A unique event in Earth's history: the eruption of Vesuvius turned human brains into glass (video).

A new analysis of the remains of a victim of the Vesuvius eruption reveals that a piece of dark glass found in their skull was once their brain, vitrified in an extremely rare set of circumstances. Scientists believe that something like this happened only once in the planet's history — in the city of Herculaneum in 79 AD, reports Science Alert.

According to the lead author of the study, volcanologist Guido Giordano from Roma Tre University in Italy, he and his colleagues conducted a comprehensive chemical and physical characterization of the material taken from the skull of the Vesuvius eruption victim. The results provide compelling evidence that the skull contains remnants of a human brain made of organic glass formed at high temperatures. Notably, this is the first instance in history where scientists have managed to document such a preservation process for human or animal tissues.

Theoretically, anything that can melt can turn into glass. However, in reality, the conditions under which this can occur with organic matter are so rare that the remains of the person from Herculaneum are the only confirmed case.

The remains of the Vesuvius victim were first discovered only a few years ago. At that time, scientists were quite surprised and could only arrive at one conclusion as to why a human skull might contain a piece of glass. They suggested that the glass was actually once the victim's brain — unfortunately, the scientific community received such conclusions with a degree of skepticism.

In the new study, scientists re-examined these conclusions and arrived at the same result. Moreover, they discovered a method by which verification could have occurred. The main issue with the vitrification of organic materials is that they need to be rapidly heated and rapidly cooled before the solidifying material has the chance to organize its atoms into a crystalline structure.

During the analysis, scientists extracted glass samples from the skull and spine of the Vesuvius eruption victim and subjected them to a series of analytical methods, including scanning electron microscopy, differential scanning calorimetry, and energy-dispersive X-ray spectroscopy.

The sample revealed well-preserved neurons, axons, and other neural structures, which aligns with previous results published back in 2020. The authors of the study also determined that the man's brain must have been rapidly heated to a temperature of at least 510 degrees Celsius and quickly cooled shortly thereafter. This indicates that pyroclastic flows from the eruption — a rapidly moving, high-density mixture of volcanic gas, ash, and other materials — could not have caused the vitrification, as they reached a maximum temperature of only 465 degrees Celsius.

However, there is another type of pyroclastic flow that could have created a glass brain. Based on observations of volcanic eruptions today, the first destructive event of the eruption could have been an overheated ash cloud that spread from Vesuvius and dissipated within minutes, catching the unfortunate victim in its path.

It is suggested that such a cloud could have exceeded the threshold of 510 degrees Celsius necessary for the victim's brain to vitrify without destroying it. Following this, the cloud could have dissipated quickly enough to ensure the cooling of the brain.