In the shadow of Mount Vesuvius, a young man lay in bed as the world around him erupted into chaos. It was AD 79, and the volcano had unleashed its fury, burying the Roman towns of Pompeii and Herculaneum under layers of ash and molten rock. While most fled, this man stayed behind and decided to meet his fate in his bedroom—a circumstance that would leave his brain preserved in a way no one could have imagined.

Two millennia later, scientists analyzed his skull and found a black, glassy substance—it’s essentially fossilized brain tissue, vitrified by the intense heat of the eruption. It’s a chilling glimpse into the destructive power of Vesuvius and the unique conditions that turned human tissue into glass.

A Glass Brain

Glass rarely forms from organic materials. It requires a liquid to cool so rapidly that its molecules freeze into a solid, rigid structure that’s not quite a crystal nor a fluid. While volcanic glass like obsidian is common, the idea of human tissue turning into glass seemed almost impossible to comprehend—until now.

The young man’s remains were discovered in Herculaneum, a coastal town obliterated by Vesuvius. Found lying face down on a bed, his skull and spinal cord contained fragments of this mysterious glass. Researchers, led by volcanologist Guido Giordano of Roma Tre University, analyzed the samples and determined that the tissue had been heated to at least 510 degrees Celsius (950 degrees Fahrenheit) before cooling rapidly.

“The process of transformation of anything liquid into glass is the fast cooling, not the fast heating,” Giordano explained. “Obsidian glass forms when lava is very quickly cooled, for example, where it enters into water.”

But the pyroclastic flows—fast-moving currents of hot gas and volcanic material—that buried Herculaneum couldn’t have caused this transformation. Their temperatures, reaching up to 465 degrees Celsius (869 degrees Fahrenheit), were too low, and they cooled too slowly. Instead, the researchers point to an even deadlier force: a superheated ash cloud.

Unlike pyroclastic flows, which hug the ground, ash clouds are airborne and can dissipate quickly. Giordano and his team believe this cloud, with temperatures exceeding 510 degrees Celsius, engulfed Herculaneum in a matter of seconds, killing its residents instantly. The intense heat liquefied the man’s brain, and as the cloud dissipated, the rapid cooling turned it into glass.

The man’s skull and spine likely shielded his brain from complete thermal breakdown, allowing fragments of the glass to form. It has always been assumed that Vesuvius’s victims died as a result of pyroclastic flows. But these findings suggest that a menacing ash cloud may have been the first deadly event.

Not everyone is convinced. Alexandra Morton-Hayward, a forensic anthropologist at the University of Oxford, questions whether the glassy substance is indeed brain tissue. “Organic tissues, which are mostly water, can only be vitrified by rapid cooling to extremely low temperatures,” she told CNN, referring to cryopreservation techniques used in modern science.

Giordano, however, stands by the findings. Previous research has identified preserved neurons and proteins in the glass, confirming its organic origin. “There was no doubt that the glass was organic in origin,” he said.

For the young man who stayed behind, his final moments were both tragic and extraordinary. His brain, preserved as glass, now tells a story of fire, ash, and the fleeting nature of life in the shadow of a volcano.

The findings appeared in the journal Scientific Reports.