The use of fire at Zhoukoudian: evidence from magnetic susceptibility and color measurements

In order to provide direct evidence for the use of fire by humans at Locality 1, Zhoukoudian, we examine the burnt and unburnt sediments of newly excavated area in Layer 4 by detailed measurements of magnetic susceptibility, color, and diffuse reflectance spectrum. Results show that the magnetic susceptibility and redness of the burnt sediments are remarkably higher than those of other areas on the same level: up to similar to 22 times for magnetic susceptibility and similar to 3 times for redness of those of the adjacent unburnt sediments. Fine-grained (superparamagnetic/stable single-domain) magnetite and hematite grains make dominant contributions to the distinctly high values of magnetic susceptibility and redness in the burnt sediments. Diffuse reflectance spectroscopy results show that the burnt sediments contain more hematite than those of other areas and localities 2 and 3. High-temperature magnetic susceptibility measurements demonstrate that the burnt sediments have been heated above 700 A degrees C. Those changes in low-frequency magnetic susceptibility and redness are impossibly resulted from natural fires, thus most likely signaling the human activities of controlled use of fire. However, further work is needed to confirm whether or not these heat-affected sediments were produced in situ.