For thousands of years, the mummies lay buried beneath the sands of the Atacama Desert, a volcanically active region along the northern Chilean coast with virtually no rainfall.
When the first ones were discovered 100 years ago, archaeologists marveled at the ancient relics, some of them fetuses, their little bodies amazingly intact.
But now the mummies, which are believed to be the oldest on Earth, are melting.
Mariela Santos, curator at the University of Tarapaca museum here, noticed a few years ago that the desiccated skins of a dozen of the mummies were decomposing and turning into a mysterious black ooze.
"I knew the situation was critical and that we'd have to ask specialists for help," said Santos, whose museum stores and displays the so-called Chinchorro mummies, which date back as far as 5000 BC and are among archaeology's most enigmatic objects.
Within weeks, university staff members had contacted Harvard scientist Ralph Mitchell, an Ireland native who specializes in finding out why relics are falling apart.
A bacteria sleuth of sorts, Mitchell has taken on assignments that included identifying a mysterious microflora breaking down Apollo spacesuits at Washington's National Air and Space Museum, analyzing dark spots on the walls of King Tut's tomb and studying the deterioration of the Lascaux cave paintings in France.
Mitchell launched an investigation of the mummies' deterioration and this year issued a startling declaration: The objects are the victims of climate change.
He concluded that the germs doing the damage are common microorganisms that, thanks to higher humidity in northern Chile over the last 10 years, have morphed into voracious consumers of collagen, the main component of mummified skin.
Mitchell believes that the case of the disintegrating Chinchorro mummies should sound a warning to museums everywhere.
"How broad a phenomenon this is, we don't really know. The Arica case is the first example I know of deterioration caused by climate change," Mitchell said. "But there is no reason to think it is not damaging heritage materials everywhere. It's affecting everything else."
Conservation of the fragile mummies has been a constant concern of researchers and curators since German researcher Max Uhle's archaeological expedition to Arica ended in 1919.
Named after the nearby beach district where Uhle uncovered them, the Chinchorro mummies — about 120 of which are at the museum — are considered special for many reasons in addition to their age.
The community that made them was at the early hunter-gatherer stage of social evolution, compared with more advanced mummy-making civilizations such as the Egyptians, who had progressed to agriculture and trade, said Bernardo Arriaza, a professor at the University of Tarapaca's Institute of Advanced Research.
"Chinchorro mummies were not restricted to the dead of the top classes. This community was very democratic," said Arriaza, who for 30 years has led archaeological digs on the 500-mile stretch of Chilean coastline where most of the mummies have been found.
Arriaza spends some of his days at a dig on a cliff overlooking Arica. A score of partially unearthed mummies, possibly of the same family, cover a sloping area about 50 feet across. It's one of many sites that construction has revealed, in this case digging for a pipeline.
Vivien Standen, an anthropology professor at Tarapaca and coauthor with Arriaza of dozens of papers on the Chinchorro mummies, said they are also unusual in that they include human fetuses.
"That's a very special facet, the empathy that it demonstrates, especially compared with modern times where fetuses are simply abandoned," Standen said.
Volcanic pollution of drinking water evident in the presence of arsenic in the mummies' tissue may hold the key to why the community began mummifying its dead.
"Arsenic poisoning can lead to a high rate of miscarriages, and infant mortality and the sorrow over these deaths may have led this community to start preserving the little bodies," Arriaza said. "Mummification could have started with the fetuses and grown to include adults. The oldest mummies we have found are of children."
Chinchorro mummies have survived into modern times only because of the arid conditions of the Atacama Desert, said Marcela Sepulveda, the university archaeologist who made the initial contact with Harvard's Mitchell.
Sepulveda said it was possible that other groups in Latin America were doing the same thing, "but what is unusual here is that thanks to the climate, the mummies have been conserved."
Arriaza and Sepulveda both direct laboratories with high-powered electron microscopes dedicated to the analysis of materials found on and around the mummies. Continued decomposition of the mummies jeopardizes their research, they said.
"Just raising them from the ground introduces the challenge of not breaking them," said Santos, the museum curator. "But over the last several years, the higher humidity — and how to deal with it — has presented a whole new challenge."
After months of growing cultures of microorganisms collected from the skins of the decomposing Chinchorro mummies and comparing their DNA with known bacteria, Mitchell identified the transgressors as everyday germs "probably present in all of us" that suddenly became opportunistic.
"It was a two-year project to identify and grow them and then putting them back on the skin to show what was breaking down," said Mitchell, a professor emeritus who donated his time to the Chileans.
Mitchell had used the same painstaking process to identify the bug causing stains on the walls of King Tut's tomb in Egypt, and to conclude that the germs weren't introduced after the tomb was discovered in 1922 but probably were on the walls of the crypt when the boy king was entombed about 1300 BC.
Similarly, Mitchell used microbial analysis to investigate the erosion of Maya monuments at Chichen Itza at the request of the Mexican government. He found that the application of a polymer coating, far from protecting the ancient carvings and buildings as intended, was actually abetting the destructive microorganisms that were causing the stone work to crumble.
He also has an ongoing project at the USS Arizona monument at Pearl Harbor, where bacteria that thrive in the oil leaking from the battleship's fuel tanks are accelerating the disintegration of the sunken World War II vessel.
Mitchell began specializing in microbial damage to cultural relics in the mid-1990s, when the Italian government invited him to look at widespread damage to centuries-old frescoes at churches and palaces.
He identified Italy's main problem as industrial pollution, and thus came to the sad conclusion he has arrived at several times since: Isolating the problem doesn't always lead to a practical solution.
Mitchell seems more optimistic in his work with the Chilean mummies. Over the next two years, he and the faculty at the University of Tarapaca will be working on possible solutions to the deterioration. He thinks humidity and temperature control offer the best chance of stabilizing the relics.
Mitchell and the archaeologists feel a sense of urgency: The Chilean government has budgeted $56 million for a new museum scheduled to open in 2020 to house the mummies, and everyone wants the right climate controls built in to the new structure to safeguard the relics.
"The next phase of the project is to look at how you protect the mummies and at possible physical and chemical solutions to the problem, which we don't have yet," Mitchell said. He and the Chileans will experiment with different combinations of humidity and temperature to determine an optimal ambience.
Optimally, each mummy will be encased in its own glass cubicle in the new museum and have its own "microclimate," Arriaza said. But the irony is not lost on him and his fellow archaeologists that mummies that survived millenniums in the ground are proving fragile in the face of changing conditions of modern times.
"I'm not optimistic we can save them," said Standen, the anthropology professor. "From the moment they are taken out of the ground, they start deteriorating."