An erupting volcano turned a young man's brain into glass, researchers say
Archaeologists have previously discovered human brains preserved in a variety of ways, including drying, freezing and tanning. Some preserved brains even resemble soap.
But now they've found something new: a brain that turned into glass.
In a paper published Thursday in the journal Scientific Reports, archaeologists and volcanologists show that the shards of black glass found in the skull of a young man who died when Mount Vesuvius erupted in 79 AD are his vitrified brain.
"This is totally counterintuitive," said Guido Giordano, a volcanologist at the Roma Tre University, a public research university in Rome.
"Under normal conditions, you cannot vitrify any organic tissue unless you drop it to well below zero very quickly. But then when it returns to ambient temperature it reverts," he said.
But after doing extensive testing on the black material, they were able to conclusively prove it was indeed vitrified tissue – the man's brain and parts of his spinal cord had turned into glass.
How did this man's brain turn to glass?
In 79 AD, Italy's Mount Vesuvius erupted, utterly destroying the towns of Pompeii and Herculaneum over two days.
On the first day of the eruption, Pompeii was covered in ash and falling debris, but nearby Herculaneum got only a light dusting of ash.
"The first few hours of the eruption of Vesuvius were scary enough to cause most of the people in Herculaneum to flee and search for rescue by the city harbor," Giordano said. "But during the night, the first pyroclastic flow was ejected from the volcano, a turbulent mix of ash, pumice and super hot gasses, and hit Herculaneum."
Most of the people were at the seashore when the first pyroclastic flow arrived because they were likely waiting for rescue. They died when the roiling cloud of hot ash hit.
But inside the Collegium Augustalium, a young man of about 20 years was lying in his wooden bed. The Collegium, located on the city's main street, was a public building dedicated to the worship of Emperor Augustus.
What happened next, as conjectured by the scientists, is as dreadful as it is fascinating.
The ash cloud that burst out of Mount Vesuvius was, at its core hot, heavy and deadly. "It's like a landslide. That material is able to knock down houses," Giordano said.
But at the cloud's edges, things are different. It was a deadly haze of superheated gray ash that billowed through the nearly empty town, reaching temperatures of between 1,000 and 1,100 degrees.
It was similar to the ash cloud from the 2018 eruption of Volcán de Fuego in Guatemala, which killed at least hundreds of people.
"In Herculaneum, this ash cloud engulfed the city, hot enough to kill people and raise the temperature of their bodies to above 500 or 600 degrees Celsius (between 930 and 1,100 degrees Fahrenheit)," Giordano said.
The young man would have died instantly. But what happened to his brain was remarkable – the only such case ever encountered by archaeologists.
Almost as soon as it swept through the town, the cloud dissipated. Modern examples of such clouds can disappear within a minute. In Herculaneum, it left only a thin layer of ash on the body and in the room, less than 1 inch.
The temperatures inside of the ash cloud would have been expected to burn up the body and destroy all soft tissues. But it came and went so rapidly that there wasn't time. Instead, scientists believe, the body very quickly cooled back down to the ambient evening air temperature.
"It needed to have first a rise in temperature well above 510° Celsius (950 degrees Fahrenheit), an event that is very fast and then very fast cooling," he said. This caused his brain to turn into glass during the cooling, locking in its structure.
"Inside the skull, there were all these black, shiny fragments," Giordano said. "They look like chips of obsidian, black, shiny and spiky."
Some time later, the next wave of pyroclastic flow reached Herculaneum and the entire town was entombed in as much as 60 feet of ash and debris from the volcano.
While the young man's body was initially excavated several years ago, archaeologists weren't sure exactly what was in the skull. By testing fragments of what was found, they were able to prove that it was indeed brain tissue and that it was indeed glass.
How are brains typically found in archaeological digs?
Given how delicate they are, preserved brains are not as uncommon as might be expected in the archaeological record.
A study published in March of last year by scientists at Oxford University found 4,405 examples of human brains being preserved, some of which were more than 12,000 years old. They included brains from Egyptian and Korean royalty, British and Scandinavian monks, Arctic explorers and a large number of bodies from the Middle Ages that were removed from the largest cemetery in Paris before the French Revolution.
Those scientists found five types of brain preservation:
◾Dehydration (often in desert climates).
◾Freezing (Arctic explorers and some freeze-dried mummies, especially in the Andes).
◾Tanning (bodies preserved in acidic, tannin-filled bogs).
◾Saponification (sometimes called "grave wax" this is when the fats in the brain turn to a soap-like clump).
◾An unknown process, often found as some brain soft tissue preserved among otherwise skeletonized remains, commonly in the presence of clay and iron.
The identification of the young Herculaneum man's brain as having turned to glass adds a new – and vanishingly rare – possibility to the list.
As far as the researchers know, "it's the only time this has occurred," Giordano said.