A tiny purple bug discovered three kilometres under Greenland ice has been reawakened from a slumber lasting more than 100,000 years.
Scientists believe the unusual bacterium, named Herminiimonas glaciei, may hold clues to life on other planets.
Researchers coaxed the dormant frozen microbes back to life by carefully warming the ice samples containing them over a period of eleven-and-a-half months.
As the bugs awakened and began to replicate, colonies of very small purple-brown bacteria started to appear.
H. glaciei belongs to a rare family of "ultramicro" bacteria that live in extreme environments.
It is tiny even for bacteria, being 10 to 50 times smaller than the food bug Escherichia coli (E. coli).
Dr Jennifer Loveland-Curtze, who led the US team at Pennsylvania State University, said: "These extremely cold environments are the best analogues of possible extraterrestrial habitats.
"The exceptionally low temperatures can preserve cells and nucleic acids for even millions of years. H. glaciei is one of just a handful of officially described ultra-small species and the only one so far from the Greenland ice sheet; studying these bacteria can provide insights into how cells can survive and even grow under extremely harsh conditions, such as temperatures down to -56C, little oxygen, low nutrients, high pressure and limited space."
She stressed that H. glaciei was not harmful to humans - which was just as well since it can pass straight through safety filters commonly used in laboratories and hospitals.
But she added that if harmful, or pathogenic, super-small bugs existed they would be hard to detect.
"If there are other ultra-small bacteria that are pathogens, then they could be present in solutions presumed to be sterile," she said. "In a clear solution very tiny cells might grow but not create the density sufficient to make the solution cloudy."
The bugs were extracted from a 120,000 year-old three kilometre-deep core sample drilled from glacier ice in Greenland.
Filling a volume of just 0.043 cubic micrometres, they consisted of thin rods with up to three long whip-like attachments called flagella.