Exceptional Preservation of Early Terrestrial Communities in Lacustrine Phosphate One Billion Years Ago  

Good terrestrial fossil assemblages are rarely seen before the Devonian (c. 350 Ma). Evidence for freshwater and terrestrial life in the Precambrian has therefore been circumstantial, and none has yet come from freshwater phosphate.  We here demonstrate that phosphate from the c. 1200–1000 Ma Mesoproterozoic lake sediments of the Torridon Group (NW Scotland) preserve a remarkable picture of freshwater and terrestrial phototrophic ecosystems.  Ephemeral lakes and streams, which developed in intermontane basins within the interior of the supercontinent of Rodinia, periodically experienced prolonged desiccation and phosphate precipitation.  Microbial remains comparable with modern eukaryote (chlorophyte) algae and cyanobacteria reveal delicate cellular and sub-cellular structures, including desiccation-resistant cysts and aplanospores.  These data suggest that Earth’s terrestrial biota and its associated phosphorus cycle were well established on land by c. 1000 Ma.