Comment and reply

A study of C isotope trends in Siberia's sub-Tommotian unconformity is criticized for lack of biostratigraphic or geochronologic control and comparative analyses. In short, the study is tagged as unenlightening to Early Cambrian history. It is argued that such study is not new and is in fact reported in an earlier study. A possible correlation between the initial observation of taxa in the stratotypic basal Tommotian rocks and the unconformity is also accepted. However, the theory must be compared with a biostratigraphic pattern widely used among Russian paleontologists.