Intense heat generated by Mt. Vesuvius’ eruption turned one victim’s brain to glass. While gruesome, the finding published in the journal Scientific Reports, lends insight into the chaotic events that fatal day in A.D. 79.

Although the eruption was a singular event, it killed people in multiple manners. Many Pompeii people suffocated from breathing in toxic fumes from a cloud of gas and ashes. Some may have been crushed by falling objects during an earthquake that may have preceded the event. Others were buried in hot lava. But the victim with the glass brain was unlucky in a specific way.

Scientists have earlier concluded that the “wall of death” cloud of ashes and gasses known as a pyroclastic flow claimed many lives. But it didn’t kill this particular individual. How do they know?

Heat of Mt. Vesuvius Eruption

It comes down to temperature, researchers conclude in the study. The conditions necessary to form glass are highly specific. Turning organic materials into glass requires a temperature above 510 degrees Celsius, followed by a rapid cooling period. The pyroclastic flows that buried Herculaneum likely didn’t exceed 465 degrees Celsius and probably cooled slowly.

“It would therefore be impossible to find organic glass embedded in volcanic deposits that have reached several hundred of Celsius degrees,” according to the paper.

The man with the glass brain was first discovered in 2020 and initially puzzled scientists because of its singularity; no other Vesuvius victim’s brain underwent a similar transformation. A team of scientists led by Guido Giordano analyzed pieces of glass from inside the man’s skull using a variety of imaging techniques, including x-rays and electron microscopy.

The imaging, which also included the skull, revealed proteins and fatty acid associated with brain tissue. The part of the brain that had been transformed into glass appeared “black and shiny, obsidian-like,” according to the paper.

Super-Heated Ash Cloud

The combined imaging data — and knowledge of the conditions required to turn organic material into glass — led them to the 510 degrees Celsius temperature. But they were still unsure what caused it — particularly since the pyroclastic flow was almost certainly cooler.

They turned to more recent volcanic eruptions for inspiration. They concluded that a super-heated ash cloud marked the first wave of Vesuvius’s eruption. Such a cloud would have appeared suddenly, then dissipated almost as quickly. The victim’s skull likely prevented the brain from completely melting away.

The only bit of good fortune for the victim was that, since his body was found on a bed, he was likely asleep. The cloud probably materialized so quickly that he didn’t have time to see it coming. He literally didn’t know what hit him.

Read More: Revisiting Human Remains at Pompeii Rewrites the Story of Mt. Vesuvius’ Victims

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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.