Thermophilic endospore-forming bacteria – “ thermospores ” – are particularly useful model organisms for exploring microbial biogeography because they remain viable for long geologic time periods owing to a dormant state that confers resistant to extreme conditions. Using high temperature incubation experiments and 16S rRNA gene amplicon sequencing, geographic and temporal thermospore dispersal in marine sediments was explored. Thermospores detected in surface sediments across the North Atlantic are likely to originate from multiple warm temperature habitats, and are viable in sediments buried ~15 000 years ago. These approaches also revealed thermospore viability following the extreme stress of prolonged -80°C exposure. Thermospore viability and dispersal on a scale of millions of years was explored in a 1.2 km long sediment core. Uneven thermospore germination posed a challenge for thermospore detection but their capacity for use as models of biological dispersal remains valid.