In what’s now Chile and Peru, a hunter-gatherer society called the Chinchorro had been mummifying their community members—men, women, children, even fetuses, and not just kings and the elite—as far back as 5050 B.C. based on radiocarbon dating. That’s at least two thousand years earlier than the mummification of ancient Egyptian pharaohs. But in the last decade, these mummies—the oldest man-made mummies in the world—have begun to decompose, and at an alarming rate. In some cases, these millennia-old mummies were rapidly turning into black ooze. Now, an examination of the decaying mummies reveals how rising humidity levels are to blame.
“In the last ten years, the process has accelerated,” says Marcela Sepulveda from the University of Tarapacá. Nearly 120 Chinchorro mummies are housed in the university’s San Miguel de Azapa Museum in Arica, Chile. The elaborate process begins with an extraction of the brains and organs. The body would then be reconstructed with fibers, and the skull cavity would be filled with straw or ash. The parts would then be sewed back together using reeds, with a stick keeping the spine straight and attached to the skull. Afterwards, an embalmer would restore the skin, sometimes using patches of sea lion skins, and the entire mummy was then covered with a paste. Over the 3,000 years of Chinchorro mummy-making, the paste has changed from manganese to ocher to mud.
To find a way to stop the deterioration, Harvard’s Ralph Mitchell and colleagues first had to figure out what was causing it. “We knew the mummies were degrading but nobody understood why,” Mitchell says in a news release. “This kind of degradation has never been studied before.”
After examining samples of both damaged and undamaged skin, the team discovered that the degradation was due to the mummies’ microbiome. The researchers then isolated the microbes present on the skin and cultured them in the lab. Before subjecting the precious samples to tests, they experimented with pig skin and found that the skin surrogates (complete with microbes) begin to degrade after 21 days of high humidity. When they repeated the tests with the actual mummy skins, they confirmed that elevated moisture in the air was damaging.
“The key word that we use a lot in microbiology is opportunism,” Mitchell explains. “With many diseases we encounter, the microbe is in our body to begin with, but when the environment changes it becomes an opportunist.”
And humidity levels in Arica have been on the rise, according to Sepulveda. The ideal humidity range is between 40 and 60 percent. Below that, acidification could damage the mummies, but above that, “the native microorganisms are going to chew these guys right up," Mitchell tells Live Science.
However, while this can be controlled in a museum, “how do you preserve them outside the museum?” Mitchell asks. “Is there a scientific answer to protect these important historic objects from the devastating effects of climate change?” Hundreds of these 7,000-year-old mummies might still be buried beneath the sandy surface of those coastal valleys.
Images: Vivien Standen (top, second), Marcela Sepulveda (third)