Limits in pyrolysis–GC–MS analysis of kerogen isolated from Archean cherts

Pyrolysis–GC–MS was recently proposed as an emerging technique for establishing biogenicity of 3.5 Gyr old insoluble organic matter in cherts (Derenne et al., 2008. Earth and Planetary Science Letters 272, 476–480). When applied to four kerogens isolated from Archean chert samples for biogenicity determination, this method highlights the importance of having a significant aliphatic component remaining in the kerogen. If not, fatty acid decarboxylation may bias the n-alkane distribution. However, in most cases, mature samples such as Archean cherts usually do not have such an aliphatic fraction. This shows the limits of the technique and the need for a new biogenicity marker.