COMPRESSION ANALYSIS AND THE BIOGENIC MODIFICATION OF ABIOGENIC SUBSTRATES

A typical rock containing trace fossils generally displays a spectrum of preservation that ranges from obvious, perhaps identifiable, ichnogenera to probable traces to ultimately ambiguous marks that may or may not be biogenic. In some cases, however, the putative traces are ambiguous from the start, as is the case of microbial traces (stromatolites). Stromatolites are laminated structures most commonly attributed to the activity of microorganisms, but, in general, the corresponding microbial fossils are seldom preserved. As a result, the biogenicity of a given stromatolite is rarely certain. In addition, some models of stromatolite morphogenesis suggest that microbes may have been present, but were not necessarily required, to build a stromatolite. This problem is particularly pertinent for the exploration of life in our solar system, as stromatolites could represent the macroscopic manifestation of microbial processes, and thus would constitute a structure visible to a rover or other imaging device. Here, we introduce a method to investigate the biotic component of stromatolites and other potentially ambiguously biogenic traces. We hypothesize that the biogenic modification of an abiogenic substrate could be discernable through compression analysis of digital images. Compression algorithms quantify the randomness in a digital file by encoding for redundant data (data files with a significant random component will compress less than files with greater redundancy). Preliminary investigation demonstrates that, at some scales, biogenetic structures compress to a greater degree than structures created by abiotic processes, and where overlap is present, the variance in compression across the biotic structure is much narrower than across an abiotic structure. Thus, compression analysis may be useful for discerning the biogenic component in initially ambiguous traces, stromatolites, and other structures.