ABSTRACT Fossilized tufted microbial mats in the 3.22 Ga Moodies Group, South Africa, record one of the oldest known microbial communities colonizing a sandy coastal‐marine system. These mats are morphologically unique among known Paleoarchean microbial structures, yet little is known about their constituent microorganisms or how they interacted with surface sedimentation during growth. To investigate the formation of their tufted topographic relief, modern tuft‐forming filamentous cyanobacteria were grown on similar medium‐ to coarse‐grained quartz sand and the resulting morphologies compared with those of the fossil examples. Our results reveal near identical grain‐sorting patterns between the fossil and laboratory‐grown mats. Specifically, modern tufts formed through a dynamic communal swarming process, in which hundreds to thousands of filaments moved in response to day‐night cycles, their motion likely coordinated by physical touch. Tuft‐forming cultures also exerted force on each other and on the surrounding substrate by rolling surface sand grains into piles beneath each tuft, thereby constructing regularly spaced coarse‐grained piles separated by finer‐grained lags. Collectively, these findings likely demonstrate an early communal behavioral adaptation to a photosynthetic lifestyle, revealing the great antiquity of coordinated bacterial motile behavior and sensing. Recognition of such behaviorally produced sedimentary textures may aid the interpretation of biosignatures both on Earth and in comparable extraterrestrial environments.
Gong et al. (Mon,) studied this question.