Opinion is divided over the likelihood of blood to survive for any period on the surface of stone or other artifactual material in a physically or biochemically identifiable way. Although the apparent presence of blood residues has been demonstrated in a limited range of modern experimental and archaeological contexts, the preservation of any detectable residue must be considered an exception rather than the rule. In the case of residues on tool surfaces, it is possible that the close association with mineral (i. e., stone or associated clay matrix) in the burial environment may have a stabilizing effect on organic material such as blood proteins, and may also protect organics from microbial attack.
Experimental studies to determine the factors controlling the survival of blood residues have been largely inconclusive, possibly due to the wide range of sediments and environments represented in the fossil record that require consideration. In order to better understand the conditions that promote the survival of blood on stone, sites from which blood residues have been successfully recovered must be thoroughly documented. Of particular interest are the sedimentary context, the environmental setting at the time of artifact deposition, the post-depositional history, and the techniques of artifact recovery.
The survival of blood residues on stone tools dated to >30 ka has been reported at the Pleistocene archaeological site of Cuddie Springs in southeastern Australia. The artifacts were deposited on the bed of an ephemeral lake (cf. waterhole), and the sediments from which the artifacts were recovered are primarily silts and clays, anaerobic, alkaline, and constantly damp. There has been little movement within the sediment since deposition and the sediments have been protected from disturbance by the formation of an old land surface capping the deposits of interest. While now in the semi-arid zone, Cuddie Springs was located within the arid zone during the period of artifact deposition. Residue survival seems optimized in the sediments formed during extended dry lake conditions when it is likely that blood would have dried relatively quickly before burial. Rapid burial post-discard may have reduced the exposure to damaging UV radiation. The residues on the Cuddie Springs artifacts were generally identified in or near unconformities such as step fractures on the stone surface, where they would have accumulated from cutting or scraping and would have been less susceptible to subsequent removal (Figure 1c). Such blood and tissue accumulation has been observed in modern experimental studies, indicating that higher residue concentration and long-term survival is more likely at disconformities such as microcracks and step fractures than on smooth areas on the tool surface.
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