," Storz told Newsweek. "However, nobody had previously guessed that they were living at such extreme elevations, more than [20,000 feet] above sea level. Our record for a live-captured mouse is 22,109.58 feet from the summit of Volcan Llullaillaco (on the Argentina-Chile border)."

"Now, with the discovery of mouse mummies from the summits of several other [>20,000 feet] volcanoes in the same region, we have more evidence for the existence of long-term populations at extreme elevations. These live-captured and mummified mice represent the highest specimen-based records of mammals in the world...The discovery is important because such extreme elevations were previously thought to be completely uninhabitable by mammals."

But, this doesn't mean the mystery is completely solved.

Avoiding Predators?

Scientists are still perplexed as to how these tiny animals can survive in such hostile environments. The Puna de Atacama, of the Andes, is one of the harshest environments on Earth.

The study notes that NASA has even visited the area in preparation for Mars research.

"Even at the base of the volcanoes, the mice are living in an extreme, Martian environment," Storz said in a press release. "And then, on the summits of the volcanoes, it's even more so. It feels like outer space. It just boggles the mind that any kind of animal, let alone a warm-blooded mammal, could be surviving and functioning in that environment. When you experience it all firsthand, it even further impresses upon you: How in God's name is anything living up there?"

One hypothesis is that the mice retreat to these peaks to avoid predators. But this is still not confirmed.

"Certainly, if you're hunkering down on top of a 6,000-meter volcano, you're at least safe from that. You just have other things to worry about. But why they're ascending to these extreme elevations is still a mystery."

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