In understanding DNA as a biomarker over geologic time scales, it is important to determine the longevity of the signal under common environmental stress. Shewanella spp of bacteria in aqueous solution were subjucted to lethal doses of UVC radiation, gamma radiation and thermal and cryogenic conditions. The species succumbed to UVC quickly with a post-mortem DNA signal at least 2 orders of magnitude longer than the life of the cell. Cryogenic stress revealed differential death, but no obvious signal degradation and gamma radiation showed some degradation with cell death but more data are needed to determine a half life for the signal. This study indicates a DNA signal could last 0 (thermal conditions) to 4 or more (cryogenic conditions) orders of magnitude beyond cell death depending on the environment and the time of cell death.