A paper published today in Scientific Reports, authored — amongst others — by Francesco Sirano, Director of Herculaneum archaeological site, and Pier Paolo Petrone, Forensic Anthropologist at the University of Federico II of Naples, Italy, reveals how “protein fingerprints” in the bones of the victims of the eruption of 79AD survived differently in Pompeii and Herculaneum.
The study considers how the post mortem chemical modifications in bone proteins were affected by the conditions caused by the eruption, with a specific focus on the role played by the victims’ exposure to the high temperatures of the pyroclastic surges.
Bones and their Protein Fingerprints
Bones are one of the most abundant biomaterials in the archaeological record. They are also time capsules, preserving details of an individual’s life and death — making bones a valuable source of information about conditions in the past.
Of crucial importance to this information is bone proteins, which contain information about how people lived and died — and unlike DNA, it has greater longevity. “Archaeologists and anthropologists are increasingly turning to ancient proteins to ask questions about history, “explained Dr. Petrone.
However, it is not just the proteins that have a story to tell; their survival rate also offers up valuable information. While proteins can survive intact in ancient bones, the older the bones, the more the proteins degrade, with only collagen remaining in most bone samples over 20,000 years old. Furthermore, certain conditions can “speed up” this protein degradation, including burials in acidic conditions that speed up microbial action.
So, conditions after death can dictate how well proteins survive — and to what extent — meaning the chemical modification of proteins can reveal information about the past.
In this latest study, the effects of the application of heat was of particular interest.
The Bones of Pompeii and Herculaneum
Pompeii and Herculaneum are excellent sources of bones to study. Remains are plentiful, well preserved, and from individuals whose lives and deaths are contemporary with each other.
Each site was also subject to slightly different conditions during and immediately after the eruption of 79 AD, giving scientists variables to consider. In Herculaneum, victims in the harbourside boathouses and the beach were killed by a pyroclastic surge of around 500 degrees Celsius, which caused the immediate destruction of the soft tissues of the victims. This was followed by a period of rapid cooling and the burial of the victims in ash. These ashy burials were then preserved in the waterlogged conditions of the immediate environment.
In contrast, in Pompeii, the temperatures of the surges that killed most of the victims were 200 degrees cooler — hot enough to kill but also cool enough to maintain the soft tissues. This meant ash formed a hard case around the bodies of the victims, where soft tissues could slowly decompose. The burial conditions in Pompeii were also less consistently wet.
A sample of bones from the necropolis of Baia Scalandrone was also considered. Contemporary with the victims of Vesuvius, these bones were not exposed to the eruption but still on a burial ground of volcanic origin, therefore having similar soil conditions to Pompeii and Herculaneum.
The Secrets of the Bones
Protein degradation in all three sets of bones was analysed with surprising results. For the results showed that the bone protein of the victims in Herculaneum were better preserved than in Pompeii — despite the higher temperatures the victims in Herculaneum were exposed to.
In fact, protein preservation in the Pompeii bones was of a lower level than the control sample from Baia, which showed a similar level of preservation to those from Herculaneum.
Therefore, the high eruption temperatures did not seem to have had the expected adverse effects. So what other factors were at play?
Heat vs The Environment
The burial conditions and soil type seem to have played the most significant role in determining whether the bone protein of the victims of Vesuvius was preserved or destroyed.
The predominant soil type of all three sites was alkaline — a soil condition generally associated with good bone preservation. The Baia site showed marked alkaline soil compared to the moderate alkalinity around Pompeii and Herculaneum. This factor explained the good protein preservation in Baia — but not the reason for the variance between the other two sites.
Instead, this variance can be explained by the different burial conditions in Pompeii and Herculaneum. For whereas the soft tissues of the bodies of Pompeii decomposed slowly in an alternating wet-dry cycle that aided microbial action, leading to rapid degeneration of proteins, the constantly waterlogged conditions of the bodies in Herculaneum protected them from detrimental microbial activity.
So what is the significance of this discovery? According to Dr Petrone, it is discovering that the “hydrogeological factors” of the burial environments were crucial to bone protein survival — rather than the issue of heat intensity. In Dr Petrone’s opinion, these findings “shed new light on a different interpretation of the evidence hitherto considered about the burial of bodies in 79 AD volcanic ash deposits.”
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