Heating and resin impregnation influence protein recovery and ZooMS identification of bone

In the quiet layers of the earth, archaeologists often find the charred remains of ancient meals, hearths, and rituals. These burned bones tell stories of what people ate, how they cooked, and even how they honored their dead. For a long time, identifying these fragments was a game of visual clues: a blackened edge might suggest a fire, while a white, chalky piece indicated intense heat. But fire is a destructive force. It shatters bone into tiny, unrecognizable pieces and, scientists have long believed, it cooks away the very molecules needed to identify the animal species. The prevailing wisdom was that once bone is burned, the proteins inside—the biological building blocks that carry an animal's genetic signature—are destroyed beyond recovery. This assumption has left a gap in our understanding of the past, as many of the most interesting fire-related finds remain anonymous.

A new study challenges this assumption, offering a clearer path forward for reading the stories hidden in burned bone. Researchers set out to test exactly how much heat a bone can take before its protein identity is lost forever, and whether the common practice of preserving these fragile finds in plastic resin affects the results. By heating modern pig ribs to specific temperatures and analyzing the remaining proteins, the team discovered that identification is possible up to a certain point, but that the method used to preserve the bone can make or break the analysis. Their work provides a practical guide for archaeologists, showing that while fire does destroy information, it does not always erase it completely, provided the right techniques are used.

The researchers began with a simple, controlled experiment using ribs from domestic pigs. They cut the bones into small chunks and placed them in a furnace, heating them in steps. They started at 50 degrees Celsius and climbed up to 350 degrees in small increments, then jumped to 100-degree steps all the way up to 750 degrees. This range covered everything from a slow roast to the intense heat of a cremation. To mimic what happens in a real archaeological lab, where fragile burned bones are often embedded in resin to be studied under a microscope, they treated half of their samples with a liquid plastic resin after heating them. They then compared these resin-treated samples to untreated ones.

The team used two main tools to examine the bones. First, they used a technique called infrared spectroscopy, which acts like a chemical fingerprint scanner. This tool measured how the bone's internal structure changed as it got hotter. They found that as the temperature rose, the bone lost weight and changed color, turning from black to white as it became fully calcined. The chemical scanner showed that the proteins inside the bone began to break down as the heat increased, but the bone mineral itself remained stable for much longer. This confirmed that the physical structure of the bone could survive high heat even when the organic parts were degrading.

The real test, however, was whether they could still identify the animal. The researchers used a method called ZooMS, which involves extracting tiny protein fragments from the bone and measuring their weight to create a unique pattern. This pattern acts like a barcode for the species. The results were clear and precise. Up to a temperature of about 200 degrees Celsius, the researchers could successfully identify the bones as pig. The protein patterns were still strong enough to give a definitive answer. But once the temperature crossed 250 degrees, the protein markers began to vanish. By the time the bones reached 300 degrees, almost all the identifiable protein signals were gone, leaving the bones unidentifiable by this method.

The study also revealed a significant complication regarding how these bones are preserved. When the researchers applied the resin to the heated samples, the results changed. The resin made it harder to extract the proteins, leading to fewer identifiable markers in the analysis. In some cases, the resin-treated samples could only be identified as a broad group, such as "hoofed animals," rather than the specific pig species. This suggests that while resin is excellent for protecting the physical shape of a fragile bone for microscopic study, it can interfere with the chemical analysis needed to identify the animal. The researchers found that the best way to handle heated, resin-embedded bones was to use a specific chemical extraction method that worked better than the others for these difficult samples, but even then, the success rate dropped compared to untreated bones.

One of the most important findings of this study was a correction to a common belief in the field. Previous guidelines suggested that if a bone showed certain chemical signs of protein preservation, it could be analyzed even if it had been heated to 450 or 550 degrees. The new data shows this is not true for burned bones. While the chemical signs might still be visible at those high temperatures, the specific protein patterns needed for identification disappear much earlier, around 200 degrees. This means that archaeologists cannot rely on older chemical thresholds when deciding if a burned bone is worth analyzing; they must be much more cautious.

The implications for archaeology are practical and immediate. When an archaeologist finds a pile of burned animal bones at a site, they now know that if the bones were heated to around 200 degrees or less, there is a good chance they can identify the species using modern protein analysis. This opens the door to understanding ancient diets and cooking practices that were previously invisible. However, if the bones were subjected to higher heat, or if they have been sitting in resin for a long time, the chances of a successful identification drop significantly. The study does not claim that burned bones are a lost cause, but it does draw a clear line in the sand: fire is a powerful eraser, and while some information survives the heat, the window for recovery is narrower than previously thought. By understanding exactly where that limit lies, scientists can better decide which fragments to study and which methods to use, ensuring that the stories of the past are not lost to the fire.