More than two dozen "surreal" viruses like nothing ever seen before have been found in ice dug up from a remote part of western China.
And half of them survived the almost 15,000-year ordeal, uniquely adapted to the "extreme environment" on the Tibetan Plateau.
"These viruses have signatures of genes that help them infect cells in cold environments - just surreal genetic signatures for how a virus is able to survive in extreme conditions," said Ohio State University microbiologist Matthew Sullivan, co-author of a new study looking at the ancient microbes.
The viruses were dug up in 2015 from ice 6.7km above sea level - just a couple of kilometres lower than the world's tallest peak, Mt Everest, located to the south.
"These glaciers were formed gradually, and along with dust and gases, many, many viruses were also deposited in that ice," said the study's lead author Zhi-Ping Zhong, also of Ohio State University.
Thirty-three different viruses were found in the sample, 28 of them new to science. It's just the third time scientists have ever successfully identified viruses in ancient glacial ice.
"We know very little about viruses and microbes in these extreme environments, and what is actually there," said professor of earth sciences at Ohio State University Lonnie Thompson, the study's senior author.
Figuring out exactly what the viruses are will be difficult, they say, because unlike other lifeforms - such as plants and animals - different viruses don't always share common genes. It appears though they evolved in plants, not animals or humans.
It's hoped the technology and methods developed to study these new viruses will assist in the hunt for life in other extreme environments - including Mars.
"The method that Zhi-Ping developed to decontaminate the cores and to study microbes and viruses in ice could help us search for these genetic sequences in other extreme icy environments," said Dr Sullivan.
The research will also help scientists figure out what might happen to microbial life and viruses as the world's climate warms. The Tibetan Plateau itself has lost about a quarter of its ice in the past 50 years.
"The documentation and understanding of that is extremely important: How do bacteria and viruses respond to climate change?" said Dr Thompson. "What happens when we go from an ice age to a warm period like we're in now?"
The study was published in journal Microbiome.