Understanding Heat-Induced Changes in Bone Embracing : A Bioarcheology of Cremation

Expert Profile

Tim Thompson is a professor of applied biological anthropology and associate Dean (Academic) in the school of health and life sciences. Tim has published over 70 papers in peer-reviewed journals and books and is a renowned expert on heat-induced changes in bone. Prior to this, he published the book The Archaeology of cremation. Tim is on the editorial boards for the ‘Journal of Forensic Sciences’, forensic anthropology and human remains and violence an interdisciplinary journal. He is also a fellow of the chartered society of forensic sciences, the royal anthropological institute, the royal society of biology and is an honorary fellow of the faculty of forensic and legal medicine. He is also a senior fellow of AdvanceHE. Tim is a practicing forensic anthropologist who has worked at home and abroad in a variety of forensic contexts.

Foreground

This topic is focused on the effect of burning on the skeleton and how new methods are being used to develop new interpretations of contexts of life and death through the study of these burned bones. The speaker has thrown light on the heat-induced changes in the bone. He has focused on the minute details as well that need to be understood while dealing with the bio-archaeology of cremation.

Burned Bone Contex

There is a number of experimental studies and there are four stages of heat-induced transformation in bone. They are dehydration, decomposition, inversion, and fusion. The dehydration and decomposition stages cause an increase in porosity in the bone, which leads to increased fracturing, fragmentation, and breakage. The evidence for dehydration is fracture patterns, weight loss, etc. The evidence for decomposition is color change, weight loss, reduction in mechanical strength, changes in porosity and the evidence for inversion is an increase in crystal size and the evidence for fusion is an increase in mechanical strength, reduction in dimensions, increase in crystal size, changes in porosity. If a bone burns, its color moves from a natural creamy-brown state to dark grey to black to light grey and then pure white. The surface also changes during burning. During this heating density increases. Wrapping and fractures also happen during burning. 1 degree and 2 degrees level of heat induced changes show the color change, weight loss, fracture formation, changes in strength, recrystallization, porosity change, dimensional change.

The Influence of Heat-Induced Change on Anthropological Techniques

Color change implies loss of organics, which causes shrinkage in color change. Weight loss implies loss of organics, which causes shrinkage in weight loss. Increased fragmentation reduces the likelihood of technology applications in fracture formation. Weaker bone increases fragmentation, which reduces the likelihood of technique application in a change in strength. Changes in microstructure may affect the shape and will affect dimensions in recrystallization. Implies loss of organics and reorganization of microstructure in porosity change. Differential size changes may affect the shape and will affect dimensions in dimensional change. Modality is the term used in radiology to refer to one form of imaging.

Stable Isotopes

High temperatures alter the stable carbon and oxygen isotope ratios of bone that inform on diet and mobility. Fully calcined bone has been demonstrated to be a reliable store of the original strontium isotope (87Sr/86Sr) composition which reflects an average of diet over the last decade. We can use color to predict the temperature of burning.

Color Change

As bone burns, its color moves from a natural creamy brown state to dark grey to black to light grey and then pure white. The problem with using color in this way is that it is not the only temperature that influences colour change, but also the duration of burning, the oxygen levels, the amount of soft tissue, and so on.

Infrared Spectrum of Burnt Bone

Infrared data was measured in reflectance mode (FTIRATR), covering a wide spectral window from the far- to the mid-IR (50 to 4000 cm−1 ), which has been shown to be a rapid, easy and cost-efficient method providing very reliable and reproducible results on bone, without any particular sample preparation, and in a completely non-destructive way. In addition, these measurements have shown a higher reproducibility as compared to transmission FTIR and other infrared methodologies such as diffuse reflectance infrared Fourier transform.

Understanding Heat Induces Change in Bone

The presence of soft tissue has a significant impact on heat-induced changes of the bone matrix in low (>3000 C) as well as high temperature (>8000 C), showing down combustion in the former and accelerating it in the latter (P<0.05). At medium temperatures, no significant difference was noted.

Funerary Deposits

Evidence from mound and enclosure complexes across the southern Brazillian indicates the development of a funerary ritual focused on cremation from AD 1000 until the contact period. Evidence suggests the articulated bodies were cremated outdoors after death in funeral pyres with high temperatures and for considerable periods of time. Bodies would eventually undergo calcination and fragment. Cremation does not seem to have been restricted to a particular group. It was practiced by a variety of male and female biological individuals, observed in both primary and secondary cremated deposits. Individual and collective secondary deposits occasionally formed sequences of cuts and surface deposits in the mounds. The funerary cycle starts with the treatment of the corpse whereas final deposition ends the cycle. He has made the important observation that the deposition of a body in the flesh is actually part of the rites of separation because it usually takes place soon after death. Some activities and rites within the funerary cycle are directly associated with the corpse and the grave and maybe archaeologically more visible than other rites, which have no direct relation to the human remains.

Conclusion

Understanding heat-induced changes in bone and embracing a bio-archaeology of cremation provides a clear-cut understanding of the effect of burning on the skeleton and how the new methods are being used to develop new interpretations of contexts of life and death through the study of these burned bones. While in the field, it’s better to do all these methods discussed above. Establishing relationships requires observations and interpreting them correctly.

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