Human ancestors that walked the earth left few traces of their passage. Some of their footprints have lithified, or turned to stone, but some survive to this day, unlithified, in soft sediment such as silt. These fragile records of ancient footprints pose a sizable challenge to archaeologists today: how do you preserve the ephemeral? According to new research published in PLOS ONE, the answer may be to “record and digitally rescue” these footprint sites.

The authors explored two methods in this study: digital photogrammetry, where researchers strategically photograph an object in order to derive measurements; and optical laser scanning, where light is used to measure the object’s physical properties. To begin, the authors filled trays with mixtures of sand, cement, and plaster and instructed a participant to walk through these samples. Four wooden 1 cm cubes were then placed beside a select number of footprints and photographs were taken. A laser scanner was then used to measure the same footprints. This simple procedure was also replicated outside of the lab, at a beach in North West England.

In their results, they found that both methods offered similar levels of precision (though, the laser scanner was “slightly more accurate”) and that differences between the two were not statistically significant. These two methods are not, however, without their respective strengths and challenges. Photogrammetry can be an advantage in situations where records need to be taken quickly and inexpensively, as field work can be completing using a camera, tripod, and measuring equipment. This practice is, however, especially subject to human error. Additionally, the accuracy of the images – and consequently the measurements derived from the images – may be compromised by extreme lighting conditions and the depth of the footprint or impression. Alternately, laser scanning is more appropriate in conditions where a high degree of precision is required and footprints are more fragile (and thus unlikely to remain in an “optimal” condition). Laser scanners are, however, more expensive and require a large energy source. The authors advocate that both methods can, and should, be used in tandem to supplement each other.

These digital tools provide an innovative solution to preserving footprint records, especially in cases where traditional on-site, or off-site, preservation is impractical and costly. To learn more about this research and the merits and challenges of digital rescue archaeology, read the full text of the study here.

Image is Figure 6 of the manuscript.

Citation: Bennett MR, Falkingham P, Morse SA, Bates K, Crompton RH (2013) Preserving the Impossible: Conservation of Soft-Sediment Hominin Footprint Sites and Strategies for Three-Dimensional Digital Data Capture. PLoS ONE 8(4): e60755. doi:10.1371/journal.pone.0060755