Impact ejected rocks are targets for life detection missions to Mars. The
Martian subsurface is more favourable to organic preservation than the
surface owing to an attenuation of radiation and physical separation from
oxidising materials with increasing depth. Impact events bring materials to
the surface where they may be accessed without complicated drilling
procedures. On Earth, different assemblages of organic matter types are
derived from varying depositional environments. Here we assess whether
these different types of organic materials can survive impact events
without corruption. We subjected four terrestrial organic matter types to
elevated pressures and temperatures in piston-cylinder experiments
followed by chemical characterisation using whole-rock pyrolysis-gas
chromatography-mass spectrometry. Our data reveal that long chain
hydrocarbon-dominated organic matter (types I and II; mainly microbial or
algal) are unresistant to pressure whereas aromatic hydrocarbondominated
organic matter types (types III and IV; mainly land plant,
metamorphosed or degraded, displaying some superficial chemical
similarities to abiotic meteoritic organic matter) are relatively resistant.
This suggests that the impact excavated record of potential biology on
Mars will be unavoidably biased, with microbial organic matter
underrepresented while metamorphosed, degraded or abiotic meteoritic
organic matter types will be selectively preserved.