Characterization of structural changes in modern and archaeological burnt bone: Implications for differential preservation bias

Abstract

Structural and thermodynamic factors which may influence burnt bone survivorship in archaeological contexts have not been fully described. A highly controlled experimental reference collection of fresh, modern bone burned in temperature increments 100–1200˚C is presented here to document the changes to bone tissue relevant to preservation using Fourier transform infrared spectroscopy and X-ray diffraction. Specific parameters investigated here include the rate of organic loss, amount of bone mineral recrystallization, and average growth in bone mineral crystallite size. An archaeological faunal assemblage ca. 30,000 years ago from Tolbor-17 (Mongolia) is additionally considered to confirm visibility of changes seen in the modern reference sample and to relate structural changes to commonly used zooarchaeological scales of burning intensity. The timing of our results indicates that the loss of organic components in both modern and archaeological bone burnt to temperatures up to 700˚C are not accompanied by growth changes in the average crystallite size of bone mineral bioapatite, leaving the small and reactive bioapatite crystals of charred and carbonized bone exposed to diagenetic agents in depositional contexts. For bones burnt to temperatures of 700˚C and above, two major increases in average crystallite size are noted which effectively decrease the available surface area of bone mineral crystals, decreasing reactivity and offering greater thermodynamic stability despite the mechanical fragility of calcined bone. We discuss the archaeological implications of these observations within the context of Tolbor-17 and the challenges of identifying anthropogenic fire.

Physicochemical Changes in Bone Bioapatite During the Late Postmortem Interval Pre- and Post-Burning

“…Exogenous K (mean 0.08 wt%) from the soil might have diffused into the OC layers and to a lesser degree from the IC end and through the HC zones. Since bioapatite is less susceptible to changes post-burning, due to increased crystallinity, 42,73,74,109 this might mean that potassium essentially depleted in the Neolithic samples prior to cremation. Therefore, these bodies might have been left to decompose prior to cremation, to a degree that endogenous potassium was no longer present.…”

Proteins, possibly human, found in World War II concentration camp artifact

“…However, the data presented here clearly demonstrate that biological material is contained within what were believed to be cement disks 2 , and that material is consistent with bone. Collagen, the most abundant protein in bone 14 , 16 , has increased protection from burning due to the large amounts of inorganic calcium that make up the bulk (~ 65%) of bone mass 24 – 26 . Marrow, a rich source of hemoglobin, and the second most abundant protein in the body, may also have some protection from the intense heat that consumes exposed soft tissues.…”

Laboratory-based experimental research into the effect of diagenesis on heated bone: implications and improved tools for the characterisation of ancient fire

“…Heating conditions are also reconstructed using analytical techniques such as TGA, FTIR, and XRD (e.g., 44 – 50 ). The reliability of the outcomes of these techniques can be severely affected by pH exposure depending on what specific part of the bone they target.…”