ABSTRACT
Subaerial bone weathering can be described in lay terms as grossly similar to what happens to exterior house paint: it bleaches, loses moisture, cracks, and flakes due to exposure to solar radiation, temperature fluctuations, precipitation, and sometimes from chemical processes and is spalled off in thin fragments (Figure 11.1). While the chemical (Nielsen-Marsh et al. 2000) and physical processes undergone by weathering bones are very different than paint, the end result is a bone that is fragmenting apart to become part of the lithosphere, completing its taphonomic pathway. The relevance of osseous weathering to forensic analyses is
Introduction 287 Processes of Weathering 289
Bone Properties 289 Patterns of Physical Degradation to Osseous Remains 290 Effects of Solar Radiation on Bleaching 295 Effects of Moisture 296 Effects of Heating and Cooling 297 Effects of Freezing and Thawing 297 Effects of Mineral Crystallization 298 Other Effects of Surface Exposure 299
Weathering and the Postmortem Interval 301 Applications to Forensic Anthropology 301 Effects of Macrohabitat 301 Effects of Microhabitat 306 Confusion with Other Taphonomic Effects 307
Distinguishing Weathering from Calcination 308 Distinguishing Weathering from Saltwater Immersion 308
Conclusions 309 Acknowledgments 309 References 309
twofold. First, it is necessary to distinguish this type of taphonomic alteration from other sources, including other processes that bleach and/or crack bone, in order to understand the context from where the bone came. This includes taphonomic alterations that might link a bone to a certain depositional setting, such as weathered remains from a surface deposit, which later get moved to a new location. Similarly, the movement of a bone from its original position while remaining in the same general location is often discernible from its weathering pattern. Second, and of most importance in forensic anthropology, is the information that osseous weathering can give regarding the postmortem interval (PMI). Estimation of the PMI in the middle range between where decomposition and entomological studies leave off (typically less than 1 year) and radiocarbon dating (prior to AD 1950) begins. Forensic anthropologists have few viable options within this interval (Beary 2005) and often must rely upon artifactual evidence accompanying remains (clothing or other personal objects), broad taphonomic patterns indicating a lack of forensic relevance (see Chapter 5, this volume), or related analyses such as the development of annual rings in trees in direct association with remains (Willey and Heilman 1987). Weathering analysis also has the potential for misuse where temporal standards developed in different environments are applied uncritically to estimate the PMI (Lyman 1994; Lyman and Fox 1989, 1997).
